CN1112763C - Surface Acoustic Wave Devices - Google Patents

Abstract

The size of a surface acoustic wave device having a substrate and an interdigital electrodes on the surface of the substrate is reduced and the selectivity of the device is improved, and then, the band of the device is widened. For this purpose: (i) a piezoelectric film is formed to cover the surface of the substrate and interdigital electrodes, or (ii) a piezoelectric film is provided on the surface of the substrate and the interdigital electrodes are formed on the surface of the film. Alternatively, (iii) the piezoelectric film is provided on the surfaces of the substrate and interdigital electrodes and a counter electrode film is formed on the surface of the piezoelectric film, or (iiii) the counter electrode film is provided on the surface of the substrate and the piezoelectric film is formed on the counter electrode film and the interdigital electrodes are formed on the surface of the piezoelectric film. The piezoelectric film has a piezoelectric axis oriented nearly perpendicularly to the surface of the substrate.

Description

Surface Acoustic Wave Devices

The invention relates to a surface acoustic wave device, which comprises: an interdigital electrode on a single crystal substrate.

In recent years, mobile communication terminal devices including cellular phones have spread rapidly. For portability, it is particularly desirable to reduce the size and weight of terminal equipment. To reduce the size and weight of a terminal device, it is necessary to reduce the size and weight of its electronic components. SAW devices are beneficial for size and weight reduction, so SAW filters are often used for high-frequency and intermediate-frequency components of terminal equipment. The surface acoustic wave device has an interdigitated electrode on the surface of the piezoelectric substrate, which is used to excite, receive, reflect and propagate the surface acoustic wave.

Important characteristic parameters of piezoelectric substrates for SAW devices include: surface wave velocity of SAW (SAW wave velocity), temperature coefficient (TCF) of filter center frequency and resonant frequency of resonator, and electromechanical coupling coefficient (k ² ). Listed in Table 1 are the characteristic parameters of different piezoelectric substrates used in existing SAW devices. Hereinafter, these piezoelectric substrates will be represented by the symbols used in Table 1. From this point of view, it should be noted that TCV (ie, temperature coefficient of surface acoustic wave velocity) is a parameter representing the relationship between surface acoustic wave velocity and temperature, just as the above-mentioned TCF represents the relationship between center frequency or resonant frequency and temperature. A large value of TCV means that the center frequency of the surface acoustic wave filter is greatly affected by temperature fluctuations.

Table 1 Symbol Composition Cut Angle Propagation Direction Surface Acoustic Wave k ² (%) TCV(ppm/℃)

Velocity (m/s) 128LN LiNbO ₃ 128°-rotation Y X 3992 5.5 -7464LN LiNbO ₃ 64°-rotation Y X 4742 11.3 -79LT112 LiTaO ₃ X 112°-rotation Y 3288 0.64 -1836LT LiTaO ₃ 36°-rotation Y X 4212 4.7 -45ST crystal quartz ST X 3158 0.14 0 (initial coefficient) BGO Bi ₁₂ GeO ₂₀ (100) (011) 1681 1.2 -122

It can be seen from Table 1 that the surface acoustic wave velocity of 64LN and 36LT is 4000m/s or higher, so it is suitable for manufacturing high-frequency components of terminal equipment. Considering this reason, various systems are currently used in mobile communications represented by cellular phones all over the world, and the frequencies used are all on the order of 1 GHz. Correspondingly, the center frequency of the filter of the high-frequency component of the terminal equipment is about 1 GHz. The center frequency of the SAW filter. It is basically proportional to the surface acoustic wave velocity of the piezoelectric substrate used, and basically inversely proportional to the width of the finger strips of the interdigitated electrodes formed on the substrate. Therefore, in order to make this filter work at high frequencies, it is best to use a substrate with a high surface acoustic wave velocity, such as 64LN and 36LT. Moreover, the filter of the high-frequency part should also adopt a wide passband with a width of 20MHz or higher. But to obtain such a wide passband, the piezoelectric substrate must have a large electromechanical coupling coefficient k ² . For these reasons, 64LN and 36LT are used a lot.

On the other hand, in mobile terminal equipment, a frequency band of 70 to 300 MHz is used as an intermediate frequency. When the filter with this frequency band as the center frequency is used to make a surface acoustic wave device, using the above-mentioned 64LN and 36LT as a piezoelectric substrate will cause the width of the electrode fingers on the substrate to be much larger than that of the above-mentioned filter for high-frequency components corresponding width.

This can be explained with reference to a rough calculation of specific values. Let d represent the electrode finger width of the SAW transducer forming the SAW filter, f ₀ represent the center frequency of the SAW filter, and V represent the SAW velocity of the piezoelectric substrate used. These values generally satisfy equation (1):

f ₀ =V/(4d) …(1) If a surface acoustic wave filter with a center frequency of 1GHz is constructed under the assumption that the wave velocity of the surface acoustic wave is 4000m/s, then the electrode index is calculated according to the formula (1) The bar width is:

d=4,000(m/s)/[4×1,000(MHz)]=1μm

On the other hand, if a piezoelectric substrate with a surface acoustic wave velocity of 4000m/s is used to construct an intermediate frequency filter with a center frequency of 100MHz, the required electrode finger width is:

d=4,000(m/s)/[4×100(MHz)]=10 μm can be seen, and its finger width is 10 times of the finger width of the high-frequency component filter. An increase in the width of the fingers means an increase in the size of the surface acoustic wave device. Therefore, it can be seen from the above formula (1) that in order to make the surface acoustic wave intermediate frequency filter smaller, a piezoelectric substrate with a small surface acoustic wave velocity V must be used.

Among the existing piezoelectric substrates with low surface acoustic wave velocity, there are BGOs mentioned in Table 1 above. The surface acoustic wave velocity of the BGO piezoelectric substrate is 1,681m/s. However, it is not suitable for making an intermediate frequency filter that separates a single channel signal, because the temperature coefficient TCV of its SAW wave velocity reaches -122ppm/℃. This is because TCV represents the relationship between SAW wave velocity and temperature, and a large value of TCV means that the center frequency of the surface acoustic wave filter is greatly affected by temperature fluctuations, which have been mentioned above, and can also be seen from formula (1) out. A large TCV is therefore not suitable for an IF filter, since undesired signals may be picked up from other channels adjacent to the desired channel.

Among the existing piezoelectric substrates with relatively low SAW velocities are the ST quartz crystals mentioned in Table 1 above. Since the TCV of the ST quartz body is almost zero (its initial temperature coefficient (primary temperature coefficient) a is zero), it is suitable for making intermediate frequency filters. For this reason, most of the intermediate-frequency surface acoustic wave filters used in mobile communication terminal equipment so far have been fabricated with ST quartz crystal piezoelectric substrates.

However, the SAW wave velocity of the ST quartz crystal substrate is 3,158 m/s or, in other words, an insufficiently low value, thereby creating a certain limit for size reduction.

Moreover, the electromechanical coupling coefficient ^k2 of the quartz Chang body is 0.14%, which is quite small. Small values of ^k2 mean that only filters with narrow passbands are obtained. Currently, most cellular phones used in mobile communications are analog systems with very narrow frequency bandwidths. For example: the Japanese NTT standard is 12.5KHz, the American AMPS standard is 30KHz, and the European TACS standard is 25KHz. Therefore, the fact that the above-mentioned ST quartz crystal has a small electromechanical coupling coefficient k ² has not caused difficult problems in the past. But in recent years, in order to effectively utilize frequency resources and consider the compatibility of digital data communication, digital mobile communication system has been developed, applied and popularized rapidly. The channel bandwidth of this digital system is very large, such as the European cellular telephone GSM mode and the cordless telephone DECT mode are 200KHz and 1.7MHz respectively. Therefore, if a surface acoustic wave filter is made of an ST quartz crystal substrate, it is difficult to make such a broadband intermediate frequency filter.

On the other hand, it is well known that forming a piezoelectric film composed of zinc oxide, lithium oxide, Cds or similar compounds on a piezoelectric substrate of LiNbO ₃ or similar substances can improve the electromechanical coupling coefficient of surface acoustic wave devices, typical as JP - Published in A8-204499. However, traditional piezoelectric substrates such as LiNbO ₃ are not suitable for this, because its temperature coefficient TCV is negative. Therefore, when a zinc oxide film is formed on it, the entire TCV value will turn sharply to the negative side.

As mentioned above, one problem with conventional surface acoustic wave devices is that when a piezoelectric substrate such as the above-mentioned 64LN, 36LT, etc. is used, its passband can be broadened, but the high SAW wave velocity of the substrate makes the size of the device smaller. big. Another problem is that when the above-mentioned BGO substrate of low SAW wave velocity is used for device size reduction, a sufficiently good selectivity cannot be obtained because the temperature coefficient TCV of the SAW wave velocity is too large. The characteristic parameters of the IF SAW filter obtained in both cases are not good enough.

The ST quartz Chang body substrate has a small SAW wave velocity temperature coefficient TCV, but the size reduction is limited by the fact that its SAW wave velocity is not small enough; and because of the fact that its electromechanical coupling coefficient is small, broadband comparison difficulty.

One of the objects of the present invention is to provide a surface acoustic wave device with small size and good enough selectivity. The second is to provide a surface acoustic wave device with small size and wide passband. The third is to provide a surface acoustic wave device with small size, good enough selectivity and wide passband.

The above object can be achieved by any one of the following embodiments 1-4. Example 1

(1) A surface acoustic wave device comprising: a substrate, interdigital electrodes on a surface of the substrate, and a piezoelectric film covering the above-mentioned surface of the substrate and the surface of the above-mentioned interdigital electrodes. Wherein: the above-mentioned substrate is a langasite (lanthanum gallium silicate) single crystal belonging to point group 32, and the above-mentioned piezoelectric film is composed of zinc oxide.

(2) In the surface acoustic wave device described in (1), said piezoelectric film has a piezoelectric axis substantially perpendicular to said surface of said substrate.

(3) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region l:

Area I:

-5°≤φ≤5°

85°≤θ≤95°

-90°≤ψ<90°

(4) In the surface acoustic wave device described in (1), when the cut angle of the above-mentioned substrate cut out from the langasite single crystal, and the propagation direction of the surface acoustic wave on the above-mentioned substrate are determined by Euler angles (φ, θ, ψ) When expressed, φ, θ and ψ fall in the following I-1 region:

Zone I-1

-5°≤φ≤5°

85°≤θ≤95°

-90°≤ψ<-70°

The surface acoustic wave device in (5), (4) satisfies:

h/λ＝0.2～0.8

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(6) In the surface acoustic wave device described in (1), when the cut angle of the above-mentioned substrate cut out from the langasite single crystal, and the propagation direction of the surface acoustic wave on the above-mentioned substrate are determined by Euler angles (φ, θ, ψ) When expressed, φ, θ and ψ fall in the following I-2 region:

Zone I-2,

-5°≤φ≤5°

85°≤θ≤95°

-70°≤ψ<-50°

The surface acoustic wave device in (7), (6) satisfies:

h/λ＝0.25～0.7

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(8) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following I-3 region:

Zone I-3,

-5°≤φ≤5°

85°≤θ≤95°

-50°≤ψ＜-35°

The surface acoustic wave device in (9), (8) satisfies:

h/λ=0.25-0.45

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(10) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following I-4 region:

Zone I-4,

-5°≤φ≤5°

85°≤θ≤95°

-35°≤ψ<-25°

The surface acoustic wave device in (11), (10) satisfies:

0<h/λ≤0.5

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(12) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following I-5 region:

Zone I-5,

-5°≤φ≤5°

85°≤θ≤95°

-25°≤ψ<-10°

The surface acoustic wave device in (13), (12) satisfies:

0<h/λ≤0.45

h is the thickness of the aforementioned piezoelectric film on the aforementioned surface of the aforementioned substrate, and λ is the wavelength of the aforementioned surface acoustic wave.

(14) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following I-6 region:

Zone I-6,

-5°≤φ≤5°

85°≤θ≤95°

10°≤ψ<25°

The surface acoustic wave device in (15), (14) satisfies:

0<h/λ≤0.4

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(16) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following I-7 region:

Area I-7,

-5°≤φ≤5°

85°≤θ≤95°

25°≤ψ<35°

The surface acoustic wave device in (17), (16) satisfies:

0<h/λ≤0.45

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(18) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following I-8 region:

Area I-8,

-5°≤φ≤5°

85°≤θ≤95°

35°≤ψ<50°

The surface acoustic wave device in (19), (18) satisfies:

0<h/λ≤0.4

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(20) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following I-9 region:

Area I-9,

-5°≤φ≤5°

85°≤θ≤95°

50°≤ψ<70°

The surface acoustic wave device in (21), (20) satisfies:

0＜h/λ≤0.15～0.7

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(22) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following I-10 region:

Area I-10,

-5°≤φ≤5°

85°≤θ≤95°

70°≤ψ<90°

The surface acoustic wave device in (23), (22) satisfies:

0＜h/λ≤0.15～0.8

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave. Example 2

(1) A surface acoustic wave device comprising: a substrate, a piezoelectric film formed on the surface of the substrate, and interdigital electrodes formed on the surface of the piezoelectric film. in:

The above substrate is a langasite single crystal belonging to point group 32, and the above piezoelectric film is composed of zinc oxide.

(2) In the surface acoustic wave device described in (1), said piezoelectric film has a piezoelectric axis substantially perpendicular to said surface of said substrate.

(3) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the above-mentioned single crystal of langasite and the propagation direction of the surface acoustic wave on the above-mentioned substrate are defined by Euler angles (φ, θ, ψ) When expressed, φ, θ and ψ fall in the following region II:

Zone II:

-5°≤φ≤5°

85°≤θ≤95°

-90°≤ψ<90°

(4) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region II-I:

Zone II-1:

-5°≤φ≤5°

85°≤θ≤95°

-90°≤ψ<-70°

The surface acoustic wave device in (5), (4) satisfies:

h/λ＝0.05～0.8

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(6) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the above-mentioned single crystal of langasite and the propagation direction of the surface acoustic wave on the above-mentioned substrate are defined by Euler angles (φ, θ, ψ) When expressed, φ, θ and ψ fall in the following region II-2:

Zone II-2:

-5°≤φ≤5°

85°≤θ≤95°

-70°≤ψ<-50°

The surface acoustic wave device in (7), (6) satisfies:

h/λ＝0.05～0.75

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(8) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region II-3:

Zone II-3:

-5°≤φ≤5°

85°≤θ≤95°

-50°≤ψ<-35°

The surface acoustic wave device in (9), (8) satisfies:

0<h/λ≤0.45

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(10) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region II-4:

Zone II-4,

-5°≤φ≤5°

85°≤θ≤95°

-35°≤ψ<-25°

The surface acoustic wave device in (11), (10) satisfies:

0<h/λ≤0.5

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(12) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region II-5:

Zone II-5,

-5°≤φ≤5°

85°≤θ≤95°

-25°≤ψ<-10°

The surface acoustic wave device in (13), (12) satisfies:

0<h/λ≤0.45

h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(14) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region II-6:

Zone II-6,

-5°≤φ≤5°

85°≤θ≤95°

10°≤ψ<25°

The surface acoustic wave device in (15), (14) satisfies:

0<h/λ≤0.4

Here, h is the thickness of the piezoelectric film on the surface of the substrate, and λ is the wavelength of the surface acoustic wave.

(16) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region II-7:

Zone II-7:

-5°≤φ≤5°

85°≤θ≤95°

25°≤ψ<35°

The surface acoustic wave device in (17), (16) satisfies:

0<h/λ≤0.45

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(18) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region II-8:

Zone II-8,

-5°≤φ≤5°

85°≤θ≤95°

35°≤ψ<50°

The surface acoustic wave device in (19), (18) satisfies:

0<h/λ≤0.4

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(20) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region II-9:

Zone II-9,

-5°≤φ≤5°

85°≤θ≤95°

50°≤ψ<70°

The surface acoustic wave device in (21), (20) satisfies:

h/λ＝0.05～0.7

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(22) In the surface acoustic wave falling part described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are defined by the Euler angles (φ, θ, ψ) When expressed, φ, θ and ψ fall in the following regions II-10:

Zone II-10,

-5°≤φ≤5°

85°≤θ≤95°

70°≤ψ<90°

The surface acoustic wave device in (23), (22) satisfies:

h/λ＝0.05～0.8

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave. Example 3

(1) A surface acoustic wave device, comprising: a substrate, interdigitated electrodes formed on the surface of the substrate, a piezoelectric film covering the above-mentioned surface of the substrate and the surface of the above-mentioned interdigitated electrodes, and an antiphase electrode on the above-mentioned piezoelectric film. Electrode film. in:

The above-mentioned substrate is a langasite single crystal belonging to point group 32, and the above-mentioned piezoelectric film is composed of zinc oxide.

(2) In the surface acoustic wave device described in (1), said piezoelectric film has a piezoelectric axis substantially perpendicular to said surface of said substrate.

(3) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region III:

Zone III:

-5°≤φ≤5°

85°≤θ≤95°

-90°≤ψ<90°

(4) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region III-1:

Zone III-1:

-5°≤φ≤5°

85°≤θ≤95°

-90°≤ψ<-70°

The surface acoustic wave device in (5), (4) satisfies:

0<h/λ≤0.1

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

The surface acoustic wave device in (6), (4) satisfies:

h/λ＝0.3～0.8

Here, h is the thickness of the piezoelectric film on the surface of the substrate, and λ is the wavelength of the surface acoustic wave.

(7) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region III-2:

Zone III-2:

-5°≤φ≤5°

85°≤θ≤95°

-70°≤ψ<-50°

The surface acoustic wave device in (8), (7) satisfies:

0<h/λ≤0.1

Here, h is the thickness of the piezoelectric film on the surface of the substrate, and λ is the wavelength of the surface acoustic wave.

The surface acoustic wave device in (9), (7) satisfies:

h/λ＝0.35～0.8

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(10) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region III-3:

Zone III-3:

-5°≤φ≤5°

85°≤θ≤95°

-50°≤ψ<-35°, except for -30°.

The surface acoustic wave device in (11), (10) satisfies:

0<h/λ≤0.15

Here, h is the thickness of the piezoelectric film on the surface of the substrate, and λ is the wavelength of the surface acoustic wave.

The surface acoustic wave device in (12), (10) satisfies:

h/λ＝0.35～0.5

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(13) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region III-4:

Zone III-4:

-5°≤φ≤5°

85°≤θ≤95°

-35°≤ψ<-25°

The surface acoustic wave device in (14), (13) satisfies:

0<h/λ≤0.15

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

The surface acoustic wave device in (15), (13) satisfies:

h/λ＝0.3～0.5

Here, h is the thickness of the piezoelectric film on the surface of the substrate, and λ is the wavelength of the surface acoustic wave.

(16) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region III-5:

Zone III-5:

-5°≤φ≤5°

85°≤θ≤95°

-25°≤ψ<-10°

The surface acoustic wave device in (17), (16) satisfies:

0<h/λ≤0.15

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

The surface acoustic wave device in (18), (16) satisfies:

h/λ＝0.3～0.45

Here, h is the thickness of the piezoelectric film on the surface of the substrate, and λ is the wavelength of the surface acoustic wave.

(19) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region III-6:

Zone III-6:

-5°≤φ≤5°

85°≤θ≤95°

10°≤ψ<25°

The surface acoustic wave device in (20), (19) satisfies:

0<h/λ≤0.45

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(21) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall into the following domain III-7:

Zone III-7:

-5°≤φ≤5°

85°≤θ≤95°

25°≤ψ<35°

The surface acoustic wave device in (22), (21) satisfies:

0<h/λ≤0.5

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(23) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region III-8:

Zone III-8:

-5°≤φ≤5°

85°≤θ≤95°

35°≤ψ<50°

The surface acoustic wave device in (24), (23) satisfies:

0<h/λ≤0.45

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

(25) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region III-9:

Zone III-9:

-5°≤φ≤5°

85°≤θ≤95°

50°≤ψ<70°

The surface acoustic wave device in (26), (25) satisfies:

0<h/λ≤0.05

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

The surface acoustic wave device in (27), (25) satisfies:

h/λ＝0.2～0.8

Here, h is the thickness of the piezoelectric film on the surface of the substrate, and λ is the wavelength of the surface acoustic wave.

(28) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region III-10:

Zone III-10:

-5°≤φ≤5°

85°≤θ≤95°

70°≤ψ<90°

The surface acoustic wave device in (29), (28) satisfies:

0<h/λ≤0.05

Wherein, h is the thickness of the above-mentioned piezoelectric film on the above-mentioned surface of the above-mentioned substrate, and λ is the wavelength of the above-mentioned surface acoustic wave.

The surface acoustic wave device in (30), (28) satisfies:

h/λ＝0.25～0.8

Here, h is the thickness of the piezoelectric film on the surface of the substrate, and λ is the wavelength of the surface acoustic wave. Example 4

(1) A surface acoustic wave device comprising: a substrate, a counter electrode film formed on the surface of the substrate, a piezoelectric film formed on the counter electrode film, and interdigital electrodes formed on the piezoelectric film. in:

The above-mentioned substrate is a langasite single crystal belonging to point group 32, and the above-mentioned piezoelectric film is composed of zinc oxide.

(2) In the surface acoustic wave device described in (1), said piezoelectric film has a piezoelectric axis substantially perpendicular to said surface of said substrate.

(3) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the above-mentioned single crystal of langasite and the propagation direction of the surface acoustic wave on the above-mentioned substrate are defined by Euler angles (φ, θ, ψ) When expressed, φ, θ and ψ fall in the following region IV:

Region IV:

-5°≤φ≤5°

85°≤θ≤95°

-90°≤ψ<90°

(4) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region IV-1:

Area IV-1:

-5°≤φ≤5°

85°≤θ≤95°

-90°≤ψ<-70°

The surface acoustic wave device in (5), (4) satisfies:

h/λ＝0.05～0.8

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(6) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the above-mentioned single crystal of langasite and the propagation direction of the surface acoustic wave on the above-mentioned substrate are defined by Euler angles (φ, θ, ψ) When expressed, φ, θ and ψ fall in the following region IV-2:

Area IV-2:

-5°≤φ≤5°

85°≤θ≤95°

-70°≤ψ<-50°

The surface acoustic wave device in (7), (6) satisfies:

h/λ＝0.05～0.8

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(8) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region IV-3:

Area IV-3:

-5°≤φ≤5°

85°≤θ≤95°

-50°≤ψ<-35°

The surface acoustic wave device in (9), (8) satisfies:

h/λ＝0.05～0.45

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(10) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region IV-4:

Area IV-4:

-5°≤φ≤5°

85°≤θ≤95°

-35°≤ψ<-25°

The surface acoustic wave device in (11), (10) satisfies:

h/λ＝0.05～0.5

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(12) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region IV-5:

Zone IV-5:

-5°≤φ≤5°

85°≤θ≤95°

-25°≤ψ<-10°

The surface acoustic wave device in (13), (12) satisfies:

h/λ＝0.05～0.45

h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(14) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region IV-6:

Region IV-6:

-5°≤φ≤5°

85°≤θ≤95°

10°≤ψ<25°

The surface acoustic wave device in (15), (14) satisfies:

h/λ＝0.05～0.45

Here, h is the thickness of the piezoelectric film on the surface of the substrate, and λ is the wavelength of the surface acoustic wave.

(16) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region IV-7:

Area IV-7:

-5°≤φ≤5°

85°≤θ≤95°

25°≤ψ<35°

The surface acoustic wave device in (17), (16) satisfies:

h/λ＝0.05～0.5

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(18) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region IV-8:

Area IV-8:

-5°≤φ≤5°

85°≤θ≤95°

35°≤ψ<50°

The surface acoustic wave device in (19), (18) satisfies:

h/λ＝0.05～0.45

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(20) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region IV-9:

Region IV-9:

-5°≤φ≤5°

85°≤θ≤95°

50°≤ψ<70°

The surface acoustic wave device in (21), (20) satisfies:

0<h/λ≤0.05～0.8

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

(22) In the surface acoustic wave device described in (1), when the cutting angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ) , φ, θ and ψ fall in the following region IV-10:

Zone IV-10:

-5°≤φ≤5°

85°≤θ≤95°

70°≤ψ<90°

The surface acoustic wave device in (23), (22) satisfies:

0<h/λ≤0.05～0.8

Here, h is the thickness of the above-mentioned piezoelectric film, and λ is the wavelength of the above-mentioned surface acoustic wave.

1 is a cross-sectional view of a typical structure of a surface acoustic wave device according to Embodiment 1 of the present invention.

2A, 2B, and 2C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using region I-1, and a ZnO thin film formed on its surface. Figures 2A, 2B, and 2C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

3A, 3B, and 3C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. , and a ZnO thin film formed on its surface. Figures 3A, 3B, and 3C are the variation curves of SAW wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

4A, 4B, and 4C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region I-3 , and a ZnO thin film formed on its surface. Figures 4A, 4B, and 4C are the variation curves of SAW wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

5A, 5B, and 5C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using region I-4 , and a ZnO thin film formed on its surface. Figures 5A, 5B, and 5C are the variation curves of SAW wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

6A, 6B, and 6C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: using a langasite single crystal substrate in the region I-5 , and a ZnO thin film formed on its surface. Figures 6A, 6B, and 6C are the variation curves of SAW wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

7A, 7B, and 7C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using region I-6 , and a ZnO thin film formed on its surface. Figures 7A, 7B and 7C are the variation curves of SAW wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

8A, 8B, and 8C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using region I-7 , and a ZnO thin film formed on its surface. Figures 8A, 8B, and 8C are the variation curves of SAW wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

9A, 9B, and 9C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using region I-8 , and a ZnO thin film formed on its surface. 9A, 9B, and 9C are respectively the variation curves of SAW wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

10A, 10B, and 10C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: using a langasite single crystal substrate in the region I-9 , and a ZnO thin film formed on its surface. Figures 10A, 10B, and 10C are the variation curves of SAW wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

11A, 11B, and 11C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using the region I-10 , and a ZnO thin film formed on its surface. 11A, 11B, and 11C are the variation curves of SAW wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

FIG. 12 is a graph illustrating changes in TCV (temperature coefficient of SAW wave velocity) of a surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region I-1, and a ZnO thin film formed on the surface thereof.

Fig. 13 is a diagram illustrating the variation of the electromechanical coupling coefficient k ² of the surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region I-1, and a ZnO thin film formed on the surface thereof.

FIG. 14 is a graph illustrating changes in TCV (temperature coefficient of SAW wave velocity) of a surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region I-10, and a ZnO thin film formed on the surface thereof.

Fig. 15 is a diagram illustrating the variation of the electromechanical coupling coefficient k ² of the surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region I-10, and a ZnO thin film formed on the surface thereof.

Fig. 16 is a cross-sectional view of a typical structure of a surface acoustic wave device according to Embodiment 2 of the present invention.

17A, 17B, and 17C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate in the region II-1, And ZnO film and interdigitated electrodes formed on its surface. 17A, 17B, and 17C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

18A, 18B, and 18C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate in the region II-2, And ZnO film and interdigitated electrodes formed on its surface. 18A, 18B, and 18C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

19A, 19B, and 19C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate in the region II-3, And ZnO film and interdigitated electrodes formed on its surface. 19A, 19B, and 19C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

20A, 20B, and 20C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: using a langasite single crystal substrate in the region II-4 , and ZnO film and interdigitated electrodes formed on its surface. 20A, 20B, and 20C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

21A, 21B, and 21C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate in the region II-5, And ZnO film and interdigitated electrodes formed on its surface. 21A, 21B, and 21C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

22A, 22B, and 22C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using the region II-6, And ZnO film and interdigitated electrodes formed on its surface. Fig. 22A, 22B, 22C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity) respectively

23A, 23B, and 23C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate in the region II-7, And ZnO film and interdigitated electrodes formed on its surface. 23A, 23B, and 23C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

24A, 24B, and 24C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: using a langasite single crystal substrate in the region II-8, And ZnO film and interdigitated electrodes formed on its surface. 24A, 24B, and 24C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

25A, 25B, and 25C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate in the region II-9, And ZnO film and interdigitated electrodes formed on its surface. 25A, 25B, and 25C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

26A, 26B, and 26C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate in the region II-10, And ZnO film and interdigitated electrodes formed on its surface. 26A, 26B, and 26C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

Fig. 27 is a graph illustrating changes in TCV (temperature coefficient of SAW wave velocity) of a surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region II-1, and a ZnO thin film and interdigital electrodes formed on the surface thereof.

Fig. 28 is a diagram illustrating the variation of the electromechanical coupling coefficient k ² of the surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region II-1, and a ZnO thin film and interdigital electrodes formed on the surface thereof.

Fig. 29 is a graph illustrating changes in TCV (temperature coefficient of SAW wave velocity) of a surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region II-10, and a ZnO thin film and interdigital electrodes formed on the surface thereof.

Fig. 30 is a diagram illustrating the variation of the electromechanical coupling coefficient k ² of the surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region II-10, and a ZnO thin film and interdigital electrodes formed on the surface thereof.

Fig. 31 is a cross-sectional view of a typical structure of a surface acoustic wave device according to Embodiment 3 of the present invention.

32A, 32B, and 32C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate in the region III-1, And interdigitated electrode, ZnO thin film and counter electrode film sequentially formed on its surface. 32A, 32B, and 32C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

33A, 33B, and 33C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using the region III-2, And interdigitated electrode, ZnO thin film and counter electrode film sequentially formed on its surface. 33A, 33B, and 33C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

34A, 34B, and 34C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using the region III-3, And interdigitated electrode, ZnO thin film and counter electrode film sequentially formed on its surface. 34A, 34B, and 34C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

35A, 35B, and 35C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate in the region III-4 , and an interdigitated electrode, a ZnO thin film and a counter electrode film sequentially formed on its surface. 35A, 35B, and 35C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

36A, 36B, and 36C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate in the region III-5 , and an interdigitated electrode, a ZnO thin film and a counter electrode film sequentially formed on its surface. 36A, 36B, and 36C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

37A, 37B, and 37C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using the region III-6, And interdigitated electrode, ZnO thin film and counter electrode film sequentially formed on its surface. 37A, 37B, and 37C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

38A, 38B, and 38C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using the region III-7, And interdigitated electrode, ZnO thin film and counter electrode film sequentially formed on its surface. 38A, 38B, and 38C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

39A, 39B, and 39C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using the region III-8, And interdigitated electrode, ZnO thin film and counter electrode film sequentially formed on its surface. 39A, 39B, and 39C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

40A, 40B, and 40C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using region III-9, And interdigitated electrode, ZnO thin film and counter electrode film sequentially formed on its surface. 40A, 40B, and 40C are respectively the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity).

41A, 41B, and 41C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: using a langasite single crystal substrate in the region III-10, And interdigitated electrode, ZnO thin film and counter electrode film sequentially formed on its surface. 41A, 41B, and 41C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

Fig. 42 is a graph illustrating changes in TCV (temperature coefficient of SAW wave velocity) of a surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region III-1, and an interdigital electrode, a ZnO thin film, and a counter electrode film sequentially formed on the surface thereof.

Fig. 43 is a diagram illustrating the variation of the electromechanical coupling coefficient k ² of the surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region III-1, and a ZnO thin film and a counter electrode film formed on the surface thereof.

Fig. 44 is a graph illustrating changes in TCV (temperature coefficient of SAW wave velocity) of a surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region III-10, and a ZnO thin film and a counter electrode film sequentially formed on the surface thereof.

Fig. 45 is a diagram illustrating the variation of the electromechanical coupling coefficient k ² of the surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region III-10, and a ZnO thin film and a counter electrode film sequentially formed on the surface thereof.

Fig. 46 is a sectional view of a typical structure of a surface acoustic wave device according to Embodiment 4 of the present invention.

47A, 47B, and 47C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using region IV-1, And the counter electrode film, ZnO thin film and interdigital electrode formed sequentially on its surface. 47A, 47B, and 47C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

48A, 48B, and 48C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using region IV-2 , and the counter electrode film, ZnO thin film and interdigitated electrodes sequentially formed on its surface. 48A, 48B, and 48C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

49A, 49B, and 49C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using region IV-3, And the counter electrode film, ZnO thin film and interdigital electrode formed sequentially on its surface. 49A, 49B, and 49C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

50A, 50B, and 50C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate in the region IV-4 , and the counter electrode film, ZnO thin film and interdigitated electrodes sequentially formed on its surface. 50A, 50B, and 50C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

51A, 51B, and 51C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using the region IV-5, And the counter electrode film, ZnO thin film and interdigital electrode formed sequentially on its surface. 51A, 51B, and 51C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

52A, 52B, and 52C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using region IV-6, And the counter electrode film, ZnO thin film and interdigital electrode formed sequentially on its surface. 52A, 52B, and 52C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

53A, 53B, and 53C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using region IV-7, And the counter electrode film, ZnO thin film and interdigital electrode formed sequentially on its surface. 53A, 53B, and 53C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

54A, 54B, and 54C are schematic diagrams illustrating the relationship between the characteristic parameters of a surface acoustic wave device and the normalized thickness h/λ of a ZnO thin film. The surface acoustic wave device includes: a langasite single crystal substrate using region IV-8, And the counter electrode film, ZnO thin film and interdigital electrode formed sequentially on its surface. 54A, 54B, and 54C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

55A, 55B, and 55C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate in the region IV-9, And the counter electrode film, ZnO thin film and interdigital electrode formed sequentially on its surface. 55A, 55B, and 55C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

56A, 56B, and 56C are schematic diagrams illustrating the relationship between the characteristic parameters of the surface acoustic wave device and the normalized thickness h/λ of the ZnO thin film. The surface acoustic wave device includes: using the langasite single crystal substrate of the region IV-10 , and the counter electrode film, ZnO thin film and interdigitated electrodes sequentially formed on its surface. 56A, 56B, and 56C are the variation curves of SAW (surface acoustic wave) wave velocity, electromechanical coupling coefficient k ² and TCV (temperature coefficient of SAW wave velocity), respectively.

Fig. 57 is a graph illustrating changes in TCV (temperature coefficient of SAW wave velocity) of a surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The acoustic surface wave device includes: a langasite single crystal substrate utilizing region IV-1, and a counter electrode film, a ZnO thin film, and interdigital electrodes formed on its surface.

Fig. 58 is a diagram illustrating the variation of the electromechanical coupling coefficient k ² of the surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region IV-1, and a counter electrode film, a ZnO thin film, and interdigital electrodes formed on the surface thereof.

Fig. 59 is a graph illustrating changes in TCV (temperature coefficient of SAW wave velocity) of a surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region IV-10, and a counter electrode film, a ZnO thin film, and interdigital electrodes formed on the surface thereof.

Fig. 60 is a diagram illustrating the variation of the electromechanical coupling coefficient k ² of the surface acoustic wave device when the normalized thickness h/λ of the ZnO thin film and the value of ψ defining the propagation direction of the surface acoustic wave vary. The surface acoustic wave device includes: a langasite single crystal substrate utilizing region IV-10, and a counter electrode film, a ZnO thin film, and interdigital electrodes formed on the surface thereof.

Example 1

In Example 1, the langasite single crystal was used as the substrate material of the surface acoustic wave device, and , θ and ψ representing the substrate cut angle cut from the langasite single crystal and the propagation direction of the surface acoustic wave along the substrate were obtained from the total Choose from Region I. This makes it possible to reduce the SAW wave velocity, increase the electromechanical coupling coefficient, and lower the TCV (temperature coefficient of SAW wave velocity). In Example 1, the surface of the langasite single crystal substrate was further covered with a thin film made of ZnO. Then, the thickness of the piezoelectric film is controlled according to the cut angle of the substrate cut from the langasite single crystal and the propagation direction of the surface acoustic wave on the substrate, thereby achieving a further increase in the electromechanical coupling coefficient and/or a further reduction in the TCV. In this way, the size of the surface acoustic wave device can be reduced, the passband width can be increased, and the temperature stability when the surface acoustic wave device is used as a filter can be improved. In particular, it is possible to obtain surface acoustic wave filters which are most suitable for use in mobile communication terminals operating at intermediate frequencies.

The total region I includes regions I-1 to I-10, and there is a preferred piezoelectric film thickness range in each region. In regions I-1 and I-10, the absolute value of TCV can be greatly reduced, in some cases substantially to zero, by the choice of piezoelectric film thickness. Thereby, it is possible to obtain a surface acoustic wave device with very good selectivity.

It is well known that forming a piezoelectric film composed of zinc oxide, lithium oxide, CdS (cadmium sulfide) or similar components on a piezoelectric substrate of LiNbO ₃ or similar compounds can improve the electromechanical coupling coefficient of a surface acoustic wave device, typically as JP- Published in A 8-204499. But so far, no surface acoustic wave device including a piezoelectric film formed on the surface of a langasite single crystal substrate has been proposed in the art. Now, the langasite substrate can be given a positive TCV value by choosing the substrate cut angle cut from the langasite single crystal and the propagation direction of the surface acoustic wave on the substrate. On the other hand, the TCV value of ZnO thin film is negative. When the ZnO film is formed on the langasite substrate, the TCV values of the two will cancel each other out, and the total TCV value will be greatly reduced. From this point of view, traditional piezoelectric substrates such as LiNbO ₃ substrates are not suitable due to their negative TCV values, because when combined with ZnO thin films, the total TCV value increases toward the negative direction. Through the combination of the specific langasite substrate in Example 1 with the ZnO thin film, a reduction in TCV can be achieved that cannot be achieved with the conventional substrate-film combination. Example 2

In Example 2, in order to construct a surface acoustic wave device, a piezoelectric thin film and interdigital electrodes were sequentially formed on a piezoelectric substrate. A single crystal substrate is used as a piezoelectric substrate, and a ZnO thin film is used as a piezoelectric film. The electromechanical coupling coefficient can be improved by forming a piezoelectric film.

It is well known that the electromechanical coupling coefficient can be improved by forming a piezoelectric film on the surface of a piezoelectric substrate, typically as disclosed in JP-A 8-204499. However, when the LiNbO ₃ matrix with negative TCV is combined with the ZnO thin film, the overall TCV value increases towards the negative direction.

In the present invention, langasite single crystal is used as a base material. A positive TCV value can be obtained for a langasite substrate by choosing the cut angle of the substrate cut from the langasite single crystal and the propagation direction of the surface acoustic wave on the substrate. On the other hand, the TCV value of ZnO thin film is negative. When the ZnO thin film is formed on the langasite substrate, the TCV values of the two will cancel each other out, and the total TCV value will be greatly reduced, so a kind of piezoelectricity that cannot be obtained by using the traditional piezoelectric substrate-film combination can be obtained. A surface acoustic wave device, that is, a surface acoustic wave device in which the electromechanical coupling coefficient is increased and the absolute value of TCV is reduced.

JP-A 8-204499 also discloses forming a piezoelectric thin film on interdigitated electrodes on a piezoelectric substrate. However, in Embodiment 2 of the present invention, the interdigital electrodes are formed on the piezoelectric film on the piezoelectric substrate. In other words, a uniform piezoelectric film was obtained in Example 2 because the piezoelectric film was formed on the smooth surface of the piezoelectric substrate. This eliminates or substantially reduces frequency fluctuations caused by irregularities in the piezoelectric film.

The total region II includes regions II-1 to II-10, and there is a preferable piezoelectric film thickness range in each region. In regions II-1 and II-10, the absolute value of TCV can be greatly reduced, in some cases substantially down to zero, by the choice of piezoelectric film thickness. Thus, a surface acoustic wave device with very good selectivity can be obtained. Example 3

In Embodiment 3 of the present invention, as shown in FIG. 31, a piezoelectric film 4 is added to a piezoelectric substrate 2 to construct a surface acoustic wave device. The piezoelectric substrate adopts langasite single crystal substrate, the piezoelectric film adopts ZnO thin film, and forms a layer of counter electrode thin film on the piezoelectric film. The electromechanical coupling coefficient of the device can be improved by forming the piezoelectric film and the counter electrode film.

It is well known that the electromechanical coupling coefficient can be improved by forming a piezoelectric film on the surface of a piezoelectric substrate, typically as disclosed in JP-A 8-204499. However, when a conventional substrate such as _LiNbO3 with a negative TCV is combined with a ZnO thin film, the overall TCV value increases towards the negative direction.

It is also known that even when the piezoelectric film is relatively thin, the electromechanical coupling coefficient can be improved by adding a counter electrode film opposite the interdigitated electrode and separating it with the piezoelectric film. Typical examples are Nikkan Kogyo Shinbun - Described in "Surface Wave Device, and Its Application" pp.98-109 published by Sha (1978). However, in conventional SAW devices with counter electrode films, non-piezoelectric substrates such as glass, silicon or sapphire substrates are used instead of piezoelectric substrates. One of the reasons may be that the traditional piezoelectric substrate-thin film combination can cause an excessive increase of TCV value in the negative direction, as mentioned above.

In Example 3 of the present invention, a langasite single crystal was used as a base material. A positive TCV value can be obtained for a langasite single crystal substrate by selecting the cut angle of the substrate cut from the langasite single crystal and the propagation direction of the surface acoustic wave on the substrate. On the other hand, the TCV value of ZnO thin film is negative. When the ZnO film is formed on the langasite substrate, the TCV values of the two will cancel each other out, and the total TCV value will be greatly reduced. Therefore, a surface acoustic wave device that cannot be obtained by using the traditional piezoelectric substrate-film combination can be obtained, that is, a surface acoustic wave device with an improved electromechanical coupling coefficient and a reduced absolute value of TCV.

In Example 3 of the present invention, , θ and ψ representing the substrate cut angle cut out from the langasite single crystal and the spreading direction of the surface acoustic wave along the substrate are selected from the general region III. This makes it possible to achieve lower SAW wave velocity, higher electromechanical coupling coefficient, and lower TCV (temperature coefficient of SAW wave velocity). Then, the thickness of the piezoelectric film is controlled according to the cut angle of the substrate cut from the langasite single crystal and the propagation direction of the surface acoustic wave on the substrate, thereby achieving a further increase in the electromechanical coupling coefficient and/or a further reduction in the TCV. In this way, the size of the surface acoustic wave device can be reduced, the passband width can be increased, and the temperature stability when the surface acoustic wave device is used as a filter can be improved. In particular, surface acoustic wave filters are obtained which are most suitable for use in mobile communication terminal equipment operating at intermediate frequencies.

The total region III includes regions III-1 to III-10, and there is a preferable piezoelectric film thickness range in each region. In regions III-1 and III-10, the absolute value of TCV can be greatly reduced, in some cases substantially to zero, by the choice of piezoelectric film thickness. Thus, a surface acoustic wave device with very good selectivity can be obtained. Example 4

In Embodiment 4 of the present invention, as shown in FIG. 46, a piezoelectric film 4 is added to a piezoelectric substrate 2 to construct a surface acoustic wave device. The piezoelectric substrate adopts langasite single crystal substrate, the piezoelectric film adopts ZnO thin film, and a layer of counter electrode film is formed between the piezoelectric film and the substrate. The electromechanical coupling coefficient of the device can be improved by forming the piezoelectric film and the counter electrode film.

It is well known that the electromechanical coupling coefficient can be improved by forming a piezoelectric film on the surface of a piezoelectric substrate, typically as disclosed in JP-A 8-204499. However, when the traditional piezoelectric substrate with negative TCV, such as _LiNbO3 substrate, is combined with ZnO thin film, the total TCV value is greatly increased toward the negative direction.

It is also known that even when the piezoelectric film is relatively thin, the electromechanical coupling coefficient can be improved by adding interdigitated electrodes on the counter electrode film and separating them with a piezoelectric film, typical as Nikkan kogyo Shinbun-sha( 1978) published "Surface Wave Device, and Its Application" pp98-109, described in. However, in a conventional SAW device with a counter electrode film, a non-piezoelectric substrate such as glass, silicon or sapphire is used instead of a piezoelectric substrate. One of the reasons may be that the conventional piezoelectric substrate-thin film combination would cause an excessive increase of TCV value towards the negative direction.

In Example 4 of the present invention, a langasite single crystal was used as a base material. A positive TCV value can be obtained for a langasite single crystal substrate by selecting the cut angle of the substrate cut from the langasite single crystal and the propagation direction of the surface acoustic wave on the substrate. On the other hand, the TCV value of ZnO thin film is negative. When the ZnO film is formed on the langasite substrate, the TCV values of the two will cancel each other out, and the total TCV value will be greatly reduced. Therefore, a surface acoustic wave device that cannot be obtained by using the traditional piezoelectric substrate-film combination can be obtained, that is, a surface acoustic wave device with an improved electromechanical coupling coefficient and a reduced absolute value of TCV.

JP-A8-204499 also discloses forming a piezoelectric thin film on interdigitated electrodes on a piezoelectric substrate. In Embodiment 4 of the present invention, however, the counter electrode film and the piezoelectric film are formed on the piezoelectric substrate, and the interdigital electrodes are formed on the piezoelectric film. In other words, a uniform piezoelectric film was obtained in Example 4 because the piezoelectric film was formed on the smooth surface of the counter electrode film. This eliminates or substantially reduces frequency fluctuations caused by irregularities in the piezoelectric film.

In Embodiment 4 of the present invention, [phi], [theta], and [psi] representing the substrate cut angle cut out from the langasite single crystal and the propagation direction of the surface acoustic wave along the substrate are selected from the total region IV. This makes it possible to achieve lower SAW wave velocity, higher electromechanical coupling coefficient, and lower TCV (temperature coefficient of SAW wave velocity). Then, the thickness of the piezoelectric film is controlled according to the cut angle of the substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the substrate, thereby achieving a further increase in the electromechanical coupling coefficient and/or a further reduction in the TCV. This can reduce the size of the surface acoustic wave device, increase the passband width, and improve the temperature stability of the surface acoustic wave device when used as a filter. In particular, it is possible to obtain surface acoustic wave filters which are most suitable for use in mobile communication terminals operating at intermediate frequencies.

The total region IV includes regions IV-1 to IV-10, and there is a preferred range of piezoelectric film thickness in each region. In regions IV-1 and IV-10, the absolute value of TCV can be greatly reduced, in some cases substantially to zero, by the choice of piezoelectric film thickness. Thereby, it is possible to obtain a surface acoustic wave device with very good selectivity.

It should be noted here that, for example, in "NUMERICAL AND EXPERIMENTAL INVESTIGATION SAW IN LANGASITE", 1995 IEEE ULTRASONICS SYMPOSIUM, Vol. 1, 389 (Reference 1), it is given that When the cut angle of the substrate cut out from the crystal and the propagation direction of the surface acoustic wave on the substrate are represented by Euler angles ((, θ, ψ), in the following cases, the SAW wave velocity, k ² /2 and Numerical calculation results of TCD (temperature coefficient of SAW delay time), etc.:

(0°, 30°, 90°)

(0°, 53°, 90°)

(0°, 61°, 0°)

(0°, 147°, 22°)

(0°, 147°, 18°)

(0°, 32°, 40°)

(0°, 156°, 0°)

(0°, θ, 0°)

(0°, 25°, ψ) In addition, in "Effect of Electric Field and of Mechanical Pressure on Surface Acoustic Waves Propagation in La ₃ Ga ₅ SiO ₁₄ Piezoelectric Single Crystals" 1995 IEEE ULTRASONICS SYMPOSIUM, Vol.1, 409 (Reference 2) In , the numerical calculation results of k ² etc. are also given when the matrix is represented by Euler angles under the following conditions:

(0°, 90°, ψ)

(0°, 90°, ψ)

(0°, 0°, ψ)

(0°, θ, 0°)

(90°, θ, 0°)

(ϕ, 90°, 0°) Moreover, in the paper "AStudy on SAW propagation characteristics on a langasite crystalplate" in "The 17th Symposium Preprint on the Fundamentals and Applications of Ultrasonic Electronics" (Reference 3) Euler angles (φ, θ, ψ) represent the calculated values of k ² , TCD, etc. at (90°, 90°, ψ), and the measured values of TCD of the substrate under the following conditions:

(0°, 0°, 90°)

(90°, 90°, 175°)

(90°, 90°, 25°) Also, in the material distributed at the 51st Symposium of the 150th Surface Acoustic Wave Technical Committee of the Japan Society for the Promotion of Science, p. 21 of the paper "Propagation direction dependence of Rayleigh Waves on a langastie In "plate", the numerical calculation results of k ² etc. are also given when the matrix is represented by Euler angles (φ, θ, ψ) in the following cases:

(0°, 0°, 4)

(90°, 90°, 4) and the TCD results calculated with the measured series of resonant frequencies of the matrix under the following conditions:

(0°, 0°, 90°)

(90°, 90°, 175°)

(90°, 90°, 15°)

(90°, 90°, 21°)

(90°, 90°, 25°) The publication date of Reference 4 is January 27, 1997, after the basic application of the present application was filed. Also, the substrate is also given in the paper "Propagation characteristics of surface acoustic waves on La ₃ Ga ₅ SiO ₁₄ " in "The 17th Symposium Preprint on the Fundamentals and Applications of Ultrasonic Electronics", using Euler angles (φ, θ, ψ) represents the numerical calculation results of k ² , etc. under the following conditions:

(90°, 90°, ψ)

(90°, 90°, ψ)

(0°, 0°, ψ)

(0°, θ, 0°)

All the above-mentioned references refer to the properties of the langasite single crystal substrate itself, but none of them disclose adding a ZnO piezoelectric film on the langasite single crystal substrate. In the present invention, by controlling the cutting angle of the substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the substrate, the optimal piezoelectric film thickness is obtained to achieve further improvement of the electromechanical coupling coefficient and/or TCV Further decrease. Accordingly, the present invention was not readily foreseeable by the above references. Example 1

A typical configuration of a surface acoustic wave device according to Embodiment 1 of the present invention is shown in FIG. 1 . The surface acoustic wave device includes: a substrate 2 , a set of input interdigital electrodes 3 and output interdigital electrodes 3 formed on the surface of the substrate 2 , and a piezoelectric film 4 covering the substrate 2 and the interdigital electrodes 3 . In each embodiment of the present invention, a langasite single crystal is used as the substrate 2, and the langasite single crystal belongs to the point group 32. In each of the embodiments of the present invention, ZnO is used as the piezoelectric film 4, and the piezoelectric axis of the piezoelectric film is substantially perpendicular to the surface of the substrate.

In Figure 1, the x, y, and z axes are perpendicular to each other. The x and y axes are located in the plane direction of the substrate 2, and the x axis defines the propagation direction of the surface acoustic wave. The z-axis is perpendicular to the substrate plane and defines the cut angle (tangent plane) of the substrate cut from the single crystal. The relationship between these x, y, z axes and the x, y, z axes of the langasite single crystal can be represented by Euler angles (φ, θ, ψ).

In the surface acoustic wave device according to Embodiment 1, when the substrate cut angle cut out from the langasite single crystal and the propagation direction of the surface acoustic wave are represented by (φ, θ, ψ), φ, θ, ψ are located at the above-mentioned in each region.

By selecting φ, θ, ψ from the total area I and forming a piezoelectric film with an appropriate thickness, it is possible to reduce the SAW wave velocity, increase the electromechanical coupling coefficient and reduce the TCV. Therefore, the size of the surface acoustic wave device is reduced, the passband width is increased, and the temperature stability when the surface acoustic wave device is used as a wave filter is improved. In particular, it is possible to obtain a surface acoustic wave filter most suitable for use in mobile communication terminal equipment operating at intermediate frequencies. More specifically, the temperature coefficient of TCV or SAW wave velocity of the substrate can be -35~60ppm/°C, the SAW wave velocity can be as high as 2900m/s, and the electromechanical coupling coefficient can be 0.1% or higher. In some cases, better performance can also be obtained.

In the regions I-1, I-6, I-7, I-8, I-9 and I-10, since the coupling coefficient can reach 0.4% or higher, a surface acoustic wave device with a wider passband can be obtained. In the regions I-1, I-7 and I-10, the coupling coefficient is 0.7% or higher, and the passband of the obtained surface acoustic wave device is wider than the above case.

In regions I-1 and I-10, the TCV can be greatly reduced, even to zero in some cases, so that the obtained SAW devices have good enough temperature stability. Especially in the region I-1, since a large coupling coefficient and a small TCV can be obtained through the selection of the piezoelectric film thickness, a SAW device with a wide passband and good enough temperature stability can be obtained.

It should be noted that the initial temperature coefficient is used here as TCV, that is, the temperature coefficient of SAW wave velocity. Even if the temperature-sound velocity curve is quadratic (initial temperature coefficient is zero), the quadratic curve can be approximated to the initial straight line by the least square method to calculate TCV. In particular, TCV can be obtained by dividing the SAW wave velocity change ΔV per unit temperature range by the SAW wave velocity V ₀ at 0°C.

The tangential direction of the matrix can be determined by X-ray diffraction.

The langasite single crystal in the present invention is generally represented by the chemical formula La ₃ Ga ₅ SiO ₁₄ , and is known as an example given in PROC.IEEE International Frequency Control Sympo.Vol.1994, pp48-57 (1994). In the present invention, langasite single crystal is used as the substrate of the surface acoustic wave device. In this case, if the tangential direction of the crystal and the propagation direction of the surface acoustic wave are specially selected, a surface acoustic wave device having high performance as described above can be obtained. If a single crystal of langasite is found to consist mainly of only langasite phase somewhere by X-ray diffraction, it can be used there. In other words, the langasite single crystal used here is not necessarily limited to the composition of the above chemical molecular formula, for example, at least a part of the lattice positions of La, Ga and Si can be replaced by other elements, and the number of oxygen can also deviate from the above stoichiometric molecular formula. Moreover, langasite single crystals may contain unavoidable impurities such as Al, Zr, Fe, Ce, Nd, Pt and Ca. There is also no particular limitation on how to fabricate the langasite single crystal, that is, it can be fabricated by a common single crystal growth process, such as the CZ process.

In Embodiment 1, the preferred piezoelectric film thickness can be determined according to the position of (φ, θ, ψ). More specifically, as previously stated, there is a preferred h/λ for each region. where h is the thickness of the piezoelectric film, λ is the wavelength of the SAW, and h/λ is the thickness of the piezoelectric film normalized by the wavelength of the SAW. In general, the greater the value of h/λ, the greater the electromechanical coupling coefficient and the SAW wave velocity in the region I-2 to I-9 in the total region I. In the regions I-1 and I-10, the larger the value of h/λ, the smaller the SAW wave velocity. Therefore, it is necessary to select a range in which the electromechanical coupling coefficient is large enough and the SAW wave velocity is small enough in each region. As h/λ increases, the temperature coefficient of TCV or SAW wave velocity of the substrate with the piezoelectric film increases in the negative direction. Therefore, when the substrate itself has a positive TCV value, the TCV value may decrease after adding the piezoelectric film.

In each embodiment of the present invention, there is no special limitation on how to form the piezoelectric film, that is, the piezoelectric film can be produced by any desired process, as long as the piezoelectric axis of the produced piezoelectric film is substantially aligned with the plane of the substrate. Just vertically. These processes include, for example, a sputtering process, an ion plating process, a CVD (Chemical Vapor Deposition) process, and the like. If proper film formation conditions are selected in advance, piezoelectric films whose piezoelectric axis or C-axis is substantially perpendicular to the surface of the substrate can be easily obtained through these processes.

In each embodiment of the present invention, the size of the substrate is not strictly required, and it is about 1-20 mm along the propagating direction of the surface acoustic wave, and about 0.5-5 mm perpendicular to the propagating direction. The thickness of the substrate is at least three times the interdigital electrode spacing (equivalent to the wavelength of the surface acoustic wave) formed on the substrate, generally about 0.2-0.5mm. It should be noted, however, that in some cases the thickness of the test specimens prepared for the purpose of estimating the properties of the matrix may exceed the above upper limit by 0.5 mm. For example, for testing purposes, the interdigitated electrodes have a bar spacing of 320 μm, and the thickness of the substrate is at least 0.96 mm.

In the present invention, each interdigital electrode formed on the substrate 2 is a periodic strip-shaped thin-film electrode, which is used to excite, receive, reflect and propagate surface acoustic waves. The interdigital electrodes are arranged in a certain way to realize the propagation of the surface acoustic wave in the above-mentioned predetermined propagation direction. The interdigitated electrodes are formed by evaporation or sputtering with Au or Al. The finger width of the interdigital electrode can be determined according to the frequency of the surface acoustic wave device, and in the preferred frequency band of the present invention, the finger width is usually about 2-10 μm. The thickness of the interdigital electrodes is usually 0.03 to 1.5 μm.

According to various embodiments of the present invention, generally speaking, surface acoustic wave devices are very suitable for filters operating in the frequency band of 10-500 MHz, especially for 10-300 MHz. The surface acoustic wave device of the present invention is also conducive to reducing the size of the surface acoustic wave delay element due to the low SAW wave velocity. Example 2

A typical structure of a surface acoustic wave device according to Embodiment 2 of the present invention is shown in FIG. 16 . The surface acoustic wave device includes: a substrate 2 , a piezoelectric film 4 formed on the surface of the substrate 2 , and a set of input interdigital electrodes 3 and output interdigital electrodes 3 formed on the surface of the piezoelectric film 4 .

In the surface acoustic wave device according to Embodiment 2, when the substrate cut angle cut out from the langasite single crystal and the propagation direction of the surface acoustic wave are represented by (φ, θ, ψ), φ, θ, ψ are located at the above-mentioned in each region.

By selecting φ, θ, ψ, and forming a piezoelectric film with an appropriate thickness from the total area II, a reduction in SAW wave velocity, an increase in the electromechanical coupling coefficient, and a reduction in TCV can be achieved. Therefore, the size of the surface acoustic wave device is reduced, the passband width is increased, and the temperature stability when the surface acoustic wave device is used as a filter is improved. In particular, it is possible to obtain a surface acoustic wave filter most suitable for use in mobile communication terminal equipment operating at intermediate frequencies. More specifically, the TCV or SAW wave velocity temperature coefficient of the substrate can be -35-60ppm/°C, the SAW wave velocity can be as high as 2900m/s, and the electromechanical coupling coefficient can reach 0.1% or higher. In some cases, better performance can also be obtained.

In the general region II, since the obtained coupling coefficient can be as high as 0.4% or more, broadband surface acoustic wave devices can be obtained. In the regions II-1 and II-10, since the coupling coefficient is as high as 0.8% or higher, a wider passband SAW device can be obtained.

In regions II-1 and II-10, since TCV can be greatly reduced, the resulting SAW device can have sufficiently good temperature stability. And in the regions II-1 and II-10, since a large coupling coefficient and a small TCV can be obtained by selecting the thickness of the piezoelectric film, the obtained SAW device can have a much wider passband and a much better temperature stability.

In Embodiment 2, the preferred piezoelectric film thickness can be determined according to the position of (φ, θ, ψ). More specifically, there is a preferred h/λ for each region. where h is the thickness of the piezoelectric film, λ is the wavelength of the SAW, and h/λ is the thickness of the piezoelectric film normalized by the wavelength of the SAW. In general, the larger the value of h/λ, the larger the electromechanical coupling coefficient and the SAW wave velocity are from the region II-2 to II-9 in the total region II. In the regions II-1 and II-10, the larger the value of h/λ, the smaller the SAW wave velocity. As h/λ increases, the temperature coefficient of SAW wave velocity or TCV of the substrate with the piezoelectric film increases in the negative direction. Therefore, when the substrate itself has a positive TCV value, the TCV value may decrease after adding the piezoelectric film.

Therefore, it should be preferred in each region to select such a value of h/λ that can greatly improve the necessary performance, or the performance of SAW wave velocity, electromechanical coupling coefficient and TCV. As mentioned earlier, within each region there exists a specific h/λ range that truly meets these performance requirements. Example 3

A typical structure of a surface acoustic wave device according to Embodiment 3 of the present invention is shown in FIG. 31 . The surface acoustic wave device includes: a substrate 2, a set of input interdigital electrodes 3 and output interdigital electrodes 3 added on the surface of the substrate 2, and a piezoelectric film 4 covering the substrate 2 and the interdigital electrodes 3 and 3. Also, on the surface of the piezoelectric film 4, a counter electrode film 5 is formed.

In the surface acoustic wave device according to Embodiment 3, when the substrate cut angle cut out from the langasite single crystal and the propagation direction of the surface acoustic wave are represented by (φ, θ, ψ), φ, θ, ψ are located at the above-mentioned in each region.

By selecting φ, θ, ψ from the total area II, and forming appropriate thicknesses of the piezoelectric film and the counter electrode film, it is possible to reduce the SAW wave velocity, increase the electromechanical coupling coefficient, and reduce the temperature coefficient of SAW wave velocity or TCV. Therefore, the size of the surface acoustic wave device is reduced, the passband width is increased, and the temperature stability when the surface acoustic wave device is used as a filter is improved. In particular, it is possible to obtain a surface acoustic wave filter most suitable for use in mobile communication terminal equipment operating at intermediate frequencies. More specifically, the temperature coefficient of SAW wave velocity or TCV of the substrate can be -35 ~ 60ppm/°C, the SAW wave velocity can be as high as 2900m/s, the electromechanical coupling coefficient can reach 0.1% or higher, and in some cases, good Much more performance.

In total region III, there are two peaks in the electromechanical coupling coefficient with respect to the piezoelectric film thickness. The peak corresponding to the thin piezoelectric film side is a practically large enough value, 0.13% or more. Especially in the region III-4, the peak value of the coupling coefficient is 0.37%. There is also a peak with respect to the thick piezoelectric film side, which is also a practically large enough value, 0.15% or more. At this time, the TCV increases by about 20 ppm/°C compared to that without the piezoelectric film.

In Embodiment 3, the preferred piezoelectric film thickness can be determined according to the position of (φ, θ, ψ). More specifically, as stated previously, there is a preferred h/λ for each region. where h is the thickness of the piezoelectric film, λ is the wavelength of the SAW, and h/λ is the thickness of the piezoelectric film normalized by the wavelength of the SAW. The larger the value of h/λ is, the smaller the SAW wave velocity is in the regions III-1 and III-10, and the larger the SAW wave velocity is in the regions III-2 to III-9. As mentioned earlier, in the total region III, the electromechanical coupling coefficient has two peaks with respect to h/λ. When the electromechanical coupling coefficient is at the peak on the large h/λ side, the absolute value of TCV becomes small. As h/λ increases, the SAW temperature coefficient of wave velocity or TCV value of the substrate with piezoelectric film increases in the negative direction. Therefore, when the TCV value of the substrate itself is positive, the TCV value may decrease after adding the piezoelectric film.

Therefore, it should be preferred to select such h/λ value in each region: it can greatly improve the necessary performance, or the performance of SAW wave velocity, electromechanical coupling coefficient and TCV. As mentioned earlier, within each region there exists a specific h/λ range that truly meets these performance requirements.

The size of the counter electrode film 5 may cover the entire piezoelectric film 4 . However, in the case of this embodiment, at least in an area opposite to the interdigital electrodes of the input and output terminals, a counter electrode film should be formed. The preferred thickness range of the counter electrode film is 0.03-0.1 μm, too thin is not suitable, because the obtained film may be discontinuous, and the potential on the film plane will become uneven due to the increase of resistance. Too thick is also not suitable, because it will cause an increase in the total weight of the counter electrode film. The material and formation method of the counter electrode film may be the same as those of the interdigital electrodes described above. The counter electrode film does not always have to be grounded, or always connected, it can be electrically isolated. Example 4

A typical structure of a surface acoustic wave device according to Embodiment 4 of the present invention is shown in FIG. 46 . The surface acoustic wave device comprises: a substrate 2, a counter electrode film 5 added on the surface of the substrate 2, a piezoelectric film 4 added on the counter electrode film 5, and a set of input fingers added on the surface of the piezoelectric film 4 Electrode 3 and output interdigitated electrode 3.

In the surface acoustic wave device according to Embodiment 4, when the substrate cut angle cut out from the langasite single crystal and the propagation direction of the surface acoustic wave are represented by (φ, θ, ψ), φ, θ, ψ are located at the above-mentioned in each region.

By selecting φ, θ, ψ from the total area IV, and forming appropriate thicknesses of the piezoelectric film and the counter electrode film, a reduction in SAW wave velocity, an increase in the electromechanical coupling coefficient, and a reduction in TCV can be achieved. Therefore, the size of the surface acoustic wave device is reduced, the passband width is increased, and the temperature stability when the surface acoustic wave device is used as a filter is improved. In particular, it is possible to obtain a surface acoustic wave filter most suitable for use in mobile communication terminal equipment operating at intermediate frequencies. More specifically, the temperature coefficient of SAW wave velocity or TCV of the substrate can be -35 ~ 60ppm/°C, the SAW wave velocity can be as high as 2900m/s, the electromechanical coupling coefficient can reach 0.1% or higher, and in some cases, even more good performance.

In the total region IV, since the obtained coupling coefficient can be as high as 0.2% or more, a broadband surface acoustic wave device can be obtained. Especially in the regions IV-1 and IV-10, since the coupling coefficient is as high as 0.8% or higher, a surface acoustic wave device with a much wider passband can be obtained.

In regions IV-1 and IV-10, since TCV can be greatly reduced, sometimes even down to zero, the resulting SAW device can have sufficiently good temperature stability. And in the regions II-1 and II-10, since a large coupling coefficient and a small TCV can be obtained by selecting the thickness of the piezoelectric film, the obtained SAW device can have a much wider passband and a much better temperature stability.

It has already been mentioned that in Embodiment 4, a preferable piezoelectric film thickness can be determined according to the position of (φ, θ, ψ). More specifically, there is a preferred h/λ for each region. where h is the thickness of the piezoelectric film, λ is the wavelength of the SAW, and h/λ is the thickness of the piezoelectric film normalized by the wavelength of the SAW. In general, the value of h/λ is larger from the region IV-2 to IV-9 in the total region IV. The greater the electromechanical coupling coefficient and the SAW wave velocity. But in regions IV-1 and IV-10, the larger the value of h/λ, the smaller the SAW wave velocity. As h/λ increases, the SAW temperature coefficient of wave velocity, or TCV, of the substrate with the piezoelectric film increases in the negative direction. Therefore, when the substrate itself has a positive TCV value, the TCV value may decrease after adding the piezoelectric film.

Therefore, it should be preferred to select such h/λ value in each region: it can greatly improve the necessary performance, or the performance of SAW wave velocity, electromechanical coupling coefficient and TCV. As mentioned earlier, within each region there exists a specific h/λ range that truly meets these performance requirements.

In the case of this embodiment, the counter electrode film 5 should be formed at least on the area opposite to the interdigital electrodes on the input and output sides. However, in order to make the piezoelectric film 4 uniform, it is preferable that the counter electrode film 5 covers the entire substrate 2 . A preferable thickness range of the counter electrode film is 0.03 to 0.1 μm. Too thin is not suitable because the resulting film may be discontinuous and the potential across the plane of the film will become non-uniform due to the increased resistance. Too thick is also not suitable, because it will counteract the increase of the total weight of the electrode film. The material and formation method of the counter electrode film may be the same as those of the interdigital electrodes described above. The counter electrode film does not always have to be grounded, or always connected, it can be electrically isolated.

The present invention is explained below in conjunction with examples. Example I-1 (embodiment 1)

The langasite single crystal is grown by the CZ process, and the langasite single crystal is cut to obtain the matrix. A surface acoustic wave transducer is formed on the surface of the substrate, the surface acoustic wave transducer includes a set of input interdigital electrodes and output interdigital electrodes, and a ZnO film is generated on the transducer by a magnetron sputtering process to manufacture surface acoustic wave devices. The interdigitated electrodes are common electrodes of the same shape, produced by evaporation of Al, with a thickness of 0.1 μm, an electrode finger width d of 15 μm, and an electrode finger spacing (4d) of 60 μm (equivalent to the wavelength of the surface acoustic wave). The number of finger pairs is 40, and the aperture width between electrode fingers is 60λ (=3.6mm). However, when the output signal is weak, the inter-finger aperture width of the above-mentioned interdigital electrode can be changed to 100λ, and the others remain unchanged. In addition, when the normalized thickness of the ZnO film exceeds 0.4, the electrode finger width is halved to 30 μm, and the aperture width is also halved to 1.8 mm (=60λ).

In this example, when the cut angle of the substrate from the langasite single crystal and the direction of surface acoustic wave propagation on the substrate are represented by Euler angles (φ, θ, ψ), φ, θ are 0° and 90°, respectively. ψ is used to determine the X-axis and the propagation direction of the surface acoustic wave, and the values of ψ selected from the total area I are shown in Figures 2A to 10C. The selection of the thickness h of the ZnO thin film on the substrate should satisfy the above normalized thickness h/λ=0.05˜0.8. In each propagation direction, the variation of SAW wave velocity, electromechanical coupling coefficient k ² , and temperature coefficient of SAW wave velocity TCV when h/λ changes is measured. The SAW wave velocity is obtained from the center frequency of the filter, while the electromechanical coupling coefficient ^k2 uses the famous Smith equivalent circuit model. It is obtained by measuring the admittance at both ends of the surface acoustic wave transducer. The measurement results of SAW wave velocity, ^k2 and TCV in each direction are plotted in Figs. 2A-10C.

At the points where the results are not marked in each figure, no surface acoustic wave signal can be detected. Considering the results of the measured electromechanical coupling coefficients, one possible reason is that the electromechanical coupling coefficients are too small to effectively convert electrical signals into SAW signals and vice versa when propagating in this range. When the normalized thickness h/λ of the ZnO film increases, the SAW mode disappears. Body waves appear. Therefore, the data obtained after the generation of body waves are not shown.

The change curve of SAW wave velocity and ^k2 shows that if the cutting angle of the substrate from the crystal and the propagation direction of the surface acoustic wave fall in the total area I, the SAW wave velocity can be reduced to 2900m/s or lower. This is more conducive to reducing the size of SAW devices compared to conventional ST quartz crystals. It was also found that the electromechanical coupling coefficient obtained in the total area I can be 0.1% or higher. This makes it possible to obtain much higher electromechanical coupling coefficients through the choice of ZnO film thickness.

Continuing to consider the change graph of TCV, when the TCV of the matrix itself is positive, in other words, when the TCV of the matrix is positive when the normalized thickness h/λ=0, it is found that as h/λ increases, the TCV value changes from The positive value changes to the negative value, thereby improving the temperature performance. On the other hand, when the substrate has a negative TCV, the ZnO film is added, and when the normalized thickness is increased, the TCV value increases greatly to the negative direction. Even in this case, the absolute value of the TCV is not too large (about 35ppm/°C or lower); it was also found that if the usual BGO matrix is used, the temperature stability of the matrix is much improved.

Below, each area is explained in detail:

It can be seen from Figures 2B and 2C that the electromechanical coupling coefficient of the device using region I-1 can be as high as 0.76% when h/λ=0.6. At this time, TCV=-26ppm/°C, which has good enough temperature performance .

It can be seen from Figures 3B and 3C that the electromechanical coupling coefficient can be as high as 0.32% when h/λ=0.5 using the device in region I-2. At this time, TCV=9ppm/°C, which has good enough temperature performance .

It can be seen from Figures 4B and 4C that the device using region I-3, when h/λ=0.4, its electromechanical coupling coefficient can be as high as 0.15%. At this time, TCV=32ppm/°C, which has a good enough temperature performance.

It can be seen from Figures 5B and 5C that the electromechanical coupling coefficient of the device using region I-4 can be as high as 0.19% when h/λ=0.4. At this time, TCV=17ppm/°C, which has good enough temperature performance.

It can be seen from Figures 6B and 6C that the electromechanical coupling coefficient of the device using region I-5 can be as high as 0.25% when h/λ=0.35. At this time, TCV=16ppm/°C, which has good enough temperature performance.

It can be seen from Figures 7B and 7C that the electromechanical coupling coefficient of the device using region I-6 can be as high as 0.61% when h/λ=0.35. At this time, TCV=17ppm/°C, which has good enough temperature performance.

It can be seen from Figures 8B and 8C that the device using region I-7, when h/λ=0.35, its electromechanical coupling coefficient can be as high as 0.72%, at this time, TCV=19ppm/°C, which has good enough temperature performance.

It can be seen from Figures 9B and 9C that the device using region I-8, when h/λ=0.35, its electromechanical coupling coefficient can be as high as 0.53%. At this time, TCV=33ppm/℃, which has good enough temperature inversion performance .

It can be seen from Figures 10B and 10C that the device using region I-9, when h/λ=0.5, its electromechanical coupling coefficient can be as high as 0.63%. At this time, TCV=12ppm/°C, which has good enough temperature performance.

It can be seen from Figures 11B and 11C that the electromechanical coupling coefficient of the device using region I-10 can be as high as 0.96% when h/λ=0.55. At this time, TCV=24ppm/°C, which has good enough temperature performance. Example 1-2 (embodiment 1)

The surface acoustic wave device made according to example 1-1 is different from 1-1 in that: φ and θ are 0° and 90° respectively, and the value of ψ used to determine the X-axis or surface acoustic wave propagation direction is from -80° To -66°, select a value every 2°. It should be noted that these values of φ, θ, ψ are within the region I-1. The TCV-h/λ (normalized thickness) relationship of these devices was measured and the results are shown in FIG. 12 . The relationship between k ² -h/λ was also measured, and the results are shown in Fig. 13 .

On the one hand, it can be seen from Fig. 12 that in the region I-1, the so-called zero-temperature performance can be obtained, and the thickness of the ZnO film corresponding to the zero-temperature performance varies with the propagation direction of the surface acoustic wave. On the other hand, it can be seen from Fig. 13 that the electromechanical coupling coefficient tends to become larger as the ZnO thin film becomes thicker. Therefore, if the thickness of the ZnO film is selected in order to obtain zero temperature performance, and the propagation direction is selected in order to obtain a sufficiently large electromechanical coupling coefficient, a SAW device with zero temperature performance and a large electromechanical coupling coefficient can be obtained. For example, if the propagation direction ψ is -70°, and the normalized thickness h/λ of ZnO is 0.35, then the TCV can be substantially reduced to zero, and ^k2 can be as high as 0.32%, so it is possible to obtain , a surface acoustic wave device with wide passband and very good temperature performance. Example 1-3 (embodiment 1)

The surface acoustic wave device made according to example 1-1 is different from 1-1 in that: φ and θ are 0° and 90° respectively, and the value of ψ used to determine the X-axis or surface acoustic wave propagation direction is from 66° to 80° Select values every 2°. It should be noted that these values of φ, θ, ψ are within the region I-10. The TCV-h/λ (normalized thickness) relationship of these devices was measured, and the results are shown in FIG. 14 . The relationship between k ² -h/λ was also measured, and the results are shown in FIG. 15 .

On the one hand, it can be seen from Fig. 14 that in the region I-10, zero temperature performance can be obtained, and the thickness of the ZnO thin film corresponding to the zero temperature performance varies with the propagation direction of the surface acoustic wave. On the other hand, it can be seen from Fig. 15 that when the ZnO thin film becomes thicker, the electromechanical coupling coefficient becomes larger. Therefore, if the thickness of the ZnO film is selected in order to obtain a sufficiently large electromechanical coupling coefficient, and the propagation direction is selected in order to obtain zero temperature performance, then a surface acoustic wave device with zero temperature performance and a large electromechanical coupling coefficient can be obtained. For example, if the propagation direction ψ is 70° and the normalized thickness h/λ of ZnO is 0.35, then the TCV can be substantially reduced to zero, and ^k2 can be as high as 0.6%, so it is possible to obtain SAW device with wide passband and very good temperature performance. Example 2-1 (embodiment 2)

A langasite single crystal was grown by CZ process, and a 0.35mm thick substrate was cut from the single crystal. A ZnO film is produced on the surface of the substrate by a magnetron sputtering process, and a surface acoustic wave transducer is produced on the ZnO film to manufacture a surface acoustic wave device. The surface acoustic wave transducer includes: a set of input interdigital electrodes and an output Interdigitated electrodes. The interdigitated electrodes are common electrodes of the same shape, produced by evaporation of Al, with a thickness of 0.1 μm, an electrode finger width d of 15 μm, and an electrode finger spacing (4d) of 60 μm (equivalent to the wavelength of the surface acoustic wave). The number of finger pairs is 40, and the aperture width between fingers is 60λ (=3.6mm). However, when the output signal is weak, the inter-finger aperture width of the above-mentioned interdigital electrode can be changed to 100λ, and the others remain unchanged. In addition, when the normalized thickness of the ZnO film exceeds 0.4, the electrode finger spacing is halved to 30 μm, and the aperture width is also halved to 1.8 mm (=60λ).

In this example, when the cut angle of the substrate from the langasite single crystal and the propagation direction of the surface acoustic wave on the substrate are represented by Euler angles (φ, θ, ψ), φ and θ are 0° and 90°, respectively. ψ is used to determine the X-axis and the propagation direction of the surface acoustic wave, and the values of ψ selected from the total area II are shown in Figures 17A to 26C. The selection of the thickness h of the ZnO thin film on the substrate should satisfy the above normalized thickness h/λ=0.05˜0.8. For comparison, a surface acoustic wave device with h/λ=0, ie without ZnO thin film, was prepared. In each direction of propagation, the SAW wave velocity, the electromechanical coupling coefficient k ² , and the SAW wave velocity are obtained from the center frequency of the filter. The electromechanical coupling coefficient k ² uses the famous Smith equivalent circuit model to measure the surface acoustic wave transducer The admittance at both ends of the device is obtained. The measurement results of SAW wave velocity, ^k2 and TCV in each direction are plotted in Figs. 17A to 26C.

As the normalized thickness h/λ of the ZnO film increases, the SAW mode disappears and bulk waves appear. Therefore, the data obtained after the generation of body waves are not shown.

The change curve of SAW wave velocity and ^k2 shows that if the cutting angle of the substrate from the crystal and the propagation direction of the surface acoustic wave fall in the general area II, the SAW wave velocity can be reduced to 2900m/s or lower. This is more conducive to reducing the size of SAW devices compared to conventional ST quartz crystals. It was also found that the electromechanical coupling coefficient obtained in the total area I can be 0.1% or higher. This makes it possible to obtain much higher electromechanical coupling coefficients through the choice of ZnO film thickness.

Continuing to consider the change graph of TCV, when the TCV of the matrix itself is positive, in other words, when the TCV of the matrix is positive when the normalized thickness h/λ=0, it is found that as h/λ increases, the TCV value changes from The positive value changes to the negative value, thereby improving the temperature performance. On the other hand, when the substrate has a negative TCV, the ZnO film is added, and when the normalized thickness is increased, the TCV value increases greatly to the negative direction. Even in this case, the absolute value of the TCV is not too large (about 35ppm/°C or lower); it was also found that if the usual BGO matrix is used, the temperature stability of the matrix is much improved.

Below, each area is explained in detail.

It can be seen from Figures 17B and 17C that the electromechanical coupling coefficient of the device using region II-1 can be as high as 0.88% when h/λ=0.8. At this time, TCV=-30ppm/℃, which has good enough temperature performance .

It can be seen from Figures 18B and 18C that the electromechanical coupling coefficient of the device using region II-2 can be as high as 0.6% when h/λ=0.55. At this time, TCV=9ppm/°C, which has good enough temperature performance.

It can be seen from Figures 19B and 19C that the electromechanical coupling coefficient of the device using region II-3 can be as high as 0.44% when h/λ=0.35. At this time, TCV=29ppm/°C, which has good enough temperature performance.

It can be seen from Figures 20B and 20C that the electromechanical coupling coefficient of the device using region II-4 can be as high as 0.56% when h/λ=0.4, and here, TCV=17ppm/°C, which has good enough temperature performance.

It can be seen from Figures 21B and 21C that the electromechanical coupling coefficient of the device using region II-5 can be as high as 0.53% when h/λ=0.35. Here, TCV=15ppm/°C, which has good enough temperature performance.

It can be seen from Figures 22B and 22C that the electromechanical coupling coefficient of the device using region II-6 can be as high as 0.59% when h/λ=0.3. At this time, TCV=16ppm/°C, which has good enough temperature performance.

It can be seen from Figures 23B and 23C that the electromechanical coupling coefficient of the device using region II-7 can be as high as 0.63% when h/λ=0.35. At this time, TCV=19ppm/°C, which has good enough temperature performance.

It can be seen from Figures 24B and 24C that the device using region II-8, when h/λ=0.3, its electromechanical coupling coefficient can be as high as 0.51%. At this time, TCV=32ppm/°C, which has good enough temperature performance.

It can be seen from Figures 25B and 25C that the electromechanical coupling coefficient of the device using region II-9 can be as high as 0.59% when h/λ=0.55, and here, TCV=11ppm/°C, which has good enough temperature performance.

It can be seen from Figures 26B and 26C that the electromechanical coupling coefficient of the device using region II-10 can be as high as 0.86% when h/λ=0.75. Here, TCV=-30ppm/°C, which has good enough temperature performance.

Example 2-2 (embodiment 2)

The surface acoustic wave device made according to example 1-1 is different from 2-1 in that: φ and θ are 0° and 90° respectively, and the value of ψ used to determine the X axis or surface acoustic wave propagation direction is from -80° To -66°, select a value every 2°. It should be noted that these values of φ, θ, ψ are within the region II-2. The TCV-h/λ (normalized thickness) relationship of these devices was measured and the results are shown in FIG. 27 . The relationship between k ² -h/λ was also measured, and the results are shown in Fig. 28 .

On the one hand, it can be seen from Fig. 27 that in the region II-1, zero temperature performance can be obtained, and the thickness of the ZnO thin film corresponding to the zero temperature performance varies with the propagation direction of the surface acoustic wave. On the other hand, it can be seen from Fig. 13 that the electromechanical coupling coefficient tends to become larger as the ZnO thin film becomes thicker. Therefore, if the thickness of the ZnO film is selected in order to obtain zero temperature performance, and the propagation direction is selected in order to obtain a sufficiently large electromechanical coupling coefficient, a SAW device with zero temperature performance and a large electromechanical coupling coefficient can be obtained. For example, if the propagation direction ψ is -70°, and the normalized thickness h/λ of ZnO is 0.35, then the TCV can be substantially reduced to zero, and ^k2 can be as high as 0.51%, so it is possible to obtain , a surface acoustic wave device with wide passband and very good temperature performance. Example 2-3 (embodiment 1)

The surface acoustic wave device made according to example 2-1 is different from 2-1 in that: φ and θ are 0° and 90° respectively, and the value of ψ used to determine the X axis or surface acoustic wave propagation direction is from 66° to 80° Select values every 2°. It should be noted that these values of φ, θ, ψ are within the region II-10. The TCV-h/λ (normalized thickness) relationship of these devices was measured and the results are shown in FIG. 29 . The relationship between k ² -h/λ was also measured, and the results are shown in Fig. 30 .

On the one hand, it can be seen from Fig. 29 that in the region II-10, zero temperature performance can be obtained, and the thickness of the ZnO thin film corresponding to the zero temperature performance varies with the propagation direction of the surface acoustic wave. On the other hand, it can be seen from Fig. 30 that the electromechanical coupling coefficient becomes larger as the ZnO thin film becomes thicker. Therefore, if the thickness of the ZnO film is selected in order to obtain a sufficiently large electromechanical coupling coefficient, and the propagation direction is selected in order to obtain zero temperature performance, then a surface acoustic wave device with zero temperature performance and a large electromechanical coupling coefficient can be obtained. For example, if the propagation direction 4 is 70° and the normalized thickness h/λ of ZnO is 0.35, then the TCV can be substantially reduced to zero, and ^k2 can be as high as 0.56%, so it is possible to obtain A surface wave device with wide passband and very good temperature performance. Example 3-1 (embodiment 3)

A langasite single crystal is grown by the CZ process, and a 0.35mm thick substrate is cut from the single crystal; a surface acoustic wave transducer is formed on the surface of the substrate, and the transducer includes: a set of input interdigital electrodes and output interdigital electrodes; A layer of ZnO film is formed on the surface wave transducer by magnetron sputtering process; then, a layer of counter electrode film is formed on the ZnO film to form a surface acoustic wave device. The interdigitated electrode and the counter electrode film are formed by Al evaporation. The interdigitated electrodes are common electrodes with the same shape, the thickness is 0.1 μm, the electrode finger width d is 15 μm, the electrode finger spacing (4d) is 60 μm, the number of electrode finger pairs is 40, and the aperture width between fingers is It is 60λ (= 3.6mm). However, when the output signal is weak, the inter-finger aperture width of the above-mentioned interdigital electrode can be changed to 100λ, and the others remain unchanged. In addition, when the normalized thickness of the ZnO film exceeds 0.4, the electrode finger spacing is halved to 30 μm, and the aperture width is also halved to 1.8 mm (=60λ). The thickness of the counter electrode film was 0.1 μm.

According to the surface acoustic wave device of embodiment 3, since in its structure, the interdigital electrode and the counter electrode film facing it are separated by the ZnO thin film therebetween, when the thickness of the ZnO thin film is close to zero, the device cannot work; Because at this time, a short circuit occurs between the interdigitated electrode and the counter electrode film. Therefore, in this example, the minimum value of the normalized thickness h/λ of the ZnO thin film is preset as 0.005. When the normalized thickness of the device is 0.005, the thickness of the interdigitated electrode is 0.1 μm, the electrode finger spacing is 320 μm (= λ), and there are 20 electrode finger pairs, the width of the finger aperture is 5 mm, and the counter electrode The film thickness is 0.07 μm and the substrate thickness is 1 mm.

In this example, when the cut angle of the substrate from the langasite single crystal and the direction of surface acoustic wave propagation on the substrate are represented by Euler angles (φ, θ, ψ), φ, θ are 0° and 90°, respectively. ψ is used to determine the X-axis and the propagation direction of the surface acoustic wave, and the values of ψ selected from the total area III are shown in Figs. 32A-40C. The selection of the thickness h of the ZnO thin film on the substrate should satisfy the above normalized thickness h/λ=0.05˜0.8. In each propagation direction, the variation of SAW wave velocity, electromechanical coupling coefficient k ² , and temperature coefficient of SAW wave velocity TCV when h/λ changes is measured. The SAW wave velocity is obtained from the center frequency of the filter, and the electromechanical coupling coefficient ^k2 is obtained by measuring the admittance at both ends of the surface acoustic wave transducer by using the famous Smith equivalent circuit model. The measurement results of SAW wave velocity, ^k2 and TCV in each direction are plotted in Figs. 32A-40C.

When the normalized thickness h/λ of the ZnO film increases, the SAW mode disappears. Body waves appear. Therefore, the data obtained after the generation of body waves are not shown.

The change curve of SAW wave velocity and ^k2 shows that if the cutting angle of the substrate cut out from the crystal and the propagation direction of the surface acoustic wave fall in the general area III, the SAW wave velocity can be reduced to 2900m/s or lower. This is more conducive to reducing the size of SAW devices compared to conventional ST quartz crystals. It was also found that the electromechanical coupling coefficient obtained in the total region III can be 0.1% or higher. This makes it possible to obtain much higher electromechanical coupling coefficients through the choice of ZnO film thickness.

Continuing to consider the change graph of TCV, when the TCV of the matrix itself is positive, in other words, when the TCV of the matrix is positive when the normalized thickness h/λ=0, it is found that as h/λ increases, the TCV value changes from The positive value changes to the negative value, thereby improving the temperature performance. On the other hand, when the substrate has a negative TCV, the ZnO film is added, and when the normalized thickness is increased, the TCV value increases greatly to the negative direction. Even in this case, the absolute value of the TCV is not too large (about 35ppm/°C or lower); it was also found that if the usual BGO matrix is used, the temperature stability of the matrix is much improved.

Below, each area is explained in detail:

From Fig. 32B, it can be seen that the electromechanical coupling coefficient of the device using region III-1 has two peaks: one at h/λ = 0.05, resulting in a coupling coefficient of 0.22%, and the other at h/λ = 0.65, The resulting coupling coefficient was 0.71%. It can be seen from Figure 32C. Here, the TCV corresponding to the former is -3ppm/°C, and the TCV corresponding to the latter is -27ppm/°C; it is necessary to obtain good enough temperature performance.

From Fig. 33B, it can be seen that the electromechanical coupling coefficient of the device utilizing region III-2 has two peaks: one at h/λ = 0.05, resulting in a coupling coefficient of 0.2%, and the other at h/λ = 0.6, The resulting coupling coefficient was 0.3%. It can be seen from Figure 33C. Here, the TCV corresponding to the former is 29ppm/°C, and the TCV corresponding to the latter is 5ppm/°C; it is necessary to obtain good enough temperature performance.

From Fig. 34B, it can be seen that the electromechanical coupling coefficient of the device utilizing region III-3 has two peaks: one at h/λ = 0.05, resulting in a coupling coefficient of 0.29%, and the other at h/λ = 0.45, The resulting coupling coefficient was 0.12%. It can be seen from Figure 34C. Here, the TCV corresponding to the former is 40ppm/°C, and the TCV corresponding to the latter is 31ppm/°C; it is necessary to obtain good enough temperature performance.

From Fig. 35B, it can be seen that the electromechanical coupling coefficient of the device using region III-4 has two peaks: one at h/λ = 0.05, resulting in a coupling coefficient of 0.37%, and the other at h/λ = 0.45, The resulting coupling coefficient was 0.2%. It can be seen from Figure 35C. Here, the TCV corresponding to the former is 32ppm/°C, and the TCV corresponding to the latter is 15ppm/°C; it is necessary to obtain good enough temperature performance.

From Fig. 36B, it can be seen that the electromechanical coupling coefficient of the device using region III-5 has two peaks: one at h/λ = 0.05, resulting in a coupling coefficient of 0.36%, and the other at h/λ = 0.4, The resulting coupling coefficient was 0.2%. It can be seen from Figure 36C. Here, the TCV corresponding to the former is 27ppm/°C, and the TCV corresponding to the latter is 14ppm/°C; it is necessary to obtain good enough temperature performance.

From Fig. 37B, it can be seen that the electromechanical coupling coefficient of the device using region III-6 has two peaks: one at h/λ = 0.05, resulting in a coupling coefficient of 0.29%, and the other at h/λ = 0.4, The resulting coupling coefficient was 0.5%. It can be seen from Figure 37C. Here, the TCV corresponding to the former is 25ppm/°C, and the TCV corresponding to the latter is 16ppm/°C; it is necessary to obtain good enough temperature performance.

From Fig. 38B, it can be seen that the electromechanical coupling coefficient of the device utilizing region III-7 has two peaks: one at h/λ = 0.05, resulting in a coupling coefficient of 0.24%, and the other at h/λ = 0.45, The resulting coupling coefficient was 0.65%. It can be seen from Figure 38C. Here, the TCV corresponding to the former is 31ppm/°C, and the TCV corresponding to the latter is 18ppm/°C; it is necessary to obtain a good enough temperature-reversal performance.

From Fig. 39B, it can be seen that the electromechanical coupling coefficient of the device using region III-8 has two peaks: one at h/λ = 0.05, resulting in a coupling coefficient of 0.18%, and the other at h/λ = 0.4, The resulting coupling coefficient was 0.45%. It can be seen from Figure 39C. Here, the TCV corresponding to the former is 39ppm/°C, and the TCV corresponding to the latter is 31ppm/°C; it is necessary to obtain good enough temperature performance.

From Fig. 40B, it can be seen that the electromechanical coupling coefficient of the device utilizing region III-9 has two peaks: one at h/λ = 0.05, resulting in a coupling coefficient of 0.13%, and the other at h/λ = 0.55, The resulting coupling coefficient was 0.6%. It can be seen from Figure 40C. Here, the TCV corresponding to the former is 29ppm/°C, and the TCV corresponding to the latter is 7ppm/°C; it is necessary to obtain good enough temperature performance.

From Fig. 41B, it can be seen that the electromechanical coupling coefficient of the device utilizing region III-10 has two peaks: one at h/λ = 0.05, resulting in a coupling coefficient of 0.14%, and the other at h/λ = 0.6, The resulting coupling coefficient was 0.89%. It can be seen from Figure 41C. Here, the TCV corresponding to the former is -2ppm/°C, and the TCV corresponding to the latter is -27ppm/°C; it is necessary to obtain a sufficiently good temperature performance.

Example 3-2 (embodiment 3)

The surface acoustic wave device made according to example 3-1 is different from 3-1 in that: φ and θ are 0° and 90° respectively, and the value of ψ used to determine the X-axis or surface acoustic wave propagation direction is from -80° To -66°, select a value every 2°. It should be noted that these values of φ, θ, ψ are within the region III-1. The TCV-h/λ (normalized thickness) relationship of these devices was measured and the results are shown in FIG. 42 . The relationship between k ² -h/λ was also measured, and the results are shown in Fig. 43 .

On the one hand, it can be seen from Fig. 12 that in the region III-1, zero temperature performance can be obtained, and the thickness of the ZnO thin film corresponding to the zero temperature performance varies with the propagation direction of the surface acoustic wave. On the other hand, it can be seen from Fig. 43 that the electromechanical coupling coefficient tends to become larger as the ZnO thin film becomes thicker. Therefore, if the thickness of the ZnO film is selected in order to obtain zero temperature performance, and the propagation direction is selected in order to obtain a sufficiently large electromechanical coupling coefficient, a SAW device with zero temperature performance and a large electromechanical coupling coefficient can be obtained. For example, if the propagation direction ψ is -78° and the normalized thickness h/λ of ZnO is 0.05, then the TCV can be substantially reduced to zero, and ^k2 can be as high as 0.21%, so it is possible to obtain , a surface acoustic wave device with wide passband and very good temperature performance. Example 3-3 (embodiment 3)

The surface acoustic wave device made according to example 3-1 is different from 3-1 in that: φ and θ are 0° and 90° respectively, and the value of ψ used to determine the X-axis or surface acoustic wave propagation direction is from 66° to 80° Select values every 2°. It should be noted that these values of φ, θ, ψ are in the region III-10. The TCV-h/λ (normalized thickness) relationship of these devices was measured, and the results are shown in FIG. 14 . The relationship between k ² -h/λ was also measured, and the results are shown in Fig. 45 .

On the one hand, it can be seen from Fig. 44 that in the region III-10, zero temperature performance can be obtained, and the thickness of the ZnO thin film corresponding to the zero temperature performance varies with the propagation direction of the surface acoustic wave. On the other hand, it can be seen from Fig. 15 that when the ZnO thin film becomes thicker, the electromechanical coupling coefficient becomes larger. Therefore, if the thickness of the ZnO film is selected in order to obtain a sufficiently large electromechanical coupling coefficient, and the propagation direction is selected in order to obtain zero temperature performance, then a surface acoustic wave device with zero temperature performance and a large electromechanical coupling coefficient can be obtained. For example, if the propagation direction ψ is 70°, and the normalized thickness h/λ of ZnO is 0.35, then the TCV can be substantially reduced to zero, and ^k2 can be as high as 0.44%, so it can be obtained with small size, A surface wave device with wide passband and very good temperature performance. Example 4-1 (embodiment 4)

A langasite single crystal was grown by the CZ process, and a 0.35 mm thick substrate was cut from this single crystal. A counter electrode film is formed on the surface of the substrate. Then a layer of ZnO thin film is formed on the surface of the counter electrode film by magnetron sputtering process. Then form a surface acoustic wave transducer on the surface of the ZnO film to form a surface acoustic wave device; the transducer includes: a set of input interdigital electrodes and output interdigital electrodes; interdigital electrodes and counter electrode films are formed by evaporation of Al . The interdigitated electrodes are common electrodes with the same shape, the thickness is 0.1 μm, and the electrode finger width d is 15 μm. The electrode finger spacing is 60 μm (=4d=λ), the number of electrode finger pairs is 40, and the aperture width between fingers is 60λ (=3.6mm). However, when the output signal is weak, the inter-finger aperture width of the above-mentioned interdigital electrode can be changed to 100λ, and the others remain unchanged. In addition, when the normalized thickness of the ZnO thin film exceeds 0.4, the electrode finger spacing (= λ) is halved to 30 μm, and the aperture width is also halved to 1.8 mm (= 60 λ).

According to the surface acoustic wave device of embodiment 4, since in its structure, the interdigital electrode and the counter electrode film facing it are separated by the ZnO thin film therebetween, when the thickness of the ZnO thin film is close to zero, the device cannot work; Because at this time a short circuit occurs between the interdigital electrode and the counter electrode film. Therefore, in this example, the minimum value of the normalized thickness h/λ of the ZnO thin film is preset as 0.005. When the normalized thickness of the device is 0.005, the thickness of the interdigitated electrodes is 0.1 μm, the electrode finger spacing is 320 μm, and there are 20 electrode finger pairs, the finger aperture width is 5 mm, and the thickness of the counter electrode film is 0.07 μm, the substrate thickness is 1mm.

In this example, when the cut angle of the substrate from the langasite single crystal and the direction of surface acoustic wave propagation on the substrate are represented by Euler angles (φ, θ, ψ), φ, θ are 0° and 90°, respectively. While ψ is used to determine the X-axis and the propagation direction of the surface acoustic wave, the values of ψ selected from the total area IV are shown in Figs. 47A to 56C. The selection of the thickness h of the ZnO thin film on the substrate should satisfy the above normalized thickness h/λ=0.05˜0.8. In each propagation direction, the variation of SAW wave velocity, electromechanical coupling coefficient k ² , and temperature coefficient of SAW wave velocity TCV when h/λ changes is measured. The SAW wave velocity is obtained from the center frequency of the filter, while the electromechanical coupling coefficient ^k2 uses the famous Smith equivalent circuit model. It is obtained by measuring the admittance at both ends of the surface acoustic wave transducer. The measurement results of SAW wave velocity, ^k2 and TCV in each direction are plotted in Figs. 47A-56C.

As the normalized thickness hλ of the ZnO film increases, the SAW mode disappears. Body waves appear. Therefore, the data obtained after the generation of body waves are not shown.

The change curve of SAW wave velocity and ^k2 shows that if the cutting angle of the substrate cut out from the crystal and the propagation direction of the surface acoustic wave fall in the total area IV, the SAW wave velocity can be reduced to 2900m/s or lower. This is more conducive to reducing the size of SAW devices compared to conventional ST quartz crystals. It was found that the electromechanical coupling coefficient obtained in the total area IV can be 0.1% or higher. This makes it possible to obtain much higher electromechanical coupling coefficients through the choice of ZnO film thickness.

Continuing to consider the change graph of TCV, when the TCV of the matrix itself is positive, in other words, when the TCV of the matrix is positive when the normalized thickness h/λ=0, it is found that as h/λ increases, the TCV value changes from The positive value changes to the negative value, thereby improving the temperature performance. On the other hand, when the substrate has a negative TCV, the ZnO film is added, and when the normalized thickness is increased, the TCV value increases greatly to the negative direction. Even in this case, the absolute value of the TCV is not too large (about 35ppm/°C or lower); it was also found that if the usual BGO matrix is used, the temperature stability of the matrix is much improved.

Below, each area is explained in detail.

It can be seen from Figures 47B and 47C that the electromechanical coupling coefficient of the device using region IV-1 can be as high as 0.88% when h/λ=0.8. At this time, TCV=-31ppm/°C, which has good enough temperature performance .

It can be seen from Figures 48B and 48C that the device using region IV-2, when h/λ=0.6, its electromechanical coupling coefficient can be as high as 0.6%. At this time, TCV=6ppm/°C, which has a good enough temperature performance.

It can be seen from Figures 49B and 49C that the device using region IV-3, when h/λ=0.4, its electromechanical coupling coefficient can be as high as 0.39%. At this time, TCV=29ppm/°C, which has a good enough temperature performance.

It can be seen from Figures 50B and 50C that the electromechanical coupling coefficient of the device using region IV-4 can be as high as 0.52% when h/λ=0.45. Here, TCV=17ppm/°C, which has good enough temperature performance.

It can be seen from Figures 51B and 51C that the electromechanical coupling coefficient of the device using region IV-5 can be as high as 0.46% when h/λ=0.4, and here, TCV=15ppm/°C, which has good enough temperature performance.

It can be seen from Figures 52B and 52C that the device using region IV-6, when h/λ=0.4, its electromechanical coupling coefficient can be as high as 0.46%. At this time, TCV=15ppm/°C, which has a good enough temperature performance.

It can be seen from Figures 53B and 53C that the electromechanical coupling coefficient of the device using region IV-7 can be as high as 0.52% when h/λ=0.45. At this time, TCV=17ppm/°C, which has good enough temperature performance.

It can be seen from Figures 54B and 54C that the device using region IV-8, when h/λ=0.4, its electromechanical coupling coefficient can be as high as 0.39%. At this time, TCV=29ppm/°C, which has a good enough temperature performance.

It can be seen from Figures 55B and 55C that the electromechanical coupling coefficient of the device using region IV-9 can be as high as 0.6% when h/λ=0.6, and here, TCV=6ppm/°C, which has good enough temperature performance.

It can be seen from Figures 56B and 56C that the electromechanical coupling coefficient of the device using region IV-10 can be as high as 0.88% when h/λ=0.8. Here, TCV=-32ppm/°C, which has good enough temperature performance. Example 4～2 (embodiment 4)

The surface acoustic wave device made according to example 4-1 is different from 4-1 in that: φ and θ are 0° and 90° respectively, and the value of ψ used to determine the X-axis or surface acoustic wave propagation direction is from -80° To -66°, select a value every 2°. It should be noted that these values of φ, θ and ψ are within region IV-1. The TCV-h/λ (normalized thickness) relationship of these devices was determined and the results are shown in FIG. 58 .

On the one hand, it can be seen from Fig. 57 that in the region IV-1, zero temperature performance can be obtained, and the thickness of the ZnO thin film corresponding to the zero temperature performance varies with the propagation direction of the surface acoustic wave. On the other hand, it can be seen from Fig. 58 that the electromechanical coupling coefficient tends to become larger as the ZnO thin film becomes thicker. Therefore, if the thickness of the ZnO film is selected in order to obtain a sufficiently large electromechanical coupling coefficient, and the propagation direction is selected in order to obtain zero temperature performance, a surface acoustic wave device with zero temperature performance and a large electromechanical coupling coefficient can be obtained. . For example, if the propagation direction ψ is -70° and the normalized thickness h/λ of ZnO is 0.35, then the TCV can be substantially reduced to zero, and ^k2 can be as high as 0.42%, so it is possible to obtain , wide passband and very good temperature performance surface acoustic wave device. Example 4-3 (embodiment 4)

The surface acoustic wave device made according to Example 4-1 is different from 4-1 in that: φ and θ are 0° and 90° respectively, and the ψ value used to determine the X axis and the surface acoustic wave propagation direction is from 66° to 80°, select a value every 2°. It should be noted that these values of φ, θ, ψ are within region IV-10. The TCV-h/λ (normalized thickness) relationship of these devices was determined and the results are shown in FIG. 59 . The relationship between k ² -h/λ was also measured, and the results are shown in Fig. 60 .

On the one hand, it can be seen from Fig. 59 that in the region IV-10, zero temperature performance can be obtained, and the thickness of the ZnO thin film corresponding to the zero temperature performance varies with the propagation direction of the surface acoustic wave. On the other hand, it can be seen from Fig. 60 that the electromechanical coupling coefficient tends to become larger as the ZnO thin film becomes thicker. Therefore, if the thickness of the ZnO film is selected in order to obtain a sufficiently large electromechanical coupling coefficient, and the propagation direction is selected in order to obtain zero temperature performance, then a surface acoustic wave device with zero temperature performance and a large electromechanical coupling coefficient can be obtained. For example, if the propagation direction ψ is 70°, and the normalized thickness h/λ of ZnO is 0.35, then the TCV can be substantially reduced to zero, and ^k2 can be as high as 0.42%, so it can be obtained with small size, SAW device with wide passband and very good temperature performance.

The advantages of the present invention are apparent from the results of the above examples.

Claims (40)

1. A surface acoustic wave device, comprising: matrix, interdigitated electrodes on the surface of the substrate, and A piezoelectric film arranged to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigital electrode; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -90°≤ψ<-70°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.2 to 0.8 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 2. A surface acoustic wave device, comprising: matrix, interdigitated electrodes on the surface of the substrate, and A piezoelectric film arranged to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigital electrode; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -70°≤ψ<-50°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.25 to 0.7 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 3. A surface acoustic wave device, comprising: matrix, interdigitated electrodes on the surface of the substrate, and A piezoelectric film arranged to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigital electrode; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -50°≤ψ<-35°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.25 to 0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 4. A surface acoustic wave device, comprising: matrix, interdigitated electrodes on the surface of the substrate, and A piezoelectric film arranged to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigital electrode; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -35°≤ψ<-25°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.5 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 5. A surface acoustic wave device, comprising: matrix, interdigitated electrodes on the surface of the substrate, and A piezoelectric film arranged to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigital electrode; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -25°≤ψ≤-10°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 6. A surface acoustic wave device, comprising: matrix, interdigitated electrodes on the surface of the substrate, and A piezoelectric film arranged to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigital electrode; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 10°≤ψ<25°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.4 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 7. A surface acoustic wave device, comprising: matrix, interdigitated electrodes on the surface of the substrate, and A piezoelectric film arranged to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigital electrode; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 25°≤ψ<35°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 8. A surface acoustic wave device, comprising: matrix, interdigitated electrodes on the surface of the substrate, and A piezoelectric film arranged to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigital electrode; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 35°≤ψ<50°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.4 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 9. A surface acoustic wave device, comprising: matrix, interdigitated electrodes on the surface of the substrate, and A piezoelectric film arranged to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigital electrode; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 50°≤ψ<70°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.15 to 0.7 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 10. A surface acoustic wave device, comprising: matrix, interdigitated electrodes on the surface of the substrate, and A piezoelectric film arranged to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigital electrode; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 70°≤ψ<90°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.15 to 0.8 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 11. A surface acoustic wave device, comprising: matrix, a piezoelectric film on the surface of the substrate, and interdigitated electrodes on the surface of the above piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -90°≤ψ<-70°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.8 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 12. A surface acoustic wave device, comprising: matrix, a piezoelectric film on the surface of the substrate, and interdigitated electrodes on the surface of the above piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -70°≤ψ<-50°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.75 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 13. A surface acoustic wave device, comprising: matrix, a piezoelectric film on the surface of the substrate, and interdigitated electrodes on the surface of the above piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -50°≤ψ<-35°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 14. A surface acoustic wave device, comprising: matrix, a piezoelectric film on the surface of the substrate, and interdigitated electrodes on the surface of the above piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -35°≤ψ<-25°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.5 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 15. A surface acoustic wave device comprising: matrix, a piezoelectric film on the surface of the substrate, and interdigitated electrodes on the surface of the above piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -25°≤ψ≤-10°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 16. A surface acoustic wave device comprising: matrix, a piezoelectric film on the surface of the substrate, and interdigitated electrodes on the surface of the above piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 10°≤ψ<25°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.4 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 17. A surface acoustic wave device, comprising: matrix, a piezoelectric film on the surface of the substrate, and interdigitated electrodes on the surface of the above piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 25°≤ψ<35°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 18. A surface acoustic wave device comprising: matrix, a piezoelectric film on the surface of the substrate, and interdigitated electrodes on the surface of the above piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 35°≤ψ<50°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.4 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 19. A surface acoustic wave device comprising: matrix, a piezoelectric film on the surface of the substrate, and interdigitated electrodes on the surface of the above piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 50°≤ψ<70°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.7 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 20. A surface acoustic wave device, comprising: matrix, a piezoelectric film on the surface of the substrate, and interdigitated electrodes on the surface of the above piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 70°≤ψ<90°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.8 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 21. A surface acoustic wave device comprising: matrix, interdigitated electrodes on the surface of the substrate, and a piezoelectric film disposed to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigitated electrode, and a counter-electrode film on the surface of the piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -90°≤ψ<-70°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.1 or 0.3≤h/λ≤0.8 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 22. A surface acoustic wave device comprising: matrix, interdigitated electrodes on the surface of the substrate, and a piezoelectric film disposed to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigitated electrode, and a counter-electrode film on the surface of the piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -70°≤ψ<-50°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.1 or 0.35≤h/λ≤0.8 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 23. A surface acoustic wave device comprising: matrix, interdigitated electrodes on the surface of the substrate, and a piezoelectric film disposed to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigitated electrode, and a counter-electrode film on the surface of the piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -50°≤ψ<-35°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.15 or 0.35≤h/λ≤0.5 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 24. A surface acoustic wave device comprising: matrix, interdigitated electrodes on the surface of the substrate, and a piezoelectric film disposed to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigitated electrode, and a counter-electrode film on the surface of the piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -35°≤ψ<-25°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.15 or 0.3≤h/λ≤0.5 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 25. A surface acoustic wave device comprising: matrix, interdigitated electrodes on the surface of the substrate, and a piezoelectric film disposed to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigitated electrode, and a counter-electrode film on the surface of the piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -25°≤ψ≤-10°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.15 or 0.3≤h/λ≤0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 26. A surface acoustic wave device comprising: matrix, interdigitated electrodes on the surface of the substrate, and a piezoelectric film disposed to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigitated electrode, and a counter-electrode film on the surface of the piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 10°≤ψ<25°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 27. A surface acoustic wave device comprising: matrix, interdigitated electrodes on the surface of the substrate, and a piezoelectric film disposed to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigitated electrode, and a counter-electrode film on the surface of the piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 25°≤ψ<35°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.5 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 28. A surface acoustic wave device comprising: matrix, interdigitated electrodes on the surface of the substrate, and a piezoelectric film disposed to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigitated electrode, and a counter-electrode film on the surface of the piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 35°≤ψ<50°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 29. A surface acoustic wave device comprising: matrix, interdigitated electrodes on the surface of the substrate, and a piezoelectric film disposed to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigitated electrode, and a counter-electrode film on the surface of the piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 50°≤ψ<70°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.05 or 0.2≤h/λ≤0.8 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 30. A surface acoustic wave device comprising: matrix, interdigitated electrodes on the surface of the substrate, and a piezoelectric film disposed to cover the above-mentioned surface of the above-mentioned substrate and the surface of the above-mentioned interdigitated electrode, and a counter-electrode film on the surface of the piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 70°≤ψ<90°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies 0<h/λ≤0.05 or 0.25≤h/λ≤0.8 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 31. A surface acoustic wave device comprising: matrix, a counter electrode film on the surface of the substrate, and A piezoelectric film on the aforementioned counter electrode film, and interdigitated electrodes on the surface of said piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -90°≤ψ≤-70°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.8 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 32. A surface acoustic wave device comprising: matrix, a counter electrode film on the surface of the substrate, and A piezoelectric film on the aforementioned counter electrode film, and interdigitated electrodes on the surface of said piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -70°≤ψ<-50°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.8 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 33. A surface acoustic wave device comprising: matrix, a counter electrode film on the surface of the substrate, and A piezoelectric film on the aforementioned counter electrode film, and interdigitated electrodes on the surface of said piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -50°≤ψ<-35°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 34. A surface acoustic wave device comprising: matrix, a counter electrode film on the surface of the substrate, and A piezoelectric film on the aforementioned counter electrode film, and interdigitated electrodes on the surface of said piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -35°≤ψ<-25°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.5 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 35. A surface acoustic wave device comprising: matrix, a counter electrode film on the surface of the substrate, and A piezoelectric film on the aforementioned counter electrode film, and interdigitated electrodes on the surface of said piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° -25°≤ψ≤-10°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 36. A surface acoustic wave device comprising: matrix, a counter electrode film on the surface of the substrate, and A piezoelectric film on the aforementioned counter electrode film, and interdigitated electrodes on the surface of said piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 10°≤ψ<25°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 37. A surface acoustic wave device comprising: matrix, a counter electrode film on the surface of the substrate, and A piezoelectric film on the aforementioned counter electrode film, and interdigitated electrodes on the surface of said piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 25°≤ψ<35°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.5 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 38. A surface acoustic wave device comprising: matrix, a counter electrode film on the surface of the substrate, and A piezoelectric film on the aforementioned counter electrode film, and interdigitated electrodes on the surface of said piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 35°≤ψ<50°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.45 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 39. A surface acoustic wave device comprising: matrix, a counter electrode film on the surface of the substrate, and A piezoelectric film on the aforementioned counter electrode film, and interdigitated electrodes on the surface of said piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 50°≤ψ<70°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.8 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave. 40. A surface acoustic wave device comprising: matrix, a counter electrode film on the surface of the substrate, and A piezoelectric film on the aforementioned counter electrode film, and interdigitated electrodes on the surface of said piezoelectric film; wherein: The above-mentioned substrate is a langasite single crystal belonging to point group 32, and when the cut angle of the above-mentioned substrate cut out from the langasite single crystal and the propagation direction of the surface acoustic wave on the above-mentioned substrate are represented by Euler angles (φ, θ, ψ), where : -5°≤φ≤5° 85°≤θ≤95° 70°≤ψ<90°, and The piezoelectric film is a c-axis oriented ZnO film that satisfies h/λ=0.05 to 0.8 Here, h is the thickness of the above-mentioned ZnO film, and λ is the wavelength of the surface acoustic wave.

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