JP2000312129A - Piezoelectric resonators and filters - Google Patents

Abstract

(57) Abstract: Provided is a piezoelectric resonator having a large electromechanical coupling coefficient Kt necessary for realizing a wideband filter in a high frequency band, and a filter using the resonator. The piezoelectric resonator includes a base, a support film formed on the surface of the base, and a resonance element formed on the surface of the support film. The piezoelectric ceramic films 7, 8 and the electrode films 4, 5, 6 are alternately laminated and formed, and the vibrations of the piezoelectric ceramic films 7, 8 vertically adjacent to each other have opposite phases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric resonator and a filter, and more particularly, to a piezoelectric resonator having a base, a support film formed on the surface of the base, and a resonance element provided on the surface of the support film. It relates to a resonator and a filter.

[0002]

2. Description of the Related Art As the frequencies used for wireless communication and electric circuits have become higher, filters used for these electric signals have been developed to correspond to higher frequencies.

[0003] In particular, microwaves in the vicinity of 2 GHz are becoming mainstream in wireless communications, and there is already a movement to establish standards of several GHz or more. Therefore, inexpensive and high-performance filters corresponding to those frequencies have been developed. It has been demanded.

Recently, a SAW filter using a surface acoustic wave resonator (SAWR), which is an acoustic wave transmitted on a surface of a solid, has been attracting attention. This filter uses a high-frequency electric field applied between comb-shaped electrodes formed on a solid surface and resonance of a surface acoustic wave, has high frequency selectivity, and is widely used as an excellent bandpass filter.

In recent years, a resonator using a thickness longitudinal vibration mode of a thin film exhibiting piezoelectricity has been proposed. This is a resonator using a piezoelectric thin film that causes a thickness longitudinal vibration with respect to an input high-frequency electric signal, and the vibration causes resonance in the thickness direction of the thin film. BAWR).

As a conventional BAWR, as shown in FIG. 18, a base 61, a support film 63 formed on the surface of the base 61, and a buffer layer 6 formed on the support film 63 are formed.
5 and a first electrode 66 formed on the buffer layer 65.
And a piezoelectric thin film 67 formed on the first electrode 66;
It comprises a pair of second electrodes 68 formed on the piezoelectric thin film 67 (see US Pat. No. 4,320,365).

A vibrating body is formed by the buffer layer 65, the first electrode 66, the piezoelectric thin film 67, and the second electrode 68. The support film 63 is formed on the upper surface of the base 61 so as to cover the vibration space A formed in the base 61, and the portion of the support film 63 that is in contact with the vibration space A vibrates due to the vibration of the vibrator.

[0008] Conventionally, as shown in FIG.
1, a support film 72 formed on the surface of the base 71, a first electrode 74 formed on the support film 72, a piezoelectric thin film 73 formed on the first electrode 74, Body thin film 7
3 and a second electrode 75 formed on
However, the thickness of each of them is 1/4 of the wavelength of the standing wave generated by the vibrating body, and a multilayer film in which a number of thin layers a and b made of two kinds of materials having different acoustic impedances are laminated. An acoustic impedance converter having such a configuration has been proposed.

The acoustic impedance converter effectively reflects the ultrasonic wave to the vibrating body in each layer, thereby suppressing energy leakage to the base 71 and acoustically insulating the vibrating body from the base 71. (WENewell, “Face
-Mounted Piezoelectric Resonators ”, Proceeding o
f the IEEE, pp.575-581, June 1965, USP 5,
373,268).

The resonance frequency of a BAW resonator is inversely proportional to the film thickness.
A z-band resonator can be formed. Further, since it can be formed directly on a semiconductor substrate such as Si or GaAs, it is attracting attention as an integrated device.

Since the resonance frequency of both SAWR and BAWR is inversely proportional to the distance between the electrodes, an attempt is made to increase the frequency by reducing the distance between the electrodes. However, S
In AWR, when the interval between the comb electrodes is １ ／ of the wavelength,
In order to generate first-order resonance, the electrode spacing is inversely proportional to four times the resonance frequency. In a frequency region exceeding 1 GHz, the distance between the comb-shaped electrodes is on the order of submicrons, and it is extremely difficult to manufacture the electrodes. For example, when using a LiTaO ₃ single crystal, in order to obtain a piezoelectric resonance of 2 GHz, the electrode interval between the comb-shaped electrodes is about 0.5 μm.

Further, since the electrode spacing is on the order of submicrons, the power durability (voltage resistance) against high frequency power is a serious problem. At present, in high-power applications such as transmission filters, high-frequency SAW filters in the 2 GHz band have not been realized due to the power durability due to the extremely small submicron electrode spacing.

On the other hand, in the BAWR, when the electrode interval is の of the wavelength, a primary resonance occurs, and the electrode interval is inversely proportional to twice the resonance frequency. For this reason, when a piezoelectric material having the same elastic property is used, BAWR is applied at the same electrode interval.
Can obtain twice the resonance frequency of SAWR. Further, the BAWR can obtain the same resonance frequency at twice the electrode spacing as the SAWR, and therefore has better power durability than the SAWR.

[0014]

However, since the frequency is rapidly increasing, there has been a demand for a filter having a higher frequency and excellent power durability. There are two methods of realizing higher frequency, that is, reducing the film thickness or using higher-order resonance. However, as described above, the higher frequency due to the reduction of the film thickness is obtained when BAWR is used. Also several GHz
At the level of the frequency, the electrode spacing is on the submicron level, so that the accuracy of the film thickness control and the power durability remain problems.

On the other hand, when a higher-order resonance is used, a high frequency twice or three times the fundamental wave can be used while the film thickness is fixed at a certain thickness. . Therefore, it is possible to provide a high-frequency resonator that can be used at twice, three times, and four times the frequency of a conventional resonator using a primary standing wave (fundamental wave).

However, the vibration of the higher-order resonance is attenuated with the order of the resonance, and the electromechanical coupling coefficient Kt that determines the bandwidth of the filter is greatly reduced. For this reason, there is a problem that even if the operating frequency can be increased, a wide band filter required in the GHz band cannot be realized.

An object of the present invention is to provide a piezoelectric resonator having a large electromechanical coupling coefficient Kt necessary for realizing a wide band filter in a high frequency band, and a filter using the resonator.

[0018]

According to the present invention, there is provided a piezoelectric resonator comprising:
A piezoelectric resonator comprising a base, a support film formed on the surface of the base, and a resonance element provided on the surface of the support film, wherein the resonance element is formed by alternately using a piezoelectric ceramic film and an electrode film. And the vibrations of the piezoelectric ceramic films vertically adjacent to each other are in opposite phases.

In the piezoelectric resonator of the present invention, the vibrations of the adjacent piezoelectric ceramic films are made to have opposite phases. For example, by using a laminated body of two piezoelectric ceramic films each having a thickness t as a resonance element, A higher-order (secondary or higher) acoustic standing wave in which the thickness t of one layer of the piezoelectric ceramic film becomes a half wavelength is most efficiently excited in the resonance element.

For this reason, although the total thickness of the piezoelectric ceramic film is the same as that of a conventional BAW resonator composed of a single layer of piezoelectric material in which a fundamental wave whose thickness 2t is a half wavelength is strongly excited, the thickness is 2t. Instead, a piezoelectric resonance exhibiting a large electromechanical coupling coefficient Kt at twice the resonance frequency can be obtained.

That is, in the piezoelectric resonator of the present invention, since the piezoelectric ceramic films disposed vertically above and below vibrate in opposite thickness longitudinal vibrations, the vibration in the fundamental mode is suppressed, and the higher-order vibration of the second or higher order is strongly affected. It becomes easy to be excited. Therefore, in the piezoelectric resonator according to the present invention using the second or higher order mode, the influence of spurious due to the vibration of the fundamental mode can be reduced.

In order to obtain the same resonance frequency as that of a conventional thin-film BAW resonator, the piezoelectric resonator of the present invention can use a higher-order mode and therefore has a thin-film BA using a conventional fundamental mode.
The film thickness can be made thicker than that of the W resonator, and the degree of freedom at the time of fabrication can be improved.
Can be improved.

In the resonator of the present invention, the polarization directions of the adjacent piezoelectric ceramic films are made the same, and the driving is performed by applying electric fields in different directions. In some cases, the polarization direction is reversed, and in the case of driving by applying an electric field in the same direction, the film thickness for obtaining a resonator having the same frequency is two times that of the conventional thin-film BAW resonator. Since the distance between the input and output electrodes during driving can be doubled, the applied electric field can be reduced by half, and the power durability can be further improved.

[0024] A piezoelectric resonator according to the present invention is a piezoelectric resonator comprising: a support film formed on a surface of the base; and a resonance element provided on the surface of the support film.
A piezoelectric ceramic film and an electrode film polarized in the thickness direction are alternately laminated and formed, and the polarization directions of the piezoelectric ceramic films vertically adjacent to each other are opposite to each other.

Therefore, according to the piezoelectric resonator of the present invention, S
2W compared to the case using AW and the conventional BAW resonator.
A wide band GHz band filter that can be used at twice as high frequency can be realized.

In particular, by setting the thickness of the piezoelectric ceramic film to 2 μm or less, strongly excited piezoelectric resonance can be obtained at a frequency of 1 GHz or more, and a good thin film piezoelectric resonator can be obtained.

Furthermore, by providing a vibration space on the side of the support film opposite to the surface on which the resonance element is formed, the vibration of the resonance element is less likely to be transmitted to the base, and a piezoelectric resonator with less spurious and good characteristics can be obtained. .

Further, by making the piezoelectric ceramic film in the outer peripheral portion of the uppermost electrode film unpolarized, the hardness of the outer peripheral portion becomes larger than that of the central portion where energy is confined, and the outer peripheral portion is oriented in a certain direction. Energy can be confined in the central portion as compared with the case of polarization, and a piezoelectric resonator having good characteristics can be obtained.

The piezoelectric ceramic film is made of a piezoelectric material containing Pb and Ti, and the support film is made of silicon nitride. The total thickness of the piezoelectric ceramic film is tp, the thickness of the support film is ts, and the thickness is ts. Assuming that the vibration order of the longitudinal vibration mode is n, the ratio ts / tp of the thickness ts of the support film to the total thickness tp of the piezoelectric ceramic film is 2.4n−5.6 ≦ ts / t.
It is preferable that p ≦ 2.7n−4.0 (however, when the vibration order n is 2, 0 <ts / tp).

In this case, Pb, T
When the piezoelectric material containing i is silicon nitride as the support film, the ratio ts / tp of the thickness of the piezoelectric ceramic film and the support film is optimized, and the electromechanical coupling coefficient in the vibration mode of each order is maximized. In addition, the electromechanical coupling coefficient of the vibration mode of an unnecessary order can be suppressed, and by using such a piezoelectric resonator, a filter having a higher frequency band and a wider band can be obtained.

The piezoelectric ceramic film is made of a piezoelectric material containing Pb and Ti, and a diamond film is used as a support film. The total thickness of the piezoelectric ceramic film is tp, the thickness of the support film is ts, and the thickness is ts. When the vibration order of the longitudinal vibration mode is n, the ratio ts / tp of the thickness ts of the support film to the total thickness tp of the piezoelectric ceramic films is 5.4n-12.1 ≦ t.
s / tp ≦ 5.8n−8.5 (However, when the vibration order n is 2, it is desirable to satisfy 0 <ts / tp).

In this case, Pb, T
When the piezoelectric material containing i is diamond as the support film, the ratio ts / tp of the thickness of the piezoelectric ceramic film and the support film is optimized, and the electromechanical coupling coefficient in each order vibration mode is maximized. In addition to being able to increase, the electromechanical coupling coefficient of the vibration mode of an unnecessary order can be suppressed.

Further, the piezoelectric resonator of the present invention uses a piezoelectric material containing Pb and Ti as the piezoelectric ceramic film, has two piezoelectric ceramic films, and operates in the thickness longitudinal vibration mode. (Km / s) is v, and the total thickness of the piezoelectric ceramic film is t
p, where ts is the thickness of the support film, and ts / t is the ratio of the thickness ts of the support film to the total thickness tp of the piezoelectric ceramic films.
p is 0 <ts / tp ≦ 0.2 in the secondary vibration mode
v-0.76, 0.25v-
1.08 ≦ ts / tp ≦ 0.54v-1.84, in the fourth-order vibration mode, 0.54v−1.75 ≦ ts / tp ≦
It is desirable to satisfy the relationship of 0.87v-2.86.

By satisfying the above conditions, when two piezoelectric ceramic films are provided, the ratio ts / tp of the thickness of the piezoelectric ceramic film to the thickness of the support film in the vibration mode of each vibration order depends on the sound velocity v of the support film. Is optimized, the electromechanical coupling coefficient in each order vibration mode can be maximized, and the electromechanical coupling coefficient in unnecessary order vibration modes can be suppressed.

Further, in the piezoelectric resonator of the present invention, the resonance element has three or more odd-numbered piezoelectric ceramic films having the same thickness, and an uppermost electrode film is formed on the upper surface of the uppermost piezoelectric ceramic film. While having a lowermost electrode film on the lower surface of the lowermost piezoelectric ceramic film, the amplitude of vibration generated in the piezoelectric ceramic film between the uppermost piezoelectric ceramic film and the lowermost piezoelectric ceramic film is smaller than that of the uppermost piezoelectric ceramic film. It is desirable that the amplitude is twice as large as the amplitude of the vibration generated in the piezoelectric ceramic film and the lowermost piezoelectric ceramic film.

Here, a pair of first extraction electrode films respectively connected to the uppermost electrode film and the lowermost electrode film, and a pair of first extraction electrode films alternately connected to the electrode film between the uppermost electrode film and the lowermost electrode film. And the amplitude of the vibration generated in the piezoelectric ceramic film between the piezoelectric ceramic film of the uppermost layer and the piezoelectric ceramic film of the lowermost layer by using these extractor electrode films. It is desirable to apply an electric field so as to have twice the amplitude of the vibration generated in the piezoelectric ceramic film and the lowermost piezoelectric ceramic film.

By adopting such a configuration, the vibration in the fundamental mode is suppressed, the vibration in the second or higher order mode is strongly excited, and it can be used in a higher frequency range, and the upper and lower adjacent piezoelectric ceramics are used. The films vibrate in thickness and longitudinal directions in opposite phases to each other, and the parts except for the uppermost piezoelectric ceramic film and the lowermost piezoelectric ceramic film have a phase opposite to that of the vibration generated in the uppermost piezoelectric ceramic film and the lowermost piezoelectric ceramic film. And the amplitude is doubled,
Vibration is offset in the uppermost electrode film and the lowermost electrode film,
No vibration occurs on the surface of the resonance element. Therefore, the vibration of the entire resonance element is confined only inside, and it is not necessary to provide a vibration space on the opposite side of the resonance element forming surface of the support film or to provide a mirror layer for attenuating the vibration of the resonance element.

The filter of the present invention is a filter comprising a base, a support film formed on the surface of the base, and a plurality of resonance elements arranged in parallel on the surface of the support film. Are formed by alternately laminating piezoelectric ceramic films and electrode films, and the vibrations of the piezoelectric ceramic films vertically adjacent to each other are in opposite phases.

In such a filter, in the resonance element, the vibration in the fundamental mode is suppressed, and the higher-order mode or higher-order vibration is easily excited. The plurality of such resonance elements are arranged in parallel. Compared with a filter using a piezoelectric resonator, a filter with a high frequency and a wide band can be obtained. Further, by controlling the film thickness ratio ts / tp of the piezoelectric ceramic film and the supporting film, the electromechanical coupling coefficient of unnecessary vibration in a lower-order mode or a higher-order mode than the used vibration order can be suppressed, and the influence of spurious is reduced. A good filter can be obtained.

[0040]

(Embodiment 1) FIG. 1 is a cross-sectional view of a piezoelectric resonator (BAWR) of the present invention, FIG. 2 is a plan view of the piezoelectric resonator of the present invention, and FIG. It is sectional drawing which follows the EE line of FIG.

As shown in FIG. 1, in the piezoelectric resonator of the present invention, a support film 2 is formed on a base 1, and a laminate 3 is provided on the upper surface of the support film 2. This laminated body 3 is composed of electrode films 4, 5, 6 and piezoelectric ceramic films 7, 8, and a resonance element 3a in which the electrode films 4, 5, 6 and piezoelectric ceramic films 7, 8 are alternately laminated. The uppermost piezoelectric ceramic film 8 has an uppermost electrode film 6 formed at the center of the upper surface thereof, and the lowermost piezoelectric ceramic film 7 has a lower electrode film 4 formed at the lower center thereof. Become.

The piezoelectric ceramic films 7, 8 are polarized in the thickness direction, and the polarization directions of the piezoelectric ceramic films 7, 8 are reversed. A vibration space A is formed on the support film 2 on the side opposite to the surface on which the resonance element 3a is formed. Further, the thickness t of each of the piezoelectric ceramic films 7 and 8 is set to 2 μm or less, and the thickness t of each of the piezoelectric ceramic films 7 and 8 is the same. As described later, the thickness t of the piezoelectric ceramic films 7 and 8 may not be the same. Further, from the viewpoint of increasing the frequency, it is desirable that the thickness t of the piezoelectric ceramic films 7 and 8 is thin, but it is sufficient to control the thickness in accordance with the frequency used.

That is, in the thin film piezoelectric resonator of the present invention, as shown in FIG. 2, one end of each of the electrode films 4, 5, and 6 has a resonance element 3a.
And the extraction electrode films 4a,
5a and 6a are formed so that they do not overlap each other. The electrode film 5 is a floating electrode used during polarization and not used during driving.

The electrode films 4, 5 and 6 are formed at the central portion X of the laminate 3.
(Resonant element 3a), and energy is confined at the central portion X. The outer peripheral portion Y of the uppermost electrode film 6, that is, the piezoelectric ceramic films 7 and 8 in the laminated body 3 other than the resonance element 3a are unpolarized. That is, the outer peripheral portion Y is formed so as to surround the central portion X, and the polarization direction in the outer peripheral portion Y is random.

On the other hand, when the polarization direction is reversed, a DC electric field may be applied between the electrode films 4 and 6 and the electrode film 5. Here, the DC electric field used for the polarization process needs to be set to a value larger than the coercive electric field of the ferroelectric.

The piezoelectric ceramic films 7 and 8 are desirably formed of a ferroelectric material. This is because the ferroelectrics can be polarized in the same direction by applying a DC electric field in the same direction between the electrode films 4, 5 and between the electrode films 5, 6.

The use of ferroelectrics for the piezoelectric ceramic films 7 and 8 is because when a piezoelectric material such as ZnO or AlN which is not ferroelectric and cannot be reversed by an electric field is used, the polarization direction of each layer cannot be controlled during fabrication. This is because the directions of polarization cannot be reversed in adjacent layers. Further, the ferroelectric has a large electromechanical coupling coefficient Kt, and thus is useful for realizing a wideband filter.

Since the piezoelectric ceramic films 7 and 8 are required to have a large electromechanical coupling coefficient particularly in the thickness longitudinal vibration mode, the piezoelectric ceramic films 7 and 8 contain Pb and Ti as main components. It is desirable to use a Pb (Zr _1-x Ti _x ) O ₃ (hereinafter abbreviated as PZT) -based or PbTiO ₃ (hereinafter abbreviated as PT) -based piezoelectric ceramic. The piezoelectric ceramic films 7 and 8 are:
It can be manufactured by a thin film manufacturing method such as a sol-gel method or a sputtering method, or a lamination technique.

The electrode films 4, 5, and 6 are made of Pt, Au, A
1 and the like, and can be similarly produced by a sputtering method, a vacuum evaporation method, or the like.

Further, since the supporting film 2 also vibrates in the thickness direction integrally with the piezoelectric ceramic films 7 and 8,
It is preferable to use a material having a high sound speed, particularly, silicon nitride, SiC, a diamond film, or the like. The support film 2 is formed by a CVD method or the like.

The base 1 is made of silicon or the like, and the vibration space A for acoustically insulating the base 1 and the resonance element 3a is KO.
It can be formed by a chemical etching method using H or the like, a reactive ion etching method, or the like. By providing the vibration space A on the side of the support film 2 opposite to the surface on which the resonance element 3a is formed, the vibration of the resonance element 3a is less likely to be transmitted to the base 1, so that it is possible to obtain a piezoelectric resonator with less spurious and good characteristics. it can.

In the piezoelectric resonator configured as described above,
Since the polarization directions of the adjacent piezoelectric ceramic films 7 and 8 polarized in the thickness direction are reversed, by applying a high-frequency AC electric field between the electrode films 4 and 6, the piezoelectric ceramic films 7 and 8 are applied. 8
A high-order acoustic standing wave whose half-wave thickness t is half-wave is most efficiently excited in the resonance element 3a, and a fundamental wave whose half-wave thickness 2t is half-wave is strongly excited. Although the thickness of the resonance element 3a is the same as that of a conventional BAW resonator made of a piezoelectric ceramic film, a piezoelectric resonator having a large electromechanical coupling coefficient Kt at twice the resonance frequency can be obtained. .

Even when the polarization direction is the same and the electric field is applied in the opposite direction, the same effect can be obtained because the vibrations of the upper and lower piezoelectric ceramic films are in opposite phases.

When the same resonance frequency as that of the conventional thin-film BAW resonator is obtained, the thickness of the piezoelectric resonator of the present invention is twice as large as that of the conventional thin-film BAW resonator. Can be improved.

Further, by making the piezoelectric ceramic films 7 and 8 in the outer peripheral portion Y of the uppermost electrode film 6 unpolarized, the hardness of the outer peripheral portion Y becomes larger than that of the central portion X, and the outer peripheral portion Y is fixed in a certain direction. Energy can be more confined in the central portion X as compared with the case where the piezoelectric resonator is polarized in the negative direction, the occurrence of ripples can be suppressed, and a piezoelectric resonator having excellent characteristics can be obtained.

The thickness t of each of the piezoelectric ceramic films 7 and 8 is set to 2 μm.
Because of the following, piezoelectric resonance can be obtained at a frequency of 1 GHz or more.

In the above example, two piezoelectric ceramic films 7 and 8 are used.
Although the example in which the resonance element 3a is configured using the electrode films 4, 5, and 6 has been described, the piezoelectric resonator of the present invention is not limited to the above-described example, and the piezoelectric resonator using three or more piezoelectric ceramic films may be used. Of course, the resonance element 3a may be configured.

FIG. 3 shows another example of the piezoelectric resonator of the present invention. In this piezoelectric resonator, the concave portion 1 is formed on the upper surface of the base 1.
By forming 1, the vibration space A is provided on the side of the support film 2 opposite to the surface on which the resonance element 3a is formed, and the other points are the same as those in FIG.

With such a piezoelectric resonator, the same effect as that of the piezoelectric resonator shown in FIG. 1 can be obtained.

FIG. 4 shows still another example of the piezoelectric resonator of the present invention. In this piezoelectric resonator, a support film 21 is formed by alternately laminating two kinds of thin layers a and b having different acoustic impedances. The thicknesses of the two types of thin layers a and b are set to の of the wavelength of the acoustic wave excited in the resonance element 3a, respectively. The same is true.

In such a piezoelectric resonator, the same effect as that of the piezoelectric resonator of FIG. 1 can be obtained without providing the vibration space A.

The present inventors have analyzed the impedance characteristics of the piezoelectric resonator of the present invention and the conventional piezoelectric resonator with respect to the resonance frequency. The analyzed piezoelectric resonator uses a diamond film having a thickness of 5 μm as a support film (insulator film) and a PbT film having a thickness of 1 μm as a piezoelectric ceramic film of a resonance element.
An iO ₃ film was used, and the number of laminated piezoelectric ceramic films was two (the piezoelectric resonator in FIG. 1).

In the piezoelectric resonator according to the present invention, a high-frequency electric field was applied to two piezoelectric ceramic films polarized in opposite directions in the stacking direction (thickness direction of the piezoelectric ceramic film) to analyze the piezoelectric resonator.
On the other hand, in the conventional piezoelectric resonator, analysis was performed by applying a high-frequency electric field by using one piezoelectric ceramic film having a thickness of 2 μm and a diamond film having a thickness of 5 μm. Here, the analysis was performed with no electrode film.

FIG. 5 shows the impedance characteristics of the piezoelectric resonator of the present invention, and FIG. 6 shows the impedance characteristics of the conventional piezoelectric resonator. From FIG. 6, in the conventional piezoelectric resonator, the primary resonance of the composite vibrator of the supporting film and the piezoelectric ceramic film is most strongly excited, and the resonance frequency fr ₁ (impedance minimum)
It can be seen that the frequency difference (fa ₁ −fr ₁ ) between the resonance frequency and the anti-resonance frequency fa ₁ (maximum impedance) is the largest as compared with other higher-order resonances. As is clear from the frequency difference between fr ₃ and fa _{3 in} the _third resonance, the difference between the resonance and the anti-resonance frequency decreases with the order of the resonance and decreases with the order.

On the other hand, in the piezoelectric resonator of the present invention, as shown in FIG. 5, the third order resonance fr ₃ (fa
_{In (3} ), the largest bandwidth (fa ₃ −fr ₃ ) is obtained. This third-order resonance is a frequency at which a half-wave standing wave is excited in one layer of the piezoelectric ceramic film. Greater electromechanical coupling coefficient K at much higher resonance frequency than conventional resonators
t can be obtained.

In order to achieve the same resonance frequency and electromechanical coupling coefficient Kt in the conventional piezoelectric resonator as in the piezoelectric resonator of the present invention, the thickness of the piezoelectric ceramic film of the conventional piezoelectric resonator must be
It is necessary to make the thickness of the piezoelectric ceramic film of the piezoelectric resonator of the present invention １ ／. At this time, a standing wave of exactly ２ wavelength is excited in the piezoelectric ceramic film, which is equivalent to a standing wave of one wavelength standing in the two-layer piezoelectric ceramic film of the piezoelectric resonator of the present invention. As described above, the piezoelectric resonator according to the present invention has a piezoelectric ceramic film having a thickness of 2 when obtaining a resonance frequency substantially equal to that of the conventional piezoelectric resonator.
It can be seen that the power durability can be further improved with respect to high frequency power.

(Embodiment 2) The piezoelectric resonator having the vibration space shown in FIGS. 1 to 3 has two piezoelectric ceramic films,
A piezoelectric material containing Pb and Ti is used as the piezoelectric ceramic film, silicon nitride is used as the support film, the total thickness of the two piezoelectric ceramic films (t ₁ + t ₂ ) is tp, and the thickness of the support film is ts.
When the vibration order of the thickness longitudinal vibration mode is n, the ratio t between the thickness ts of the support film and the total thickness tp of the piezoelectric ceramic films is t.
s / tp is 2.4n−5.6 ≦ ts / tp ≦ 2.7n
-4.0 (however, when the vibration order n is 2, 0 <ts /
tp).

By satisfying such a relationship, when a piezoelectric material containing Pb and Ti is used as the piezoelectric ceramic film and the silicon nitride is used as the support film, the film thickness ratio ts / tp of the piezoelectric ceramic film and the support film is used. Is optimized, the electromechanical coupling coefficient in each order vibration mode can be maximized, and the electromechanical coupling coefficient in unnecessary order vibration modes can be suppressed to a small value.

The present inventors conducted an impedance analysis by computer simulation using the finite element method for the structure shown in FIG. 7 schematically showing the above-described piezoelectric resonator. Support film 2 made of silicon nitride as analysis conditions
3 (Young's modulus 294 GPa, density 3200 kg / m ³ )
And PZT (Young's modulus 80 GPa, density 7600 kg / m ³ ) was used as the piezoelectric ceramic films 24 and 25. Here, the thicknesses t ₁ and t ₂ of the piezoelectric ceramic films 24 and 25 are each 0.6 μm, that is, the total thickness tp of the piezoelectric ceramic films 24 and 25 is 1.2 μm, and the electrode films 26, 27 and 28 are formed. Was changed with the thickness of 0.2 μm and the thickness ts of the support film 23 as a parameter. The polarization directions of the two piezoelectric ceramic films 24 and 25 are set to the same direction, and the piezoelectric ceramic films 24 and
5, an electric field in the opposite direction was applied.

FIG. 8 shows an example of the analysis result as the supporting film 23.
7 shows impedance characteristics when the film thickness ts of the sample is 3.6 μm (ts / tp = 3). In this example, it can be seen that the vibration in the tertiary thickness longitudinal vibration mode is strongly excited.

FIG. 9A shows the dependence of the electromechanical coupling coefficient Ktn (%) in the nth-order thickness longitudinal vibration mode on the film thickness ratio ts / tp. Here, the electromechanical coupling coefficient Ktn (%) in the nth-order thickness longitudinal vibration mode is calculated from the nth
The resonance frequency Frn and the anti-resonance frequency Fan of the next thickness longitudinal vibration mode were obtained, and were calculated by the following equations.

Ktn (%) = ((Fan-Frn) / F
rn) ^(1/2) × 100 From FIG. 9A, by controlling the film thickness ratio ts / tp to an optimum value, the electromechanical coupling coefficient in the nth-order thickness longitudinal vibration mode can be increased, and the nth-thickness longitudinal vibration mode can be increased. It can be seen that the electromechanical coupling coefficients in the −1st order or less and the (n + 1) th or more order vibration modes can be suppressed small. For example, when ts / tp is about 3, it can be seen that the third-order vibration mode is strongly excited and the electromechanical coupling coefficient of the second-order or fourth-order or higher mode can be reduced. From the viewpoint of increasing the electromechanical coupling coefficient, it is desirable to use the second to fourth-order vibration modes.

According to the graph of FIG. 9A, the maximum value Kt of the electromechanical coupling coefficient Ktn is obtained at each vibration order n.
n (max) is obtained, and the maximum value Ktn (max) is set to 1
The electromechanical coupling coefficient Ktn when it was set to 00 was calculated, and each electromechanical coupling coefficient Ktn was normalized by Ktn (max), and this was shown in FIG. 9B. For example, Ktn (max) of the third-order vibration mode is 30%. If Ktn (max) is represented as 100, a graph shown in FIG. 9B is obtained.

In FIG. 9B, the film thickness ratio ts / tp is determined so that the normalized electromechanical coupling coefficient is 80% or more and 90% or more at each vibration order n. Is plotted as a function of vibrational order n, yielding FIG. Standardized electromechanical coupling coefficient is 80
% And the upper limit value of the film thickness ratio of 90% or more can be regarded as a linear function of the vibration order n, and an approximate expression is obtained as shown in a graph. In the graph of FIG. 10, the vibration order is represented by a linear function, where n represents the vibration order and y represents the film thickness ratio ts / tp (the broken line is 80%, and the solid line is 90%).
%). For example, in the third vibration mode, the lower limit of the film thickness ratio at which the normalized electromechanical coupling coefficient is 80% or more is about 2, and the upper limit is about 4.

From the graph of FIG. 10, when the nth-order thickness longitudinal vibration mode is used, the film thickness ratio ts / tp is 2.4n so that the normalized electromechanical coupling coefficient becomes 80% or more.
-5.6 ≦ ts / tp ≦ 2.7n−4.0 (however, when the vibration order n is 2, it is understood that it is necessary to satisfy 0 <ts / tp). Therefore, it can be seen that when ts / tp satisfies the above relationship, the electromechanical coupling coefficient can be maximized in the nth-order thickness longitudinal vibration mode. That is, 2
In the case of the next vibration mode, 0 <ts / tp ≦ 1.4, 3
In the case of the next vibration mode, 1.6 ≦ ts / tp ≦ 4.
In the case of the first and fourth order vibration modes, 4 ≦ ts / tp ≦ 6.
It becomes 8.

FIG. 10 shows the lower limit and the upper limit of the film thickness ratio at which the normalized electromechanical coupling coefficient is 90% or more as a linear function of the vibration order n (solid line). In order for the normalized electromechanical coupling coefficient to be 90% or more, 2.5n−5.4 ≦
ts / tp ≦ 2.6n−4.2 (provided that the vibration order n is 2
In this case, it is necessary to satisfy 0 <ts / tp). In this case, it can be seen that the electromechanical coupling coefficient at the desired vibration order n can be further increased.

The same analysis is performed for the two-layer piezoelectric ceramic films 24, 2
The polarization direction of No. 5 was reversed, and the same experiment was performed on the piezoelectric resonator when an electric field was applied in the same direction. The result was the same as that shown in FIG.

(Embodiment 3) The piezoelectric resonator having the vibration space shown in FIGS. 1 to 3 has two piezoelectric ceramic films, a piezoelectric material containing Pb and Ti is used as the piezoelectric ceramic film, and a diamond film is used as the support film. When the total sum of the thicknesses of the two piezoelectric ceramic films is tp, the thickness of the support film is ts, and the vibration order of the thickness longitudinal vibration mode is n, the thickness ts of the support film and the piezoelectric ceramic film The ratio ts / tp to the sum tp of the film thickness of 5.4 is 5.4.
n-12.1 ≦ ts / tp ≦ 5.8n-8.5 (however,
When the vibration order n is 2, it is desirable to satisfy 0 <ts / tp).

In this case, when a piezoelectric material containing Pb and Ti is used as the piezoelectric ceramic film and a diamond film is used as the support film, the ratio ts / tp of the thickness of the piezoelectric ceramic film to the support film is used.
Is optimized, the electromechanical coupling coefficient in each order vibration mode can be maximized, and the electromechanical coupling coefficient in unnecessary order vibration modes can be suppressed.

The present inventors made the support film a diamond film (Young's modulus 1210 GPa, density 3500 kg / m ³ ).
The analysis was performed in the same manner as in Embodiment 2 except for the above. FIG.
FIG. 1A shows the dependency of the electromechanical coupling coefficient Ktn (%) in the nth-order thickness longitudinal vibration mode on the film thickness ratio ts / tp. From the graph of FIG. 11A, a normalized electromechanical coupling coefficient was obtained, and the relationship between the normalized electromechanical coupling coefficient and the film thickness ratio ts / tp is shown in FIG. 11B.

Further, the normalized electromechanical coupling coefficient is 80%
And the film thickness ratio ts / tp to be 90% or more.
Was obtained, and the film thickness ratio was plotted as a function of the vibration order n to obtain FIG.

From FIG. 12, when the nth-order thickness longitudinal vibration mode is used, the film thickness ratio ts / tp is 5.4n-12.m when the normalized electromechanical coupling coefficient becomes 80% or more.
1 ≦ ts / tp ≦ 5.8n−8.5 (however, the vibration order n
Is 0, it is necessary to satisfy 0 <ts / tp), and if it is 90% or more, 5.2n-11.0 ≦ ts
It can be seen that it is necessary to satisfy /tp≦5.9n−9.4. That is, the secondary vibration mode in which the normalized electromechanical coupling coefficient is 80% or more is 0 <ts / tp ≦ 3.1, the tertiary vibration mode is 4.1 ≦ ts / tp ≦ 8.9, the quaternary mode. Is 9.5 ≦ ts / tp ≦ 14.7.

[0083] Further, in this case, the thickness t ₂ of the upper piezoelectric ceramic layer 25 having a thickness t ₁ and the lower side of the piezoelectric ceramic layer 28
The analysis was also performed when the ratio t ₁ / t ₂ was changed as a parameter. In this analysis, the conditions were such that the film thickness ts of the support film 23 and t ₁ + t ₂ were constant so that the third-order mode was optimal. FIG. 13 shows the results.

FIG. 13 shows that the thickness ratio t _{1 of the} piezoelectric ceramic film is obtained.
It can be seen that even when / t ₂ is changed, the electromechanical coupling coefficient in the third mode remains large and the electromechanical coupling coefficient in the second and fourth modes remains small. In other words, it is understood that even if the thickness ratio of the piezoelectric ceramic film deviates from 1, there is no adverse effect. The same analysis was performed for the case where the support film was made of silicon nitride, but the same tendency was observed.

(Embodiment 4) In the piezoelectric resonator of the present invention, the piezoelectric resonator having the vibration space shown in FIGS. 1 to 3 has two piezoelectric ceramic films, and Pb, T
When a piezoelectric material containing i is used, the sound velocity (km / s) of the support film is set to v, the total thickness of the two piezoelectric ceramic films is set to tp, and the thickness of the support film is set to ts, In the secondary vibration mode, the ratio ts / tp of the thickness ts to the total thickness tp of the piezoelectric ceramic films is 0 <ts / tp ≦ 0.2v−0.76,
In the third vibration mode, 0.25v−1.08 ≦ ts /
tp ≦ 0.54v-1.84 In the fourth-order vibration mode,
0.54v-1.75≤ts / tp≤0.87v-2.
86 is desirably satisfied.

By satisfying such a relationship, when the piezoelectric ceramic film has two layers, the ratio (ts) of the thickness of the piezoelectric ceramic film to the thickness of the support film in the vibration mode of each vibration order n according to the sound velocity v of the support film. / Tp) is optimized, the electromechanical coupling coefficient in each order vibration mode can be maximized, and the electromechanical coupling coefficient in unnecessary order vibration modes can be suppressed.

The present inventors conducted impedance analysis by computer simulation using the finite element method for the structure shown in FIG. 7 schematically showing the above-described piezoelectric resonator.

As analysis conditions, PZT was used as the piezoelectric ceramic film, and the thicknesses t ₁ and t ₂ of the piezoelectric ceramic film were 0.6 μm each.
m, that is, the sum of the thicknesses of the piezoelectric ceramic films is tp = 1.2 μm.
m, the thickness of the electrode film is 0.2 μm, and the sound velocity v of the support film is
(Km / s) and the film thickness ts (μm) as parameters, and the electromechanical coupling coefficients in the second, third and fourth vibration modes are obtained. 14A, the lower limit and the upper limit of the film thickness ratio at which the normalized electromechanical coupling coefficient is 80% or more are expressed as linear functions of the sound velocity v of the support film. ) Is expressed as a linear function. The upper limit is indicated by a solid line, and the lower limit is indicated by a broken line.

As the supporting film, a silicon nitride film and a diamond film were used.
((Λ + 2μ) / ρ) ^1/2 (where λ and μ are lame constants and ρ is density).

From FIG. 14A, in the second, third and fourth vibration modes, the normalized electromechanical coupling coefficient 8
In order to reach 0% or more, the film thickness ratio ts / tp must be 0 <ts / tp ≦ 0.2v−0.76, 3 in the secondary vibration mode.
In the next vibration mode, 0.25v−1.08 ≦ ts / t
p ≦ 0.54v-1.84 In the fourth-order vibration mode,
0.54v-1.75≤ts / tp≤0.87v-2.
86, it is necessary to satisfy the relationship.

FIG. 14B shows that the film thickness ratio ts / tp is necessary for the normalized electromechanical coupling coefficient to be 90% or more.
However, in the second vibration mode, 0 <ts / tp ≦ 0.13
In the third-order vibration mode, 0.29v-0.32
1.12 ≦ ts / tp ≦ 0.49v−1.70 In the fourth-order vibration mode, 0.59v−1.94 ≦ ts / tp ≦
It turns out that it is necessary to satisfy the relationship of 0.82v-2.67.

(Embodiment 5) FIGS. 15 and 16 show another piezoelectric resonator of the present invention. FIG. 15 is a sectional view and FIG.
FIG. 15 is a plan view, and FIG. 15 is a sectional view taken along line FF of FIG.

This piezoelectric resonator has a structure as shown in FIG.
A support film (adhesion layer) 32 is formed on a base 31, and a laminate 33 is provided on the upper surface of the support film 32. The laminate 33 is composed of electrode films 34, 35, 36, and 37 and piezoelectric ceramic films 38, 39, and 40.
5, 36, 37 and the piezoelectric ceramic films 38, 39, 40 are alternately laminated, and the uppermost electrode film 37 is formed at the center of the upper surface of the uppermost piezoelectric ceramic film 40. The lowermost electrode film 34 is formed at the center of the lower surface of the lowermost piezoelectric ceramic film 38.

The piezoelectric ceramic films 38, 39, and 40 are polarized in the same direction in the thickness direction. The thickness t of the piezoelectric ceramic films 38, 39, and 40 is desirably the same. However, as long as the thickness variation is within 0.1%, there is no problem as the same thickness. It is desirable that the thickness of the electrodes 34, 35, 36, and 37 is the same, but the thickness variation is not more than 0.1.
There is no problem if it is within 1%.

In the thin-film piezoelectric resonator of the present invention, as shown in FIG. 16, one end of each of the electrode films 34, 35, 36, and 37 is drawn out of the resonance element 33a. 35a, 36a and 37a are formed so as not to overlap each other.

That is, the uppermost layer electrode film 37 and the lowermost layer electrode film 34 are connected to a pair of extraction electrode films 34a, 37a provided at opposing positions, respectively. The electrodes 35 and 36 are respectively connected to a pair of extraction electrode films 35a and 36a provided at opposing positions.

The electrode films 34, 35, 36, and 37 are overlapped at the central portion X (resonant element 33 a) of the laminate 33.
Energy is confined in the central portion X.

The outer peripheral portion Y of the uppermost electrode film 37, that is, the piezoelectric ceramic films 38, 39, and 40 in the laminated body 33 other than the resonance element 33a are unpolarized. That is, the outer peripheral portion Y is formed so as to surround the central portion X, and the polarization direction in the outer peripheral portion Y is random.

In the piezoelectric resonator configured as described above,
Between the electrode film 36 and the uppermost electrode film 37, and between the electrode film 35
The electrode film 35 and the electrode film 36 are located between the
Half of the electric field (0.476-
The electric signal applied to the extraction electrode films 34a, 35a, 36a, and 37a is controlled so that an electric field having a magnitude of (0.588 times) is generated.

By performing such a control, the amplitude of the vibration generated in the piezoelectric ceramic film 39 between the uppermost piezoelectric ceramic film 40 and the lowermost piezoelectric ceramic film 38 is reduced. The amplitude of the vibration generated in the membrane 40 and the amplitude of the vibration generated in the lowermost piezoelectric ceramic film 38 are opposite to each other and are twice as large, so that the uppermost piezoelectric ceramic film 40 and the lowermost piezoelectric ceramic film 38 are formed.
Outside, ie, the uppermost electrode film 37 and the lowermost electrode film 34, the vibration is canceled out, and the three-layer piezoelectric ceramic films 38, 3
It is possible to produce a piezoelectric resonator in which only the inside of 9 and 40 vibrates and the outer surface does not vibrate.

The polarization direction of the piezoelectric ceramic film 39 is reversed from the polarization directions of the uppermost piezoelectric ceramic film 40 and the lowermost piezoelectric ceramic film 38. Are in the opposite phase, the same effect can be obtained.

When the piezoelectric ceramic film has five or more layers,
Except for the uppermost piezoelectric ceramic film and the lowermost piezoelectric ceramic film, the remaining three or more piezoelectric ceramic films are twice as large as the amplitudes of the vibrations generated in the uppermost piezoelectric ceramic film and the lowermost piezoelectric ceramic film, respectively. What is necessary is to make it.

By adopting such a structure, the adjacent upper and lower piezoelectric ceramic films 38, 39, and 40 vibrate in thickness and longitudinal directions in opposite phases to each other, and the uppermost piezoelectric ceramic film 36 and the lowermost piezoelectric ceramic film 36 In portions other than the film 38, the amplitude of the vibration generated in the uppermost piezoelectric ceramic film 36 and the lowermost piezoelectric ceramic film 38 is twice, so that the vibration is canceled out in the uppermost electrode film 37 and the lowermost electrode film 34. Thus, no vibration occurs on the surface of the resonance element 33a. Therefore, the vibration of the entire resonance element 33a is confined only inside, and it is necessary to provide the vibration space A on the side of the support film 32 opposite to the surface on which the resonance element 33a is formed, or to provide a mirror layer for attenuating the vibration of the resonance element 33a. Absent.

FIG. 17 shows a filter according to the present invention. This filter has two resonance elements. That is, as shown in FIG.
Two resonance elements 43a and 43b are arranged side by side at a predetermined interval on one, and the resonance element 43a is formed by alternately stacking piezoelectric ceramic films 45 and 47 and electrode films 48a, 49 and 50a. The resonance element 43b is
5, 47 and the electrode films 48b, 49, 50b are alternately laminated, and the two resonance elements 43a, 43 arranged in parallel are arranged.
The b piezoelectric ceramic films 45 and 47 are extended and connected.
The piezoelectric ceramic films 45 and 47 are polarized in the same direction, and the resonance elements 43a and 43b operate in the thickness longitudinal vibration mode.

The electrode films 48, 49 and 50 are provided with the extraction electrode film 5
3a, 53b, 54, 55a, and 55b are formed. That is, the extraction electrode film 5 of the electrode film 48a and the electrode film 48b
3a and 53b are exposed on opposite side surfaces, and the extraction electrode film 54 of the electrode 49 is exposed on a side surface different from the side surface on which the end surfaces of the extraction electrode films 53a and 53b are exposed. An extraction electrode film 55a of the electrode film 50b,
55b is exposed on the opposing side surface. The extraction electrode films 53a, 53b, 54, 55a, and 55b are not limited to these.

In this filter, the extraction electrode films 53a, 53a,
5a and a voltage of a different polarity are applied to the extraction electrode film 54,
The output voltage is extracted from the extraction electrode film 53b and the extraction electrode film 55b and used.

Such a filter is, for example, a support film 4
1, an electrode film 48a and an electrode film 48b are formed in parallel, a piezoelectric ceramic film 45 is formed so as to cover these electrode films 48a and 48b, and an electrode film 4 is formed on the surface of the piezoelectric ceramic film 45.
9 (ground electrode), a piezoelectric ceramic film 47 is formed on the electrode 49, and the electrode film 5 is formed on the piezoelectric ceramic film 47.
It can be manufactured by forming Oa and 50b.

In the arrangement of the electrode films 48, 49, and 50 on the plane, the pass band is designed using even mode and odd mode in the bulk thickness longitudinal filter,
Structural design similar to that performed for movement is applied. Here, the shapes of the electrode films 48, 49, and 50 are produced by various design techniques for adjusting the resonance frequency of the main even mode and the odd mode, and for keeping away or eliminating ripples that occur.

In the filter configured as described above, the piezoelectric ceramic films 45 and 47 are polarized in the same direction. For example, voltages of different polarities are applied to the extraction electrode films 53a and 55a and the extraction electrode film 54. The piezoelectric ceramic film 45
And the vibrations of the piezoelectric ceramic film 47 have opposite phases.

In such a filter, vibration in the fundamental mode is suppressed in the resonance element, and second-order or higher-order mode vibrations are easily excited, and a plurality of such resonance elements are arranged in parallel. Compared with a filter using a piezoelectric resonator, a filter with a high frequency and a wide band can be obtained. Further, by controlling the film thickness ratio ts / tp of the piezoelectric ceramic film and the supporting film, the electromechanical coupling coefficient of unnecessary vibration in a lower-order mode or a higher-order mode than the used vibration order can be suppressed, and the influence of spurious is reduced. A good filter can be obtained.

[0111]

According to the piezoelectric resonator of the present invention, the vibrations of the adjacent piezoelectric ceramic films are made to have opposite phases. For example, by using a laminated body in which two piezoelectric ceramic films each having a thickness t are stacked as a resonance element. The vibration of the fundamental mode is suppressed, and a higher-order (secondary or higher) acoustic standing wave in which the thickness t of one layer of the piezoelectric ceramic film becomes a half wavelength is most efficiently excited in the resonance element. Although the total thickness of the piezoelectric ceramic film is the same as that of a BAW resonator made of a single layer of piezoelectric material in which a fundamental wave having a film thickness of 2t and having a half wavelength is strongly excited, the resonance frequency is twice as large. A piezoelectric resonance exhibiting a large electromechanical coupling coefficient Kt can be obtained.

Further, in the filter of the present invention, since the filter is configured using a resonator having a large electromechanical coupling coefficient of the vibration order to be used, a high-frequency and wide-band filter can be obtained. In addition, since the electromechanical coupling coefficient of unnecessary vibration due to a mode lower or higher than the vibration order to be used can be suppressed, good filter characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a piezoelectric resonator of the present invention.

FIG. 2 is a plan view of FIG.

FIG. 3 is a sectional view showing another example of the piezoelectric resonator of the present invention.

FIG. 4 is a sectional view showing still another example of the piezoelectric resonator of the present invention.

FIG. 5 is a diagram showing impedance characteristics of the piezoelectric resonator of the present invention.

FIG. 6 is a diagram illustrating impedance characteristics of a conventional piezoelectric resonator.

FIG. 7 is an explanatory diagram showing a polarization direction and a voltage application method of the piezoelectric resonator of the present invention.

FIG. 8 shows a piezoelectric resonator of FIG.
T, the support film is silicon nitride, and the thickness ts of the support film is 3.6 μm.
It is a figure showing the impedance characteristic in case of m.

FIG. 9A is a graph showing the relationship between the electromechanical coupling coefficient Ktn (%) of the nth-order thickness longitudinal vibration mode and the thickness ratio ts / tp of a piezoelectric resonator having a piezoelectric ceramic film of PZT and a support film of silicon nitride. (B) is a diagram showing the dependence of the normalized electromechanical coupling coefficient Ktn (%) of the nth-order thickness longitudinal vibration mode on the film thickness ratio ts / tp.

FIG. 10 shows a piezoelectric resonator in which the piezoelectric ceramic film is PZT and the support film is silicon nitride, and the normalized electromechanical coupling coefficient is 80%.
It is a graph when the lower limit value and the upper limit value of the film thickness ratio ts / tp of 90% or more are regarded as linear functions of the vibration order n.

11A is a diagram showing a piezoelectric resonator in which a piezoelectric ceramic film is PZT and a support film is diamond, and FIG. 11A shows a film thickness ratio ts / t of an electromechanical coupling coefficient Ktn (%) in an nth-order thickness longitudinal vibration mode.
(b) shows the film thickness ratio ts / t of the normalized electromechanical coupling coefficient Ktn (%) in the nth-order thickness longitudinal vibration mode.
It is a figure which shows p dependence.

FIG. 12 shows a piezoelectric resonator in which a piezoelectric ceramic film is PZT and a support film is a diamond film, and a normalized electromechanical coupling coefficient is 8
0% and the lower limit of the film thickness ratio ts / tp to be 90%,
It is a graph when an upper limit is considered as a linear function of the vibration order n.

FIG. 13 is a graph showing the electromechanical coupling coefficients in the second, third, and fourth modes when the thickness ratio of the two piezoelectric ceramic films is changed.

FIG. 14 (a) shows the lower limit and the upper limit of the film thickness ratio at which the normalized electromechanical coupling coefficient becomes 80% or more as 1 of the sound velocity v of the supporting film.
It is a graph when it is considered as a quadratic function. It is a graph at the time of doing.

FIG. 15 is a sectional view showing a piezoelectric resonator having a three-layer piezoelectric ceramic film of the present invention.

16 is a plan view of the piezoelectric resonator shown in FIG.

FIG. 17 (a) is a partial cross-sectional perspective view of the filter of the present invention, and FIG. 17 (b) is a plan view.

FIG. 18 is a sectional view showing a basic structure of a conventional piezoelectric resonator.

FIG. 19 is a cross-sectional view showing a basic structure of another example of a conventional piezoelectric resonator.

[Explanation of symbols]

1, 31 ... base 2, 21, 23, 32, 41 ... support film 4, 5, 6, 26, 27, 28, 34, 35, 36, 3
7, 48a, 48b, 49, 50a, 50b ... Electrode film 7, 8, 24, 25, 38, 39, 40, 45, 47
··· Piezoelectric ceramic membranes 3a, 33a, 43a, 43b ··· Resonant element A · · · Vibration space X · · · Central part Y · · · Peripheral part tp · · · Total thickness of piezoelectric ceramic films ts · · ·・ Support film thickness

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hirotaku Tsuyoshi 1-4-4 Yamashita-cho, Kokubu-shi, Kagoshima Inside the Kyocera Research Institute

Claims (11)

[Claims] 1. A piezoelectric resonator comprising: a base; a support film formed on the surface of the base; and a resonance element provided on the surface of the support film, wherein the resonance element is a piezoelectric ceramic film. A piezoelectric resonator formed by alternately laminating electrode films with each other, and wherein vibrations of the piezoelectric ceramic films disposed vertically adjacent to each other have opposite phases. 2. A piezoelectric resonator comprising: a base; a support film formed on the surface of the base; and a resonance element provided on the surface of the support film, wherein the resonance element is polarized in a thickness direction. A piezoelectric resonator film formed by alternately laminating the formed piezoelectric ceramic films and electrode films, and wherein the piezoelectric ceramic films disposed vertically adjacent to each other have opposite polarization directions. 3. The piezoelectric resonator according to claim 1, wherein a vibration space is provided on a side of the support film opposite to a surface on which the resonance element is formed. 4. The piezoelectric ceramic film according to claim 1, further comprising an uppermost electrode film on the upper surface of the uppermost piezoelectric ceramic film, wherein the piezoelectric ceramic film at an outer peripheral portion of the uppermost electrode film is unpolarized. 3. The piezoelectric resonator according to any one of 3. 5. The piezoelectric resonator according to claim 1, wherein the piezoelectric resonator operates in a thickness longitudinal vibration mode. 6. The piezoelectric resonator according to claim 1, comprising two piezoelectric ceramic films. 7. The piezoelectric ceramic film is made of a piezoelectric material containing Pb and Ti, the support film is made of silicon nitride, the total thickness of the piezoelectric ceramic film is tp, the thickness of the support film is ts, and the thickness is ts. Assuming that the vibration order of the longitudinal vibration mode is n, the total thickness tp of the thickness ts of the support film and the thickness of the piezoelectric ceramic film is tp.
And the ratio ts / tp to 2.4n−5.6 ≦ ts / tp ≦ 2.7n−4.0 (where 0 <ts / tp when the vibration order n is 2). The piezoelectric resonator according to claim 6, wherein 8. The piezoelectric ceramic film is made of a piezoelectric material containing Pb and Ti, the support film is made of a diamond film, the total thickness of the piezoelectric ceramic film is tp, the thickness of the support film is ts, and the thickness is ts. Assuming that the vibration order of the longitudinal vibration mode is n, the ratio ts / tp of the thickness ts of the support film to the total thickness tp of the piezoelectric ceramic films is 5.4n-12.1 ≦ ts / tp ≦ 5. .8n-8.5
7. The piezoelectric resonator according to claim 6, wherein 0 <ts / tp is satisfied when the vibration order n is 2. 9. A piezoelectric material containing Pb and Ti is used as the piezoelectric ceramic film, the sound velocity (km / s) of the support film is v, the total thickness of the piezoelectric ceramic film is tp, and the thickness of the support film is ts
When the ratio ts / tp of the thickness ts of the supporting film to the total thickness tp of the piezoelectric ceramic films is 0 <ts / tp ≦ 0.2v−0.76 in the second-order vibration mode, In the third vibration mode, 0.25v-1.08 ≦ ts / tp ≦
0.54v-1.84, in the fourth vibration mode, 0.5
7. The piezoelectric resonator according to claim 6, wherein a relationship of 4v-1.75≤ts / tp≤0.87v-2.86 is satisfied. 10. The resonance element has three or more odd-numbered piezoelectric ceramic films having the same thickness, an uppermost electrode film on the upper surface of the uppermost piezoelectric ceramic film, and a lower surface of the lowermost piezoelectric ceramic film. The lowermost electrode film, the amplitude of the vibration generated in the piezoelectric ceramic film between the piezoelectric ceramic film of the uppermost layer and the piezoelectric ceramic film of the lowermost layer, the piezoelectric ceramic film of the uppermost layer and the lowermost layer The piezoelectric resonator according to any one of claims 1 to 5, wherein the amplitude is twice as large as the amplitude of vibration generated in the piezoelectric ceramic film. 11. A filter comprising a base, a support film formed on the surface of the base, and a plurality of resonance elements arranged in parallel on the surface of the support film, wherein the resonance element is a piezoelectric ceramic film. A filter, which is formed by alternately laminating electrode films with each other, and wherein vibrations of the piezoelectric ceramic films disposed vertically above and below are in opposite phases.