JP2000341083A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a spurious reflection wave at an end face of a piezoelectric substrate of a surface acoustic wave device without increasing the device size and the number of manufacture processes. SOLUTION: In the surface acoustic wave device provided with a piezoelectric substrate 1, interdigital electrodes 2, 3 provided on the surface of the piezoelectric substrate 1 to stimulate a surface acoustic wave, and a sound absorbing members 5 provided between the end faces of the piezoelectric substrate 1 and the interdigital electrodes 2, 3, an angle between a direction perpendicular to a main propagation direction of the surface acoustic wave and the end face of the piezoelectric substrate 1 is restricted within a range of an excess of 0 degree and 15 degree or below, and a coating width W of the sound absorbing member 5 is restricted within a range between 2.5λ and 5λ, where λ is a wavelength of the surface acoustic wave.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device and a communication device using the same, and more particularly to a surface acoustic wave device in which the influence of unnecessary reflected waves from the end face of a piezoelectric substrate is reduced and the size of the device is reduced. The present invention relates to a wave device and a communication device using the same.

[0002]

2. Description of the Related Art In general, in order to suppress the influence of reflection at the end face of a Rayleigh wave, which is the main propagation mode of a surface acoustic wave,
As shown in FIG. 11, a sound absorbing material 5 is applied between the IDTs 2 and 3 and the end surface of the piezoelectric substrate 1, and the surface acoustic wave traveling toward the substrate end surface and the surface acoustic wave reflected from the substrate end surface are applied. Absorption method was adopted. In the figure, reference numeral 4 denotes a shield electrode, 6 denotes an end face reflected wave, and 7 denotes a surface acoustic wave traveling toward the end face of the substrate.

The sound absorbing material 5 is generally made of silicon, UV-curable polybutadiene resin, or the like. In order to completely absorb the Rayleigh wave, it is usually necessary to apply the sound absorbing material 5 having a width of about 10 times or more (for example, 15 times) the wavelength of the propagating surface acoustic wave. In particular, when the operating frequency of a device such as an intermediate frequency filter is relatively low, the application area of the sound absorbing material 5 becomes extremely large, which inevitably increases the chip size and increases the manufacturing cost.

Further, in anisotropic substrates such as lithium niobate and lithium tantalate which are often used as the substrate 1 of a surface acoustic wave device, in addition to Rayleigh waves, the direction of particle displacement is perpendicular to the propagation direction of surface acoustic waves. There is a piezoelectric shear wave (SH wave) parallel to the surface. However, since the SH wave is not absorbed by the sound absorbing material 5, the frequency characteristic is degraded as an unnecessary reflected wave at the end face of the substrate.

Conventionally, in order to effectively suppress unnecessary reflected waves generated by reflection of a surface acoustic wave on the end face of a substrate,
Various contrivances have been made. For example, JP-A-10-842
In Japanese Patent Publication No. 49 (first known example), the angle θa between the propagation direction of the surface acoustic wave and the long side of the substrate is defined as 0 ° <θa <θb (θ
b is the angle between the long side of the substrate and the diagonal line) to prevent surface acoustic waves such as Rayleigh waves and SH waves from being directly incident on the electrodes, and reduce the influence of the end face reflected waves.

[0006] Japanese Patent Application Laid-Open No. Hei 9-116378 (second
In the known example, the IDT in which reflectors are arranged on both sides of the IDT
In the T excitation device, an angle greater than or equal to a specified angle is provided between the propagation direction of the surface acoustic wave and the long side direction of the substrate to suppress the influence of the reflected wave.

According to these known examples, there is an effect that the influence of the end face reflected wave can be reduced without applying a sound absorbing material.

Further, in Japanese Patent Application Laid-Open No. 7-321597 (third known example), two types of sound absorbing materials having different hardness are applied to the end face of the substrate, and the end face of the substrate is processed obliquely to suppress the reflected wave. ing. According to the third known example, it is possible to suppress the reflected wave on the end face of the substrate and also suppress the reflection of the surface acoustic wave on the end face of the sound absorbing material.

[0009]

However, in the first and second known examples, the end face reflected wave is directly
Although it is avoided to be incident on T, the surface acoustic wave reflected obliquely to the long side of the substrate at the end face of the substrate is incident on the IDT and becomes spurious, so that the frequency characteristics of the surface acoustic wave device deteriorate, especially, This has resulted in deterioration of the degree of suppression outside the band, increase of ripple within the band, deterioration of the group delay characteristic, and the like.

Furthermore, in order to further suppress the end face reflected wave, it is necessary to increase the angle between the long side of the substrate and the main propagation direction of the surface acoustic wave, which increases the device size and increases the manufacturing cost. Was.

Further, in the third known example, since two types of sound absorbing materials having different hardnesses are applied, the application area of the sound absorbing material is increased, the chip size is increased, and the working process is complicated and increased. Therefore, there is a problem that the manufacturing cost of the device is increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has excellent characteristics by suppressing unnecessary reflected waves at an end face. Moreover, the present invention reduces the device size and the cost. It is an object of the present invention to provide a surface acoustic wave device capable of performing the above-described operations and a communication device using the same.

[0013]

In order to achieve the above object, a first means of the present invention is to provide a piezoelectric substrate and a blind for exciting a surface acoustic wave provided on the surface of the piezoelectric substrate. The present invention is directed to a surface acoustic wave device including a shape electrode and a sound absorbing material provided between an end face of the piezoelectric substrate and the IDT.

The angle θ between the direction perpendicular to the main propagation direction of the surface acoustic wave and the end face of the piezoelectric substrate is restricted to a range of more than 0 ° to 15 °, and the coating width W of the sound absorbing material is
When the wavelength of the surface acoustic wave is λ, the wavelength is regulated in the range of 2.5λ to 5λ.

The second means is the first means,
The angle θ is restricted to a range of 3 to 8 °.

The third means may be the first means or the second means.
In the means, at least one of the interdigital transducers is a cross-width weighting electrode, and the sound absorbing material straddles an electrode portion which does not participate in the surface acoustic wave excitation of the cross-width weighting electrode located near the substrate end face. Is provided.

Further, the fourth means includes the first to third means.
In any one of the above means, a metal thin film having a boundary at an angle larger than 0 ° with respect to a direction perpendicular to the main propagation direction of the surface acoustic wave is provided between the end face of the substrate and the IDT. It is assumed that.

Further, the fifth means includes a piezoelectric substrate, an interdigital electrode provided on the surface of the piezoelectric substrate for exciting a surface acoustic wave, and an interdigital transducer between the end face of the piezoelectric substrate and the interdigital electrode. The angle θ between the direction perpendicular to the main propagation direction of the surface acoustic wave and the end face of the piezoelectric substrate is restricted to a range of more than 0 ° and 15 °, and the sound absorbing material is provided. The reception signal is filtered by using a surface acoustic wave device in which the application width W of the surface acoustic wave is restricted to a range of 2.5λ to 5λ when the wavelength of the surface acoustic wave is λ.

The sixth means is the fifth means,
The communication device is a mobile communication device used in, for example, an in-vehicle communication system.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. In all the drawings describing each embodiment, components having the same function are denoted by the same reference numerals. FIG. 1 is a schematic diagram illustrating a configuration of a surface acoustic wave device according to a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a piezoelectric substrate, for example, using a lithium niobate single crystal. Reference numerals 2 and 3 denote an IDT made of an aluminum thin film deposited and formed by photolithography, 4 a shield electrode for suppressing direct waves, 5 a sound absorbing material made of an ultraviolet-curable polybutadiene-based resin applied by screen printing, 6 Is an end surface reflected wave, and 7 is a surface acoustic wave directed to the end surface of the substrate, including a Rayleigh wave and an SH wave.

In this embodiment, the short side of the rectangular piezoelectric substrate 1 and the main propagation direction of the surface acoustic wave (indicated by a dashed line in the figure) are set at an angle of θ = 6 °. The short side of the piezoelectric substrate 1 forms an end face of the surface acoustic wave device. The width W of the sound absorbing material 5 is W = 5λ.
(Λ: wavelength of surface acoustic wave). The Rayleigh wave in the Rayleigh mode among the surface acoustic waves 7 propagating toward the substrate end face is largely absorbed by the sound absorbing material 5.

Also, regarding the residual reflection Rayleigh wave not absorbed by the sound absorbing material 5 and the end face reflection wave 6 due to the SH wave, the main propagation direction is not perpendicular to the substrate end face, so that they are obliquely incident on the IDTs 2 and 3. , Its effects are reduced. That is, since the residual reflected Rayleigh wave not absorbed by the sound absorbing material 5 and the end face reflected wave 6 due to the SH wave have a much smaller amplitude than the main signal, the short side of the piezoelectric substrate 1 and the main surface acoustic wave It is not necessary to increase the angle θ with respect to the propagation direction, and the same degree of suppression is obtained when θ <7 ° and θ ≧ 7 °.

Further, since the width W of the sound absorbing material 5 is as short as 5λ, as shown in FIG. 2A, the response 8 on the time axis of the end face reflected wave 6 is delayed from the response 9 on the time axis of the main signal. Time τ is short.

On the other hand, the ripple exerted on the frequency amplitude characteristic and the group delay characteristic by the end face reflected wave 6 has a cycle of 1 /
2B, the influence of the end face reflected wave 6 on the frequency amplitude characteristic is reduced as shown in FIG.

FIGS. 2C and 2D show the conventional time axis characteristics and frequency amplitude characteristics when the application width of the sound absorbing material 5 is 15λ. The response 8 of the end face reflected wave 6 on the time axis is shown.
Is the delay time τ ′ from the response 9 on the time axis of the main signal.
And the ripple period affecting the frequency amplitude characteristic is 1 /
τ ′. In FIG. 2D, it can be seen that the ripple period due to the end face reflected wave 6 is short, so that the influence is particularly noticeable in the band.

As described above, according to the present embodiment, the device size can be reduced without increasing the number of manufacturing steps, and the effect of the end face reflected wave 6 can be effectively reduced.

FIG. 3 is a characteristic diagram showing the relationship between the application width W of the sound absorbing material 5 and the degree of suppression of the end face reflected wave 6. In this test, θ is set to 6, and the coating width W of the sound absorbing material 5 is changed from 2.5λ, which is the minimum width that can be formed by a screen used for coating, to 5.5.
The degree of suppression of the end face reflected wave was measured in the range of λ. As is clear from this figure, a sufficient suppression effect can be obtained in the range of 2.5λ to 5λ. In practice, the range of 4λ to 5λ is preferable from the viewpoint of workability during coating. It has been experimentally confirmed that this tendency can be obtained even if θ is changed within the range of the present invention.

FIG. 4 is a characteristic diagram showing the relationship between the angle θ between the direction perpendicular to the main propagation direction of the surface acoustic wave, the end face of the piezoelectric substrate, and the degree of suppression. In this test, the application width W of the sound absorbing material 5 was determined.
Was set to 5λ, and the angle θ was changed variously to measure the degree of suppression of the end face reflected wave. As is clear from this figure, it is understood that a sufficient suppression effect can be obtained if the angle θ is restricted to a range of more than 0 ° and 15 °, preferably 3 to 8 °. It has been experimentally confirmed that this tendency can be obtained even if the coating width W of the sound absorbing material 5 is changed within the range of the present invention.

FIG. 5 is a schematic diagram illustrating the configuration of a surface acoustic wave device according to a second embodiment of the present invention. In the present embodiment, the metal thin film 10 is provided between the sound absorbing material 5 and the IDTs 2 and 3 at a predetermined angle with respect to the propagation direction of the surface acoustic wave. The metal thin film 10 is made of, for example, aluminum or the like, is deposited on the surface of the piezoelectric substrate 1 by the same photolithography technique as the IDTs 2 and 3, and the sound absorbing material 5 is applied thereon by screen printing. The speed of the surface acoustic wave is lower when it propagates through the metal thin film 10 than when it propagates on the surface of the piezoelectric substrate 1.

Therefore, the surface acoustic wave 7 traveling from the IDTs 2 and 3 toward the substrate end face is refracted at the boundary between the metal thin film 10 and the piezoelectric substrate 1 and its propagation angle changes, so that the direction is perpendicular to the main propagation direction. Can be set smaller, and the device size can be further reduced.

FIG. 6 is a schematic diagram illustrating the configuration of a surface acoustic wave device according to a third embodiment of the present invention. In the present embodiment, a part of the IDT 3 in which the electrode finger intersection length is weighted, that is, the dummy electrode portion (shown by a broken line in the drawing) 3a which is not involved in surface acoustic wave excitation is located on the side close to the substrate end surface. The sound absorbing material 11 is applied so as to cover a part. In this case, the longest width W ′ of the application width of the sound absorbing material 11 in the surface acoustic wave propagation path can be set to W ′> W.

By doing so, it is possible to increase the application area of the sound absorbing material 11, not only to obtain a further effect of suppressing the reflected wave on the end face, but also to unnecessary excitation of the surface acoustic wave due to charge accumulation at the end of the IDT. Suppression can be achieved, and further improvement in characteristics can be obtained.

FIG. 7 is a schematic diagram illustrating the configuration of a surface acoustic wave device according to a fourth embodiment of the present invention. In the present embodiment, the sound absorbing material 12 is screen-coated on dummy electrode portions (shown by broken lines in the figure) on both upper and lower sides of the main propagation axis of the surface acoustic wave. In this case, the longest width W ″ of the application width of the sound absorbing material 11 in the surface acoustic wave propagation path can be set to W ″> W. According to this configuration, the application width of the sound absorbing material 12 can be made larger than in the third embodiment, and unnecessary excitation of surface acoustic waves due to charge accumulation at the end of the IDT can be further suppressed.

FIG. 8 is a schematic diagram illustrating the configuration of a surface acoustic wave device according to a fifth embodiment of the present invention. This embodiment has a resonator structure in which reflectors 14 and 15 that reflect surface acoustic waves and concentrate the energy inside are arranged on both sides of the IDT 13 that excites surface acoustic waves.

FIG. 9 is a schematic diagram illustrating the configuration of a surface acoustic wave device according to a sixth embodiment of the present invention. In the present embodiment, the resonator shown by the fifth embodiment (dotted line 16)
2) of the transversal filter (indicated by a dotted line 17) used in the first embodiment.
Two devices are provided on the same piezoelectric substrate 1.

That is, according to the present invention, since the size of the piezoelectric substrate 1 can be reduced, a plurality of devices can be arranged on the same piezoelectric substrate 1 without increasing the device size. A high-performance surface acoustic wave device can be realized.

FIG. 10 is a diagram for explaining a vehicle-mounted communication system using the surface acoustic wave device according to the sixth embodiment. The antenna 19 is an antenna for receiving a signal of a nonstop automatic toll collection system (ETC system), and the antenna 20 is an antenna for receiving a signal of a navigator system by GPS.

The signals received by the antennas 19 and 20 are
The signals from the local oscillators 21 and 22 and the mixer 2
The signals are mixed at 3, 24 and down-converted to respective intermediate frequency signals. The signal converted to the intermediate frequency band is input to the transversal filter and the resonator of the surface acoustic wave device 18 used in the sixth embodiment, and after being filtered, output from the output ports 25 and 26. It is detected. According to the present embodiment, a plurality of signal processes can be performed by the same surface acoustic wave device, and the size of the system can be reduced.

In each of the above embodiments, the input and output I
Although it was related to a transversal type surface acoustic wave device with DT, the device structure is not limited to the transversal type, but also a resonator type structure with a reflector and a structure using a unidirectional electrode. Also, the present invention can be easily applied to a matched filter, a chirp filter, a ladder type filter, and the like using a surface acoustic wave.

[0041]

As described above, the present invention provides a piezoelectric substrate, an interdigital electrode provided on the surface of the piezoelectric substrate for exciting surface acoustic waves, and an end face of the piezoelectric substrate. A surface acoustic wave device provided with a sound absorbing material provided between the electrodes, wherein the angle θ between the direction perpendicular to the main propagation direction of the surface acoustic wave and the end face of the piezoelectric substrate exceeds 15 ° and exceeds 15 °. And the coating width W of the sound-absorbing material is 2.5λ to 2.5λ when the wavelength of the surface acoustic wave is λ.
It is characterized in that it is restricted to the range of 5λ.

According to the present invention, the end face reflected wave can be effectively suppressed without increasing the device size and the manufacturing process, and the frequency amplitude characteristics can be improved without increasing the device manufacturing cost. be able to.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a surface acoustic wave device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a time axis response and a frequency amplitude characteristic of the surface acoustic wave device of the present invention and a conventional example.

FIG. 3 is a characteristic diagram showing a relationship between an application width of a sound absorbing material and a degree of suppression.

FIG. 4 is a characteristic diagram showing a relationship between an angle formed by a direction perpendicular to a main propagation direction of a surface acoustic wave, an end face of a piezoelectric substrate, and a degree of suppression.

FIG. 5 is a diagram illustrating a configuration of a surface acoustic wave device according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a configuration of a surface acoustic wave device according to a third embodiment of the present invention.

FIG. 7 is a diagram illustrating a configuration of a surface acoustic wave device according to a fourth embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration of a surface acoustic wave device according to a fifth embodiment of the present invention.

FIG. 9 is a diagram illustrating a configuration of a surface acoustic wave device according to a sixth embodiment of the present invention.

FIG. 10 is a diagram illustrating an in-vehicle communication system using a surface acoustic wave device according to a sixth embodiment.

FIG. 11 is a diagram illustrating a configuration of a conventional surface acoustic wave device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2, 3 IDT 3a Dummy electrode part 4 Shield electrode 5, 11 Sound absorbing material 6 Edge reflected wave 7 Surface acoustic wave heading to the substrate end face 8 Response of end face reflected wave on time axis 9 Main Response of signal on time axis 10 Metal thin film 18 Surface acoustic wave device 19, 20 Antenna 21, 22 Local oscillator 23, 24 Mixer 25, 26 Output port θ Direction perpendicular to main propagation direction of surface acoustic wave and end face of piezoelectric substrate Angle λ surface acoustic wave wavelength W coating width of sound absorbing material

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Katsunori Takayanagi 1 Kitano, Makino, Mizusawa-shi, Iwate F-term in Hitachi Media Electronics Co., Ltd. 5J097 AA04 AA13 AA33 BB11 EE07 GG07 HA02 JJ10 KK01

Claims (6)

[Claims] 1. A piezoelectric substrate, an interdigital electrode provided on a surface of the piezoelectric substrate for exciting surface acoustic waves, and a sound absorbing member provided between an end face of the piezoelectric substrate and the interdigital electrode. A surface acoustic wave device comprising: a material that regulates an angle θ between a direction perpendicular to a main propagation direction of the surface acoustic wave and an end face of the piezoelectric substrate to a range of more than 0 ° and 15 °; A surface acoustic wave device characterized in that the coating width W of the material is regulated in the range of 2.5λ to 5λ, where λ is the wavelength of the surface acoustic wave. 2. The method according to claim 1, wherein the angle θ is 3
A surface acoustic wave device, wherein the surface acoustic wave device is restricted to a range of up to 8 °. 3. The method according to claim 1, wherein
At least one of the interdigital transducers is a cross-width weighting electrode, and the sound absorbing material is provided across an electrode portion of the cross-width weighting electrode located near the substrate end surface which is not involved in exciting surface acoustic waves. A surface acoustic wave device. 4. The method according to claim 1, wherein the angle between the substrate end face and the IDT is greater than 0 ° with respect to a direction perpendicular to the main propagation direction of the surface acoustic wave. A surface acoustic wave device comprising a metal thin film having a boundary. 5. A piezoelectric substrate, an interdigital electrode provided on a surface of the piezoelectric substrate for exciting surface acoustic waves, and a sound absorbing member provided between an end face of the piezoelectric substrate and the interdigital electrode. Material, the angle θ between the direction perpendicular to the main propagation direction of the surface acoustic wave and the end face of the piezoelectric substrate is restricted to a range of more than 0 ° to 15 °, and the application width W of the sound absorbing material is controlled.
Is 2.5λ to 5 when the wavelength of the surface acoustic wave is λ.
A communication device for filtering a received signal using a surface acoustic wave device restricted to a range of λ. 6. The communication device according to claim 5, wherein the communication device is a mobile communication device.