JPH09116374A - Surface acoustic wave device and communication equipment using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the diffraction effect and to eliminate characteristic degradation. SOLUTION: In this surface acoustic wave(SAW) device composed of a SAW substrate 1 and interdigital electrodes 2 for input and output formed on the substrate 1, propagating angle dependency for the velocity of SAW excited by the interdigital electrode 2 for input and propagating angle dependency for the velocity of SAW received at the interdigital electrode 3 for output are made respectively different so that the degradation of frequency characteristics caused by the diffraction effect can be reduced. More specifically, a non-conductive thin film is formed on the surface of the SAW substrate 1 so that either the interdigital electrode 2 for input or the interdigital electrode 3 for output can be covered.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a surface acoustic wave filter and a communication device using the same.

[0002]

2. Description of the Related Art The deterioration of the out-of-band characteristics of a surface acoustic wave filter includes the effects of diffraction and secondary effects such as direct waves and bulk waves. As a measure against the deterioration of the out-of-band characteristics due to the diffraction effect, the IDT is weighted by a phase weighting electrode (C. Atzeni et.al .: Synthesis of Amplification).
itude-Modulated SAW filters with Constant-lengthFi
ngers: 1973 IEEE Ultrasonic Symposium, 414) and Apodized IDT considering the diffraction effect have already been reported, but a great deal of design effort is expected to design a general filter.

[0003]

Due to the relationship between the surface acoustic wave excitation intensity and the propagation angle, the signal wave propagating in an oblique direction by diffraction is higher than the main signal wave propagating perpendicularly to the electrode fingers at the out-of-band frequency. Is getting stronger. The signal wave due to this diffraction causes deterioration of the out-of-band characteristic.

An object of the present invention is to realize a surface acoustic wave device in which the influence of diffracted waves is suppressed and the characteristic deterioration is improved.

[0005]

In order to achieve the above object, in the present invention, in order to suppress the influence of a wave propagating in an oblique direction by diffraction, the velocity of the surface acoustic wave on the input electrode side and the output electrode side is suppressed. By making the propagation angle dependence different, the angular distribution of the excitation intensity of the surface acoustic wave at the input electrode and the angular distribution of the received wave intensity at the output electrode are made different. As this method, by forming an isotropic non-conductive thin film on either the input or output interdigital electrode, by ion implantation, or by using a different surface acoustic wave substrate. To achieve.

By adopting the above method, in the angular distribution of the total signal represented by the product of the excitation intensity distribution of the surface acoustic wave excited from the input electrode and the received distribution of the surface acoustic wave at the output electrode, θ Signals other than = 0 °, that is, the diffracted surface acoustic waves are canceled out, so that the characteristic deterioration of the surface acoustic wave device can be reduced.

As disclosed in Japanese Patent Laid-Open No. 3-6113, a ZnO film is formed on the entire surface of a surface acoustic wave substrate,
Surface acoustic wave devices having interdigital electrodes formed thereon are known, but these are for exciting Rayleigh waves and Sezawa waves, and are transmitted and received at the input and output interdigital electrodes. The angular dependence of the velocity of the surface acoustic wave is the same.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a surface acoustic wave device of the present invention is shown in FIG. FIG. 2 shows the relationship between the surface acoustic wave excitation intensity and the propagation angle at the pole frequency of the frequency characteristics of the surface acoustic wave filter using the present invention.

[0009]

(Equation 1)

It is calculated by the above equation and is standardized by the excitation intensity at the center frequency at the propagation angle of 0 °. A solid line 6 in FIG. 2 indicates that the surface acoustic wave substrate is rotated by 128 degrees Y-X.
In the case of LiNbO ₃ (see solid line 8 in FIG. 3), the broken line 7 shows the one using the ZnO film (see broken line 9 in FIG. 3) in which the acoustic velocity of the surface acoustic wave is isotropic.

FIG. 2 shows the angular distribution of the excitation intensity of the surface acoustic wave propagating from the input electrode. These distributions are the angular distribution of the received wave intensity of the output electrode on the output electrode side.

If the 128-degree rotated Y-X LiNbO ₃ shown by the solid line 6 in FIG. 2 is applied to both the input electrode side and the output electrode side, a surface acoustic wave diffracted from the input electrode and propagating in an oblique direction, that is, θ = 0 °. Surface acoustic waves (hereinafter, referred to as diffracted waves) propagating at propagation angles other than the above are received by the output electrode having the same angular distribution of the received wave intensity. Therefore, the total signal shown by the solid line 10 in FIG. The wave propagating in the direction perpendicular to the finger, that is, the signal due to the diffracted wave is clearly stronger than the main signal. The effect of this diffracted wave appears as deterioration of the out-of-band suppression characteristic in the frequency characteristics of the surface acoustic wave filter.

Therefore, according to the present invention, the ZnO film 4 having the characteristic shown by the broken line 7 in FIG. 2 is formed on the output electrode side, and the angular dependence of the velocity of the surface acoustic wave excited by the input electrode 2 is
By making the propagation angle dependence of the velocity of the surface acoustic wave received by the output electrode 3 different, the angular distribution of the surface acoustic wave excitation intensity at the input electrode 2 and the angular distribution of the received wave intensity at the output electrode 3 can be made different. As a result, the influence of the diffracted wave can be suppressed as in the total signal indicated by the broken line 11 in FIG.

In this embodiment, the ZnO film 4 is formed on the output side electrode.
To make the propagation angle dependence of the surface acoustic wave velocity on the input electrode side and the output electrode side different.
Non-conductive thin film such as AlN film and SiO ₂ film is formed, ion implantation, etc. are used to make the propagation angle dependence of the velocity of the surface acoustic wave on the input electrode side and the output electrode side different. It goes without saying that what you do is fine.

With the use of this embodiment, as shown in FIG. 5, the out-of-band characteristics show a broken line 1 as compared with the conventional one shown by a solid line 12.
As shown by 3, the out-of-band suppression degree can be improved by about 5 dB.

FIG. 6 shows a second embodiment of the surface acoustic wave device of the present invention. In the surface acoustic wave device of this embodiment, the AlN film 15 is formed on the output electrode side so as to cover the output electrode 14, and the propagation angle dependence of the velocity of the surface acoustic wave excited by the input electrode 16 and the output electrode 14 The propagation angle dependence of the velocity of the surface acoustic wave excited by is varied.

In this embodiment, the AlN film 15 is formed in order to make the propagation angle dependence of the surface acoustic wave velocity on the input electrode side and the output electrode side different, but this non-conductive thin film is made of ZnO. The propagation angle dependence of the velocity of the surface acoustic wave propagating through them such as a film and a SiO ₂ film is different from the propagation angle dependency of the velocity of the surface acoustic wave peculiar to the piezoelectric substrate, and the diffracted wave is suppressed by the total signal Needless to say, it can be anything.

According to this embodiment, the diffraction effect, which is the cause of deterioration of the out-of-band suppression degree, is suppressed, and the out-of-band suppression degree is 5 dB.
It is possible to improve the degree.

FIG. 7 shows a third embodiment of the surface acoustic wave device of the present invention. In the surface acoustic wave device of this embodiment, by forming the AlN film 15 on the output electrode side and forming the output electrode 14 on the thin film, the propagation angle dependence of the velocity of the surface acoustic wave excited by the input electrode 16 is dependent. And the dependence of the velocity of the surface acoustic wave excited by the output electrode 14 on the propagation angle. As a result, it is possible to suppress the diffraction effect that is the cause of deterioration of the out-of-band suppression degree.

In this embodiment, the AlN film 15 is formed in order to make the propagation angle dependence of the surface acoustic wave velocity on the input electrode side and the output electrode side different, but this non-conductive thin film is made of ZnO. The propagation angle dependence of the velocity of the surface acoustic wave propagating through them such as a film and a SiO ₂ film is different from the propagation angle dependency of the velocity of the surface acoustic wave peculiar to the piezoelectric substrate, and the diffracted wave is suppressed by the total signal Needless to say, it can be anything.

As described above, since the electrode is not in contact with the surface acoustic wave substrate by forming the electrode on the non-conductive thin film, it is less susceptible to the propagation angle dependency peculiar to the surface acoustic wave substrate, and further, It is possible to improve the out-of-band suppression degree.

FIG. 8 shows a fourth embodiment of the surface acoustic wave device of the present invention. The end of the non-conductive thin film 17 formed on the surface acoustic wave substrate is inclined from the vertical with respect to the traveling direction of the surface acoustic wave. Although the shape shown in FIG. 8 is used here, the shape of the end of the non-conductive thin film 17 may be any shape such as oblique or curved as long as it is not perpendicular to the traveling direction of the surface acoustic wave. Needless to say.

By using this embodiment, the non-conductive thin film 17
It is possible to obtain a good surface acoustic wave device that suppresses the influence of the unnecessary reflected wave generated at the edge of.

FIG. 9 shows a surface acoustic wave device according to a fifth embodiment of the present invention. When the wavelength at the center frequency of the surface acoustic wave is lambda _0, the end of the non-conductive thin film 17 formed on the surface acoustic wave on the substrate _{λ 0/4 + n (n} = 1,
2, 3, ...) Protrusions are provided. In the present embodiment, as shown in FIG. 9, one convex portion is provided at the end of the non-conductive thin film 17, but it goes without saying that the convex portion may be provided at several places.

Using this embodiment, the non-conductive thin film 17
It is possible to obtain a good surface acoustic wave device that suppresses the influence of the unnecessary reflected wave generated at the edge of.

FIG. 10 shows a sixth surface acoustic wave device of the present invention.
1 shows an embodiment. In the surface acoustic wave device of this embodiment, ion implantation 18 is performed on the output electrode side to determine the propagation angle dependence of the velocity of the surface acoustic wave excited by the input electrode 16 and the velocity of the surface acoustic wave excited by the output electrode 14. Different propagation angle dependence.

In this embodiment, ion implantation is performed in order to make the propagation angle dependence of the velocity of the surface acoustic waves on the input electrode side and the output electrode side different, but the propagation angle of the velocity of the substrate specific surface acoustic wave is different. Any type can be used as long as it can change the dependency.

By using the present embodiment, by changing the density of ions to be implanted, an arbitrary propagation angle dependency can be obtained, the diffraction effect which is the cause of deterioration of the out-of-band suppression degree can be suppressed, and the out-of-band comparison can be achieved. It is possible to improve the degree of suppression by about 5 dB.

FIG. 11 shows a seventh surface acoustic wave device of the present invention.
1 shows an embodiment. Surface acoustic wave substrate having different propagation angle dependence of velocity of surface acoustic wave, 128 ° YX
LiNbO ₃ 19 and 112 ° Y—X LiTaO ₃ 20 are molecularly bonded, and the propagation angle dependence of the velocity of the surface acoustic wave excited by the input electrode 16 and the velocity of the surface acoustic wave received at the output electrode 14 are determined. Different propagation angle dependence. As a result, it is possible to suppress the diffraction effect that is the cause of deterioration of the out-of-band suppression degree.

In this embodiment, in order to make the propagation angle dependence of the surface acoustic wave velocity on the input electrode side and the output electrode side different, a surface acoustic wave substrate having different propagation angle dependency of the surface acoustic wave velocity is used. Although they are molecularly bonded, this surface acoustic wave substrate shows that the propagation angle dependence of the velocity of the surface acoustic wave propagating through them such as LiNbO ₃ , LiTaO ₃ , and quartz is different on the input electrode side and the output electrode side. It goes without saying that any signal that suppresses diffracted waves may be used.

In this embodiment, since the propagation angle dependence peculiar to the surface acoustic wave substrate is different on the input electrode side and the output electrode side, the degree of suppression of diffracted waves is high, and the degree of out-of-band suppression is further improved. It is possible.

FIG. 12 shows the eighth embodiment of the surface acoustic wave device of the present invention.
1 shows an embodiment.

The present television receiving apparatus has an antenna 2
1, a tuner unit 22, an intermediate frequency filter 23, a demodulation unit 24, a video signal output unit 25, and an audio signal output unit 26. Here, the surface acoustic wave filter according to the present invention is used as the intermediate frequency filter 23. By using this embodiment, a television receiver having good demodulation performance can be obtained.

FIG. 13 shows a ninth surface acoustic wave device of the present invention.
1 shows an embodiment.

This satellite broadcast receiving apparatus comprises a parabolic antenna 27, an outdoor unit 28, an indoor unit 29 and an oscillator 3.
0, mixer 31, intermediate frequency filter 32, demodulator 33,
It is composed of a video signal output unit 34 and an audio signal output unit 35. Here, the surface acoustic wave filter according to the present invention is used as the intermediate frequency filter 32. By using this embodiment, a satellite broadcast receiver having good demodulation performance can be obtained.

FIG. 14 shows a first surface acoustic wave device according to the present invention.
0 shows an embodiment.

This CATV receiver is provided with a cable terminal 3
6, a tuner section 37, an intermediate frequency filter 38, a demodulation section 39, a video signal output section 40, and an audio signal output section 41. Here, the surface acoustic wave filter according to the present invention is used as the intermediate frequency filter 38. Using this embodiment, a CATV receiver having good demodulation performance can be obtained.

[0038]

As described above, the propagation angle dependence of the velocity of the surface acoustic wave excited by the input electrode and the propagation angle dependence of the velocity of the surface acoustic wave received at the output electrode are made different. As a result, compared to the conventional surface acoustic wave device, by using the present invention, the diffraction effect of the surface acoustic wave can be suppressed and the out-of-band suppression degree can be improved.

By using the surface acoustic wave device of the present invention for the communication device, a communication device having good demodulation performance can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a relationship between a surface acoustic wave excitation (received wave) intensity and a propagation angle.

FIG. 3 is a diagram showing a relationship between a velocity of a surface acoustic wave and a propagation angle.

FIG. 4 is a diagram showing a relationship between a surface acoustic wave excitation (received) intensity and a propagation angle of a total of input and output electrodes.

FIG. 5 is a diagram showing frequency characteristics of a surface acoustic wave filter.

FIG. 6 is a diagram showing a surface acoustic wave device according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a surface acoustic wave device according to a third embodiment of the present invention.

FIG. 8 is a diagram showing a surface acoustic wave device according to a fourth embodiment of the present invention.

FIG. 9 is a diagram showing a surface acoustic wave device according to a fifth embodiment of the present invention.

FIG. 10 is a diagram showing a surface acoustic wave device according to a sixth embodiment of the present invention.

FIG. 11 is a diagram showing a surface acoustic wave device according to a seventh embodiment of the present invention.

FIG. 12 is a diagram showing a configuration of a television receiving device using a surface acoustic wave device according to an eighth embodiment of the present invention.

FIG. 13 is a diagram showing a configuration of a satellite broadcast receiving device using a surface acoustic wave device according to a ninth embodiment of the present invention.

FIG. 14 is a diagram showing a configuration of a CATV receiver using a surface acoustic wave device according to a tenth embodiment of the present invention.

[Explanation of symbols]

1 Surface Acoustic Wave Substrate 2 Input Electrode 3 Output Electrode 4 ZnO Film 5 Absorber 14 Output Electrode 15 AlN Film 16 Input Electrode 17 Non-conductive Thin Film 18 Ion Implantation 19 128 Degree Y-X LiNbO ₃ 20 112 Degree Y-X LiTaO ₃ 21 antenna 22 tuner section 23 intermediate frequency filter 24 demodulator 25 video signal output section 26 audio signal output section 27 parabolic antenna 28 outdoor unit 29 indoor unit 30 oscillator 31 mixer 32 intermediate frequency filter 33 demodulation section 34 video signal Output unit 35 Audio signal output unit 36 Cable terminal 37 Tuner unit 38 Intermediate frequency filter 39 Demodulation unit 40 Video signal output unit 41 Audio signal output unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Shiba 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Hitachi Ltd. Multimedia System Development Division

Claims (11)

[Claims] 1. A surface acoustic wave device comprising a surface acoustic wave substrate and input and output interdigital electrodes formed on the substrate, wherein velocity propagation of a surface acoustic wave excited by the input interdigital electrode is propagated. By making the angle dependence and the propagation angle dependence of the velocity of the surface acoustic wave received at the output interdigital electrode different, it is possible to reduce the deterioration of the frequency characteristics due to the diffraction effect. Wave device. 2. The non-conductive thin film according to claim 1, wherein a non-conductive thin film is formed on the surface of the surface acoustic wave substrate so as to cover either the input interdigital electrode or the output interdigital electrode. The surface acoustic wave device according to claim 1. 3. The non-conductive thin film is formed on the surface of the surface acoustic wave substrate on the electrode side of either the input interdigital electrode or the output interdigital electrode, and the nonconductive thin film is formed on the nonconductive thin film. A surface acoustic wave device, wherein the interdigital transducer is arranged. 4. The non-conductive thin film according to claim 2, wherein the thin film end is inclined with respect to the traveling direction of the surface acoustic wave in order to suppress reflection of the surface acoustic wave occurring at the thin film end face. A surface acoustic wave device having a curved shape. 5. The non-conductive thin film according to claim 2, wherein the non-conductive thin film has a wavelength at a center frequency of λ in order to suppress reflection of a surface acoustic wave occurring at the end face of the thin film.
₀ and when one or more positions in a non-conductive thin film edge, lambda _0/4 +
A surface acoustic wave device comprising n (n = 0, 1, 2, 3, ...) Convex portions. 6. A surface acoustic wave device comprising a surface acoustic wave substrate and interdigital electrodes for input and output formed on the substrate, wherein both or one of the input electrode side and the output electrode side is provided. Dependence of Velocity of Surface Acoustic Wave Excited by Input Interdigital Electrode and Propagation Angle of Velocity of Surface Acoustic Wave Received by Output Interdigital Electrode A surface acoustic wave device characterized in that deterioration of frequency characteristics due to a diffraction effect is reduced by making the characteristics different from each other. 7. A surface acoustic wave device comprising a surface acoustic wave substrate and input and output interdigital electrodes formed on the substrate, and a surface acoustic wave substrate on which an input interdigital electrode is arranged, and an output. Surface acoustic wave substrate on which the interdigital transducer is arranged is different from the surface acoustic wave substrate, and the surface acoustic wave excited by the input interdigital electrode and the surface acoustic wave received by the output interdigital electrode are Surface acoustic wave device characterized in that the propagation angle dependence of the velocity of the wave is changed. 8. A communication device using the surface acoustic wave device according to any one of claims 1 to 7 as a filter. 9. A television receiver using the surface acoustic wave device according to any one of claims 1 to 7 as a filter. 10. A satellite broadcast receiving device using the surface acoustic wave device according to any one of claims 1 to 7 as a filter. 11. A C using the surface acoustic wave device according to any one of claims 1 to 7 as a filter.
ATV receiver.