JPS62281608A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To obtain the desired impulse response without giving distortions to the frequency amplitude characteristics or the group delay characteristics, by forming an electrode deleting part having approximately the same width and same area as a sound reflecting part at a prescribed position where an exciting electrode, a reseption electrode or a shielding electrode crasses the transmission line for surface acoustic waves where the sound. reflecting part is formed. CONSTITUTION:An electrode deleting part 6b having approximately the same width and same area as a sound reflecting part 6a is formed at a prescribed position where an exciting electrode 3, a reception electrode 4 or a shielding electrode 5 crosses the transmission line for surface acoustic waves where the part 6a is formed. Therefore the same phase speed of the surface acoustic wave is secured between a transmission line containing the part 6a and that containing no part 6a. Thus it is possible to obtain the desired impulse response without giving distortions to the frequency amplitude characteristics or the group delay characteristics.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Object of the Invention] (Field of Industrial Application) The present invention relates to a surface acoustic wave device used for, for example, a delay line, a filter, etc.

(Prior Art) Conventionally, a surface acoustic wave device used as a filter, for example, has a piezoelectric substrate, and an excitation device consisting of a pair of comb-tooth electrodes formed by intersecting a positive comb-tooth electrode and a negative comb-tooth electrode. A receiver consisting of an electrode and a pair of comb-tooth electrodes arranged with a predetermined gap in the propagation direction of the surface acoustic waves excited from the excitation electrode and made by crossing a positive comb-tooth electrode and a negative comb-tooth electrode. electrodes are formed. In addition, the pitch between the electrode fingers of these comb-shaped electrodes is 1/4λ0 (however, λO
indicates the wavelength of surface acoustic waves. In other words, the center frequency is FO
And if the propagation speed of the surface acoustic wave is vSaW, the wavelength λo =Vsaw/Fo. ) is closed.

The comb-shaped electrode formed with the pitch between electrode fingers of 174λ0 has the effect of canceling out acoustic interference, but on the other hand, electrical reflection may occur.

For this reason, if we attempt to reduce insertion loss by matching the impedance between the surface acoustic wave device and the external circuit connected to the surface acoustic wave device in the mouth, electrical reflections will occur significantly.
As a result, the triple transit echo becomes larger,
Since ripples appear within the band, there is a drawback that insertion loss cannot be reduced.

In order to compensate for such drawbacks, as shown in FIG. 6, among the electrode fingers 1.1...1 with a pitch of 174λ0,
Acoustic reflection parts 1a, 1a, . . . 1a are provided by short-circuiting adjacent electrode fingers within the same comb-teeth electrode to generate an acoustic reflection, and roughly make this acoustic reflection have the same amplitude as the electrical reflection. , and the phase is inverted, thereby canceling out the electrical reflection by this acoustic fouling.

(Problems to be Solved by the Invention) By the way, a surface acoustic wave is excited from the excitation electrode provided with the above-mentioned acoustic reflection section 1a, and when this surface acoustic wave propagates through the piezoelectric substrate, the excitation electrode, etc., the surface acoustic wave There is a difference in the phase velocity of the surface acoustic wave between the propagation path with and without the acoustic reflection section 1a.In other words, there is a difference between the propagation velocity of the material constituting the piezoelectric substrate and the acoustic reflection section. The above-mentioned difference occurs due to the difference in propagation speed of the material constituting the material.As a result, there is a problem in that the frequency amplitude characteristic or the group delay characteristic is distorted, and a desired impulse response cannot be obtained.

The present invention was devised in view of the above-mentioned circumstances, and an object of the present invention is to provide a surface acoustic wave device that can obtain a desired impulse response without causing distortion in frequency amplitude characteristics or group delay characteristics. The purpose is

[Structure of the Invention] (Means for Solving the Problems) That is, the surface acoustic wave device of the present invention includes a piezoelectric substrate and a pair of comb-shaped electrodes formed on the piezoelectric substrate, at least a portion of which is composed of a plurality of comb-shaped electrodes. At least a portion of each electrode is made up of a plurality of excitation electrodes each having electrode fingers intersecting each other, and a pair of comb-shaped electrodes formed in the propagation direction of surface acoustic waves excited from this excitation electrode. a receiving electrode formed by intersecting electrode fingers; and a shield electrode formed between the excitation electrode and the receiving electrode, wherein the excitation electrode and the comb-shaped electrodes of the receiving electrode are the same. In the surface acoustic wave device including an acoustic reflecting section formed by short-circuiting adjacent electrode fingers of a plurality of intersecting electrode fingers within the comb-shaped electrode, the excitation electrode, the reception electrode, or the shield electrode may , an electrode removed portion having approximately the same width and area as the acoustic reflecting portion is provided at a predetermined position intersecting the propagation path of the surface acoustic wave where the acoustic reflecting portion is provided.

(Function) In the surface acoustic wave device of the present invention, the excitation electrode, the reception electrode, or the shield electrode is placed at a predetermined position that intersects the propagation path of the surface acoustic wave provided with the acoustic reflection part, and has a width that is approximately the same as that of the acoustic reflection part. By having electrode-removed portions having approximately the same area, it is possible to make the phase velocity of the surface acoustic wave the same in the propagation path provided with the acoustic reflection portion and the propagation path not provided with the acoustic reflection portion. Therefore, no distortion occurs in the frequency amplitude characteristics or the group delay characteristics, and a desired impulse response can be obtained.

(Example) Hereinafter, details of an example of the present invention will be described based on the drawings.

FIG. 1 is a plan view without showing a surface acoustic wave device according to an embodiment of the present invention.

As shown in the figure, the surface acoustic wave device of this embodiment includes a pair of comb-toothed electrodes 3a, 3a formed by crossing a positive comb-tooth electrode and a negative comb-tooth electrode on a piezoelectric substrate 2. An excitation electrode 3 and a pair of comb-tooth electrodes arranged at a predetermined interval in the propagation direction of the surface acoustic waves excited from the excitation electrode 3 and formed by crossing a positive comb-tooth electrode and a negative comb-tooth electrode. (*A receiving electrode 4 consisting of 4a, 4a and a shield electrode 5 arranged between the mouth excitation electrode 3 and the receiving electrode 4 are formed.The piezoelectric substrate 2 is made of lithium niobate. , the electrode consists of A,2.

Roughly speaking, the pitch between the electrode fingers 6 of the comb-shaped electrode mentioned above is 1/
4λO (However, λO indicates the wavelength of the surface acoustic wave. In other words, the center frequency is FO and the propagation velocity of the surface acoustic wave is y.
When it is assumed that saw, the wavelength λo=Vsaw/FO. )
It is said that

Further, this surface acoustic wave device includes an acoustic reflecting section 6a formed by short-circuiting adjacent electrode fingers 6 within the same comb-shaped electrode of the comb-shaped electrodes 3a and 4a of the excitation electrode 3 and the receiving electrode 4.
・ is provided.

Roughly speaking, the electrode fingers 6 of the excitation electrode 3 and reception electrode 4 are as follows:
At predetermined positions intersecting the surface acoustic wave propagation path provided with the acoustic reflecting section 6a, there are electrode removed portions 6b having substantially the same shape as the acoustic reflecting section 6a. In addition,
The electrode finger 6 provided with the electrode removed portion 6b can be used as the excitation electrode 3 or the receiving electrode 4 due to the electrode removed portion 6b.
Since it has a part that is electrically independent from the other, it cannot perform its function. Therefore, in this embodiment, electrical independence is achieved by providing a conductor pattern 6C that is connected to the adjacent electrode finger 6 at a position other than the propagation path of the surface acoustic wave, or by combination U with other electrode fingers 6. I've lost the part I did.

The surface acoustic wave device configured as described above can cancel out electrical reflections by acoustic reflections generated from the acoustic reflection section 6a, reducing triple transit echoes.
Ripples are less likely to appear within the band. Therefore, insertion loss can be reduced.

Further, electrode fingers 6 of the excitation electrode 3 and the receiving electrode 4 have an electrode removed portion 6b having approximately the same shape as the acoustic reflecting portion 6a at a predetermined position where the electrode finger 6 intersects the propagation path of the surface acoustic wave provided with the acoustic reflecting portion 6a. By doing so, the surface acoustic wave propagated through the acoustic reflection section 6a and delayed is made to have the same phase velocity of the surface acoustic wave in the propagation path of the surface acoustic wave in the surface acoustic wave propagation path where the acoustic reflection section 6a is not provided by the electrode removed section 6b. It can be made into Therefore, no distortion occurs in the frequency amplitude characteristics or the group delay characteristics, and a desired impulse response can be obtained.

The portion surrounded by the acoustic reflecting portion 6a and the electrode fingers 6 caused by providing the acoustic reflecting portion 6a roughly can be eliminated by the electrode removed portion 6b. Therefore, when forming the excitation electrode 3 and the reception electrode 4 on the piezoelectric substrate 2 by wet etching, a flow path for the etching solution is formed, making the etching process easier and allowing the desired electrode pattern to be formed with high precision. become.

Next, the center frequency is 145 Hz, 1 d [3 hand width 6, O
Surface acoustic wave devices designed with MH2 and flat group delay characteristics according to the present invention and those according to the prior art were fabricated, and their frequency amplitude characteristics and lid delay characteristics were measured. The results are shown in Figs. 2 and 3. show.

FIG. 2 shows frequency amplitude characteristics and group delay characteristics of a surface acoustic wave device to which the present invention is applied, and FIG. 3 shows frequency amplitude characteristics and group delay characteristics of a surface acoustic wave device according to the prior art. As is clear from these figures, in conventional surface acoustic wave devices, the frequency amplitude characteristics are degraded to the out-of-band level due to the non-uniformity of the phase velocity of the surface acoustic waves.
In the group delay patent application, progress is made near the center frequency.

On the other hand, in the surface acoustic wave device to which the present invention is applied, there is less deterioration in the out-of-band level, and the group delay characteristic is less likely to advance near its center frequency.

In the above-described embodiment, the electrode removed portion 6b was provided on the excitation electrode 3 and the reception electrode 4, but the present invention is not limited to this, and the electrode removal portion 6b is provided as shown in FIG. 4 or FIG. As shown, an electrode removed portion 5a having approximately the same width and approximately the same area as the acoustic reflecting portion 6a may be provided on the shield electrode 5 at a position intersecting the propagation path of the surface acoustic wave where the acoustic reflecting portion 6a is provided. stomach.

[Effects of the Invention] As explained above, according to the surface acoustic wave device of the present invention,
No distortion occurs in frequency amplitude characteristics or group delay characteristics, and a desired impulse response can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view showing a surface acoustic wave device according to an embodiment of the present invention, FIG. 2 is a graph showing frequency 1 axis width characteristics and group delay characteristics of a surface acoustic wave device to which the present invention is applied 3
The figure is a graph showing frequency amplitude characteristics and group delay characteristics of a conventional surface acoustic wave device, FIGS. 4 and 5 are schematic plan views showing modifications of the present invention, and FIG. 6 is a conventional surface acoustic wave device. FIG. 2...Piezoelectric substrate 3...Excitation electrode 4...Reception electrode 5...Shield electrode 6a.・・・Acoustic reflection part 6b・・・Electrode removal part Applicant Toshiba Corporation Patent attorney Satoshi Suyama - Mitt Figure 2 118 1% +40 146 152
+5R164 Blade Dumoku (Mon 1-1.) Figure 3. Figure 5

Claims (1)

[Claims] (1) A piezoelectric substrate, an excitation electrode formed by a pair of comb-shaped electrodes formed on the piezoelectric substrate, and each electrode finger intersecting each other so that at least some of the electrode fingers intersect, and excitation from the excitation electrode. a receiving electrode formed of a pair of comb-shaped electrodes formed in the propagation direction of surface acoustic waves, each of which has its electrode fingers crossed so that at least a portion of each interdigitated electrode intersects; and the excitation electrode and the receiving electrode. and a shield electrode formed between the excitation electrode and the receiving electrode, and the comb-shaped electrodes of the excitation electrode and the receiving electrode short-circuit between adjacent electrode fingers of the plurality of intersecting electrode fingers within the same comb-shaped electrode, respectively. In the surface acoustic wave device including an acoustic reflection section, the excitation electrode, the reception electrode, or the shield electrode is located at a predetermined position intersecting the propagation path of the surface acoustic wave provided with the acoustic reflection section, A surface acoustic wave device comprising an electrode-removed portion having approximately the same width and approximately the same area as the acoustic reflecting portion.