JPS58145214A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To realize broad band characteristics, by providing a unidirectional transducer combining normal electrodes and chirp electrodes, taking one as the power feeding section and the other as the reflection section. CONSTITUTION:The normal form electrode 14 and the chirp electrode 15 are provided on the surface of an elastic substance substrate 13 so as to be orthogonal to the propagating direction X of the surface acoustic wave and both electrodes are arranged to contact at a vertical line Y-Y' on a common electrode 16. In using the normal form electrode 14 as the power feeding section and the chirp electrode 15 as the reflection section, a signal source 10 is connected to the electrode 14 via a matching circuit 11, a reactance circuit 12 is connected to the electrode 15, acting like the unidirectional transducer. Thus, the broad band characteristics are realized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave device equipped with a unidirectional transducer that makes it possible to achieve broadband characteristics.

Waves that propagate with concentrated energy along the flat surface of an elastic body, so-called surface acoustic waves, are superior in various respects to conventionally used bulk waves. Surface acoustic wave devices are being applied to various electronic components including filters. 1st
The figure shows a filter as an example, where 1 is a piezoelectric substrate, 2 is an input transducer consisting of a pair of interdigital electrodes 3A and 3B, and 4 is a pair of interdigital electrodes 5A.

Output transducer consisting of 5B, input terminal IN
The input signal is converted into a surface acoustic wave by the input transducer 2, propagates on the surface of the piezoelectric substrate 1 as shown by the arrow, and reaches the output transducer 4, where it is converted into an electrical signal and output. It is configured to be taken out from the terminal OUT.

By the way, in the case of a film in which two transducers 2.4 each including a pair of interdigital electrodes 3A, 3B and 5A, 5B are arranged, as in the surface wave device having the structure shown in FIG. Since each acts to propagate surface waves in both left and right directions, electro-mechanical conversion loss is unavoidable, and there is a drawback that the loss increases as a filter.

In order to eliminate this drawback, a so-called unidirectional transducer has been proposed, which is designed to propagate surface waves only in one direction on the surface of a piezoelectric substrate. Specific configurations of this unidirectional transducer include a method using a 120" phase shifter as shown in Fig. 4, a method using a rainbow phase shifter, and a method using a reflector as shown in Fig. 3. It is being

In FIG. 2, 6.6A and 6B are electrodes having a phase difference of 120", and 6 is constructed such that a gap 7 or an insulating film is interposed between it and another electrode 6A to generate surface waves. It works to propagate in one direction only.

However, this method of using a phase shifter has the disadvantage that the manufacturing process is complicated because it is necessary to provide a crossing portion in the 5Th electrode as described above. Furthermore, the design of the phase shifter itself to obtain desired characteristics is extremely complicated, making adjustment difficult and making it difficult to achieve broadband characteristics.

On the other hand, in FIG. 3, 8A and 8B are a power feeding part and a reflecting part provided to constitute a part of the interdigital electrode, both of which are regular electrodes, and 9 is the electrode 8A.
, 8B, 10 is a signal source, .multidot.1 is a matching circuit, and 12 is a reactance circuit. In the above, the signal applied from the signal source 10 via the matching circuit 11 is converted into a surface acoustic wave from the power feeding section 8A and propagated in both left and right directions. At this time, the surface wave propagated in the left direction is reflected by the reflection section 8B connected to the actance circuit 12 and returned to the right direction, and the surface wave propagated in the right direction and the reflected surface wave are combined in the power feeding section 8A. It will be done. As a result, when the center frequencies of surface waves are the same, the two waves overlap, but when they deviate from the center frequency, the waves act to cancel each other out, so the surface waves move in the opposite direction to the PI direction. will be propagated. Therefore, there is a drawback that the propagation characteristics of the surface waves are limited to narrow band characteristics.

The present invention has been made in response to the above problems, and is configured such that a regular electrode and a chilblain electrode are arranged side by side, and one electrode is used as a power feeding section and the other electrode is used as a reflecting section. An object of the present invention is to provide a surface acoustic wave device including a transducer. Embodiments of the present invention will be described below with reference to the drawings.

4(a) and 4(b) are a schematic top view and a schematic sectional view showing a surface acoustic wave device according to an embodiment of the present invention, in which regular electrodes are formed with equal electrode periods on the surface of an elastic substrate 13 made of a piezoelectric material. A shaped electrode 14 and a chirp electrode 15 formed so that the electrode period changes with respect to the propagation direction X of the surface acoustic wave are provided perpendicular to the propagation direction X, and these electrodes 14 and 15 are a common electrode. Vertical line Y-Y on 16
' are arranged so that they touch each other. Now, if the normal electrode 14 is used as a power supply part and the chirp electrode 15 is used as a reflection part, the power supply part electrode 14 is equipped with a matching circuit I.
A signal source 10 is connected to the reflector electrode I5, and an actance circuit 12 is connected to the reflector electrode I5.

In the above, among the surface acoustic waves generated from the power feeding part electrode 14 and propagated in the left-right direction on the surface of the elastic substrate 13, the surface waves propagated in the left direction actance circuit 12.
Since there is a reflective part electrode 15 terminated by , the light is reflected by this reflective part electrode 15 and returned to the right again. At this time, the point (isometric surface wave generation point) at which a surface wave can be considered to be generated in the power supply electrode 14 is designated as C, and the contact line Y between the electrodes 14 and 15 from this point (゛)
If the distance to -Y is 'tl, then the transit angle θ0 corresponding to this distance l can be expressed as follows.

θQ・−2πf−l/fo・λ0 where fo: center frequency of surface wave λ0: wavelength N of center frequency, logarithm of feeding section electrode f: operating frequency, and reflection section electrode 15 consisting of a chirp electrode is Due to its nature, the reflection point of surface waves differs depending on the operating frequency. Now let the reflection point (isometric surface wave reflection point) at the operating frequency f be D, and from this point the above contact line Y-
Assuming that the distance to Y is 11, the transit angle θ1 corresponding to this distance ll can be expressed as follows.

θl-2πf-ll/fO・λ0...
- (2) Here, the power feeding part electrode 14 and the reflecting part electrode 1
In order to operate the transducer including 5 as unidirectional, a surface wave propagating to the right from the feed electrode 14, a surface wave propagating to the left, reflected by the reflection electrode 15, and returning to the right. It is necessary to match the phase. For this purpose, it is necessary to form the reflective part electrode 15 (chirp electrode) so that the transit angle θ of the reflected and returned surface wave satisfies the following expression.

θ-(θ0+θ1)X2=2 n (2N+-)
-(3) By combining the above equations (1) to (3) tta, the following equation is derived.

By designing a chirp electrode that operates as a reflector electrode so as to satisfy equations (3) and (4) above, it is possible to match the phases of both surface waves as described above over a wide operating frequency range. Therefore, it can be operated as a unidirectional transducer. Furthermore, the electrode shape of the transducer that satisfies the above conditions can be easily manufactured using well-known photoetching techniques. Further, by terminating with the reflector electrode or actance circuit formed in this way, the adjustment can be easily performed.

FIG. 5 is a schematic top view showing another embodiment of the present invention, showing a configuration in which the chirp electrode 15 is operated as a power feeding section and the normal electrodes 1.1 are operated as a reflecting section. A signal source 10 is connected to the reflector electrode 14 via a matching circuit 1, and an actance circuit 12 is connected to the reflector electrode 14. In this case, the feeder electrode 1 consists of a chirp electrode.
5, the surface wave generation point differs depending on the operating frequency due to its geometrical properties, but in the reflecting part electrode 14 made of a regular electrode, the surface wave reflection point is the same for all operating frequencies. For the same reason as in the above embodiment, the surface wave that propagates to the right from the power supply streetcar $J+5, is reflected by the reflection section electrode 14, and returns to the left direction is located at the same position of the power supply section electrode 15 as the generation point. When it returns, it is matched in phase with the surface wave that was originally propagated to the left.

Therefore, the transducer operates so as to propagate the surface waves only in one direction, to the left, so that a similar effect can be obtained.

In each of the above embodiments, the chirved electrode 15 and the IE square electrode 1
4 are in contact with each other at the vertical IIM (contact line) y-y'; If so, it can be operated as a unidirectional transducer.

Note that the elastic substrate 13 is not limited to a piezoelectric material;
As shown in a) to (d), a combination of a non-piezoelectric substrate 17 and a piezoelectric film 18, or a metal film 19 may be used.

As is clear from the above description, according to the present invention, a normal electrode and a chilblain electrode are arranged side by side, and the unidirectional electrode is used as a power feeding part and the other electrode is used as a reflecting part. Since it constitutes a transducer, wideband characteristics can be achieved. In addition, since the manufacturing process is W5 and a half, manufacturing costs can be reduced, and adjustment to obtain desired characteristics is easy, so it can be widely applied to various surface acoustic wave devices such as filters. .

[Brief explanation of drawings]

Figures 1 to 3 are all schematic diagrams showing conventional examples;
Figures (a) and 5 are both schematic top views showing an embodiment of the present invention, and Figures 4 (b) and 6 (a) to (d) are both schematic sectional views showing an embodiment of the present invention. . 10... Signal source, II... Matching circuit, 12...
Reactance circuit, 13... Elastic substrate, 14...
Regular electrode, 15... Chirp electrode, 16... Common electrode, 17... Non-piezoelectric substrate, 18... Piezoelectric film, 19
...Metal film. Patent applicant Clarion Co., Ltd. agent Patent attorney Nagai 1) Take 3 part 4 A ′ilJ decoy (G) 6 乍4 decoy

Claims (1)

[Claims] A transducer is characterized in that a regular electrode and a chirp electrode are arranged side by side, one electrode is used as a power feeding section, and the other electrode is used as a reflecting section. Surface acoustic wave device. 2. The surface acoustic wave device according to claim 1, wherein a signal source is connected to the power feeding part electrode, and an actance is connected to the reflecting part electrode. 3. The chirp electrode is set so that the distance l from the contact line between the normal electrode and the chirp electrode to the point corresponding to the operating frequency of the chirp electrode is 1-(4)2f-f, 2°28 f. A surface acoustic wave device mounted on the first or second apex He of claim 1 or 2, characterized in that the surface acoustic wave device is formed by: 4. The surface acoustic wave device according to any one of claims 1 to 3, wherein the chirp electrode is used as a reflecting section.