JPH0817304B2 - Surface acoustic wave resonator and multimode filter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface acoustic wave resonator using a reflector and a surface acoustic wave multimode filter in which a plurality of the resonators are coupled to each other, and particularly to a structure of electrodes thereof. It is a thing.

[Prior art]

Interdigital electrodes (ID
T), a surface acoustic wave resonator in which reflectors sandwiching it are arranged on both sides, and a filter using the same are used in various fields.

In this resonator, the surface acoustic wave excited by the IDT is multiple-reflected by the reflector and a standing wave is generated to achieve energy confinement. Therefore, the number of reflectors must be increased, and in order to obtain a Q of 10,000 or more, the number of reflectors must be set to 500 to 1000.

〔Task〕

As described above, in the conventional surface acoustic wave resonator, it is necessary to increase the number of reflectors, which causes a problem that the size of the element becomes very large.

Therefore, there is a demand for a surface acoustic wave resonator that can obtain a high Q even if the number of reflectors is reduced.

In addition, when this resonator is used as a filter, there is a problem that ripples occur in the pass band and the characteristics deteriorate. The removal of this ripple is also a big problem to be solved in terms of use as a filter.

The present invention aims to solve such problems.

[Means for solving the problem]

The present invention solves the above problem by forming a conductor pattern on the propagation path of the surface acoustic wave between the IDT and the electrode of the reflector.

That is, in a surface acoustic wave resonator having an interdigital electrode and two reflectors sandwiching the interdigital electrode on one surface of a substrate having piezoelectricity, an electrode finger at an outer end of the interdigital electrode and the interdigital electrode of the reflector are provided. It is characterized in that it has a conductor pattern formed on the propagation path of the surface acoustic wave, which is connected to the electrode at the end portion on the electrode side.

It can be used not only as a resonator, but also as a filter in which resonators are connected in multiple stages and also as a multimode filter using coupling.

When used as a filter, forming a conductor pattern for connecting the electrode of the IDT on the side connected to the ground potential and the electrode of the reflector can significantly improve the characteristics.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of the present invention, which is an example of a resonator. A conductive film of aluminum or the like is formed on a substrate 10 having a piezoelectric property such as crystal, and electrodes are formed by photolithography. At the center, an IDT 11 is formed with comb-teeth-shaped electrodes crossing each other. A reflector 12 composed of a strip electrode is arranged in the propagation direction (both sides) of the surface acoustic wave to be excited.

A conductor pattern 13 is formed to connect an electrode finger on the outer end of the IDT 11 and an electrode (strip line) on the IDT side of the reflector 12. The conductor pattern 13 includes an IDT 11 and a reflector 12.
At the same time, they are integrally formed. In this example, the conductor pattern 13 is formed on the bus bar side of the electrode finger at the outer end of the IDT 11.

In the resonator to which the conductor pattern 13 is added in this way, the Q when not added was 10,000, while it increased to 16,000.

FIG. 2 is a plan view showing another embodiment of the present invention,
Similarly, an example of a resonator is shown. The point that the IDT 21 and the reflector 22 are formed on the substrate 20 is the same as the above-mentioned example, but the position where the conductor pattern 23 is formed is different.

In this example, the conductor pattern 23 is formed on the tip side of the electrode finger on the outer end of the IDT 23. That is, it is formed on the side far from the bus bar to have a width half the width of the propagation path.

In this case, when Q was measured similarly, it rose to 18,000. The reason why the Q becomes high in this way has not been completely clarified, but it is thought that it is firstly to prevent electric charges from concentrating on the electrode fingers at the outer end portion due to the edge effect. It is considered that this is because the Q becomes higher when the conductor pattern is formed on the tip side.

Secondly, it is considered that the presence of the conductor pattern changes the sound velocity in that portion, and the position of the standing wave is optimized.

The conductor pattern may be formed to fill the width of the propagation path of the surface acoustic wave, but it is most effective when it is formed to have a width of about half.

FIG. 3 is a plan view showing an embodiment of a surface acoustic wave multimode filter according to the present invention. A conductor film such as aluminum is formed on the substrate 30 having piezoelectricity such as crystal,
The electrodes are formed by photolithography. IDT31 formed by crossing comb-shaped electrodes in the center
Is formed. The IDT31 has a structure in which two IDTs 31a and 31b are connected in series. Therefore, the intermediate comb-tooth-shaped electrode has a common bus bar. A reflector 32 formed of a strip electrode is arranged in the propagation direction (both sides) of the excited surface acoustic wave.

A conductor pattern 33 is formed to connect the electrode finger at the outer end of the IDT 31 and the IDT-side electrode (strip line) of the reflector 32. The conductor pattern 13 includes an IDT 31 and a reflector 32.
At the same time, they are integrally formed. In this example, the conductor pattern 33 is formed on the bus bar side of the electrode finger at the outer end of the IDT 31.

Reflector 32 is typically connected to ground potential. Therefore, it is desirable that the electrode finger on the outer end of the IDT 31 connected to the conductor pattern 33 is also the electrode finger on the ground potential side. That is, it is better not to form a conductor pattern connected to the reflector on the electrode connected to the input / output terminal.

As shown in FIG. 3, looking at the bandpass characteristics of the filter having the conductor pattern 33 formed, the ripple in the passband was about 0.6 dB as shown in FIG. Ripple is 1.0 dB when the conductor pattern is not formed with the same electrode arrangement.
However, it showed that the characteristics were improved.

Similarly, FIG. 4 is a plan view showing an example of the filter, and the electrode configuration is the same as that in the case of FIG. The difference is that the conductor pattern is divided into two parts. A conductor pattern 43a connected to one IDT 41a and a conductor pattern 43b connected to the other IDT 41b are formed. This is because the conductor pattern was formed by connecting to the electrode finger on the ground potential side, and the conductor pattern was formed on the tip portion of the electrode finger. Similar to the resonator shown in FIG. 2, it was more effective to form the conductor pattern on the tip of the electrode finger. That is, in this case, as shown in FIG. 6, the ripple in the pass band was lowered to 0.3 dB.

〔effect〕

According to the present invention, the Q of the surface acoustic wave resonator can be significantly improved. Therefore, the number of reflectors can be reduced, and a surface acoustic wave resonator having a small chip size and a high Q can be realized.

Also, when used as a filter, a filter having a good pass band characteristic can be realized, which is extremely useful as a filter in a high frequency band.

[Brief description of drawings]

1 to 4 are plan views showing an embodiment of the present invention, and FIGS. 5 and 6 are explanatory views of characteristics of the surface acoustic wave multimode filter according to the present invention. 10,20,30,40 …… Board 11,21,31,41 …… IDT 12,22,32,42 …… Reflector 13,23,33,43 …… Conductor pattern

Claims (9)

[Claims] 1. A surface acoustic wave resonator comprising an interdigital electrode and two reflectors sandwiching the interdigital electrode on one surface of a substrate having piezoelectricity, wherein an electrode finger adjacent to an electrode finger at an outer end of the interdigital electrode. A surface acoustic wave resonator, comprising a conductor pattern for connecting a portion facing the interdigital electrode side end of the reflector and a part of a surface acoustic wave propagation path. . 2. The surface acoustic wave resonator according to claim 1, wherein the conductor pattern is formed with a width that is half the opposing length of the electrode fingers of the interdigital electrode. 3. The surface acoustic wave resonator according to claim 1, wherein the conductor pattern is formed on a tip end side of an electrode finger of an outer end of the interdigital electrode. 4. A plurality of surface acoustic wave resonators each having an interdigital electrode and two reflectors sandwiching the interdigital electrode on one surface of a substrate having piezoelectricity are arranged in proximity to each other in a direction perpendicular to the propagation direction of the surface acoustic wave. In the surface acoustic wave multi-mode filter, a surface acoustic wave connecting a portion of an outer end of the interdigital electrode facing an adjacent electrode finger to an electrode of an end portion of the reflector on the interdigital electrode side. A surface acoustic wave multimode filter characterized by comprising a conductor pattern covering a part of a wave propagation path. 5. The surface acoustic wave multimode filter according to claim 4, wherein the conductor pattern is formed with a width that is half the opposing length of the electrode fingers of the interdigital electrode. 6. The surface acoustic wave multimode filter according to claim 4, wherein the conductor pattern is formed on the tip end side of the electrode finger of the outer end of the interdigital electrode. 7. A plurality of surface acoustic wave resonators each having an interdigital electrode and two reflectors sandwiching the interdigital electrode on one surface of a substrate having a piezoelectric property and arranged in proximity to each other in a direction perpendicular to a propagation direction of the surface acoustic wave. In the surface acoustic wave multimode filter, the electrode finger at the outer end of the interdigital electrode is connected to the bus bar connected to the ground potential, and the electrode finger at the outer end of the interdigital electrode faces the adjacent electrode finger. A surface acoustic wave multimode filter, comprising: a conductor pattern for connecting a portion of a propagation path of the surface acoustic wave, which connects the electrode of the reflector and the end portion of the reflector on the side of the interdigital electrode. 8. The surface acoustic wave multimode filter according to claim 7, wherein the conductor pattern is formed with a width that is half the opposing length of the electrode fingers of the interdigital electrode. 9. The surface acoustic wave multimode filter according to claim 7, wherein the conductor pattern is formed on the outer end of the interdigital electrode on the tip side of the electrode finger.