JPH01321714A - Surface acoustic wave resonators and multimode filters - Google Patents

Abstract

PURPOSE:To considerably improve the Q value of a surface acoustic wave resonator to reduce the number of reflectors by forming a conductor pattern on the surface acoustic wave propagation path between an IDT(interdigital electrode) and the electrode of a reflector. CONSTITUTION:A conductor film consisting of aluminium or the like is formed on a piezoelectric substrate 10 consisting of crystal or the like, and electrodes are formed by photolithography. An IDT 11 where electrodes like comb teeth cross is formed in the center. Reflectors 12 consisting of strip electrodes are arranged (on both sides of the IDT) in the direction of propagation of the surface acoustic wave excited by the IDT. Conductor patterns 13 are formed which connect electrode fingers in outer end parts of the IDT 11 and electrodes (strip lines) on the IDT side of reflectors 12. Conductor patterns 13 are formed as one body together with the IDT 11 and reflectors 12 simultaneously with formation of them. In this example, conductor patterns 13 are formed on the bus bar side of outermost electrode fingers of the IDT 11 Q in the resonator where conductor patterns are added rises up to 16000 though Q in the resonator where conductor patterns are not added is 10000.

Description

DETAILED DESCRIPTION OF THE INVENTION 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 such resonators are coupled, and particularly relates to the structure of their electrodes. It is something.

[Prior art]

An interdigital electrode (IDT) is placed on a piezoelectric substrate.
), a surface acoustic wave resonator with reflectors on both sides sandwiching the resonator, and filters using this resonator are used in various fields.

In this resonator, the surface acoustic wave excited by the IDT is multiple reflected by the reflector, generating a standing wave and achieving energy confinement. Therefore, the number of reflectors had to be increased, and in order to obtain a Q of more than to, ooo, the number of reflectors had to be 500 to 1000.

(Problem) As mentioned above, the conventional surface acoustic wave resonator requires a large number of reflectors, which causes the problem that the size of the element becomes very large.

Therefore, there is a need for a surface acoustic wave resonator that can provide a high Q even when the number of reflectors is reduced.

Furthermore, when this resonator is used in a filter, there is a problem in that ripples occur within the passband and the characteristics deteriorate. Removal of this ripple can also be used as a filter.
This is a big problem that must be solved.

The present invention aims to solve such problems.

[Means to solve the problem]

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

That is, in a surface acoustic wave resonator that includes an interdigital electrode on one surface of a piezoelectric substrate and two reflectors sandwiching it, the electrode finger at the outer end of the interdigital electrode and the interdigital electrode of the reflector. It is characterized by having a four-body pattern formed on the propagation path of the surface acoustic wave, which connects the electrode at the end 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 as a multimode filter that uses coupling.

When used as a filter, the characteristics can be significantly improved by forming a conductor pattern connecting the electrode of the IDT connected to the ground potential and the electrode of the reflector.

〔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, and is an example of a resonator. A conductive film made of aluminum or the like is formed on a piezoelectric substrate IO such as crystal, and electrodes are formed by photolithography. [DTll] is formed in the center by intersecting comb-shaped electrodes. Reflectors 12 made of strip electrodes are arranged in the propagation direction (on both sides) of the excited surface acoustic waves.

Electrode fingers and reflector l2OIDT on the outer end of IDTII
A conductor pattern 13 is formed to connect the side electrodes (strip lines). This conductor pattern 13 is [D
Tll is formed integrally with the reflector 12 at the same time. In this example, a conductor pattern 13 is formed on the bus bar side of the electrode finger at the outer end of the IDT II.

In the resonator with the conductor pattern 13 added in this way, the Q was 10,000 when it was not added, whereas,
,000.

FIG. 2 is a plan view showing another embodiment of the present invention, also showing an example of a resonator. IDT21 and reflector 22
is the same as the previous example in that it is formed on the substrate 20, but
The positions at which the conductor patterns 23 are formed are different.

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

In this case, Q was similarly measured and found to have increased to 18,000. Although the reason for such a high Q has not been completely elucidated, it is believed that the first reason is to prevent charge from being concentrated on the electrode fingers at the outer end due to the edge effect. This is considered to indicate that Q becomes higher when a four-body pattern is formed on the tip side.

Second, it is thought that the presence of the conductor pattern changes the sound speed in that area, optimizing the position of the standing wave.

Although the conductor pattern may be formed to cover the entire width of the surface acoustic wave propagation path, it is most effective if it is formed to approximately half the width.

FIG. 3 is a plan view showing an embodiment of the surface acoustic wave multimode filter according to the present invention. A conductive film such as aluminum is formed on a piezoelectric substrate 30 such as crystal,
The electrodes are formed by photolithography. IDT3 in which intersecting comb-shaped electrodes are formed in the center.
1 is formed.

The IDT 31 has a structure in which two IDTs 31a and 31b are connected in series. Therefore, the bus bar of the intermediate comb-shaped electrode is common. Reflectors 32 made of strip electrodes are arranged in the propagation direction (on both sides) of the excited surface acoustic waves.

Electrode finger on the outer end of IDT 31 and IDT on reflector 32
A conductor pattern 33 is formed to connect the side electrodes (strip lines). This conductor pattern 13 has an ID
T31 and reflector 32 are formed simultaneously and integrally. In this example, a conductive pattern 33 is formed on the bus bar side of the electrode finger at the outer end of the IDT 31.

Typically, reflector 32 is connected to ground potential. Therefore, it is desirable that the electrode finger at the outer end of the IDT 31 connected to the door pattern 33 is also an electrode finger on the ground potential side.

In other words, it is better not to form a conductive pattern connected to the reflector on the electrode connected to the input/output terminal.

Looking at the bandpass characteristics of the filter in which the conductor pattern 33 was formed as shown in FIG. 3, the ripple within the passband was approximately 0.6 dB as shown in FIG. If a conductor pattern is not formed with a similar electrode arrangement, the ripple will be 1
．． 0 dB, indicating that the characteristics were improved.

Similarly, FIG. 4 is a plan view showing an example of a filter, and the electrode configuration is the same as that in FIG. 3. The difference is that the four-body pattern is formed in two parts. One ID741
The conductor pattern 43a connected to b and the other ID741
A conductor pattern 43b connected to the conductor pattern 43b is formed, respectively. This is because a conductor pattern is formed by connecting to the electrode finger on the ground potential side, and the conductor pattern is formed at the tip of the electrode finger. Similar to the resonator shown in FIG. 2, the effect was greater when a conductive pattern was formed at the tip of the electrode finger. That is, in this case, as shown in FIG. 6, the ripple within the passband was down to 0.3 dB.

〔effect〕

According to the present invention, the Q of a surface acoustic wave resonator can be significantly improved. Therefore, it is possible to reduce the number of reflectors, and a surface acoustic wave resonator with a small chimp size and high Q can be realized.

Furthermore, when used as a filter, a filter with good passband characteristics can be realized, and is extremely useful as a high frequency band filter.

[Brief explanation of the drawing]

1 to 4 are plan views showing embodiments of the present invention, and FIGS. 5 and 6 are explanatory diagrams of the characteristics of the surface acoustic wave multimode filter according to the present invention.

Claims (9)

[Claims] (1) In a surface acoustic wave resonator that has an interdigital electrode on one surface of a piezoelectric substrate and two reflectors sandwiching it, the electrode finger at the outer end of the interdigital electrode and the electrode finger of the reflector A surface acoustic wave resonator comprising a conductor pattern formed on a propagation path of a surface acoustic wave, which connects an electrode at an end on the digital electrode side. (2) The surface acoustic wave resonator according to claim 1, wherein the conductor pattern is formed to have a width that is half the width of the propagation path of the surface acoustic wave. (3) The surface acoustic wave resonator according to claim 1, wherein the conductive pattern is formed on the tip side of the electrode finger at the outer end of the interdigital electrode. (4) A surface where a plurality of surface acoustic wave resonators each having an interdigital electrode and two reflectors sandwiching it are arranged close to each other in a direction perpendicular to the propagation direction of the surface acoustic wave on one surface of a piezoelectric substrate. In an acoustic wave multimode filter, a conductor pattern formed on a propagation path of a surface acoustic wave connects an electrode finger at an outer end of the interdigital electrode and an electrode at an end of the reflector on the interdigital electrode side. A surface acoustic wave multimode filter characterized by: (5) The surface acoustic wave multimode filter according to claim 4, wherein the conductor pattern is formed to have a width that is half of the propagation path of each surface acoustic wave. (6) The surface acoustic wave multimode filter according to claim 5, wherein the conductor pattern is formed on the tip side of the electrode finger at the outer end of the interdigital electrode. (7) A surface where a plurality of surface acoustic wave resonators each having an interdigital electrode and two reflectors sandwiching it are arranged close to each other in a direction perpendicular to the propagation direction of the surface acoustic wave on one surface of a piezoelectric substrate. In the acoustic wave multimode filter, the electrode fingers at the outer ends of the interdigital electrodes are connected to a bus bar connected to ground potential, and the electrode fingers at the outer ends of the interdigital electrodes and the electrode fingers at the outer ends of the reflector are connected to the bus bar connected to the ground potential. A surface acoustic wave multimode filter comprising a conductor pattern formed on a propagation path of a surface acoustic wave and connected to an electrode at an end. (8) The surface acoustic wave multimode filter according to claim 4, wherein the conductor pattern is formed to have a width that is half of the propagation path of each surface acoustic wave. (9) The surface acoustic wave multimode filter according to claim 5, wherein the conductor pattern is formed on the tip side of the electrode finger at the outer end of the interdigital electrode.