JPH027613A - Multiplex mode resonator type surface acoustic wave filter and its band pass characteristic adjusting method - Google Patents

Abstract

PURPOSE:To improve the pass band characteristic by forming a capacitance between connecting conductor pattern and a ground conductor pattern of interdigital electrodes(IDT) between resonators. CONSTITUTION:Two resonators each consists of an IDT 11 and a reflector 12 arranged at both sides on the surface of a piezoelectric substrate 10 made of a material such as crystal are arranged in the title filter and both ends of each electrode of the reflector 12 are connected together. The conductor pattern 15 is extended from conductors connecting the two IDTs 11 and formed opposite in parallel with the connection conductor pattern of the reflector 12. Then a dielectric substance film 18 made of zinc oxide is formed on the surface of the substrate 10 between the connection conductor patterns to the conductor pattern 15 and the reflector 12. A capacitance is formed between the opposite conductor patterns and the dielectric substance film 18 is formed thereupon, then the capacitance is much large. Thus, the band pass characteristic as the filter is improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a multimode resonator type surface acoustic wave filter in which a plurality of resonators are elastically coupled, and a method for adjusting the bandpass characteristics of the filter. It is related to.

[Prior art]

Two surface acoustic wave (SAW) resonators are placed close to each other,
When they are elastically coupled, two modes of vibration occur. That is, in two vibration modes, a symmetric mode and an anti-symmetric mode, the resonant frequency of the symmetric mode and the anti-resonant frequency of the anti-symmetric mode are made to match, thereby forming a dual mode SAW filter.

FIG. 4 is a plan view of an example of the dual mode SAW filter, in which interdigital electrodes (
A resonator is configured by the IDT 41 and the reflector 42 sandwiching it, and another resonator is arranged in a direction perpendicular to the SAW propagation direction.

A multimode filter can also be configured by arranging three or more resonators. Such a multi-mode resonator type surface acoustic wave filter is shown in Electronics) 11 IEICE Ultrasound Study Group Material US-77-33 (1977) and the like. In addition, two interdigital electrodes were placed in each resonator.
There are also boat types.

〔assignment〕

In the multi-mode resonator type surface acoustic wave filter as described above, if you try to widen the band by increasing the frequency space of one mode 1' and the other mode, the solid line 5 in Fig. 5
A waveform stop band is generated as shown in 3.

Furthermore, since the Q is very high, about 10,000, the characteristic impedance near the second atmosphere point is low, and a shoulder appears near the limit of the passband, as shown by the solid line 63 in FIG.

The present invention aims to solve these problems and obtain a multimode resonator type surface acoustic wave filter with good passband characteristics.

Furthermore, it is an attempt to efficiently improve the characteristics using the minimum space.

Furthermore, the characteristics can be adjusted at the same time.

[Failure to solve the problem]

The present invention solves the above problem by forming a capacitance between a connecting conductor pattern of an IDT between resonators and a ground conductor.

That is, in a multi-mode resonator filter that utilizes the elastic coupling of a plurality of resonators each consisting of interdigital electrodes and reflectors sandwiching them on the surface of a piezoelectric substrate, a conductor connecting the interdigital electrodes is used. Particularly, the first conductive conductor extending from the pattern and the grounded second conductive pattern are arranged to face each other, and a dielectric film is provided on the substrate surface between the first and second conductive patterns. It has the following.

In other words, in a method for adjusting the bandpass characteristics of a multimode resonator filter, which utilizes the elastic coupling of a plurality of resonators each consisting of an interdigital electrode and a reflector sandwiching the interdigital electrodes on the surface of a piezoelectric substrate. A first conductive pattern extending from the conductive pattern connecting the interdigital electrodes and a grounded second conductive pattern are arranged to face each other, and a dielectric is applied to the substrate surface between the first and second conductive patterns. The feature is that a body film is formed and a capacitance is formed between two conductor patterns.

There are various bottle patterns that form a capacitance, and the capacitance can also be adjusted by adjusting the amount of dielectric material.

C Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of the present invention.

Two resonators each consisting of an IDT II and reflectors 12 placed on both sides thereof are arranged on the surface of a piezoelectric substrate 10 made of crystal or the like. Each electrode of the reflector has a structure in which both ends are connected.

A conductor pattern 15 extends from the conductor pattern connecting the two IDTs, and is formed so as to extend parallel to and opposite to the connection conductor pattern of the reflector. and,
A dielectric film 18 such as zinc oxide is formed on the surface of the substrate between the conductor pattern 15 and the connection conductor pattern of the reflector.

A capacitance is formed between the opposing conductor patterns. Furthermore, since a dielectric film is formed thereon, the capacitance value becomes larger. 0.0 before forming the dielectric film 18.
The capacitance, which was 1 to 1 pF, became 1 to 59 F after forming the dielectric film 18 of zinc oxide.

FIG. 2 is a plan view showing another embodiment of the invention. I
DT21 and reflector 22 are the same as in the previous example, but with ID
In addition to electrodes 25 extending from the conductor pattern between the T's, a conductor pattern 26 is also formed which is connected to a reflector 22 connected to ground potential. The conductor pattern 25 and the conductor pattern 26 extend close to each other in parallel and are arranged to face each other. A dielectric film 28 made of zinc oxide or the like is formed on these two conductor patterns.

In this way, by arranging two conductive patterns close to each other, the capacitance value can be increased. Furthermore, in order to further increase the capacitance value, an electrode having a structure similar to an IDT may be formed so that a plurality of conductor patterns face each other.

FIG. 3 shows a state in which a dielectric film is formed on and between two conductor patterns. A dielectric film 38 is applied over the parallel conductor patterns 35, 36 on the substrate 30. The thickness of the electrode is usually about 3 microns, and the thickness of the dielectric film is about 100 mils.

When a zinc oxide film is formed on a crystal substrate, the capacitance is 0.05p when the AI main electrode is 1mm opposite to the main electrode before the film is formed.
In contrast, when a zinc oxide film was formed, a capacitance of 0.14 pF per mm was obtained.

In addition to zinc oxide (dielectric constant 10), silicon dioxide (4,5) and aluminum nitride (8,5) are used as dielectric films.
, alumina (10,5), titanium oxide (130), etc. can be used. As a forming method, a sputtering method, a CVD method, etc. can be used.

As mentioned above, since the dielectric constant differs depending on the material of the dielectric film, it is possible to arbitrarily set the capacitance between the conductor patterns by changing the material or changing . This also makes it possible to correct variations in device characteristics.

Note that the position where the conductor pattern forming the capacitance is provided is not limited to the above example, but by providing it between the resonators,
It also has the effect of breaking unnecessary elastic bonds when they are placed close to each other. Further, conductor patterns directly connected to the ground potential may be arranged facing each other.

The above explanation is about an example of a multi-mode resonator type filter, but it can be applied to all types of filters in which resonators are formed in multiple stages.

〔effect〕

According to the present invention, bandpass characteristics as a filter are significantly improved. This is because the shift in resonance frequency is compensated by the formation of capacitance.

Improving impedance also contributes.

Further, since the conductor pattern for this purpose can be formed in a small space between the resonators, it is advantageous in terms of miniaturization of the device.

Furthermore, the capacitance can be easily adjusted, and the characteristics can also be easily adjusted.

[Brief explanation of the drawing]

1 and 2 are plan views showing embodiments of the present invention,
FIG. 3 is a partial side sectional view of the same embodiment. Figure 4 is a plan view of a conventional dual motor 1' resonator filter;
FIG. 6 is an explanatory diagram of its characteristics.

Claims (6)

[Claims] (1) A plurality of resonators consisting of interdigital electrodes and reflectors sandwiching them are arranged on the surface of a piezoelectric substrate, and the interdigital electrodes are connected in a multimode resonator filter that utilizes the elastic coupling. A first conductive pattern extending from the conductive pattern and a grounded second conductive pattern are arranged to face each other, and a dielectric film is provided on the substrate surface between the first and second conductive patterns. Multimode resonator type surface acoustic wave filter. (2) The multimode resonator type surface acoustic wave filter according to claim 1, wherein the second conductive pattern is a conductive pattern connecting a grounded reflector. (3) The multimode resonator type surface acoustic wave filter according to claim 1, wherein the second conductor pattern is connected to a grounded reflector and is parallel to the first conductor pattern. (4) Claim 1, wherein at least one of the first conductor pattern and the second conductor pattern is divided into two or more parallel conductor patterns, which face each other with the other conductor pattern in between.
The multimode resonator type surface acoustic wave filter according to item 1 or 3. (5) A method for adjusting the bandpass characteristics of a multimode resonator filter in which a plurality of resonators each consisting of interdigital electrodes and reflectors sandwiching the interdigital electrodes are arranged on the surface of a piezoelectric substrate and the elastic coupling thereof is utilized. A first conductor pattern extending from a conductor pattern connecting the interdigital electrodes and a grounded second conductor pattern are arranged so as to face each other,
Bandpass characteristic adjustment of a multimode resonator type surface acoustic wave filter, characterized in that a dielectric film is formed on the substrate surface between the first and second conductor patterns, and a capacitance is formed between the two conductor patterns. Method. (6) The method for adjusting bandpass characteristics of a multimode resonator type surface acoustic wave filter according to claim 5, wherein the capacitance is adjusted by adjusting the coating amount of the dielectric film.