JPH01321715A - Surface acoustic wave resonator - Google Patents

Abstract

PURPOSE:To use only an element having a small inductance element as external parts to form a desired LC resonance circuit by using a reflector, which occupies a wide area in a surface acoustic wave resonator, for formation of a capacity to reduce external parts. CONSTITUTION:An interdigital electrode (IDT) 11 where electrodes like comb line being crossed is formed on the surface of a piezoelectric substrate 10 consisting of crystal or the like. The surface acoustic wave excited by the IDT 11 is propagated in both directions orthogonal to the lengthwise direction of electrode fingers. Reflectors 12 are formed on this propagation path in the vicinity of and on both sides of the IDT 11. Reflectors 12 are so arranged that strip lines are orthogonal to the propagation direction of the surface acoustic wave. Reflectors 12 are short type where end parts of strip lines are connected. An electrode 13 is formed on all of the rear face of the substrate and is connected to the earth potential. Reflectors 12 and the electrode 13 on the rear face of the substrate face each other to form a capacitor. Reflectors normally consist of several hundred electrodes and have a large area, and the area of reflectors facing the electrode 13 is large.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a surface acoustic wave resonator, and particularly to a surface acoustic wave resonator having a short reflector.

[Prior art]

Resonators are used in various fields, including interdigital electrodes that excite surface acoustic waves made by intersecting comb-shaped electrodes, and reflectors formed by strip electrodes on both sides of the interdigital electrodes in the propagation direction. Particularly, high frequency bands are attracting attention. You can also use this as it is as a filter,
It is often used as a filter by connecting resonators on two sides.

In such a case, it may be necessary to add an external capacitance or inductance to achieve matching. In that case, external components are required, and in some cases, a very large inductance must be added.

Generally, an LC parallel resonant circuit is added, but ■00MH
2, when adding only inductance, μ
You will need something on the order of I.

〔assignment〕

The present invention requires fewer external parts, and
The purpose is to obtain matching simply by adding an element with a small value.

To this end, the objective is to provide the surface acoustic wave resonator itself with a relatively large capacity.

[Means to solve the problem]

The present invention solves the above problems by utilizing a reflector that occupies a large area in a surface acoustic wave resonator to form a capacitance.

That is, in a surface acoustic wave resonator including an interdigital electrode on the surface of a piezoelectric substrate and a short reflector sandwiching the interdigital electrode, at least one bus bar of the interdigital electrode is connected to one of the reflectors, It is characterized in that a capacitance is formed between the electrode of the reflector and the electrode on the back surface of the substrate.

The electrode of the short reflector and the electrode on the back surface of the substrate become opposing capacitor electrodes, forming a capacitance.

If the capacitance can be increased, the inductance of the LC resonant circuit can be small, which facilitates the circuit configuration.

〔Example〕

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

FIG. 1 is a plan view (81) and a front cross-sectional view (bl) showing an embodiment of the present invention.
DT) 11 is formed. The surface acoustic waves excited by IDTII propagate in both directions perpendicular to the longitudinal direction of the electrode fingers. Reflectors 12 are formed on this propagation path close to IDTII and on both sides thereof. This reflector 12 is arranged so that the strip line is perpendicular to the direction of propagation of the surface acoustic wave.

The reflector 12 is of a short type in which the ends of the strinoplas are connected. These two reflectors 12 and IDT
The two busbars of II are electrically connected.

In this example, the conductor pattern extends linearly from the bus bar, but any pattern may be used for connection.

An electrode 13 is formed on the entire back surface of the substrate.

This electrode is die-bonded and connected to ground potential during assembly. This electrode 13 does not necessarily need to be formed on the entire surface, but may be formed at least on a part of the position facing the reflector 12.

The reflector 12 and the electrode 13 on the back surface of the substrate face each other, forming a capacitor. The thinner the substrate, the greater the capacity, but in terms of mechanical strength, the substrate needs to be about five times as thick as the wavelength of the surface acoustic wave. Also, reflector 1
3 is usually formed of several hundred electrodes and has a large area. Therefore, the area facing the electrode 13 on the back surface can be increased, and the capacitance value can also be relatively increased.

FIG. 2 shows an equivalent circuit of the surface acoustic wave resonator according to the present invention. The resonator is composed of capacitances c + and C2 and inductance L1, but in the surface acoustic wave resonator according to the present invention, capacitances C1 and C4 are added to both sides. If inductances L2 and L3 are added externally, an LC resonant circuit is formed by C3 and L2 and C4 and L3.

The capacitance between the reflector and the back electrode varies depending on the number of reflectors, but usually a capacitance of 2 to 4 pl' can be obtained.

In order to increase the capacitance value, the width of the short electrode of the reflector may be increased to increase the area of the surface conductor. Alternatively, a conductive pattern may be formed separately and used as an additional electrode to be connected to the reflector. Furthermore, this additional electrode can also serve as a bonding pad.

FIG. 3 is a plan view showing another embodiment of the invention. I
The shape and connection of the DT 31 and the reflector 32 are the same as in the previous example, but bonding pads 35a and 35b are drawn out from the reflector 32, respectively. In this way, by forming bonding pads in the diagonal direction of the substrate and connecting them to terminals, it is possible to reduce the coupling between input and output, which also improves the characteristics.

〔effect〕

According to the present invention, it is possible to form a relatively large capacitance in the surface acoustic wave resonator element itself. Therefore, not only can the number of externally attached components be reduced, but also a desired LC resonant circuit can be formed simply by externally attaching an element with a small inductance value.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention (al is a plan view, (b)
2 is a front sectional view, FIG. 2 is an equivalent circuit diagram thereof, and FIG. 3 is a plan view showing another embodiment of the present invention. to, 30...... Substrate IL31... IDT 12.32... Reflector 13... Electrode

Claims (6)

[Claims] (1) In a surface acoustic wave resonator comprising an interdigital electrode on one surface of a piezoelectric substrate and a short reflector sandwiching the interdigital electrode, at least one bus bar of the interdigital electrode is connected to one of the reflectors. , A surface acoustic wave resonator characterized in that a capacitance is formed between the electrode of the reflector and the electrode on the back surface of the substrate. (2) The surface acoustic wave resonator according to claim 1, wherein terminal connection pads connected to the bus bars of each of the interdigital electrodes are drawn out from the two reflectors near the ends of the substrate. (3) The surface acoustic wave resonator according to claim 2, wherein the terminal connection pad is drawn out to the opposite side across the propagation path of the surface acoustic wave. (4) In a surface acoustic wave resonator comprising an interdigital electrode on one surface of a piezoelectric substrate and a short reflector sandwiching the interdigital electrode, at least one bus bar of the interdigital electrode is connected to one of the reflectors. Along with
A surface acoustic wave resonator characterized in that a conductive pattern connected to the reflector is formed on the surface of the substrate, and a capacitance is formed between the electrode of the reflector and the conductive pattern and the electrode on the back surface of the substrate. (5) The surface acoustic wave resonator according to claim 4, wherein the conductor pattern is formed integrally with the short electrode portion of the reflector. (6) The surface acoustic wave resonator according to claim 4 or 5, wherein the conductor pattern is a bonding pad.