JPH03129915A - Surface acoustic wave resonator - Google Patents

Abstract

PURPOSE:To heighten the impedance of a resonator without lowering Q by providing in series two or more bamboo blind-like converter groups in the propagation direction of a surface acoustic wave, in a Love wave type surface acoustic wave resonator. CONSTITUTION:The resonator is constituted so that two inter digits(IDT) 2a, 2b are provided so that phases of surface waves excited from the respective IDTs becomes the same phase in the surface acoustic wave propagation direction, and connected electrically in series between a terminal 4 and a terminal 5. When a capacitance of one IDT is denoted as C0, a capacitance C2 in the case two IDTs are connected in series becomes 1/2 of C0. On the other hand, a capacitance C1 at the time when two IDTs are connected electrically in parallel becomes two folds of C0. Accordingly, C1/C2=4. Also, by providing three pieces or more or IDTs in series in the propagation direction, the impedance can be further raised, as well.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention relates to a Love-wave type surface acoustic wave resonator, and in particular, the present invention relates to a Love-wave type surface acoustic wave resonator, in particular, a monocrystalline piezoelectric substrate having gold (Au), silver (Ag), platinum (1
This invention relates to a surface acoustic wave resonator that excites Love waves by attaching heavy metals such as 't) as electrodes of a transducer.

(Prior art and its problems) 128゛ Rotation Y-cut LiNbO3, X-cut LiT
Rayleigh (R) excited on the surface of a0z or ST crystal, etc.
A Love wave (SH wave) resonator has been proposed which has a much larger electromechanical coupling coefficient than a conventional resonator that uses an eyleigh wave type surface wave (p+sv wave). (Unexamined Japanese Patent Publication No. 6
3-260213) FIG. 1 is a plan view showing a configuration example of a conventional Love wave type surface acoustic wave resonator. In the figure, l indicates the piezoelectric substrate, 2 indicates the interdigital transducer, and 3 indicates the crossing width.

As shown in FIG. 1, gold (Au) is deposited on a piezoelectric substrate 1 (particularly a 1Nb01 rotating Y plate) in which pseudo-surface acoustic waves exist.

Heavy metals such as silver (Ag) and platinum (Pt) are deposited thickly as interdigital electrodes to change pseudo-surface acoustic waves with large propagation attenuation into love waves without attenuation, and convert electrical signals into surface waves. Interdig transducer 2
The resonator is composed only of an internal transducer (hereinafter abbreviated as IDT).

Generally, a surface acoustic wave resonator is used to generate a voltage controlled oscillator (V
CO), it is advantageous to have a high impedance in order to increase the frequency variable width, and it is advantageous to have a high Q in order to increase the carrier wave level (C/N) with respect to the noise level. be. On the other hand, the impedance of the resonator as shown in FIG. 1 is determined by the logarithm of the IDT 2 and the crossing width 3, that is, the length of the mutually crossing portions of the IDT electrodes. Therefore, in order to increase the impedance of the resonator, it is sufficient to reduce the logarithm of the IDT 2 or to reduce the crossing width 3.

However, since the resonator with the configuration shown in FIG. 1 forms a surface wave waveguide and does not have a grating reflector in the surface acoustic wave propagation direction unlike a conventional Rayleigh wave resonator, In other words, since IDT2 itself also serves as a reflector, reducing the logarithm of IDT2 lowers the reflectance and Q
When the intersection width 3 is made smaller, the amount of surface wave energy leaking from the waveguide region to the outside due to surface wave diffraction increases, so that the Q of the resonator decreases. Therefore, the conventional method has the disadvantage that when attempting to obtain a resonator with high impedance, the Q value decreases.

(Object of the Invention) An object of the present invention is to provide a surface acoustic wave resonator in which the impedance of the resonator is increased without reducing Q.

(Structure and operation of the invention) The surface acoustic wave resonator of the present invention is made of gold (Au), silver (Ag) that converts an electric signal into a surface acoustic wave on the surface of a piezoelectric substrate.
In a Love wave surface acoustic wave resonator with a large electromechanical coupling coefficient, which is equipped with interdigital transducers made of heavy metals such as platinum (PT), a plurality of interdigital transducers are arranged in the propagation direction of the surface acoustic wave. an elastic surface arranged in series and electrically connected in series between the input and output of the resonator, the plurality of interdigital transducers being excited by the interdigital transducers; It has a configuration in which the waves are in phase with each other and are arranged in parallel in the propagation direction of the surface acoustic waves, and furthermore, heavy metals such as gold, silver, and platinum are placed on the surface of the piezoelectric substrate to convert electrical signals into surface acoustic waves. In a Love-wave type surface acoustic wave resonator with a large electromechanical coupling coefficient, in which two or more interdigital transducers are arranged, two or more groups each having at least one interdigital transducer are used to propagate surface acoustic waves. the transducers in each group are electrically connected in parallel;
The two or more groups are electrically connected in series between the input and output of the resonator.

The present invention will be explained in detail below with reference to the drawings.

FIGS. 2 and 3 are plan views showing the electrode structure of a Love wave type surface acoustic wave resonator according to an embodiment of the present invention, and the piezoelectric substrate is not shown. In the figure, two IDTs 2a and 2b are arranged in the surface acoustic wave propagation direction so that the phases of the surface waves excited by each IDT are in the same phase, and electrical connections are made between terminals 4 and 5. The configuration is connected in series.

In the configuration of FIG. 2, the cross width is 3 and the I DT is 2
For the case where the sum of the logarithms of 2a and 2b is made equal to the case in Figure 1, that is, by dividing IDT2 in Figure 1 into two and connecting the two IDTs 2a and 2b electrically in series, the result is as shown in Figure 2. Let's consider the case where it is configured as follows.

If the capacitance of one IDT in Fig. 2 is 00, then the second
The capacitance C2 when two IDTs are connected in series as shown in the figure is C,-(1/2)CO, and when two IDTs are electrically connected in parallel as shown in Figure 1. The capacitance CI in this case is C,=2C.

becomes. Therefore, C,/C,=4, and the impedance in the configuration of FIG. 2 is four times that of the configuration in FIG. 1.

In the configuration shown in Figure 2, the two IDTs 2a and 2b are configured with the same logarithm, but the impedance can be changed by using different logarithms, and three or more IDTs can be connected in series in the surface acoustic wave propagation direction. It is also possible to increase the impedance.

In the configuration shown in FIG. 2, the terminal pair 4.5 is exposed on one side of the resonator, but it can also be divided into upper and lower parts as in the configuration shown in FIG.

FIG. 4 is a plan view of an IDT showing a second embodiment of the present invention, in which three IDTs 2 are arranged in the surface acoustic wave propagation direction (arrow).
a, 2b, 2c are arranged in series, and I on both sides
The DTs 2b and 2c are electrically connected in parallel to form one group, and connected in series with the central IDT 2a.

By adopting the configuration shown in FIG. 4, it is possible to increase the impedance and at the same time prevent the IDT from coupling with the longitudinal primary mode existing in the longitudinal direction (the surface acoustic wave propagation direction indicated by the arrow).

Next, FIG. 5 will be explained.

FIG. 5 is a plan view of an IDT showing a third embodiment of the present invention, in which surface acoustic waves excited from the two IDTs 2d and 28 are in the same phase and in the propagation direction (arrow). terminal 6 and terminal 7.
This figure shows the configuration of an IDT of Love wave type surface acoustic wave resonators electrically connected in series between the two sides.

The configuration shown in FIG. 5 can be thought of as having the cross width 3 of the electrodes in the configuration shown in FIG. It is clear that it can be done. Further, in the embodiment shown in FIG. 5, the impedance is divided into two, but if it is divided into three or more, the impedance can be further increased.

(Effects of the Invention) As explained in detail above, in a Love wave type surface acoustic wave resonator, the resonator can be impedance can be increased.

Figure 1 Invitation 2 Figure 3

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of the structure of a conventional Love wave type surface acoustic wave resonator, and FIGS. 2 to 5 are plan views showing examples of the electrode structure of the Love wave type surface acoustic wave resonator of the present invention. It is. DESCRIPTION OF SYMBOLS 1... Voltage board, 2, (2a-2e)... Interdigital transducer
ducer), 3...Cross width, 4-7...Terminal.珀4 figure ￥15 figure

Claims (3)

[Claims] (1) A transducer in the form of a heavy metal such as gold, silver, or platinum is arranged on the surface of the piezoelectric substrate to convert electrical signals into surface acoustic waves, and a Love wave type surface acoustic wave with a large electromechanical coupling coefficient is excited. In the Love wave type surface acoustic wave resonator composed of the transducers, the plurality of transducers are arranged in series in the propagation direction of the surface acoustic wave, and the transducers are arranged in series between the input and output of the resonator. A surface acoustic wave resonator characterized by being electrically connected in series. (2) The plurality of interdigital transducers are characterized in that the surface acoustic waves excited by the interdigital transducers are in phase with each other and are arranged in parallel in the propagation direction of the surface acoustic waves. A surface acoustic wave resonator according to claim 1. (3) A transducer in the form of a heavy metal such as gold, silver, or platinum is disposed on the surface of the piezoelectric substrate to convert electrical signals into surface acoustic waves, and a Love wave type surface acoustic wave with a large electromechanical coupling coefficient is excited. In the Love wave type surface acoustic wave resonator composed of the interdigital transducers, at least one interdigital transducer constitutes one group2.
two or more groups are arranged in series in the propagation direction of the surface acoustic wave, the interdigital transducers in each group are electrically connected in parallel, and the two or more groups are arranged in series in the propagation direction of the surface acoustic wave; A surface acoustic wave resonator characterized in that its outputs are electrically connected in series.