JPH06164297A - Surface acoustic wave resonator - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce spurious of a Love wave type surface acoustic wave resonator provided with a diamond-shaped weighted interdigital transducer on a piezoelectric substrate. An electrode real part 2c in which the electrode width of an electrode neck portion 2b of electrode fingers connected in parallel from a bus bar 2a of a interdigital transducer electrode is rhombically weighted over a length of 1.5 / λ or more. The feature is that it is narrower than the width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a filter for communication equipment,
Surface acoustic wave (SA used as a resonator, delay line, etc.
The present invention relates to a W: Surface Acoustic Wave device, and more particularly to a weighted surface acoustic wave resonator.

[0002]

2. Description of the Related Art A typical example is a love wave (SH wave) type resonator. FIG. 3 is a plan view showing a configuration example of a conventional Love wave type surface acoustic wave resonator having rhombus weighting.
In the figure, 1 is a piezoelectric substrate and 2 is a interdigital transducer (hereinafter abbreviated as IDT). The piezoelectric substrate 1 is not shown in other drawings unless otherwise specified. As shown in FIG. 3, the electrode of the IDT 2 on the piezoelectric substrate 1 in which the pseudo surface acoustic wave exists is replaced with gold (Au),
By forming a heavy metal such as silver (Ag) or platinum (Pt), it is possible to make a pseudo-surface acoustic wave with large propagation attenuation into a Love-wave type surface wave without attenuation, and to provide an elastic surface only by providing an IDT. A wave resonator is constructed.

FIG. 4A shows a resonator similar to that shown in FIG.
FIG. 4B shows the displacement distribution of the fundamental vibration mode of the resonator in the lateral direction. As can be seen from FIG. 4, the grating portion 3 including the electrode fingers of the IDT 2 acts as a surface wave waveguide (guide) because the speed of sound becomes slower than the speed of sound on the free surface of the outer piezoelectric substrate, but the energy of that waveguide is used. It also exists on both outer sides in a form that decreases exponentially.

[0004]

FIG. 5 (A) is a partially enlarged view of the electrode portion A of FIG. 3 enlarged. Also, FIG.
(B) is a free surface portion on the piezoelectric substrate outside the waveguide,
Propagation velocities v _f and v of the surface waves of the bus bar 2a and the grating part, which connect a large number of electrode fingers.
_It shows _m and v _i . As shown in FIG. 5B, in the portion A of FIG. 3, there are two speed differences. Figure 5
(B) As seen from the sides near the conventional resonator waveguide, v _f> v _m> v _{for i} is the speed difference, disturbed in the surface wave energy distribution, causing spurious problem There is a point. An object of the present invention is to solve the above problems, to eliminate the disturbance of the surface wave energy distribution near both sides of the waveguide, and to provide a surface acoustic wave resonator free of spurious waves.

[0005]

A surface acoustic wave resonator according to the present invention is a surface acoustic wave resonator in which a interdigital transducer is formed on a piezoelectric substrate, and a large number of the interdigital transducers are connected in parallel to the busbar of the interdigital transducer. The electrode width of the electrode neck of the electrode finger
It is characterized in that the extension from the electrode neck is narrowed over a length of 1.5 times the wavelength or more as compared with the electrode width of the real weighted electrode.

[0006]

The present invention will be described in detail below with reference to the drawings. As a typical example, a Love wave type surface acoustic wave resonator will be described.
FIG. 1A is a plan view of an electrode structure showing an embodiment of the present invention, and FIG. 1B shows the displacement distribution of its transverse mode. Figure 2
1A is a partially enlarged view of FIG. 1A, and FIG. 2B is a view showing the propagation velocity of the surface wave. 2A shows a bus bar, 2b an electrode neck portion, and 2c a real electrode portion. The white arrows v _f , v _m , v _i1 , and v _i2 are respectively on the free surface of the piezoelectric substrate, on the bus bar 2a, and on the electrode neck 2b.
The upper part shows the velocity of the surface wave propagating on the real electrode part 2c.

As shown in FIG. 2A, the electrode neck portion 2 of all the electrode fingers
By making the electrode finger width of b smaller than the electrode finger width of the actual electrode portion 2c, a step is generated in the velocity of the surface wave propagating above each. This difference in electrode width acts to determine the surface wave waveguide. The length of the electrode neck 2b is 1.5λ
By making (λ: wavelength of surface wave) or more, only the velocity difference of v _i1 > v _i2 occurs in the range where the surface wave energy exists, and the displacement distribution is as shown in FIG. 1 (B).

[0008]

As described in detail above, according to the present invention, since the velocity difference is only one step in the range where the surface wave energy exists, the disturbance of the energy distribution is suppressed, so that the spurious noise is suppressed. It is possible to realize a surface acoustic wave resonator that does not have a surface acoustic wave.

[Brief description of drawings]

FIG. 1 is a plan view and a displacement distribution diagram showing an electrode structure according to an embodiment of the present invention.

FIG. 2 is a partially enlarged view of a main part of the present invention and a diagram showing a propagation velocity.

FIG. 3 is a plan view of a conventional configuration example.

FIG. 4 is an explanatory diagram showing a conventional configuration and displacement.

FIG. 5 is a partially enlarged view of a conventional electrode and a diagram showing a propagation velocity.

[Explanation of symbols]

 1 piezoelectric substrate 2 interdigital transducer electrode 2a bus bar 2b electrode neck 2c electrode real part 3 waveguide (guide)

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Tadashi Kanda 2-3-13 Toranomon, Minato-ku, Tokyo International Electric Co., Ltd. Number 12

Claims (1)

[Claims] 1. A surface acoustic wave resonator in which a interdigital transducer is formed on a piezoelectric substrate, wherein the electrode width of the electrode neck of electrode fingers connected in parallel from the busbar of the interdigital transducer is the electrode width. A surface acoustic wave resonator, characterized in that an extension from a neck portion is narrowed over a length of 1.5 times or more of a wavelength as compared with a weighted electrode real portion electrode width.