JPS62257211A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To obtain the transmission characteristic with less ripple by applying a viscoelastic substance or a gel to a path where a surface acoustic wave is propagate through a piezoelectric substrate except an interdigital electrode so as to eliminate a low frequency undesired wave. CONSTITUTION:A viscoelastic substance or gel 5(5') is applied to reflectors 3, 3'. In applying the viscoelastic substance or the gel to the reflectors 3, 3' in this way, a Rayleigh wave induced together with a shear horizontal surface acoustic wave in the interdigital electrode 2 and the Rayleigh wave induced by the mode conversion while being reflected in the reflectors 3, 3' are absorbed by the viscoelastic substance or gel, but the shear horizontal surface acoustic wave is not almost absorbed. Thus, a low frequency undesired wave due to the Rayleigh wave is eliminated and only the shear horizontal surface acoustic wave only is propagated and the excellent transmission characteristic with less ripple is attained.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a resonator, a filter, a delay line, etc. having a reflector made of a metal strip, a comb-like electrode, etc. on a piezoelectric substrate on which a shear horizontal type surface acoustic wave propagates. The present invention relates to a surface acoustic wave device.

``Prior art and its problems J Surface acoustic wave elements have traditionally been used for special military purposes, but in recent years they have begun to be used in consumer equipment such as FM channels and TVWs, and have suddenly come into the spotlight. Specifically, surface acoustic wave elements that have come to be used include delay elements, oscillators,
It has been commercialized as a filter, etc. The characteristics of these various surface acoustic wave devices are that they are small, lightweight, and highly reliable, and that their manufacturing process is similar to that of integrated circuits, making them suitable for mass production. Nowadays, it is mass-produced as an indispensable electronic component.

There are a few types of surface acoustic waves that propagate on the surface of piezoelectric media, but
Rayleiq is commonly used.
h) It is called a wave. In addition, as an example of surface acoustic waves, a shear horizontal type surface acoustic wave is also known, in which particles are displaced in the direction perpendicular to the propagation direction of the surface acoustic waves within the surface layer of the piezoelectric substrate where the surface acoustic waves propagate. It is attracting attention because of its large coupling coefficient (an index that indicates the efficiency with which electrical energy is converted into imaging energy).

As an example of a conventional surface acoustic wave element, an example of a surface acoustic wave resonator is shown in FIG. It is constructed by forming interdigital electrodes 2 for surface acoustic wave excitation, and reflectors 3.3° in which a large number of metal strips are periodically arranged at right angles to the propagation direction of the surface acoustic waves. and,
When a voltage of a specific frequency is applied to the interdigital electrodes 2, an electric field is applied to the surface of the piezoelectric substrate 1 in the gap between the interdigital electrodes 2, and a strain proportional to the voltage is generated due to the piezoelectricity of the piezoelectric substrate 1.
The strain propagates to both sides as a surface wave at a sound speed determined by the material of the piezoelectric substrate 1. This surface wave is reflected by the grid-like reflectors 3.3 degrees on both sides, returns to the interdigital electrode 2 again, and resonates.

By the way, in the above-mentioned conventional surface acoustic wave resonator, a viscoelastic substance such as silicone resin or epoxy resin is applied at 4.4 degrees to both end edges of the piezoelectric substrate 10 located in the direction in which surface acoustic waves propagate. Unwanted waves passing through the reflector 3.3° are absorbed by the viscoelastic material 4.4'. This viscoelastic material's angle of 4.4° was particularly effective for absorbing Rayleigh waves.

However, the above-mentioned viscoelastic material 4.4゛ only absorbs the Rayleigh waves that have reached both ends of the piezoelectric substrate, so the Rayleigh waves reflected by the reflector 3.3° and the Rayleigh waves induced by the interdigital electrodes are Rayleigh waves propagating through the piezoelectric substrate cannot be removed. On the other hand, even in a surface acoustic wave element using a piezoelectric substrate in which shear horizontal surface acoustic waves propagate, Rayleigh waves are induced in addition to shear horizontal surface acoustic waves by applying voltage to the interdigital electrodes. Then, when a part of this Rayleigh wave is reflected by the reflector 3.3°, a shear horizontal type surface acoustic wave, or a Rayleigh wave by the reflector 3.3°, the Rayleigh wave 8
Since the Rayleigh wave is mixed with the shear horizontal surface acoustic wave by mode conversion to an il surface wave, this spurious This appeared as ripples in the transmission characteristics, which was a problem.

"Objective of the Invention" An object of the present invention is to solve the problems of the prior art described above, and to provide a surface acoustic wave device using a piezoelectric substrate in which shear horizontal surface acoustic waves propagate, with an operating frequency that is lower than that caused by Rayleigh waves. The aim is to eliminate unnecessary waves on the low frequency side and obtain a custom transmission with less ripple.

"Structure of the Invention" The surface acoustic wave element of the present invention includes at least one set of sagging electrodes on a piezoelectric substrate through which shear horizontal surface acoustic waves propagate, and a path through which the surface acoustic waves of the piezoelectric substrate propagate. The device is characterized in that a viscoelastic material or a gel-like material is applied to a portion other than the interdigital electrode.

Therefore, the Rayleigh wave induced by the interdigital electrode along with the shear horizontal surface acoustic wave, and the Rayleigh wave generated by mode conversion when reflected by the reflector in the case of an element with a reflector, are as follows: It is absorbed by a viscoelastic substance or gel-like substance provided in its propagation path. On the other hand, shear horizontal type surface acoustic waves are hardly absorbed by the above-mentioned viscoelastic materials and gel-like materials.As a result, unnecessary waves at frequencies lower than the operating frequency caused by Rayleigh waves are removed, resulting in good results with less ripples. transmission characteristics i can be obtained.

"Embodiments of the Invention" FIGS. 1 and 2 show an embodiment in which the present invention is applied to a surface acoustic wave resonator.

That is, this surface acoustic wave resonator has a piezoelectric substrate,
- A pair of interdigital interdigital electrodes 2 and reflectors 3.3' are formed on both sides thereof. In this surface acoustic wave resonator, the reflector 3.3' may be of an open type or may be of a short circuit type.

As the piezoelectric substrate 1, a piezoelectric substrate in which sheer horizontal surface acoustic waves propagate, such as lithium niobate with a 41-degree or 64-degree rotation Y-axis cut, or lithium tantalate with a 36-degree rotation Y-axis cut, is used. Ru.

The interdigital electrode 2 and the reflector 3.3' consist of a metal strip formed by patterning a metal film. It is preferable that the interdigital electrode 2 and the reflector 3.3° be made of the same metal, but from the viewpoint of the characteristics of the reflector 3.3°, ease of process, cost, etc., it is preferable to use metal ^l or A1. An alloy is preferable, or a multilayer structure of AI or A1 alloy and a high melting point metal is preferable.

A feature of the present invention is that a viscoelastic substance or a gel material is coated at 5.5 degrees on the 3.3 degree portion of the reflector. In this case, as the viscoelastic substance, for example, silicone rubber, epoxy resin, etc. can be used, and as the gel-like substance, for example, gel-like silicone resin can be used.

In this way, by applying a viscoelastic material or a gel-like material 5.5 degrees to the reflector 3.3", the Rayleigh wave induced along with the shear horizontal type surface acoustic wave at the straggly electrode 2, Rayleigh waves generated by mode conversion when reflected by the reflector 3.3' are absorbed by the viscoelastic material or gel material 5.5' and are no longer reflected by the reflector 3.3'. In addition, shear horizontal type surface acoustic waves are hardly absorbed by the viscoelastic material or the gel material, so unnecessary waves on the low frequency side caused by Rayleigh waves are removed.
Only shear horizontal type surface acoustic waves are propagated, and good transmission characteristics with few ripples can be obtained.

3 and 4 show an embodiment in which the present invention is applied to a surface acoustic wave filter.

In this surface acoustic wave filter, two sets of interdigital electrodes 2.2' for input and output are provided on a piezoelectric substrate i.

A viscoelastic substance or gel-like substance 5 is applied between the two pairs of interdigital electrodes 2.2°. Therefore, in this embodiment, the Rayleigh wave induced together with the shear horizontal type surface acoustic wave by the input interdigital electrode 2 passes through the viscoelastic material while propagating to the output interdigital electrode 2. Alternatively, it will be absorbed by the gel-like substance 5. Then, only the shear horizontal type surface acoustic waves reach the 2° output interdigital electrode, and good transmission characteristics with few ripples can be obtained.

Example 1 A piezoelectric substrate 1 made of lithium niobate with a Y-axis force of 41 degrees rotation, and 10 logarithmic pairs of interdigital electrodes 2 formed of a 100 OA At film, each consisting of 200 elements on both sides. A surface acoustic wave resonator was fabricated by forming a reflector of 3.3''. Then, silicone rubber (viscoelastic material 5, 5') was applied to the reflector 3.3' to a thickness of about 0.1 mm. As a result, the ripple in the transmission characteristic was reduced from IdB to O, IdB or less, compared to the conventional one without silicone rubber Ti cloth. It should be noted that no deterioration of the main resonance level was observed in the measurements.

Note that similar results were obtained when epoxy resin or gel silicone resin was used instead of silicone rubber. Roughly speaking, similar results were obtained when the piezoelectric substrate 1 was replaced with lithium niobate with a 644-degree rotation Y-axis cut or lithium tantalate with a 36-degree rotation Y-axis cut.

Example 2 Lithium niobate with 41 degree rotation Y-axis cut on piezoelectric substrate 1
Used for input/output interdigital electrodes 2.2' with 100OA At film! A surface acoustic wave filter was produced by forming 10 logarithmic pairs. And the interdigital electrode 2.2°
Epoxy resin (viscoelastic material 5) was applied to the gate to a thickness of about 0.1 mm. As a result, the ripple in the transmission characteristics was reduced from IdB to 0.2dB or less, compared to the conventional one in which no epoxy resin was applied.

Note that similar results were obtained when silicone rubber or gel silicone resin was used instead of the epoxy resin. In general, similar results were obtained when the piezoelectric substrate 1 was replaced with lithium niobate, which was rotated 64 degrees and cut on the Y axis, or lithium tantalate, which was rotated 36 degrees and cut on the Y axis.

"Young Fruit of the Invention" As explained above, according to the present invention, a viscoelastic substance or a gel-like substance is applied to the surface acoustic wave propagation path of the piezoelectric substrate other than the interdigital electrodes. Therefore, unnecessary waves at frequencies lower than the operating frequency caused by Rayleigh waves are selectively removed by the viscoelastic material or gel-like material.
Good transmission customization with less ripple can be obtained.

[Brief explanation of drawings]

FIG. 1 is a side sectional view showing an embodiment in which the present invention is applied to a surface acoustic wave resonator, and FIG. 2 is a plan view of the same surface acoustic wave resonator.
Fig. 3 is a partial side sectional view showing an embodiment in which the present invention is applied to a surface acoustic wave filter, Fig. 4 is a partial plan view of the same surface acoustic wave filter, and Fig. 5 is an example of a conventional surface acoustic wave resonator. FIG. In the figure, 1 is the piezoelectric substrate, 2.2° is the interdigital electrode, 3.3
゛ is a reflector, and 5.5゛ is a viscoelastic material or gel-like substance. Patent applicant: Alps Electric Co., Ltd.

Claims (3)

[Claims] (1) In a surface acoustic wave element including at least one set of interdigital electrodes on a piezoelectric substrate through which shear horizontal type surface acoustic waves propagate, a path through which the surface acoustic waves of the piezoelectric substrate propagate, In the part other than the interdigital electrode,
A surface acoustic wave element coated with a viscoelastic substance or a gel-like substance. (2) The surface acoustic wave device according to claim 1, wherein reflectors are provided on both sides of the interdigital electrode, and the viscoelastic substance or gel-like substance is applied to the reflector portions. (3) The surface acoustic wave element according to claim 1, wherein two sets of the interdigital electrodes are provided, and the viscoelastic substance or gel material is applied between the two sets of interdigital electrodes.