JPH0443707A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To attain excellent power withstanding performance without change in a conventional design parameter by covering a side wall of each conb-like electrode in a propagation direction of a surface acoustic wave element with an insulation protection film. CONSTITUTION:An insulation protection film 15 with a thickness enough to suppress the effect of the deterioration in each conb-like electrode 13 onto an adjacent electrode due to application of power and neglecting the effect on the characteristic of a surface acoustic wave device is formed to a side wall of each comb-like electrode to protect the film device. Thus, the scattered discontinuous points is attained, the concentration of a stress of a surface acoustic wave is not caused, the power withstanding performance is improved and since the upper face of each electrode remains exposed, the design parameter of a conventional surface acoustic wave device is not required to be changed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave device in which comb-shaped poles are formed on a piezoelectric substrate.

[Prior Art] FIG. 3 shows an example of a surface acoustic wave device, which is an element using surface acoustic waves propagating on a solid surface.

A regular comb-shaped electrode 12 is formed in the center of the piezoelectric substrate 10,
A pair of reflectors 14, 16 are formed on either side of the regular comb-shaped pole 12. In the regular comb-shaped electrode 12, two comb-shaped $ poles 12a and 12b each made of a large number of fine aluminum electrodes with a width of several μm are arranged so that each tS is engaged with each other. Bonding pads 18 and 20 are formed at the bases of the comb-shaped electrodes 12a and 12b. The surface acoustic waves propagate on the comb-shaped electrodes 12a and 12b in the left and right directions in FIG.

When transmitting large amounts of power to such a surface acoustic wave device, the device deteriorates. When we observed the deterioration status of the surface acoustic wave device, we found that the main cause of failure was the deterioration of the electrode part of the comb-shaped electrode. It became clear. In other words, when power is applied, a lock occurs on the comb-shaped @pole electrode.
As the lock grows, a short circuit occurs between adjacent electrodes, causing a large current to flow, eventually causing the electrodes to melt.

[Lesson 1 that the invention attempts to solve! ! ! ] In order to prevent such deterioration of the comb-shaped electrode, attempts have been made to add other metals such as titanium and copper to the aluminum electrode material to increase the power resistance.

However, there is a problem in that changing the composition of the electrode material requires a fundamental review of the design parameters of the surface acoustic wave device. In addition, when other metals are added to aluminum to form the @ electrode material, it is difficult to form electrodes with a uniform composition, and as a result, there is a problem that the characteristics of the surface acoustic wave device vary. .

The present invention has been made in consideration of the above circumstances, and it is an object of the present invention to provide a surface acoustic wave device that has excellent power durability and less variation in element characteristics without changing conventional design parameters. .

[Means for Solving the Problem] The above object is to provide a surface acoustic wave device in which a comb-shaped electrode is formed on a piezoelectric substrate, in which the side wall of each electrode of the comb-shaped electrode in the surface acoustic wave propagation direction is covered with an insulating protective film. This is achieved by a surface acoustic wave device characterized by:

[Function] According to the present invention, since the side wall of each electrode of the comb-shaped electrode in the surface acoustic wave propagation direction is covered with an insulating protective film, the mechanical strength of the comb-shaped electrode is reinforced, discontinuous points are dispersed, and the elastic surface is Stress caused by waves is not concentrated, and power durability can be improved. Further, since the insulating protective film is provided on the side wall of each electrode and the upper surface of each electrode remains exposed, there is no need to change the design parameters of the conventional surface acoustic wave device.

[Example] A surface acoustic wave device according to an example of the present invention will be described with reference to FIG.

FIG. 1 is an enlarged cross-sectional view of a part of a comb-shaped electrode of a surface acoustic wave device. Each electrode 1 of the comb-shaped electrode 12 is placed on the piezoelectric substrate 10.
3 is formed. As the piezoelectric substrate 10, Li2B4O7 single crystal substrate with a large electromechanical coupling constant, LiNb
0. A single crystal substrate or the like is used. Each electrode 13 of the comb-shaped electrode 12 is made of aluminum. Each electrode 13 has a width of several μm and is arranged at intervals of several μm.

In this example, the IPIW of each electrode 13 is 5iozl! J
,5iSN4! l! It is covered with an insulator protection M15 such as M15 to strengthen the power resistance. That is, on the side wall of each electrode 13,
sufficient to suppress the effects of electrode degradation caused by the application of power on adjacent electrodes, and
In this embodiment, an insulating protective layer 15 of about 50 to 100 A is formed on the side wall of each electrode 13 to protect it by forming an insulating layer 11M15 with a thickness such that the effect on the characteristics of the surface acoustic wave device is negligible. are doing.

According to this embodiment, since the side wall of each @ electrode 13 is covered with the insulating film 111M15, the insulating protective film 15 is in close contact with the side wall of the piezoelectric substrate 10 and the electrode 13, and the comb-shaped electrode 12 is
It can strengthen the mechanical strength and improve the power resistance. In addition, by covering the side wall of each electrode 13 with an insulating protection M15, discontinuous points are dispersed, stress caused by surface acoustic waves is not concentrated, and the electric field is improved! A-continued boundary (
end of each electrode 13) and mass discontinuous boundary (insulating
The ends of the WA 15) are separated, and stress concentration can be further alleviated.

Further, according to this embodiment, even if the insulating protective film 15 is provided, the upper surface of each electrode 13 remains exposed, and the effect of its thickness on the characteristics of the surface acoustic wave device is negligible. Therefore, conventional surface acoustic wave devices can be used as they are without changing their design parameters.

A method of manufacturing the surface acoustic wave device according to this embodiment will be explained using FIG. 2.

First, aluminum is etched on the piezoelectric substrate 10 to form striped electrodes 13 (FIG. 2(a)).

Next, 5i is applied to the entire surface using a film forming method such as sputtering.
An insulating film 17 of n2WA, Si)N4M, etc. is formed (FIG. 2(b)).

Next, the electrode 13 is etched by an anisotropic etching method such as RIE.
When the insulator 117 is etched until the upper surface is exposed, the insulator 1117 remains only on the side wall portion of the electrode 13, and an insulator protective film 15 is formed (FIG. 2(C)).

The present invention is not limited to the above-mentioned embodiments, and various modifications are possible.

For example, the present invention can be applied to all types of surface acoustic wave devices, not just those of the above embodiments. In addition to the comb-shaped electrode, other strips 44 [! There is also insulation on the side walls of gAi! A film may also be formed.

[Effects of the Invention] As described above, according to the present invention, since the side wall of each electrode of the comb-shaped electrode in the surface acoustic wave propagation direction is covered with the insulating image 1iILWA, the power durability can be improved without changing the conventional design parameters. can be strengthened.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of the main parts of a surface acoustic wave device according to an embodiment of the present invention, FIG. 2 is a process diagram of a method for manufacturing a surface acoustic wave device according to an embodiment of the present invention, and FIG. FIG. 1 is a diagram showing an example of a surface acoustic wave device. In the figure, 10...Piezoelectric substrate 12...Regular comb-shaped electrodes 12a, 12b...Comb-shaped electrode 13...@pole 14.16...Reflector 15...Insulator image KM 17...・Insulating film

Claims (1)

[Claims] 1. 1. A surface acoustic wave device in which a comb-shaped electrode is formed on a piezoelectric substrate, wherein a side wall of each electrode of the comb-shaped electrode in the surface acoustic wave propagation direction is covered with an insulating protective film.