JPH04369915A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To attain excellent durability by covering at least electrode fingers with a nonpiezoelectric protection film so as to prevent the deterioration in a piezoelectric substrate. CONSTITUTION:An electrode member 2 made of Al or the like is vapor- deposited onto a piezoelectric substrate 1 made of Li2B4O7 or the like, a photoresist pattern 3 is formed on the member 2, the electrode member 2 is etched by using a mask to form electrode fingers 4 whose width is several mm at the interval of several mm on the piezoelectric substrate 1. Then a nonpiezoelectric protection film 5 made of SiO2 or Si3N4, etc., is formed to the surface by a proper film forming method such as the sputtering method. Furthermore, the photoresist is removed together with the protective film formed thereon by a lift-off method. Thus, the protective film 5 is formed between the electrode fingers and between interdigital electrodes. When the thickness of the protective film 5 is 50-100Angstrom , the progress of deterioration in the piezoelectric substrate 1 is sufficiently prevented and the interdigital electrodes themselves are exposed, then the adverse effect onto the surface acoustic wave device is suppressed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device, and particularly to a surface acoustic wave device with excellent durability.

0002

[Prior Art] A surface acoustic wave device is a circuit element that utilizes surface waves generated on a piezoelectric substrate, in which minute electrode fingers with a width of several μm called comb-shaped electrodes are arranged alternately on the piezoelectric substrate. Electrodes are provided with a structure arranged at.

[0003] When such a surface acoustic wave device transmits a large amount of power, there is a problem in that the device deteriorates.

0004

[Problems to be Solved by the Invention] The present invention has solved the above-mentioned drawbacks, and an object of the present invention is to provide an elastic material with excellent durability while following the conventional electrode structure dimensions of surface acoustic wave devices. The purpose of the present invention is to provide a surface wave device.

[0005]

[Means and Effects for Solving the Problems] The present inventor observed the deterioration state of the surface acoustic wave device when the device deteriorates by transmitting a large amount of power, and found that cleaning after forming electrodes on the piezoelectric substrate It was discovered that during the process, the exposed surface between the electrode fingers of the piezoelectric substrate undergoes metamorphosis, which is one of the main causes of failure in the deterioration of surface acoustic wave devices when large amounts of power are subsequently transmitted.

In other words, when transmitting large amounts of power, the deterioration of the exposed portion of the piezoelectric substrate between the electrode fingers is accelerated, and in extreme cases, a portion of the substrate may come off, resulting in a significant deterioration of the frequency characteristics. Ta.

From the above findings, in a surface acoustic wave device in which comb-shaped electrodes are formed on a piezoelectric substrate, it is necessary to cover at least the spaces between the electrode fingers on the surface of the piezoelectric substrate, excluding the area between the comb-shaped electrodes, with a non-piezoelectric protective film. As a result, it was possible to suppress deterioration of the piezoelectric substrate due to storage, cleaning, etc., and to obtain a surface acoustic wave device with excellent durability.

[0008] In the present invention, the reason why the surface of the piezoelectric substrate except for the comb-shaped electrodes is covered with a non-piezoelectric protective film is that even if the entire surface including the comb-shaped electrodes is covered with a protective film, the comb-shaped electrodes themselves The characteristics of the surface acoustic wave device (
This is because the design parameters have to be fundamentally reconsidered, which has a large effect on the frequency characteristics (particularly the frequency characteristics), which is a problem.Also, it requires a two-step photolithography process to open holes in the pad area, which is economically disadvantageous. This is because.

Furthermore, in the present invention, the reason why at least the spaces between the electrode fingers of the piezoelectric substrate are covered with a non-piezoelectric protective film is that deformation of the exposed surface between the electrode fingers is the main cause of device deterioration. This is because it is more preferable to simultaneously cover the exposed surfaces of the piezoelectric substrates between the two with a protective film.

The present invention makes it possible to significantly improve the durability of surface acoustic wave devices using piezoelectric substrates with poor water resistance, such as LB substrates, and also has the advantage that conventional design parameters can be used as they are. A surface acoustic wave device can be obtained.

[0011]

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. First, Li2B has a large electromechanical coupling constant.
An electrode material 2 made of aluminum metal or the like is deposited on a piezoelectric substrate 1 made of 4O7 or the like. (Figure 1(a))

Next, a photoresist pattern 3 is formed on the electrode material 2. (FIG. 1(b)) By etching the electrode material 2 using the photoresist pattern 3, electrode fingers 4 made of aluminum metal or the like and having a width of several μm are formed on the piezoelectric substrate 1 at intervals of several μm. . (Figure 1(c))

Next, a non-piezoelectric protective film 5 made of SiO2, Si3N4, etc. is formed on the surface by a suitable film-forming method such as sputtering. (Figure 1(d))

Furthermore, the photoresist is removed together with the protective film 5 formed thereon by a lift-off method. (Figure 1(e))

By the above steps, the protective film 5 can be formed between the electrode fingers and between the comb-shaped electrodes.

If this protective film has a thickness of about 50 to 100 Å, it can sufficiently maintain the function of preventing the progress of deterioration of the piezoelectric substrate, and the comb-shaped electrode itself can maintain an exposed structure. Adverse effects on surface acoustic wave devices can be suppressed.

Furthermore, according to the present invention, since electrode formation and protective film formation can be accomplished in the same photolithography process, there is also an extremely large economic advantage.

Furthermore, according to the present invention, the protective film is also in close contact with the side surfaces of the electrode fingers, reinforcing the mechanical strength of the comb-shaped electrode.

[0019]

[Effects of the Invention] As explained above, according to the present invention,
Since the surface of the piezoelectric substrate except for the comb-shaped electrodes is covered with a non-piezoelectric protective film, deterioration of the piezoelectric substrate can be prevented and a surface acoustic wave device with excellent durability can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of a method for forming a protective film according to the present invention.

Claims (1)

[Claims] 1. A surface acoustic wave device in which comb-shaped electrodes are formed on a piezoelectric substrate, characterized in that at least the spaces between the electrode fingers on the surface of the piezoelectric substrate excluding the comb-shaped electrodes are covered with a non-piezoelectric protective film. surface acoustic wave device.