JPH0318367B2 - - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention relates to a surface wave device, and more particularly, an inorganic photosensitive substrate is exposed and developed to form a reflector for surface acoustic waves propagating on the surface of the inorganic photosensitive substrate. The present invention relates to a surface acoustic wave device as described above.

Prior Art A surface acoustic wave (hereinafter simply referred to as surface wave) device having interdigital electrodes on the surface of a piezoelectric material is
In the VHF and UHF regions, it is an excellent telecommunications circuit device that has the advantages of simple structure, small size, and low loss, and its practical application is considered extremely promising.

Traditionally, surface wave devices of this type have been made using quartz crystal or LiNb, as shown in Figure 1, for example.
It is generally known that a transducer-like electrode 12 for surface wave transmission/reception is formed on the surface of a piezoelectric crystal substrate 11 such as O ₃ , and surface wave reflectors 13 and 14 are formed on both sides thereof.

The surface wave reflectors 13 and 14 are piezoelectric crystal substrates 1
By periodically providing grooves on the surface of the piezoelectric crystal substrate 11 or periodically attaching a lattice-like thin film of metal or dielectric material, the acoustic impedance is periodically changed on the surface of the piezoelectric crystal substrate 11, and surface waves are generated. perform the reflection.

In order to provide the above grooves on the surface of the piezoelectric crystal substrate 11, the surface of the piezoelectric crystal substrate 11 is selectively etched using a device such as ion etching. Forming grooves in the piezoelectric crystal substrate 11 in this manner requires a large-scale ion etching apparatus, and has the drawback that this ion etching process requires a large amount of time. Furthermore, since the process of forming the grooves is different from the process of forming the interdigital electrodes 12, relative positional deviation between the interdigital electrodes 12 and the reflectors 13 and 14 occurs due to alignment errors in the second fine pattern manufacturing process. . Therefore, loss increases and resonance characteristics deteriorate, which is undesirable.

On the other hand, surface wave reflectors 13 and 14 using dielectric lattice coatings usually select a thin film material whose density or elastic constant is significantly different from that of the substrate material in order to obtain good reflection efficiency. A film is formed by vapor deposition or sputtering, and then etched into a desired lattice shape using a photoetching method. In this case as well, similar to the groove-shaped surface wave reflector described above, the surface wave reflectors 13 and 14 have drawbacks due to the fact that the formation process is different from that of the interdigital interdigital electrode 12.

Furthermore, for a highly piezoelectric substrate such as _LiNbO3 , a metal thin film is used for the surface wave reflectors 13 and 14. However, Li Nb O ₃ has poor temperature stability, and an elastic wave device using it has a problem of lack of practicality.

Purpose of the Invention The present invention has been made in view of the above circumstances, and an object thereof is to form a surface wave reflector by exposing and developing an inorganic photosensitive substrate to form grooves for reflecting surface waves. The object of the present invention is to facilitate the formation of surface acoustic wave devices, thereby simplifying the manufacturing of surface acoustic wave devices and improving their characteristics.

SUMMARY OF THE INVENTION Therefore, the present invention provides a method for forming a piezoelectric thin film and at least one set of interdigital electrodes on a part of the main surface of a flat inorganic photosensitive substrate, while forming an inorganic photosensitive substrate on both sides of the piezoelectric thin film. It is characterized in that a surface wave reflector consisting of a plurality of grooves substantially parallel to each other is formed by exposing and developing.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

In FIG. 2, 21 is an inorganic photosensitive substrate;
2 is a piezoelectric thin film, 23 is a blind-shaped interdigital electrode for transmitting and receiving surface waves, and 24 and 25 are surface wave reflectors.

The inorganic photosensitive substrate 21 is made of, for example, photosensitive glass, and when exposed to light, that portion changes color, and the discolored portion becomes easily soluble in a developer such as hydrofluoric acid.

The inorganic photosensitive substrate 21 has a rectangular shape,
ZnO or AlN is placed in the center of one main surface.
A rectangular piezoelectric thin film 22 made of a piezoelectric material such as the above is formed, and an interdigital electrode 23 is formed thereon by photoetching, mask vapor deposition, or the like.

The interdigital electrode 23 has a plurality of finger electrodes 26, 26, . . . formed in parallel, and these finger electrodes 26, 26, . 27b, respectively.

Inorganic photosensitive substrates 2 on both sides of the piezoelectric thin film 22
1, the inorganic photosensitive substrate 21 is exposed and developed as described below to form a surface comprising a plurality of grooves 28, 28, . . . parallel to the finger electrodes 26, 26, . . . of the interdigital electrode 23. Wave reflectors 24 and 25 are formed, respectively.

Grooves 2 constituting the surface wave reflectors 24 and 25
The width and pitch of the finger electrodes 26, 26, ... of the interdigital electrode 23 are usually on the order of several microns, but these are determined by the set frequency of the surface acoustic wave device, and the width and pitch of the finger electrodes 26, 26, ... of the interdigital electrode 23 are determined by the set frequency of the surface acoustic wave device. Approximately match.

Grooves 28, 28 of the surface wave reflectors 24, 25,
... can be formed as follows.

First, as shown in FIG. 3a, a photosensitive glass substrate 31 that will become the inorganic photosensitive substrate 21 of the surface acoustic wave device shown in FIG. 2 is prepared. The positions where the grooves 28, 28, . . . are formed are exposed by projecting ultraviolet light 32, as shown in FIG. 3b.

In this exposure, for example, when forming the interdigital electrodes 23, a metal thin film is simultaneously formed in areas other than the grooves 28 in the areas of the reflectors 24 and 25, and the grooves 28 are exposed using the metal thin film as a mask. For example, the interdigital electrodes 23 and the grooves 28 can be aligned without any problem.

As described above, when the ultraviolet rays 32 are projected, that portion of the photosensitive glass substrate 31 changes color.

Next, when the photosensitive glass substrate 31 is immersed in a developer such as hydrofluoric acid, the photosensitive glass substrate 3
The discolored part of No. 1 is dissolved, and as shown in Figure 3c,
Grooves 28, 28, . . . are formed.

In this way, the surface wave reflectors 24 and 25 can be formed directly on the photosensitive glass substrate 31 without using a photoresist. The depth of the grooves 28, 28, . . . can also be easily adjusted by adjusting the amount of exposure to light such as ultraviolet rays.

The present invention is not limited to the surface acoustic wave device having the electrode structure shown in FIG. 2, but is widely applicable to surface acoustic wave devices having other electrode structures.

For example, interdigital electrodes 23 may be formed between piezoelectric thin film 22 and inorganic photosensitive substrate 21.

Further, the piezoelectric thin film 22 may be attached over the entire surface of the substrate 21 including the grooves 28.

Effects of the Invention As is clear from the above detailed description, the present invention uses an inorganic photosensitive substrate to form the grooves of the surface wave reflector of a surface acoustic wave device. The grooves of the reflector can be formed by exposing and developing the substrate itself, making it extremely easy to form the reflector.

Further, the inorganic photosensitive substrate has a small attenuation constant of surface acoustic waves, and a surface acoustic wave device with small propagation loss in a high frequency range can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a conventional surface wave device, FIG. 2 is a perspective view of an embodiment of the surface wave device according to the present invention, and FIGS. FIG. 3 is an explanatory diagram of a process for forming a reflector of the surface acoustic wave device shown in the figure. 21... Inorganic photosensitive substrate, 22... Piezoelectric thin film, 2
3... Interdigital electrode, 24, 25... Reflector, 28... Groove, 31... Photosensitive glass substrate, 32...
Ultraviolet light.

Claims (1)

[Claims] 1. A piezoelectric thin film and at least one set of interdigital electrodes are formed on the main surface of a flat inorganic photosensitive substrate, and the main surface of the inorganic photosensitive substrate is exposed and developed to form a plurality of electrodes substantially parallel to each other. A surface wave device characterized in that a surface wave reflector is formed of grooves.