JPH0347603B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a composite piezoelectric resonator that utilizes bulk waves and has a piezoelectric thin film formed on a dielectric substrate.

Prior Art In a bulk wave resonator using a piezoelectric substrate, in order to trap energy, the thickness of the piezoelectric substrate in the vibrating part is made thicker than in other parts depending on the size of Poisson's ratio. You can make it thinner or thinner.

By the way, it is extremely difficult to partially increase or decrease the thickness of a piezoelectric substrate as described above, and for this reason, energy confinement has traditionally been carried out using the mass addition effect of electrodes, piezoelectric reaction, etc. However, compared to the case where the plate thickness was changed, the energy trapping effect was insufficient.

On the other hand, in order to use a piezoelectric resonator in a high frequency range, it is sufficient to reduce the thickness of the piezoelectric substrate over the entire surface or to reduce the thickness of the vibrating portion.

However, if the piezoelectric substrate is made completely thin, it will be easily broken and difficult to handle.

For this reason, we have proposed a high-frequency piezoelectric resonator that uses bulk waves, in which a piezoelectric thin film is formed on a silicon substrate, and a recess is formed by anisotropic etching on the other side of the silicon substrate facing the piezoelectric thin film. However, the problem was that it required a SiO ₂ mask, a boron-doped layer, etc., and was very time-consuming to manufacture.

Purpose of the Invention The present invention has been made in view of the above-mentioned circumstances regarding a piezoelectric resonator that utilizes bulk waves, and its object is to provide a piezoelectric resonator that utilizes bulk waves, which is formed by forming a piezoelectric thin film on a dielectric substrate. In this method, by using an inorganic photosensitive substrate as a dielectric substrate, the inorganic photosensitive substrate is directly exposed and developed, and the thickness of the inorganic photosensitive substrate in the part facing the piezoelectric thin film is made different from that in other parts. The purpose is to make it easy to process different parts.

SUMMARY OF THE INVENTION Therefore, the present invention provides a method for forming a piezoelectric thin film on one main surface of a flat inorganic-textured photosensitive substrate, the piezoelectric thin film having an electrode formed on each of the opposing main surfaces, and The other principal surface is exposed and developed to make the thickness of the inorganic photosensitive substrate at the portion facing the piezoelectric thin film different from that at other portions.

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

In FIG. 1, 11 is an inorganic photosensitive substrate;
2 is one main surface 11a of the inorganic photosensitive substrate 11;
The piezoelectric thin films 13 and 14 formed on the piezoelectric thin film 12 are electrodes provided on both opposing main surfaces of the piezoelectric thin film 12, respectively.

The inorganic photosensitive substrate 11 is made of a photosensitive glass substrate, generally called photosensitive glass for chemical cutting, which changes color when exposed to ultraviolet rays or the like, and the discolored portion becomes easily soluble in a developer such as hydrofluoric acid. Examples of the photosensitive glass for chemical cutting include SiO ₂ , Li ₂ O, Na ₂ O, K ₂ O, Al ₂ O ₃ , AgCl,
In addition to CeO ₂ , it is possible to use something called Photoceram (trade name), which contains trace amounts of Au, Ag, and Cu, and when irradiated with light, these precipitate and become chemically soluble.

On the other hand, the piezoelectric thin film 12 is made of a piezoelectric material such as ZnO or AlN, and is formed on one main surface 11a of the inorganic photosensitive substrate 11 by a method such as sputtering, ion plating, or CVD.

The inorganic photosensitive substrate 11 has the other main surface 1
1b is exposed and developed as described below to form a concave portion 15 concave from the main surface 11b toward the piezoelectric thin film 12, and to reduce the thickness of the inorganic photosensitive substrate 11 below the piezoelectric thin film 12. The thickness of the plate is thinner than that of other parts.

The recess 15 can be formed as follows.

First, as shown in FIG. 2a, a photosensitive glass substrate 21, which will become the inorganic photosensitive substrate 11 of FIG. 1, is prepared.

As shown in FIG.
When exposure is performed by projecting ultraviolet rays 22, the portion 23 onto which the ultraviolet rays 22 are projected changes color.

Next, when this photosensitive glass substrate 21 is immersed in a developer such as hydrofluoric acid, the above-mentioned portion 23 onto which the ultraviolet rays 22 have been projected is dissolved, and a recess 15 is formed as shown in FIG. 2c. Ru.

The depth of the recess 15 is preferably set so that the thickness of the inorganic photosensitive substrate 11 under the piezoelectric thin film 12 is from several microns to several tens of microns.

As described above, it can be seen that if the inorganic photosensitive substrate 11 is used, the thickness of the inorganic photosensitive substrate 11 below the piezoelectric thin film 12 can be easily adjusted by only exposure and development.

Next, other embodiments of the present invention are shown in FIGS. 3, 4, and 5.

In both the embodiments shown in FIGS. 3 and 4, the thickness of the inorganic photosensitive substrate 11 is increased in the embodiment shown in FIG. 1, and the piezoelectric resonator shown in FIG. Then, a ring-shaped recess 16 is formed so that the thickness of the inorganic photosensitive substrate 11 under the piezoelectric thin film 11 is thicker than the thickness of the surrounding area.
In the piezoelectric resonator shown in FIG. 4, a piezoelectric thin film 1 is formed.
The recessed portion 17 is formed so that the thickness of the lower portion of the recessed portion 17 is thinner than the thickness of the surrounding portion. These are intended to achieve the so-called energy trapping effect.

By doing the above, even if the thickness of the vibrating part becomes thinner due to higher frequencies, the thickness of the inorganic photosensitive substrate 11 can be increased, and the piezoelectric resonator can be made strong against vibrations and shocks. Obtainable.

In addition, simply aiming at the effect of confining energy, the piezoelectric thin film 12 is made such that the thickness of the inorganic photosensitive substrate 11 under the piezoelectric thin film 12 is thicker than the thickness of the surrounding area, as shown in FIG. The other main surface 11b of the inorganic photosensitive substrate 11 may be exposed and developed, leaving the inorganic photosensitive substrate 11 at the bottom.

Effects of the Invention As is clear from the above detailed description, the present invention provides a piezoelectric resonator using a bulk wave using a dielectric substrate and a piezoelectric thin film, in which an inorganic photosensitive substrate is used as the dielectric substrate. Since the thickness of the inorganic photosensitive substrate in the portion facing the piezoelectric thin film is made different from that in other portions by exposure and development processing, the thickness of the inorganic photosensitive substrate in the portion facing the piezoelectric thin film is The piezoelectric resonator can be easily processed to adjust the plate thickness, has more perfect energy confinement, and can easily be made to operate at higher frequencies.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an embodiment of a piezoelectric resonator according to the present invention, and FIGS. Explanatory drawings of the forming process, FIGS. 3, 4, and 5 are sectional views of embodiments different from those in FIG. 1, respectively. 11... Inorganic photosensitive substrate, 11a... One main surface, 11b... Other main surface, 12... Piezoelectric thin film, 13, 14... Electrode, 15, 16, 17...
Recessed portion, 21...photosensitive glass substrate, 22...ultraviolet light.

Claims (1)

[Claims] 1. A piezoelectric thin film having electrodes formed on opposing main surfaces is formed on one main surface of a flat inorganic photosensitive substrate, and the other main surface of the inorganic photosensitive substrate is exposed to light and developed. A composite piezoelectric resonator characterized in that the thickness of the inorganic photosensitive substrate in the portion facing the piezoelectric thin film is different from that in other portions.