JPH02239715A - Surface acoustic wave substrate using diamond - Google Patents

Abstract

PURPOSE:To form a substrate with a high sound velocity for ultrahigh frequency processing of a surface acoustic wave element by adhering a piezoelectric thin film onto a substrate of crystal structure close to a diamond or a diamond substrate itself. CONSTITUTION:A natural diamond is expensive and also it is difficult to obtain a substrate with a size proper to the propagation of the surface acoustic wave. Then a piezoelectric thin film 2 is adhered onto a diamond substrate or a substrate 1 with crystal structure close to a diamond. Otherwise, a material 2 with crystal structure close to a diamond or a diamond is adhered onto the substrate 3 and a piezoelectric thin film 2 is adhered to the material 2 as the structure of the substrate. Thus, a surface acoustic wave substrate with a high sound velocity is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave substrate using diamond, which is a material with the highest propagation speed of acoustic waves on earth.

The sound speed of longitudinal waves in diamond is approximately 18,000 m/sec,
The sound speed of transverse waves is about 12,000 m/sec, and the sound speed of surface acoustic waves is about 11,000 m/sea, making it the material with the highest sound speed of any substance on earth. On the other hand, in order to achieve ultra-high frequencies in surface acoustic wave devices, a surface acoustic wave substrate material with a high sound velocity is required, and diamond is the optimal material for this purpose. However, since diamond does not have piezoelectricity, it is not possible to excite acoustic waves using an electric signal using diamond alone, so it is not suitable for use in surface acoustic wave devices. Furthermore, not only is natural diamond expensive, but it is also difficult to obtain a substrate of a size suitable for propagation of surface acoustic waves. The present invention relates to a surface acoustic wave substrate having a structure that combines artificially grown diamond and a piezoelectric thin film, or a combination of diamond and a piezoelectric single crystal.

As shown in FIG. 1(a), a surface acoustic wave substrate having a structure consisting of a piezoelectric thin film 2 deposited on a diamond substrate or a substrate l with a crystal structure similar to diamond, or as shown in FIG.
As shown in b), by fabricating a substrate with a structure in which diamond or a material 2 having a structure similar to diamond is adhered on the substrate 3, and a piezoelectric thin film 2 is further adhered thereon, an elastic surface with a high sound velocity can be created. A wave board can be obtained.

In claim 1, as shown in FIG. 2(a), in the substrate of FIG. 1(a) or FIG. 1(b), an interdigital electrode is provided between the diamond l and the piezoelectric thin film 2. 4, it is possible to obtain a surface acoustic wave substrate that can electrically excite and receive surface acoustic waves.

Further, as shown in FIG. 2(b), a similar surface acoustic wave substrate can be obtained by attaching interdigital electrodes 4 on the piezoelectric thin film. Furthermore, as shown in FIG. 2(C), a surface acoustic wave substrate having a structure in which a conductive film 5 is attached to the surface of the substrate having the structure shown in FIG. 2(a), or a
Figure (b) On the substrate, diamond l and piezoelectric thin film 2
By attaching the conductor film 5 between the two, a surface acoustic wave substrate with a large electromechanical coupling coefficient can be obtained. As an example of the overall bird's-eye view diagram in these cases, a diagram in the case of FIG. 2(1) is shown in FIG. 2(e). Figure 2 (b), (c), (d
) can also be obtained as a bird's-eye view similar to that in Figure 2(e).

As shown in FIG. 3, by producing a substrate in which interdigital electrodes are attached on a piezoelectric substrate 6 and diamonds are attached on the substrate, or a substrate in which diamonds 7 are attached on a piezoelectric substrate, A surface acoustic wave substrate having a higher sound velocity than a piezoelectric substrate can be obtained. Further, as shown in FIG. 4, by attaching a strip of diamond 8 on the piezoelectric substrate 6, a surface acoustic wave substrate having a large reflection coefficient can be obtained. The above-mentioned interdigital electrodes include unidirectional transducers or electrodes having a structure in which transmitting and receiving interdigital electrodes are combined. Also,
Although artificially synthesized diamond and diamond synthesized on a substrate have been described as diamond, surface acoustic wave substrates using natural diamond are also included in this patent.

Although a surface acoustic wave substrate has been described above, an acoustic wave functional element or an electronic functional element using the above structure is also included in this patent.

[Brief explanation of drawings]

Figure 1(a). (b) is a surface acoustic wave substrate with a structure in which a piezoelectric film is attached to a diamond substrate;
FIG. 3A is a cross-sectional view of a structure in which a piezoelectric film is adhered to a diamond substrate, and FIG. 3B is a cross-sectional view of a substrate in which a piezoelectric film is further adhered to a diamond substrate. l...Diamond, 2...Piezoelectric film, 3...
Substrate, FIG. 2(a). (b). (c). (d) is a cross-sectional view of a substrate having a structure that excites and receives surface acoustic waves using interdigital electrodes on a substrate made of a substrate, diamond, and a piezoelectric film.
a) is a sectional view taken along the line AA° in FIG. 2(e); Figure 2 (e) is a bird's-eye view of Figure 2 (a), and Figure 2 (
b), (c). A similar bird's-eye view can be obtained in (d), except that the positions of the interdigital electrodes and the metal film are different. 4...Interdigital electrode, 5...Metal film, Figure 3 shows a substrate with a structure in which surface acoustic waves are excited using interdigital electrodes on a substrate with a diamond film attached on a piezoelectric substrate. FIG. 6...Piezoelectric substrate, 7...Diamond film FIG. 4 is an explanatory view of a substrate having a structure in which a strip-shaped diamond film is adhered onto a piezoelectric substrate.

Claims (3)

[Claims] (1) A surface acoustic wave substrate having a structure consisting of a piezoelectric thin film 2 deposited on a diamond substrate or a substrate 1 with a crystal structure similar to diamond, as shown in FIG. 1(a), or as shown in FIG. 1(b). A surface acoustic wave substrate having a structure in which diamond or a material 2 having a structure similar to diamond is deposited on a substrate 3, and a piezoelectric thin film 2 is further deposited thereon. (2) In claim 1, as shown in FIG. 2(a), in the substrate of FIG. 1(a) or FIG. 1(b), between the diamond 1 and the piezoelectric thin film 2, A surface acoustic wave substrate with an interdigital electrode 4 attached thereto, or as shown in FIG. 2(b), an interdigital electrode 4
A surface acoustic wave substrate having a structure in which a conductive film 5 is attached on a piezoelectric thin film, or a surface acoustic wave substrate having a structure in which a conductor film 5 is attached to the surface of a substrate having the structure shown in FIG. 2(a) as shown in FIG. 2(c). In the substrate or the substrate of FIG. 2(b) as in FIG. 2(d),
A surface acoustic wave substrate having a structure in which a conductive film 5 is attached between a diamond 1 and a piezoelectric thin film 2. (3) As shown in FIG. 3, a substrate has a structure in which an interdigital electrode 4 is attached on a piezoelectric substrate 6 and a diamond 7 is further attached thereon, or a diamond 7 is attached on a piezoelectric substrate 6. A surface acoustic wave substrate having a structure in which diamonds 8 are attached on top of a piezoelectric substrate 6 as shown in FIG. 4.