JP2602222B2 - Surface acoustic wave convolver - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monolithic surface acoustic wave device capable of processing a correlation signal with high efficiency.

[Conventional technology]

A surface acoustic wave has a propagation speed about five orders of magnitude lower than an electromagnetic wave,
When applied to the processing of electric signals, the element can be reduced in size and no adjustment is required, so that it has been put to practical use as a filter element or the like. Furthermore, since energy is concentrated on the material surface, research and development of surface acoustic wave devices that perform correlation processing, convolution integration, etc. using the surface acoustic wave itself and nonlinear effects with semiconductors have been conducted. I have. For such a device, for example, the Japan Society for the Promotion of Science
It is discussed in the 150th committee's first document, "Monolithic Surface Acoustic Wave Convolver". In the above document, there is a surface acoustic wave device formed monolithically by forming a piezoelectric thin film on the surface of a semiconductor substrate as a particularly efficient configuration,
30 to 40 compared to a device using only the nonlinear effect of surface acoustic waves
It has the effect of improving the efficiency of dB.

[Problems to be solved by the invention]

A surface acoustic wave device using the above-mentioned semiconductor substrate requires efficient excitation of surface acoustic waves, improvement of electromechanical coupling coefficient, improvement of electric field intensity leaking into a semiconductor, etc. from the viewpoint of improving the efficiency of correlation signal processing. However, in the prior art, no special consideration has been given to a device configuration suitable for improving the leakage electric field.

Another object of the present invention is to achieve an improvement in the efficiency of correlation signal processing.

[Means for solving the problem]

In a surface acoustic wave device in which a piezoelectric thin film is formed on the surface of a semiconductor substrate, a protective layer is provided for stabilizing the semiconductor surface. The above object is achieved by using a material having a large relative dielectric constant and a high electric field leakage to a semiconductor substrate for the protective layer.

[Action]

The coupling between the surface acoustic wave and the carrier in the semiconductor is due to the leakage of the electric field generated when the surface wave propagates through the piezoelectric body into the semiconductor. Therefore, as described above, in order to improve the efficiency of the correlation signal processing, it is necessary to improve the electromechanical coupling coefficient and to increase the leakage electric field by using a material having a large relative dielectric constant. Conventionally, a silicon dioxide (SiO ₂ ) thin film has been used as a protective film between the semiconductor substrate and the piezoelectric thin film, but its relative dielectric constant is about 3 to 4. The present invention improves the leakage electric field strength into the semiconductor due to the surface acoustic wave by using a material having a large relative dielectric constant instead of silicon dioxide for the protective film, thereby improving the efficiency of the correlation signal processing. Things.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a sectional view of a device schematically showing an embodiment of a surface acoustic wave convolver of the present invention. In this apparatus, a silicon substrate was used as a semiconductor substrate 1, a titanium oxide thin film was formed as a protective film 2 on the surface thereof, and a zinc oxide thin film was further formed as a piezoelectric thin film 3, thereby producing a laminated substrate 10. The output gate electrode 4, the input comb electrodes 5, 6 and the ground electrode 9 were formed of an aluminum thin film.

The electric signal applied to the input terminal 7 is converted into a surface acoustic wave by the comb-shaped electrode and propagates on the substrate surface, and a correlation signal is output from the output gate electrode by a non-linear action with carriers in the semiconductor.

The relative dielectric constant of titanium oxide is 50 to 150, which is at least one order of magnitude larger than that of silicon dioxide, which has the effect of improving the strength of the leakage electric field into the semiconductor as compared with the conventional case.

FIG. 2 shows another embodiment of the present invention. In this embodiment,
The structure of the laminated substrate is composed of a semiconductor substrate, a protective film and a piezoelectric film as in the first embodiment, but alumina is used here as the material of the protective film. Alumina has a relative dielectric constant of about 10, and can improve the leakage electric field as compared with silicon dioxide. In the present embodiment, a unidirectional electrode is used as the comb-shaped electrode, so that surface acoustic waves can be efficiently excited.

FIG. 3 shows a third embodiment of the present invention.
1. The structure is similar to that of the second embodiment. In the present invention, a higher-order mode Rayleigh wave is used, and it is difficult to perform signal processing in a wide band because of speed dispersion. Therefore, in the present embodiment, a delay time is changed as a chirped electrode in which the period of the input comb-shaped electrode is continuously changed to compensate for the speed dispersion. Thereby, signal processing in a wider band can be performed as compared with the related art.

〔The invention's effect〕

According to the present invention, the protective layer of the surface acoustic wave convalbo,
Since titanium oxide and alumina, which are materials having a large relative dielectric constant and a high leakage electric field strength, are used, the efficiency of the correlation signal processing can be improved. Therefore, if the present apparatus is used in a spread spectrum communication system or the like, the error rate can be reduced and the performance can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a surface acoustic wave device according to one embodiment of the present invention,
FIG. 2 is a plan view showing a second embodiment of the present invention, and FIG. 3 is a plan view showing a third embodiment. DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 2 ... Protective film 3 ... Piezoelectric thin film, 4 ... Gate electrode 5, 6 ... Comb electrode for input 7 ... Input terminal, 8 ... Output terminal 9 ... Ground electrode 10: laminated substrate 11: unidirectional electrode, 12: phase shifter 13: chirp electrode

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Jun Yamada 292 Yoshidacho, Totsuka-ku, Yokohama-shi Inside the Home Appliances Research Laboratory, Hitachi, Ltd. (56) References JP-A-56-79487 (JP, A)

Claims (1)

(57) [Claims] 1. A protective layer and a piezoelectric layer are sequentially formed on a surface of a semiconductor substrate, a gate electrode is provided on the surface of the piezoelectric layer, and a comb-shaped input electrode is provided on the surface of the piezoelectric layer with the gate electrode interposed therebetween. A surface acoustic wave convolver provided, wherein the protective layer is made of titanium oxide (TiO ₂ ) or alumina (Al ₂ O ₃ ) having a leakage electric field intensity higher than that of silicon dioxide (SiO ₂ ) to the semiconductor substrate. Characteristic surface acoustic wave convolver.