JPS60106217A - Surface wave filter - Google Patents

Abstract

PURPOSE:To increase electrostatic dielectric strength and to stabilize quality by interposing a dielectric material film of a dielectric as a layer between a comb- shaped electrode and a conductive film. CONSTITUTION:Plural couples of positive and negative comb-shaped electrodes 2 and 3, and 2a and 3a are arranged on a substrate 1. The dielectric material film 6 is arranged on the comb-shaped electrodes, a piezoelectric film 4 is formed, and electrodes for surface acoustic wave excitation which have conductive films 5 and 5a are further provided thereupon. Thus, the electrostatic dielectric strength is improved and the quality is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a surface wave filter used in VIP circuits of television receivers and video tape recorders.

Conventional Structure and Problems Conventionally, this type of surface acoustic wave filter, as shown in Figs. A piezoelectric film 4 formed by sputtering and depositing ZnO is placed on top of the piezoelectric film 4, and conductive films 5 and 5a made of aluminum are placed on top of the piezoelectric film 4 to form a surface acoustic wave excitation electrode. It was composed of

However, in the above configuration, the comb spacing in the comb-shaped electrodes is about 10 microns, whereas the spacing between the comb-shaped electrodes and the conductive film is several microns.

There were cases in which short-circuit failures occurred between the comb-shaped electrodes and the conductive film due to static electricity. In addition, the input/output impedance of a surface wave filter is determined by the shape of the comb-shaped electrodes and the surface resistance between the combs, but since a piezoelectric film of a semiconductor ZnO layer is formed on it, the input/output impedance is determined by the shape of the comb-shaped electrodes and the surface resistance between the combs. Since it is low and unstable, it has the problem of poor matching with the circuit.

OBJECTS OF THE INVENTION The present invention aims to eliminate the above-mentioned conventional drawbacks and provide a surface acoustic wave filter with strong static electricity resistance and stable quality.

Structure of the Invention In order to achieve all of these objects, the present invention utilizes an elastic material in which a dielectric material film is disposed on comb-shaped electrodes on a substrate, a piezoelectric film is disposed on top of the dielectric material film, and a conductive film is further disposed on top of the dielectric material film. It is equipped with an electrode for surface wave excitation.

DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to FIG.
”, and the same parts are given the same numbers and explained.

As shown in FIG. 3, in the present invention, a plurality of pairs of comb-shaped electrodes 2, 3, and 2a, each consisting of positive and negative pairs, are provided on a substrate 1.

3a, a dielectric film 6 is placed thereon, a piezoelectric film 4 is placed thereon, and conductive films 5, 5 are placed thereon.
The device is equipped with a surface acoustic wave excitation electrode arranged with a.

FIG. 4 shows the electrostatic breakdown voltage when the thickness of the dielectric material film 6 is changed in the present invention! It can be seen that the ll1% static electricity breakdown voltage tends to increase in proportion to the thickness of the dielectric material film 6.

Effects of the Invention According to the present invention configured as described above, since a layer of dielectric material as an insulator is interposed between the comb-shaped electrode and the conductive film, the electrostatic breakdown voltage depends on the thickness of the dielectric material film. There is a tendency for the voltage to increase almost in proportion to the voltage, and this effect is particularly noticeable when the thickness of the dielectric material film is 0.1 μm or more, and the electrostatic withstand voltage can be reduced from the conventional 100V to approximately 200V. Furthermore, since the comb-shaped electrodes are encapsulated by the substrate as an insulator and the dielectric film, the input/output impedance is high, and the electrodes are electrically stable and are well matched with the circuit.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a conventional surface wave filter seen from above, Fig. 2 is a sectional view taken along line A-B in Fig. 1, and Fig. 3 shows an embodiment of a surface wave filter according to the present invention. cross section,
FIG. 4 is a diagram showing the relationship between the thickness of the dielectric material film and the electrostatic breakdown voltage in the filter of the present invention. 1... Board, 2, 3, 2a, 3a...
Comb-shaped electrode, 4...Piezoelectric film, 6, 5a...
...Conductive film, 6...Dielectric material film. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 4 → Dielectric material film

Claims (2)

[Claims] (1) Elasticity in which multiple pairs of comb-shaped electrodes (positive and negative) are placed on a substrate, a dielectric film is placed on top of the pairs, a piezoelectric film is placed on top of that, and a conductive film is placed on top of that. A surface wave filter characterized by comprising a surface wave excitation electrode. (2) The surface acoustic wave filter according to claim 1, wherein the dielectric material film has a thickness of 0.1 μm or more.