JPH04150511A - Surface acoustic wave element and its manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD 1 The present invention relates to a surface acoustic wave element suitable for use as a filter circuit or a resonator circuit for communication equipment, for example. 2. Description of the Related Art A surface acoustic wave element is known as an element that utilizes surface acoustic waves generated by applying a voltage to a piezoelectric material. FIG. 1 shows an external view of the main body of the surface acoustic wave device. As shown in this figure, the surface acoustic wave element 10 has comb-shaped electrodes 2a and 2b and comb-shaped electrodes 3a and 3b on a piezoelectric substrate l.
is formed. Each comb-shaped electrode 2a is connected to a pad part 4a, each comb-shaped electrode 2b is connected to a pad part 4b, each comb-shaped electrode 3a is connected to a pad part 5a, and each comb-shaped electrode 3b is connected to a pad part 5b. . The pad portion 4a is connected to the external electrode 68, the pad portion 4b is connected to the external electrode 6b, the pad portion 5a is connected to the external electrode 7a, and the pad portion 5b is connected to the external electrode 7.
connected to b. FIG. 4 is an enlarged front view of the comb-shaped electrodes 2a and 2b and the pad portions 4a and 4b.
and 3b and pad portions 5a and 5b have similar shapes. FIG. 5 shows a cross-sectional view of the horizontal electrodes 2a and 2b. The cross sections of the comb-shaped electrodes 3a and 3b also have similar shapes. Each pitch of the comb-shaped electrode 2a and each pitch of the comb-shaped electrode 2b are opposed to each other, and each pitch of the comb-shaped electrode 3a and each pitch of the comb-shaped electrode 3b are also opposed to each other. The comb-shaped electrodes 28 and 2b and the horizontal electrodes 3a and 3b are usually made of aluminum metal thin films, and are formed to have a thickness of about 1000A to 5000mm, and an electrode pitch of about 1mrs=10μ. In this surface acoustic wave element 10, when a high frequency signal is input between a pair of comb-shaped electrodes, for example, comb-shaped electrodes 2a and 2b, through external electrodes 6a and 6b, mechanical strain is generated on the surface of the piezoelectric substrate 1 at a period corresponding to the electrode pitch. occurs. This mechanical strain propagates on the surface of the piezoelectric substrate 1 as a surface wave and reaches the other pair of comb-shaped electrodes 3a and 3b. This mechanical strain generates an electromotive force in the comb-shaped electrodes 3a and 3b, which can be detected as an electrical signal. At this time, the comb-shaped electrodes 2a and 2b and the comb-shaped electrode 3
Signals with input frequencies that do not match the pitches of 8 and 3b are canceled out by a large number of electrode pitches and are not transmitted, and only frequency signals that match the electrode pitches are transmitted. The surface acoustic wave device described above is used as a filter circuit or a resonator circuit. To complete a surface acoustic wave device as a circuit component, it is necessary to attach the surface acoustic wave device to a metal base, connect the comb-shaped electrode pads to external connection terminals with wires (wire bonding), and attach the surface acoustic wave device to a metal base. It is necessary to cover the cap with a cap and seal the surrounding area by welding. Because surface acoustic wave devices use piezoelectric substrates, static electricity can be generated due to mechanical friction and temperature changes encountered during these operations. At this time, since the electrode pitch of the comb-shaped electrodes is very narrow, discharge may occur between the electrodes, and the surface acoustic wave element may be destroyed by discharge. Additionally, the piezoelectric substrate is easily charged and attracts dust in the air, which poses manufacturing difficulties.

[Problem B that the invention attempts to solve]

The present invention was made in order to eliminate the above-mentioned disadvantages of conventional surface acoustic wave devices, and provides a surface acoustic wave device that does not suffer from electrical discharge destruction during the manufacturing process and a manufacturing method thereof. It is something to do.

[Means to solve the problem]

A surface acoustic wave device to which the present invention is applied in order to solve the above-mentioned problems is constructed on a piezoelectric substrate 1 whose surface is covered with a photoconductive thin film 11, as shown in FIGS. , forming horizontal electrodes 2a and 2b and 3a and 3b. As shown in the figure, the surface acoustic wave device to which the present invention is applied is such that after the surface of a piezoelectric substrate 1 is coated with a photoconductive thin film 11, comb-shaped electrodes 2a, 2b, and 3a are formed on the covered piezoelectric substrate 1. 3b is formed, and the photoconductive thin film 11 is irradiated with light, and then the wire 9 is connected and the cap 14 (third
(See figure) Weld and seal.

[Effect]

In the surface acoustic wave device of the present invention, since the surface of the piezoelectric substrate 1 is covered with the photoconductive thin film 11, if light is irradiated,
Even with mechanical friction and temperature changes encountered during work steps such as connecting the wires 9 and welding and sealing the cap 14, static electricity does not build up on the piezoelectric substrate l. Therefore, it is possible to prevent the surface acoustic wave element from being destroyed by discharge due to discharge between the electrodes. Furthermore, since dust in the air is not attracted by static electricity during operation, manufacturing is easy.

【Example】

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view of a surface acoustic wave element IO to which the present invention is applied, and the second side is an enlarged sectional view of the surface acoustic wave element IO. As shown in FIGS. 1 and 2, a surface acoustic wave device 10
, comb-shaped electrodes 28 and 2b and 3a and 3b are formed on a piezoelectric substrate l covered with amorphous silicon 11. Each comb-shaped electrode 2a is connected to a pad portion 4a, each comb-shaped electrode 12b is connected to a pad portion 4b, each comb-shaped electrode 3a is connected to a pad portion 5a, and each comb-shaped electrode 3b is connected to a pad portion 5b. . The pad portion 4a is connected to the external electrode 6a, the pad portion 4b is connected to the external electrode 6b, the pad portion 5a is connected to the external electrode 7a, and the pad portion 5b is connected to the external electrode 7b. comb-shaped electrodes 2a and 2b and pad portions 4a and 4b,
The enlarged shapes of the comb-shaped electrodes 3a and 3b and the pad portions 5a and 5b are shown in FIG. The method for covering the surface of the piezoelectric substrate 1 with the photoconductive thin film 11 of amorphous silicon is as follows. Using plasma CVD (chemical vapor deposition), amorphous silicon is formed on the surface of the piezoelectric substrate 1 to a thickness of approximately 1000 nm while keeping the temperature of the piezoelectric substrate 1 below 200"C. Comb-shaped electrodes 2a, 2b, 3a and 3b, pad portions 4a and 4b, and 5a and 5b are created by the ring graph pattern forming method as described below.First, approximately 3000 aluminum thin films are formed on the piezoelectric substrate l by vacuum evaporation.A photoresist is applied on this. The photoresist is then uniformly coated to a thickness of approximately IXLm.It is then irradiated with ultraviolet light through a photomask having a pattern of comb-shaped electrodes and pads.Then, the photoresist is developed to form a pattern of comb-shaped electrodes and pads. The exposed areas of the aluminum thin film are removed and the surface of the aluminum thin film is exposed.When this is soaked in a mixture of phosphoric acid/acetic acid/nitric acid to dissolve the exposed parts of the aluminum thin film, they are covered with photoresist. After washing this with water and removing the photoresist, the comb-shaped electrodes 2a, 2b, 3a and 3b and pad portions 4a, 4b, 5 made of the aluminum thin film remain.
Patterns a and 5b are formed. The surface acoustic wave device 10 produced as described above is further completed as a circuit component through the following steps. It should be noted here that the following steps are performed while irradiating light, that is, while the amorphous silicon 11, which is a photoconductive thin film, is conductive. As shown in FIG. 3, the surface acoustic wave element 10 is attached to the metallic paste 8. A wire 9 is connected to the pad portion 4a of the comb-shaped electrode 2a, and the wire 9 is further connected to the external connection terminal 6.
connected to a. Similarly, the pad portion 4b of the comb-shaped electrode 2b is connected to the external connection terminal 6b, the pad portion 5a of the horizontal electrode 3a is connected to the external connection terminal 7a, and the pad portion 5b of the comb-shaped electrode 3b is connected to the external connection terminal 7b by wire. . After these wire bondings are completed, a transparent glass cap 14 is placed on the metal base 8, and its peripheral portion is brazed to make it airtight. Further, the transparent cap 14 is coated with black paint to block light so that light does not reach the photoconductive thin film, and the circuit component is completed. The amorphous silicon used as the photoconductive thin film has a conductivity of 10-' to 10-'/Ω・cm when irradiated with light, and a large change in conductivity in the dark of to-' to IQ-10/Ω・cm. do. Therefore, in the process of irradiating the piezoelectric substrate with light, the charges on the piezoelectric substrate are always neutralized through the photoconductive thin film. On the other hand, since the circuit components of the completed surface acoustic wave device are shielded from light, the photoconductive thin film has a sufficiently high resistance as described above, and the input impedance of the surface acoustic wave device is maintained. In the above embodiment, the cap 14 is made of transparent glass, but it can also be made of transparent plastic. Light blocking is not limited to painting, but may also include other light blocking means such as pasting a cover. Further, if the completed circuit components are placed in a dark place when assembled into a set, the above-mentioned light shielding is unnecessary. Note that even if the photoconductive thin film 11 is made of polycrystalline silicon, the same effect as that of amorphous silicon can be obtained.

【Effect of the invention】

As explained above, the surface acoustic wave device to which the present invention is applied and the surface acoustic wave device manufactured by the method to which the present invention is applied are as follows:
It can prevent electrical discharge damage during the manufacturing process, and
Since there is no electrostatic adsorption of dust, there are advantages in that the production yield increases dramatically and the quality becomes uniform.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a surface acoustic wave device to which the present invention is applied, FIG. 2 is a sectional view of the surface acoustic wave device, FIG. 3 is a perspective view of a circuit component incorporating the surface acoustic wave device, and FIG. FIG. 5, which is an enlarged view of a comb-shaped electrode, is a cross-sectional view of a main part of a conventional surface acoustic wave element. 1...Piezoelectric substrate 2a, 2b, 3a, 3b--...Comb-shaped electrode 4a
, 4b, 5a, 5b--Pad portions 6a, 6b, 7a
, 7b-External electrode 8...Metallic base 9...Wire 10...Surface acoustic wave element 11...Photoconductive thin film 14...Cap Figure 2 Figure 3 Figure 4 Figure 5

Claims (3)

[Claims] 1. A surface acoustic wave device characterized in that a surface of a piezoelectric substrate is coated with a photoconductive thin film, and a comb-shaped electrode is formed on the surface of the piezoelectric substrate. 2. 2. The surface acoustic wave device according to claim 1, wherein said photoconductive thin film is amorphous silicon or polycrystalline silicon. 3. After the surface of the piezoelectric substrate is covered with a photoconductive thin film and a comb-shaped electrode is formed on the photoconductive thin film, the wires are connected and the cap is welded and sealed while irradiating the photoconductive thin film with light. A method for manufacturing a surface acoustic wave device, characterized in that: