JPH04150510A - Surface acoustic wave element and its manufacture - Google Patents

Abstract

PURPOSE:To prevent discharge breakdown in the course of a manufacturing work process by covering the surface of a comb line electrode with a photoconductive thin film. CONSTITUTION:Since the comb line electrodes 2a, 2b and 3a, 3b on a piezoelectric base board 1 are covered with the photoconductive thin film 11, each comb line electrode 2a and 2b and the electrode 3a and 3b are made conductive as long as they are irradiated with light. Therefore, even in the case of the occurrence of mechanical friction or temperature change to encounter during the working process such as the connection of wire or the welding and sealing of a cap, etc., static electricity is never accumulated on the piezoelectric base board 1. Accordingly, a surface acoustic wave element can be prevented from being discharge-broken by discharge between the electrodes. Further, even if conductive dust and the like is stuck by mistake, the electrodes are never shortcircuited because of being shielded by the photoconductive thin film.

Description

[Detailed description of the invention] [Industrial application field]

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.

[Conventional technology]

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. 4 shows an external view of a conventional surface acoustic wave device main body. As shown in this figure, the surface acoustic wave element 10 is
On a piezoelectric substrate 1, comb-shaped electrodes 2a and 2b and comb-shaped electrodes 3a and 3b are 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 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. FIG. 5 is an enlarged front view of the comb-shaped electrodes 2a and 2b and the pad portions 4a and 4b.
A and 5b also have similar shapes. FIG. 6 shows a cross-sectional view of the comb-shaped electrodes 28 and 2b. The cross sections of the comb-shaped electrodes 3a and 3b also have similar shapes. Comb-shaped electrode 2a
Each pitch of the comb-shaped electrode 2b 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 2a and 2b and the comb-shaped electrodes 3a and 3b are usually aluminum metal thin films with a thickness of 1000 mm.
The electrode pitch is about 1μIl to IOB, with a depth of about 50 circles. In this surface acoustic wave element IO, when a high frequency signal is applied manually 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 is transmitted as a surface wave on the surface of the piezoelectric substrate l and reaches the other pair of comb-shaped electrodes 3a and 3b. This mechanical strain generates an electromotive force in the horizontal 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 3a
Signals with input frequencies that do not match the pitches of and 3b are canceled by each other at 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 perform surface acoustic wave It is necessary to cover the element 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 was extremely narrow, discharge occurred between the electrodes, and one surface acoustic wave element was sometimes destroyed by discharge.

[Problem to be solved by the invention]

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 is not destroyed by discharge during the manufacturing process and a method for manufacturing the same.

[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 has five piezoelectric substrates 1 with comb-shaped electrodes 2a and 2b, 3a and 3 as shown in FIGS.
The surfaces of the comb-shaped electrodes 2a and 2b and 3a and 3b are covered with a photoconductive thin film 11. Similarly, the surface acoustic wave device to which the present invention is applied has the surfaces of comb-shaped electrodes 28 and 2b and 3a and 3b formed on the piezoelectric substrate l, as shown in Section 1 and FIG. is coated with a photoconductive thin film 11, and the photoconductive thin film 11
Connect the wire 9 and connect the cap 14 while applying light to the
Weld and seal (see Figure 3).

[Effect]

The surface acoustic wave device of the present invention has a comb-shaped electrode 2 on a piezoelectric substrate l.
Since a and 2b and 3a and 3b are covered with a photoconductive thin film 11, each comb-shaped electrode 2a and 2b is covered with light if irradiated with light.
And 3a and 3b are electrically connected. Therefore, static electricity will not accumulate on the piezoelectric substrate l even if there is mechanical friction or temperature changes encountered during the work steps such as connecting the wire 9 and welding and sealing the cap 14. Therefore, it is possible to prevent the surface acoustic wave element from being destroyed by discharge due to discharge between the electrodes. Furthermore, even if conductive dust or the like passes through the electrode, it is blocked by the photoconductive thin film, so the electrodes will not be short-circuited.

[Example 1] Hereinafter, an example of the present invention will be explained in detail by section. As shown in FIG. 1, the surface acoustic wave element 1O has comb-shaped electrodes 12a and 2b and 3a and 3b formed on a piezoelectric substrate 1. 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 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. The enlarged shapes of the horizontal electrodes 28 and 2b, the pad portions 4a and 4b, the comb-shaped electrodes 3a and 3b, and the pad portions 5a and 5b are shown in FIG. As shown in FIG. 2, the surfaces of the comb-shaped electrodes 2a and 2b are coated with amorphous silicon, which is a photoconductive thin film 11. The surfaces of the comb-shaped electrodes 3a and 3b are similarly coated with amorphous silicon. The comb-shaped electrodes 2a and 2b and 3a and 3b are created by the Sogelaf pattern forming method as described below. First, approximately 3,000 aluminum thin films are formed on a piezoelectric substrate 1 by vacuum evaporation or sputtering. A photoresist is uniformly coated on this to a thickness of about 1 μm. If the photoresist is then irradiated with ultraviolet light through a photomask having a comb-shaped electrode pattern and then developed, the light-irradiated portion leaving the comb-shaped electrode pattern is removed and the surface of the aluminum thin film is exposed. Ru. When this is immersed in a mixed solution of phosphoric acid/acetic acid/nitric acid to dissolve the exposed portion of the aluminum thin film, the portion covered by the photoresist remains. After washing this with water and removing the photoresist, patterns of comb-shaped electrodes 2a and 2b and 3a and 3b made of aluminum thin films are formed. The process of covering the surfaces of comb-shaped electrodes 2a and 2b and 3a and 3b with amorphous silicon 11 is as follows. Portions other than the comb-shaped electrodes 2a and 2b and 3a and 3b on the piezoelectric substrate l on which the comb-shaped electrode pattern is formed as described above are coated with photoresist by the same pattern forming method. Then, 200 to 100% amorphous silicon is deposited on the piezoelectric substrate 1 by plasma CVD (chemical vapor deposition) or photoCVD while keeping the temperature of the piezoelectric substrate 1 below 200°C.
When the zero-order photoresist formed to a thickness of 000 is removed, the amorphous silicon other than the electrode portions is also removed. Finally, the electrodes of pad portions 4a and 4b and pad portions 5a and 5b are formed as follows. Portions other than pad portions 4a and 4b and pad portions 5a and 5b on the substrate 1 on which the comb-shaped electrode pattern and amorphous silicon are formed as described above are coated with photoresist by the same pattern forming method. Approximately 5,000 aluminum thin films are formed on this by vacuum evaporation or sputtering. Thereafter, by removing the photoresist, the electrodes of pad portions 4a and 4b and pad portions 5a and 5b can be formed. The surface acoustic wave device 10 produced as described above is further completed as a circuit component through the following steps. Note that the following steps are performed while irradiating light, that is, with the amorphous silicon, which is a photoconductive thin film, conducting. As shown in FIG. 3, the surface acoustic wave element 10 is attached to a metal base 8. The surface acoustic wave device 10 shown in this figure is an example in which the comb-shaped electrodes 2a and 2b are covered with a photoconductive thin film 12, and the comb-shaped electrodes 3a and 3b are covered with a photoconductive thin film 1113, respectively. A wire 9 is connected to the pad portion 4a of the comb-shaped electrode 2a, and the wire 9 is further connected to an external connection terminal 6a. 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 comb-shaped 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 7o.
are connected to each other by wires. After these wire bondings are completed, a transparent glass cap 14 is placed over the metal base 8, and the periphery thereof 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 high conductivity of 10-'-10-'/Ω-cm when irradiated with light and 10-''-10-1'/Ω-cm of dark conductivity. Therefore, in the process of irradiating light, the static electricity accumulated in the comb-shaped electrode is abundantly discharged through the photoconductive thin film.On the other hand, the circuit components of the completed surface acoustic wave device are shielded from light. Therefore, the photoconductive thin film has a sufficiently high resistance as mentioned above, and the input impedance as a surface acoustic wave element is maintained.Furthermore, even if conductive dust accidentally gets into the cap, the photoconductive thin film Since the comb-shaped electrodes 2a and 2
b and the comb-shaped electrodes 3a and 3b will not be short-circuited. 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. Effects of the Invention As described 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,
It is possible to prevent discharge damage during the manufacturing process, and furthermore, there is no short-circuiting of the electrodes due to dust, etc., which has the advantage of dramatically increasing the manufacturing yield and making the quality 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 cross-sectional view of its main parts, Fig. 3 is a perspective view of a circuit component incorporating the surface acoustic wave device, and Fig. 4 is a conventional FIG. 5 is an enlarged view of a comb-shaped electrode, and FIG. 6 is a sectional view of a main part of a conventional surface acoustic wave device. l...Piezoelectric substrates 2a, 2b, 3a, 3b -...Comb-shaped electrodes 4a, 4b
, 5a, 5b-i-pad portion 6a, 5b, 7a
, Tb-external electrode 8...metallic base 9...wire 10...surface acoustic wave element 11, 12. 13-... Photoconductive thin film 14... Cap Figure 3

Claims (3)

[Claims] 1. 1. A surface acoustic wave device comprising comb-shaped electrodes formed on a piezoelectric substrate, characterized in that the surface of the comb-shaped electrodes is covered with a photoconductive thin film. 2. 2. The surface acoustic wave device according to claim 1, wherein said photoconductive thin film is amorphous silicon or polycrystalline silicon. 3. A surface characterized by coating the surface of a comb-shaped electrode formed on a piezoelectric substrate with a photoconductive thin film, and connecting wires and welding and sealing a cap while irradiating the photoconductive thin film with light. A method for manufacturing an acoustic wave device.