JPS62216302A - Manufacture of thin film varistor - 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 Field of Industrial Application The present invention relates to a method of manufacturing a thin film varistor that is suitable for downsizing and weight reduction of equipment and is effective at low voltage, and further relates to a method of manufacturing a microscopic chip-shaped thin film varistor.

An element whose electrical resistance rapidly decreases as the applied voltage increases is generally called a varistor.

In the past, SiC was well known as a varistor, but in recent years, ZnO-based materials have come into widespread use.

ZnO-based varistors contain a small amount of B 1p 3 in ZnO powder.
+ Co 205 + MnO2, 5b203, etc. are added, and after molding, it is heated and sintered.

The rising stain pressure of a varistor varies depending on its thickness, and by making it thinner, the voltage can be lowered.

In recent years, electronic components have become smaller and more dense, and various consumer electronic devices have been developed. These require thin varistors that operate at low voltages.

Furthermore, if a varistor is to be used to control an extremely small element, a large number of thin and minute varistors are required.

Since there is a limit to how thin a film can be made using the conventional powder molding method, a method has been proposed in which a thin varistor film is manufactured by subsequent sintering or rolling (Japanese Unexamined Patent Publications No. 58-86702, No. 58-58).
86704, 58-101403, etc.).

To make a thin film varistor by sputtering, a thin film varistor is made by sputtering on a substrate such as At203.
A varistor thin film is provided on the t thin film, and an At thin film is further applied thereon by vacuum evaporation or the like.

pt and At serve as electrodes (Japanese Patent Laid-Open No. 58-86704).

When making a ZnO-based thin film varistor by sputtering, it is necessary to bake the thin film at a temperature higher than the crystallization temperature of ZnO, for example, about 1200°C, and cracks may occur, and the varistor material is still and the board,
The varistor may react with the electrode, resulting in poor V-I characteristics of the varistor.

Therefore, a method has been proposed in which the varistor film is separated from the substrate etc. and only the film is fired (Japanese Patent Laid-Open No. 58-101403
). In this method, a BaO layer is provided on a substrate such as quartz, a varistor film is formed on this layer, the BaO is dissolved in water, the film and the substrate are separated, and the film is fired.

In addition, instead of sputtering, there is a method of kneading raw material powder to form a green sheet using a doctor blade method or the like, and then sintering the green sheet (% 1982-82404).

Problems to be Solved by the Invention In the present invention, the varistor film is fired separately from the substrate etc. in order to improve its characteristics. However, JP-A-58-101403
In this method, the thin film is thin and the area is large, so there is a high possibility that the thin film will be damaged during handling, such as by dissolving the alkaline earth oxide of the underlying layer. The membrane may be damaged when cutting. Furthermore, it is extremely difficult with current ceramic technology to produce a thin film several micrometers thick by the method of forming green sheets and sintering them.

An object of the present invention is to provide a method by which a varistor film can be easily separated from a substrate, and also to provide a method by which microscopic chip-shaped thin film varistors can be easily obtained.

For this reason, in the present invention, a resin that is stable at the sputtering temperature is used as the substrate, and after the sputtered film is formed, separation from the substrate is performed by dissolving the substrate in an organic solvent.

In this case, in order to obtain a minute chip-shaped varistor film, the film may be mechanically cut into small pieces while attached to the substrate, and then the substrate may be dissolved and removed using an organic solvent.

The resin used for the substrate needs to be stable at the Sumi 4 Tsuttering temperature. Sputtering temperature is usually 5
Since the temperature is 0 to 150°C, resins that can withstand this temperature and dissolve in organic solvents include polyethylene terephthalate,
General-purpose engineering glass materials such as nylon, polyacetal, polycarbonate, modified polyphenylene oxide, and polybutylene terephthalate; and special thermoplastic materials such as polysulfone, polyether sulfone, polyphenylene sulfide, polyarylate, polyamideimide, polyetherimide, and polyetheretherketone. Materials such as engineering plastics that have good heat resistance and are soluble in solvents are used. That is, a target is made of a sintered body of the material that forms the sputtered film, and ionized argon gas is bombarded against this target in a reduced pressure tank to evaporate the target material. This is a method in which a film is deposited on a substrate.

The thickness of the film can be freely changed depending on the sputtering conditions, such as time, but in the present invention, it is as thin as possible within a manageable range, for example, 0.5 μm to 10 μm.
m is preferred. At this time, it is preferable that the snoot or tsutaring device used be of the RF magnetron type.

What are the ingredients for Su/mother Tsutaring? It is possible to form a film by tuttering and has varistor properties. Usually, the composition described above is used, which is mainly composed of ZnO and added with B12O3, etc., but the composition is not limited to this, and other compositions are also possible.

After forming a varistor film on a substrate, it is immersed in an organic solvent to dissolve the substrate. Suitable solvents are N-methyl 2-pyrrolidone m-cresol when the substrate is polyethersulfonimide, and dichloroethane when the substrate is polyethylene terephthalate. A suitable solvent may be used for other resins as well.

The varistor film separated from the substrate is fired in air or the like at a temperature higher than the crystallization temperature of its components to form a product (thin film varistor). In the case of ZnO type, the temperature is about 800°C to 1200°C. When using it, make it the required size and attach electrodes on both sides. However, with this method, the thin film is extremely fragile, making it difficult to obtain microchips.

Therefore, the second aspect of the present invention is to cut the varistor film onto the substrate into small pieces using, for example, a dicing machine used for cutting silicon wafers.

In this case, in order to facilitate subsequent handling, the substrate is not cut, but the film on the substrate is cut, for example, vertically and horizontally. If you put this in an organic solvent and dissolve the substrate, the minute 1 of the varistor film will be removed.
You will get horns. Using this method, it is possible to use a square chip with a side length of approximately 5IJ4n.

Although there is no upper limit to the size, the second aspect of the present invention is particularly effective for making small items, for example, 5 to 500 μm.

After the substrate is removed, the varistor film is fired under the same conditions as described above.

If the varistor film is fired with the substrate attached, the varistor film will be thin and brittle, and problems such as the film breaking due to shrinkage of the resin during the firing process will occur.

Once fired, the microscopic chip-shaped varistor is ready for use with electrodes attached.

Example 1 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the cross-sectional structure of a varistor element according to the present invention, which was produced by the following method.

First, a TPI (polyether sulfonimide) base film (1) with a thickness of about 50 μm is appropriately degreased, washed, and etched in a conventional manner, loaded into a vacuum chamber, and subjected to a high-frequency magnetron snoring method. ZnO(2)/Bi203(3)/Zn on the substrate
An O(4)03 layer film was formed. In this case, the thickness of the thin film is the most preferable thickness 1, OIim,
0.3 μm.

It was set to 1.0 μm. The sputtering conditions will be explained below.

[S/mother tuttering conditions]

(1) Sputtering Turdut Material The sputtering Turdut material was sintered by hot pressing and had a purity of 4N or higher.

still? The metal bending method was used for cooling efficiency.

(2) Suze ivy output, su suguta gas type 1,
ZnO film: Considering damage to the target, thermal shock to the base resin, film formation efficiency, etc., the output is 150 W.
(1,85W/cm2), Ar pressure is 8, OX
10"" (Torr).

At this time, by using a mixed gas of Ar and 02, Zn
The composition of the O film can be controlled.

2. Bt203 film: The output was set to 150 W for the same reason as in the previous section. In addition, when evaporating the B12o3 sintered body, O2 was used as the gas to supplement O2.

The pressure of 0□ is 8. OX 10""' [Torr].

(3) Substrate temperature and cooling method In order to prevent thermal deformation of the substrate resin film, sufficient attention was paid to cooling and the substrate temperature was kept below 150°C.

Cooling was performed by bringing the back surface of the substrate film into contact with a cooling plate. In this case, it is preferable that the thickness of the film be as thin as possible within a range that can withstand the thermal shock of the film. (TPI of this example: 50 μm) For the same reason, the cooling efficiency was improved by exposing the substrate intermittently to the target.

(4) Regarding membrane purity, in order to avoid contamination of impurities into the membrane, at least 3.0 O
Evacuation was performed until the pressure reached X 10-6 [Torr] or less. Pre-sputtering was performed for at least 30 minutes to remove any impurities still attached to the surface of the TARDAT. Further, in FIG. 1, in order to increase the purity of the interface between each layer, the snowcutter of ZnO+B12O3 was performed in the same chamber.

[How to make a barista chip]

Next, the laminated film of FIG. 1 obtained by sputtering was cut into chips of 50 μm square using a Guising tool. At this time, the sputtered film is completely cut, but the substrate film has a
A groove machining method was used in which cuts (11) of about IJ/rrL were made. (Fig. 2) The substrate is fixed by taping, and the dicing blade has an outer diameter of 50 m and an inner diameter of 4 m. Otan.

A piece with a thickness of 15 pieces was used.

The thus obtained TPI film substrate was coated with N-methyl-2
- By immersing it in pyrrolidone and dissolving only the TPI film! 1150 edition Chizzo's ZnO/B12O3
/ ZnO varistor membrane can be separated and recovered.

[Sintering]

The varistor chip obtained by the above method was placed in the atmosphere for 8
B12O by heat treatment at 00°C for 1 hr.
The three films were crystallized and a barrier was formed at the interface with the ZnO film, resulting in a highly stable varistor.

Example 2 In order to evaluate the voltage/current characteristics (VI characteristics) of the varistor thin film according to the present invention, a sample as shown in FIG. 3 was prepared. An Au electrode (62) was created by vapor deposition on the TPI film (5),
On top of that Z no (7) / B ] 203 (8)
/ A three-layer film of ZnO(9) is formed by sputtering. Moreover, Au (10) is further deposited thereon as a counter electrode by vapor deposition. Thickness is Au 2000
i, ZnO1,Ol1m.

B12 o 303 μm, and the snow f stumbling conditions were the same as in Example 1. It has been found that a high performance and stable varistor film can be obtained by the above method.

Varistor films with these characteristics can greatly contribute to the miniaturization of equipment by incorporating them into, for example, low-voltage drive circuits.

Effects of the Invention According to the present invention, only a thin film varistor can be manufactured easily by separating it from a substrate, and it can be used in a wide range of applications. Further, the fine varistor thin film obtained by the present invention is effective in controlling extremely small elements.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a thin film varistor attached to a substrate.
FIG. 2 is a perspective view of the device shown in FIG. 1 with cuts made, and FIG. 3 is a cross-sectional view of a thin film varistor assembled with electrodes attached to it for measuring electrical characteristics. 1, 5-TPI board, 2, 4, 7, 9...Z
n0.3゜8''' Bt203.6, 10-Au electrode, 11-...cut.

Claims (3)

[Claims] (1) forming a varistor thin film by sputtering on a resin substrate that is stable at the sputtering temperature, dissolving the substrate in an organic solvent and separating the varistor thin film from the substrate;
A method for manufacturing a thin film varistor, which comprises firing the thin film varistor. (2) The resin substrate is made of polyethylene terephthalate, polycarbonate, polyacetal, polybutylene terephthalate, polysulfone, polyether sulfone, nylon, polyphenylene sulfide, polyarylate, polyetherimide, polyether sulfonimide, modified polyphenylene oxide, polyamideimide, polyether ether A method for producing a thin film varistor according to claim 1, wherein the thin film varistor is made of a heat-resistant engineering plastic such as ketone. (3) Form a varistor thin film by sputtering on a resin substrate that is stable at the sputtering temperature, cut the thin film into microchips while still attached to the substrate, and separate the varistor thin film from the substrate by dissolving the substrate in an organic solvent. A method for producing a minute thin-film varistor, which is characterized by firing the varistor.