JPH02296301A - Manufacture of voltage nonlinear resistance element - Google Patents

Abstract

PURPOSE:To make it excellent in mechanical strength and surge quantity resistance and to facilitate manufacturing process by grinding the face, on which an electrode of a sintered body formed by mixing and baking powder of an zinc oxide and a very small amount of additive powder to generate voltage nonlinearity, is provided, and then forming the electrode. CONSTITUTION:Proper amounts of Pr, Co, B, etc., in the form of compounds such as oxides, etc., are added to ZnO powder, and then those are mixed and granulated so as to make up granulated powder for ZnO varistor. Thus granulated powder is formed into a disc shape 1.25mm in thickness using a mold 17mm in diameter, and next this compact is baked for 4 hours at a temperature of 1350 deg.C in oxidizing atmosphere. The size of a sintered body being obtained is 14mm in diameter and 1.0mm in thickness. Both opposed main faces 1 of the sintered body being made this way are ground by 1-2mum for one face by ultrasonic grinding, and silver paste is applied on this sintered body, and then this is baked so as to constitute a varistor. Hereby, it becomes excellent in mechanical strength and surge quantity resistance, and process management in manufacturing becomes easy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage nonlinear resistance element for low voltage circuits containing zinc oxide as a main component, and particularly to the formation of metal electrodes on a zinc oxide sintered body.

[Conventional technology]

Ceramics, which are made by mixing ZnO with a small amount of additives and sintering it as a main component, are known to exhibit excellent voltage nonlinearity, and are useful for suppressing abnormal voltages (surges) in electrical circuits. It is widely used as a varistor for control purposes. Such a varistor is manufactured according to the steps shown in FIG.

The voltage nonlinearity of the ZnD varistor is due to double Schottky barriers formed at the grain boundaries of Zn[] grains. In a practical varistor, the varistor voltage per grain boundary layer formed by the combination of ZnO crystal grains is almost constant regardless of the crystal grain size, and its value is 2
It is about V. (Varistor voltage is the voltage between the terminals when a current of 1 m is passed through the varistor, and is usually expressed as VImA.) Therefore, the varistor voltage of the voltage nonlinear resistance element is It is determined by the number of grain boundary layers that exist between the electrodes provided in the .

[Problem to be solved by the invention]

By the way, silver and aluminum are used for the electrodes of ZnO balisks, but except for Zn[] elements for lightning arresters, it is common to bake silver paste and use this as the electrode.

In this case, a Schottky barrier is formed at the interface between the silver electrode and the ZnO sintered body, and when a current of 1 m is passed, the electrode/ZnO
A voltage of approximately 3V is generated due to the Schottky barrier at the interface of the sintered body. Therefore, this electrode/ZnO sintered body interface barrier becomes impossible to ignore as the varistor voltage becomes lower.

For example, when applying a Zn(] varistor to a DC12V circuit, a varistor voltage of 22V is generally used in consideration of circuit voltage fluctuations, but as mentioned above, the varistor voltage per grain boundary layer is approximately 2V. Therefore, 11 layers of grain boundaries exist between the opposing electrodes of this element.However, due to the electrode/ZnD sintered body interface barrier mentioned above,
t'+I] Varistor voltage and electrode of grain boundaries of sintered body/
The total varistor voltage at the sintered body interface must be 22V. In practice, as the varistor voltage decreases, the difference between the varistor voltage determined from the number of sintered bodies and the actually measured varistor voltage increases, so the number of grain boundaries in the sintered body must be reduced. For this reason, unless the thickness of the sintered body is reduced, (1) the mechanical strength of the sintered body will decrease (2) the ability to absorb surge energy (surge resistance) such as lightning surges and switching surges will depend on the volume of the sintered body. Since it is proportional to

In addition, the Schottky barrier at the electrode/sintered body interface is
The Njotsky barrier existing at the grain boundaries of the sintered body itself has a low relative Vesage resistance, so the lower the varistor voltage is, the greater the change in varistor voltage due to surges becomes. There is a problem in that the varistor voltage is easily fluctuated during the assembly process, such as the soldering process and the resin molding process, making process control of the varistor voltage difficult.

This invention was made in view of the above points, and its purpose is to eliminate the Schottky barrier between the sintered body and the metal electrode, thereby providing a low-voltage voltage with excellent mechanical strength and surge resistance, and easy process control. An object of the present invention is to provide a non-linear resistance element.

[Means to solve the problem]

According to the present invention, the above-mentioned purpose is to grind the surface of a sintered body prepared by mixing zinc oxide powder and a small amount of additive powder that causes voltage nonlinearity, and then to form an electrode. shall be taken as a thing.

[Effect]

By ultrasonic grinding or blast processing the surface on which the electrodes are to be provided, a surface defect layer is formed in the surface layer between the nuclei due to destruction, thereby creating a low resistance region.

The low resistance layer eliminates the Schottky barrier that would otherwise be formed at the sintered body/electrode interface.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

FIG. 2 shows the manufacturing process of a resistance element according to an embodiment of the present invention. First, an appropriate amount of Pr', 'Co-B, etc. is added to ZnO powder in the form of compounds such as oxides, and then mixed.
Granulated powder for ZnO barisque is produced.

This granulated powder was molded into a mold with a diameter of 17 mm to a thickness of 1.2 mm.
Form into a disk shape with 5 layers and a thickness of 5 mm. Next, this molded body is fired at a temperature of 1350° C. for 4 hours in an oxidizing atmosphere.

The size of the obtained sintered body was 14 mm in diameter and 10 mm in thickness.
Met.

Both opposing principal surfaces of the sintered body produced as described above were ground by 1 to 2 μm on one side by ultrasonic grinding.

The surface resistance of the ultrasonically ground defect layer was less than 1Ω when a current of 1 mA was applied. The untreated one was less than 20Ω.

A varistor was constructed by applying silver paste to the sintered body treated as described above and then baking it. A schematic cross-sectional view is shown in FIG. 3
is a sintered body, 2C and 2B are defect layers formed by grinding, and 1Δ and IB are metal electrodes. Subsequently, the varistor characteristics were measured.

We also evaluated the varistor characteristics after assembly. The results are shown in Table 1.

/ Table 1 and Table 2 show the surge resistance (A) after assembly when a surge is applied. However, the surge resistance is 8/20
The current was defined as the current at which the rate of change in VlmA after passing a μs standard current pulse through the device twice at 2-minute intervals was ±10%.

Table 2 Table 1 shows vl. The variation coefficient of A + VlmA, the voltage nonlinear coefficient α in the current 100 μΔ ~ 1 mA region,
A comparison with the conventional method is shown after one assembly after electrode attachment.

Furthermore, as reference data, characteristics when using a ZnD sintered body and a 1n-Ga electrode that does not form a Schottky barrier are also shown. From these results, it can be seen that the method of the present invention has no characteristic variation after electrode attachment and after assembly, and is superior to the conventional method.

As is clear from Table 2, the method of the present invention is superior. The reason for this is thought to be as follows. That is, the surge withstand capacity of the sintered body itself is 1200OA, but in the conventional element, the barrier formed at the electrode/sintered body interface is less likely to change due to a surge, which is 5V 1mA, but 2.
This is because in the case of a 0V element, a 2V change in the electrode/sintered body interface barrier results in a 10% change. In this way, the lower the varistor voltage, the lower the ZnO produced by the conventional method.
This eliminates the drawback that the surge resistance of the varistor element is apparently low.

In addition, although the above-mentioned example described the method of forming the low resistance layer by ultrasonic grinding, a similar effect was confirmed by blasting. Further, although the embodiments have been described with respect to a disk-shaped sintered body, the effects of the present invention are not dependent on the shape, and can be confirmed not only when the electrodes are opposed to each other but also when two electrodes are provided on the same plane.

〔Effect of the invention〕

According to this invention, the sintered body is produced by mixing zinc oxide powder and a small amount of additive powder that causes voltage nonlinearity and firing the surface of the sintered body on which the electrode is to be provided by ultrasonic grinding or blasting. / A low resistance layer can be introduced between the electrodes, which eliminates the Schottky barrier between the sintered body and the electrodes, resulting in voltage non-linearity with excellent mechanical strength and surge resistance, and easy manufacturing process control. A resistive element is obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing a voltage nonlinear resistance element according to an embodiment of the present invention, FIG. 2 is a flowchart showing the manufacturing process of a resistance element according to an embodiment of this invention, and FIG. It is a flow chart showing a manufacturing process. 1Δ, IB Metal electrode, 2A, 2B Defect layer, Fig.

Claims (1)

[Claims] 1) Voltage nonlinearity, which is characterized by grinding the surface of a sintered body made by mixing zinc oxide powder and a small amount of additive powder that causes voltage nonlinearity, on which electrodes are to be provided, and then forming the electrodes. A method of manufacturing a resistive element.