JPS643041B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a voltage nonlinear resistor, which comprises a sintered body containing zinc oxide as a main component and metallic zinc as a starting material, and containing at least magnesium oxide and bismuth oxide as additives. In recent years, with the rapid development of semiconductor elements and circuits such as ICs, transistors, and thyristors, and their applications, the use of semiconductor elements and circuits in measurement, control, communication equipment, and power equipment has become widespread, and the miniaturization of these equipment, High performance is progressing rapidly. However, with such progress, the withstand voltage, surge and noise resistance of these devices and their parts cannot be said to be sufficient.
For this reason, protecting these devices and components from abnormal surges and noise, or stabilizing circuit voltages, has become an extremely important issue. To address these issues, we have developed a new battery that has extremely high voltage nonlinearity, high discharge capacity, and excellent life characteristics.
Moreover, there is a growing demand for the development of inexpensive voltage nonlinear resistors. Conventionally, voltage nonlinear resistors such as SiC varistors and Si varistors, Zener diodes, and the like have been used for these purposes. Recently, varistors have been developed that contain zinc oxide as a main component and add additives to it. The current-voltage characteristics of a varistor are generally expressed by the following relationship: I=(V/C). Here, V is the voltage applied to the varistor and I is the current flowing through the varistor. Further, C is a constant corresponding to the voltage when a given current is passed. α=1 is an ordinary resistor that follows Ohm's law, and it can be said that the larger α is, the better the nonlinearity is. Here, instead of expressing the varistor characteristics by C and α, it is expressed by the rising voltage VlmA at lmA and α. Conventionally used SiC varistors are made by baking SiC particles with a magnetic binder, and their nonlinearity is due to the voltage dependence of the contact resistance between the SiC particles. Therefore, the C value can be controlled by changing the thickness in the direction of the current flowing through the varistor. However, the nonlinear coefficient α is relatively small, ranging from 3 to 7. Moreover, it is necessary to sinter in a non-oxidizing atmosphere. on the other hand
Since the nonlinearity of the Si varistor is caused by the P-n junction of Si, it is impossible to control the C value over a wide range. Zener diodes similarly use a P-n junction of Si, so they have extremely high voltage nonlinearity, but they also have the disadvantage of being difficult to make a high-voltage element, and having a low discharge withstand capacity and being susceptible to surges. . In addition, bismuth oxide is used as a ceramic varistor whose main component is zinc oxide.
Those containing cobalt oxide, manganese oxide, antimony oxide, etc. have recently been developed. This has the advantage that its nonlinearity is very large. However, these have a high varistor voltage VlmA per mm of sintered body of around 200V, making it difficult to use them for the purpose of protecting semiconductors and semiconductor circuits with low withstand voltage. Therefore, in order to protect semiconductors and semiconductor circuits with low withstand voltage from abnormal surges and noise, the varistor voltage per 1 mm of sintered body thickness is increased.
It was necessary to develop a varistor with a VlmA of 20 to 30V. For this reason, methods for manufacturing varistors having a high nonlinear coefficient α over a wide voltage range are disclosed in, for example, Japanese Patent Application Laid-open Nos. 151304-1982, 153301-1982, 158603-1983, −158604
Publication No. 158605, Japanese Patent Publication No. 158605, Japanese Patent Publication No. 158605-
Publication No. 158606, Japanese Patent Publication No. 56-37604, Japanese Patent Publication No.
Methods characterized by containing zinc oxide as a main component and metallic zinc as a starting material have also been proposed, as in JP-A No. 56-37605, JP-A-56-38802, and JP-A-56-38803. However, there was a need to improve the current-voltage characteristics and moisture resistance life characteristics in the low current region below VlmA. If the current-voltage characteristics in the low current region are poor, leakage current will be large and wasteful power loss will occur. If the humidity resistance life characteristics are poor, the current-voltage characteristics in the low current region will deteriorate when used for a long time in a high humidity atmosphere. This increases leakage current and causes wasteful power loss. If the process progressed further, the current flowing into the varistor would increase, creating the risk of destroying the varistor itself. In order to eliminate the above-mentioned drawbacks, the present invention provides a sintered body containing zinc oxide as a main component and metallic zinc as a starting material, by adding at least magnesium oxide and bismuth oxide as additives to the sintered body. Varistor voltage per 1mm thickness
It is an object of the present invention to provide a method for manufacturing a voltage nonlinear resistor that has a low VlmA of 20 to 30V, a high nonlinear coefficient α, excellent current-voltage characteristics in a low current region, and excellent moisture resistance and life characteristics. . The details of the present invention will be explained below based on examples. First, the present invention has zinc oxide as a main component, contains 0.01 to 20 mol% of metallic zinc as a starting material, and contains 0.01 to 5 mol% of each of magnesium oxide and bismuth oxide as additives, which are essential components. and, if necessary, other additives such as NiO, BaO, CaO, CuO, MnO, SrO,
PbO, CdO, TiO ₂ , SnO ₂ , MnO ₂ , SiO ₂ ,
ZrO ₂ , GeO ₂ , ThO ₂ , Sb ₂ O ₃ , Cr ₂ O ₃ , Co ₂ O ₃ ,
Fe ₂ O ₃ , Al ₂ O ₃ , B ₂ O ₃ , Sc ₂ O ₃ , In ₂ O ₃ , La ₂ O ₃ ,
Y ₂ O ₃ , Ga ₂ O ₃ , Li ₂ O, MoO ₃ , WO ₃ , MeF ₂ (Me
=Ca, Ba, Cd, Zn, Mg, Mn, Ni, Sn, Zr,
Ti, Ge), Me′F ₃ (Me′=Cr, Al, Fe, Ce, Y)
One or more kinds of metal oxides other than magnesium oxide and bismuth oxide are added, these are thoroughly mixed, formed into a plate shape or column shape, and sintered at a high temperature of 800 to 1500°C to form a sintered body. A pair of electrodes is attached to the sintered body, and a terminal is attached to the electrodes. The exterior is then formed of synthetic resin or the like. Next, Table 1 shows an example of comparison of characteristics between the embodiment of the present invention and a conventional reference example. Examples 1 to 9 and Reference Examples 10 to 16 were weighed according to their respective composition ratios, mixed, formed into a disk shape, and sintered at a high temperature of 1250°C on both sides of a sintered body of 15 mm in diameter x 1 mm in thickness. diameter
The characteristics were measured using a 11.3mm silver electrode.
It shows a comparison between the varistor voltage V1mA per 1mm of sintered body thickness and the nonlinear coefficient α at that time.

【table】

[Table] From Table 1, metallic zinc is used as a starting material in the composition.
In the case of Examples 1 to 9 containing 0.01 to 20 mol%, the nonlinear coefficient α = 19 to 21 and VlmA / mm = 20 to 26,
In the case of Reference Examples 10, 11, 12, and 15 that do not contain metallic zinc or contain less than 0.01 mol%, the nonlinear coefficient α = 10 ~
13 and the metal zinc content exceeds 20 mol%
In the case of 13, 14, and 16, VlmA/mm = 30 to 32, which is high. In addition, in the case of Examples 1 to 9 where magnesium oxide and/or bismuth oxide is 0.01 to 5 mol%,
Reference examples 10, 11, and 12 have large nonlinear coefficients and low VlmA/mm, but do not contain magnesium oxide and/or bismuth oxide, or are less than 0.01 mol%, and have small nonlinear coefficients, conversely exceeding 5 mol%. In the case of Reference Examples 13, 14, and 16, VlmA/mm is high.
Next, Example 1, Example 2, Example 6 in Table 1,
FIG. 1 shows the current-voltage characteristics in the low current region of each sample of Example 7, Example 9, Reference Example 10, and Reference Example 12. It can be seen from FIG. 1 that the current-voltage characteristics in the low current region of the example are significantly improved compared to the reference example. FIG. 2 also shows Example 1, Example 2, Example 6, Example 7, Example 9, and Reference Example.
10. Each sample of Reference Example 12 was heated at a temperature of 40℃ and a relative humidity of 95%.
This shows the current-voltage characteristics in the low current region, that is, the rate of change in varistor voltage in the low current region, when the device was left in an atmosphere of 1,000 hours. It can be seen from FIG. 2 that the moisture resistance life characteristics of the example are significantly improved compared to the reference example. As detailed above, according to the present invention, the main component is zinc oxide, 0.01 to 20 mol % of metallic zinc is included as a starting material, and at least 0.01 to 5 mol % of magnesium oxide and bismuth oxide are each added as additives.
By containing mol%, the varistor voltage VlmA per 1 mm thickness of the sintered body is as low as 20 to 30 V, and it has a high nonlinear coefficient α, and has excellent current-voltage characteristics in the low current region and excellent moisture resistance and life characteristics. A method for manufacturing a voltage nonlinear resistor can be provided.

[Brief explanation of drawings]

FIG. 1 is a curve diagram showing a comparison of current-voltage characteristics in a low current region between an embodiment of the present invention and a conventional reference example;
FIG. 2 is a curve diagram of moisture resistance life characteristics showing the rate of change of varistor voltage in a low current region.

Claims (1)

[Scope of Claims] 1. It is characterized by containing zinc oxide as a main component, containing 0.01 to 20 mol% of metallic zinc as a starting material, and containing at least 0.01 to 5 mol% of each of magnesium oxide and bismuth oxide as additives. A method for manufacturing a voltage nonlinear resistor. 2. The method for manufacturing a voltage nonlinear resistor according to claim 1, which contains one or more metal oxides other than magnesium oxide and bismuth oxide as additives.