JPH02135704A - Manufacture of varistor - Google Patents

Abstract

PURPOSE:To obtain a varistor excellent in a non-linear coefficient in a high current region by a method wherein a specific amount of an element selected from group III or its oxide is added to ZnO for heat treatment to make ZnO semiconductive followed by crushing for making material powder to be molded into a desired shape and baked so as to obtain a sintered body. CONSTITUTION:Not less than 0.01mol% and not exceeding 5mol% of an element selected from group III or its oxide is added to ZnO for heat treatment to make ZnO semiconductive and crushed. Next, an auxiliary component functioning as varistor is added to make raw material powder and this raw material powder is molded into a desired shape and sintered to obtain a sintered body. In this case, when an amount of addition is less than 0.01mol%, almost no semiconductive effect is obtained and in case 5mol% is exceeded, instead a varistor characteristic is worsened. As a result, when resistance value is lowered by heat treatment, especially by solid solution of an addition metal in ZnO to reduce resistance value, a non-linear coefficient can be so much enlarged. Thereby, the non-linear coefficient in a high current region can be sharply improved so as to obtain the varistor excellent in a surge absorption characteristic by lowering limit voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a varistor that functions as a voltage nonlinear resistor, and particularly to a method for manufacturing a varistor that has an excellent nonlinear coefficient in a high current aH range.

[Conventional technology]

Conventionally, a varistor has been known as a resistor element whose resistance value changes non-linearly depending on an applied voltage. Examples of such a varistor include a disk-shaped varistor, which is formed by forming electrodes on both sides of a varistor element made of semiconductor ceramics;
Alternatively, there is a laminated type varistor in which varistor layers and internal electrodes are alternately laminated and integrally sintered. This barista is
For example, it is used as a surge absorption element to prevent overvoltage from being applied to electronic circuits.

The voltage-current characteristics of such a varistor are expressed by the following equation.

1o/I+-(Vo/V+)'' where !., Il is the current flowing through the element, v.

(1) 1 is the applied voltage. Also, α in the above equation is a nonlinear coefficient (hereinafter simply referred to as α), which indicates how the voltage is controlled when the varistor is incorporated into an electric circuit, and the larger the α value, the more Voltage nonlinear characteristics are excellent. This α is experimentally determined by the following equation.

= log (I o / + +) / i! og(
Vo /vl) From this equation, it can be seen that α depends on the area in which the current and voltage are measured. Generally, the voltage-current characteristics of ZnO-based varistors are approximately 10-'A/cIa"
The following first fil area, approximately 10A/(♂
It is divided into a second area up to and a third fil area beyond this area.

[Problem that the invention seeks to solve]

By the way, it is desirable that α is excellent in all of the first to third regions, but for example, a varistor manufactured by adding oxides such as Bi, Co, Mn, and Sb to ZnO is 1-10mA/cs+” in the second area
α in the third region is 50 or more, whereas α in the third region is 10 or more.
~100 A/cm", it is a very low value of 20 or less. If α in this high current region called the third ffl region is small, the limiting voltage will become high, and as a result, the protected circuit will be exposed to abnormally high voltages. There is a problem that the ability to protect against voltage is poor, and there is a need to improve α in this high current region.

An object of the present invention is to provide a varistor with excellent α in the high 1i flow region.

Means for Solving Problem c] The inventors of the present invention have conducted intensive studies to improve α in the high current region, and have found the solution described in the above 2. Focusing on the fact that α in the third region is determined by the resistance value of the ZnO particles themselves, they discovered that by changing the resistance value of ZnO, that is, if the resistance value could be reduced, α could be increased accordingly. It was completed.

Therefore, in the present invention, an element selected from group (1) or an oxide thereof is added to ZnO in an amount of 0.01 to 5 so j! % range and heat treatment to turn the ZnO into a semiconductor, and a second step of pulverizing this ZnO and adding thereto a subcomponent that functions as a varistor to create a raw material powder. The third step is to mold and sinter the raw material powder into a desired shape to obtain a sintered body.
A method of manufacturing a varistor is characterized by comprising the steps of:

Here, the elements selected from the above group (■) are A41, Y
, Ga, etc., and one or more types of these may be added.

In addition, the above addition amount should be increased to 0.01 moj% or more.
n! % or less is specified when the amount added is 0.01s+o
This is because if it is less than 1%, hardly any effect of semiconductor formation can be obtained, and if it exceeds 5 mo 1%, the varistor characteristics will deteriorate.

Furthermore, the varistor of the present invention is a single-plate varistor.

Alternatively, a laminated varistor formed by alternately stacking varistor layers and internal electrodes may be considered, but is not particularly limited.

[Effect]

According to the method for manufacturing a varistor according to the present invention, in the first step, a metal selected from group ① is added to ZnO, and this is heat-treated to obtain semiconducting ZnO. The additive metal dissolves in ZnO and lowers the resistance value of ZnO. Therefore, this semiconductor Z
By manufacturing a varistor using nO according to the second and third steps, it is possible to significantly improve the α bond in the high current region, reduce the limiting voltage, and obtain a varistor with excellent surge absorption characteristics.

〔Example〕

The present invention will be explained in detail below.

In this embodiment, a case where the present invention is applied to a disk type varistor will be explained.

First step■ First, An! selected from the periodic table of elements is added to ZnO powder. , Y, Ga, Gd and other metals 6 or their oxide powders at 0.01 mo 1% or more 5 ago 1%
Add and mix within the following range.

(2) Next, the above mixed powder is heat treated at 1300° C. for 1 hour. Then, the above-mentioned metal becomes a solid solution in ZnO and turns the ZnO powder into a semiconductor.

2nd Step (2) The semiconducting ZnO pre-sintered body is pulverized and made into powder again. Then, 0.5s+o of B180, which is a subcomponent that functions as a varistor, is added to this ZnO powder.
j%, MnO 0.5 aoj! %,C.

20, 0.5soj! %, Sb wealth 0! 0.7moj
% and then mixed, and further mixed with an organic binder to form a green sheet.

3rd step ■ Next, punch out the green sheet into a disk shape and
．． 0 φX1. A varistor element of Ot is formed, and this varistor element is heated and fired in air at 1100° C. for 2 hours to obtain a sintered body.

(2) Finally, Ag paste b is applied to both main surfaces of the sintered body and baked to form electrodes, followed by lead processing and dip exterior packaging. In this way, the disk type varistor of this example is manufactured.

As described above, according to the manufacturing method of this embodiment, since the group (III) metal and metal oxide are added to ZnO and the ZnO is heat-treated to become a semiconductor, the resistance value of ZnO can be reduced, and the third region can be reduced accordingly. α can be improved. the result,
The function as a surge absorption element that protects the protected circuit from abnormal high voltage can be improved.

Next, the effects of the varistor manufactured by the method of this example are as follows.
I will explain the experiment I conducted to confirm this.

In this experiment, A1t's and Yt's were added to ZnO powder, respectively.
Add 0.005 moi 1% to 10 moJI% of oxide powder of Ox, Gas O3, and GdlO, and heat it at 1300 tx for 1 hour to convert it into a semiconductor, and then manufacture a varistor according to the manufacturing method described in (1) to (3) above. It was created. And V+-a of each varistor, 1 to 10mA
The nonlinear coefficient α8. and the nonlinear coefficient α at l~IOA
, was measured. For comparison, similar measurements were also performed on a varistor that had not been subjected to semiconductor processing.

The results are shown in the table. As is clear from the same table, when the amount of each oxide powder added is 0.005 tsol,%, α2 in the high t'a 6i region is as low as 20 or less, and almost no effect is obtained. , the above addition amount is lO■o
In the case of 1%, both VI6A+ α and α2 deteriorated. In contrast, the amount added is 0.01mo 1% to 5a
+oj! % range, both VImA + α1 are able to secure the specified values, and α2 is both 20.
The above results are obtained, and it can be seen that α in the intuition'lJL fin region is excellent.

In the above embodiments, the method for manufacturing a disk-type varistor was explained as an example, but the present invention is of course not limited to this. It can also be applied to multilayer varistors.

〔Effect of the invention〕

As described above, according to the method for manufacturing a varistor according to the present invention, zero of the elements selected from group (1) or their oxides are added to ZnO.
．． Since ZnO is made into a semiconductor by adding 12% of O1-5no and heat-treating it, the nonlinear coefficient in the high current region can be improved and the limiting voltage can be lowered.

Claims (1)

[Claims] 1) A first step of converting the ZnO into a semiconductor by adding 0.01 mol% to 5 mol% of an element selected from Group III or an oxide thereof to ZnO and heat-treating the same, and pulverizing the semiconducting ZnO. and a second step in which a subcomponent that functions as a varistor is added to this to create a raw material powder, and a third step in which this raw material powder is molded into a desired shape and then fired to obtain a sintered body. A method for manufacturing a barista characterized by: