JPS59188905A - Semiconductor porcelain composition for voltage nonlinear resistor - 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 The present invention relates to a semiconductor magnetic composition for a voltage nonlinear resistor.

In recent years, resistors with non-linear voltage-current characteristics, so-called varistors, whose element bodies are made of strontium titanate-based semiconductor ceramics have been developed.

As this type of voltage nonlinear resistor, (a) M
Apply a paste containing metal oxides such as n, Zn, and Go, and heat to 1200 to 130 in air or nitrogen atmosphere.
The element body is an insulating layer formed on the crystal grain boundaries of the semiconductor porcelain by heat treatment at a temperature of 0°C, and an electrode is attached to this, or (b) a semiconductor is formed on the main component of strontium titanate. Promoting metal oxides, e.g. Nb2O6
, Ta 20s, La2O3, CeO2, Nd203
, WO3, etc., and metal oxides for improving voltage-current nonlinear characteristics such as M2O5, Cr2O3, CuO, Cu02, M
It is known that the element body contains 2O3, Mn02, etc., and electrodes are attached to the element body. This voltage nonlinear resistor has a perovskite crystal structure and exhibits ferroelectricity, so it functions not only as a varistor but also as a capacitor.
It has the advantage that it can absorb abnormally high voltage (surge) and stabilize the voltage by itself.

However, in conventional products using strontium titanate-based semiconductor ceramics, for example, in the case of (a) above, metal oxides such as Mn, Zn, and Go are applied to the surface of the small semiconductor ceramics in order to insulate the grain boundaries. The manufacturing process is complicated;
In addition to involving processes that are difficult to control, there are large variations in characteristics such as the nonlinear index (-) and threshold voltage (Vth) of voltage nonlinear resistors due to the fact that the characteristics are easily influenced by manufacturing conditions. There were drawbacks. In addition, in the latter case, when firing in a neutral or reducing atmosphere, the metal oxide for improving voltage-current nonlinear characteristics becomes metallized and evaporates.
It may damage the furnace materials of the firing furnace, it may be difficult to obtain the desired composition, and the nonlinear index μ) or threshold voltage (Vth)
The disadvantage was that it caused variations in characteristics such as.

The present invention provides a semiconductor ceramic composition that does not vary in composition or characteristics depending on manufacturing conditions and can easily manufacture a voltage nonlinear resistor with less variation in characteristics such as threshold voltage and nonlinear index. The purpose is to use the formula: % formula %) (wherein, X and γ are the mole fractions of each component, and 0.03≦X≦
0.30.0.02≦y≦0.20) and 99.0 to 99.9 mol% of the main components, rare earth elements, N
The present invention provides a semiconductor ceramic composition for a voltage nonlinear resistor, which contains 0.1 to 1.0 mol % of at least one semiconductor forming agent selected from the group consisting of oxides of B, W, and Ta.

In one embodiment of the invention, the composition includes up to 5 mol% of 5i02 and/or Al2O3 as a mineralizing agent.
It is carried out to contain. In other embodiments, 1 mol % or less of MnO2 and other components may be included. The reason why the content of these components is limited as described above is that if the content exceeds the above-mentioned content, the properties are adversely affected.

The reason why the composition of the semiconductor ceramic composition according to the present invention is limited as described above is as follows. That is, B in the principal component
When the molar fraction X of a is less than 0.03, the nonlinear index is small, and when it exceeds 0.30, the threshold voltage becomes high.
Since it is not practical, it is set in the above range. Zr in the main component
The mole fraction y was set to 0.02 to 0.20 because y was 0.
．． This is because if it is less than 0.02, the nonlinear index becomes small, and if it exceeds 0.20, the threshold voltage becomes high, and both are not practical. The reason why the content of the semiconducting agent is set to 0.1 to 1.0 mol% is that if the content is less than 0.1 mol%, the threshold voltage will be high, and if it exceeds 1.0 mol%, the varistor characteristics will deteriorate. This is because you will not be able to obtain it.

The semiconductor ceramic composition for a voltage nonlinear resistor according to the present invention includes:
The main component of the strontium titanate-based ceramic composition having the above composition and the semiconducting agent are mixed in a predetermined ratio, an appropriate organic binder is added thereto, and the mixture is granulated.
After molding under pressure of KSI/cn, 10
Preliminary firing at 00 to 1,200°C, further firing at 1,350 to 1,400°C in a neutral or reducing atmosphere to form a semiconductor, and then 1,000 to 1,000 in a natural atmosphere or an oxidizing atmosphere.
By heat-treating at 200°C, a semiconductor porcelain with insulated grain boundaries is obtained, and by forming electrodes on the surface of this semiconductor porcelain, a voltage nonlinear resistor can be obtained.

The semiconductor ceramic composition according to the present invention makes it possible to manufacture a voltage nonlinear resistor that has a large nonlinear index in a low threshold voltage region and has little variation in characteristics, and also has crystal grain boundaries. There is no need for the process of coating and diffusing metal oxides to form an insulating layer on the material, and in addition, during the reduction treatment to convert into a semiconductor, the components rarely metalize and evaporate, making it easy to manufacture. It has excellent advantages such as high yield and no damage to the firing furnace.

Examples of raw materials include SrCO3, BaCO3, TiO2
Using R02, these were weighed so as to obtain the main components of the composition shown in Table 1, mixed in a ball mill for 10 hours, dehydrated and dried, and heated to 1100 to 1250 in air.
℃ for 2 hours, flattened at the ratio shown in Table 1, sufficiently wet mixed in a ball mill, dehydrated, and granulated with 6% by weight of organic binder added to a pressure of 2000 to 7/ci. was added and formed into a disk.

This molded product was pre-fired at 1150°C for 1 hour in a natural atmosphere, and then in a reducing atmosphere (95% N2 and 15% I]2).
Baked at 1350-1400℃ for 12 hours to create a diameter of 8w.
A semiconductor porcelain with a thickness of 1 wn and a thickness of 1 wn was obtained, and this was heat-treated at 1000 to 1200° C. in a natural atmosphere to obtain a semiconductor porcelain whose crystal grain boundaries were insulated. Silver paste was printed and coated on opposing surfaces of this semiconductor ceramic and baked at 800° C. in a natural atmosphere to form electrodes and obtain a voltage nonlinear resistor.

The threshold voltage (Vth) and nonlinear index (α) of each voltage nonlinear resistor obtained in this manner were determined.

The results are also shown in Table 1. In Table 1, samples with numbers marked with * indicate those outside the scope of the present invention, and V
th is the voltage when lQmA flows through the voltage nonlinear resistor (
■□. ), and α is the above v1o].

This value is calculated from the voltage (Vl) when mA is applied using the following equation.

α-1/7? Og (■1o/■1) Comparative Example 5rTi0 99.3 mol%, Y2O30, 2 mol% and cuo□, 5 mol% were weighed and mixed, thoroughly wet mixed in a ball mill, dehydrated and dried. , 6% by weight of an organic binder was added and granulated, and a pressure of 2,000 to 9/ctR was applied to form a disc. Next, this molded product was pre-fired at 1150°C in a natural atmosphere for 1 hour, then fired at 1380°C in a reducing atmosphere (95% N2 + 5% H2) for 2 hours, and then heat-treated at 1100°C in a natural atmosphere to crystallize. A semiconductor ceramic having a straightness of 8+++n and a thickness of 1wn with insulated grain boundaries was obtained, and electrodes were formed thereon in the same manner as in the example to obtain a voltage nonlinear resistor.

Threshold voltage (Vth) and nonlinear index before and after applying a pulse voltage of 300 V for the voltage nonlinear resistors of sample numbers 3 and 6 obtained in the example and the voltage nonlinear resistor obtained in the comparative example (α) was calculated.

The results are shown in Table 2. Table 2 shows the average value (X) and deviation value (d) for each 100 samples. In the column for each sample, the upper row shows the results before pulse application, and the lower row shows the results after pulse application. It is.

As is clear from the results in Tables 1 and 2, the voltage nonlinear resistor using the semiconductor ceramic composition according to the present invention is
The threshold voltage is low and the nonlinear index is large, and the variation in characteristics is very small, less than half the deviation value of the threshold voltage and the nonlinear index, compared to the conventional one shown in the comparative example.

As is clear from the above description, the present invention eliminates the disadvantage of a large variation in characteristics in conventional voltage nonlinear resistors using strontium titanate semiconductor ceramic as an element body, and improves the threshold voltage. A process of coating and diffusing metal oxides in order to make it possible to manufacture voltage nonlinear resistors with a low and large nonlinearity index and with little variation in characteristics, and to form an insulating layer at grain boundaries. This patent is characterized by excellent effects such as no need for oxidation and almost no evaporation of components during reduction treatment, which is easy to manufacture, has a good yield, and does not damage the firing furnace. Masato Murata Manufacturing Co., Ltd.
Patent attorney Aohaku Ao and 1 other person 20-

Claims (1)

[Claims] (1) Formula: (Sr1-xBax)(Ti1-γZry)
03 (where x+ Y is the mole fraction of each component, 0.03
99.0 to 99.9 mol% of the main components expressed as
1. A semiconductor ceramic composition for a voltage nonlinear resistor, comprising 0.1 to 1.0 mol % of at least one semiconductor forming agent selected from the group consisting of oxides of B, W, and Ta.