JPS61271802A - Voltage non-linear resistor ceramic composition - 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 voltage non-linear resistor ceramic composition, specifically for use in surge absorption, overvoltage suppression or spark extinguishing of various electronic devices.
The present invention relates to a ceramic composition for voltage nonlinear resistors (hereinafter simply referred to as varistors) used for noise removal and the like.

[Conventional technology]

Generally, a resistance element whose voltage-current characteristics are nonlinear is called a varistor, and its characteristics are expressed by the following relational expression.

α 1− (V/C) In the formula, ■ represents current, ■ represents voltage, C is a constant, and α is an index indicating voltage nonlinearity.

Conventionally, SiC varistors and ZnO-based varistors are well known as varistors having such voltage non-linear characteristics, and the value of α is about 2 to 4 for SiC varistors, while for ZnO
Varistors with a hardness of about 20 to 60 have been obtained. Further, C is a constant determined by the material, etc., but in practical terms, vl is the voltage between the terminals of the varistor element (usually called the varistor voltage) when a constant current, for example, 10 mA, is passed. It is expressed as follows.

Since the voltage-current characteristics of varistors have non-linearity, they exhibit excellent performance in absorbing abnormally high voltages such as surges, but on the other hand, the capacitance is 0.18 to 2.6
Since it is relatively small at nF, it has almost no effect on absorbing noise, etc.Therefore, strontium titanate (SrTiC)1)-based semiconductor ceramic capacitors are used for the purpose of absorbing noise, etc. This also had the disadvantage that it would be destroyed if a large surge was applied.

However, in recent years, 5rTiQ has improved these drawbacks.
Varistors made of type 3 semiconductor porcelain have been developed, some of which are disclosed in Japanese Patent Publication No. 5B-21806. This varistor has 5rT10 as its main component, and a semiconductor-promoting metal oxide, such as niobium oxide (N
b! Os ), tantalum oxide (T az os ), tantalum oxide (T az os
), lanthanum oxide (La2O5), etc., and metal oxides for nonlinearity improvement, such as CuOsM
This varistor has a perovskite crystal structure and exhibits ferroelectricity, so it functions not only as a varistor but also as a capacitor. It also has excellent noise removal performance.

However, its manufacturing method is to convert the compact into a semiconductor by firing it in a neutral or reducing atmosphere, and then heat-treat it in air or an oxidizing atmosphere to form a semiconductor porcelain with an insulating layer formed at the grain boundaries. Therefore, there is a problem in that the electrical properties of the obtained semiconductor ceramics vary due to variations in manufacturing conditions such as firing temperature, firing time, firing atmosphere, etc.

[Problem that the invention seeks to solve]

The present invention was made by focusing on such problems of S r Ti Os optical semiconductor ceramic compositions, and various varistor voltages V,. A voltage nonlinear resistor ceramic composition that has a voltage nonlinearity index α, has a larger capacitance than conventional varistors, and has a varistor with less variation in electrical characteristics even when manufacturing conditions change. The purpose is to provide.

[Means for solving problems]

As a result of intensive research to achieve this objective, the present inventors found that the above-mentioned S r Ti Ox is the main component, niobium (Nb) is used as a semiconductor promoting substance, Mn is used as a nonlinearity improving substance, By adding silica (Si0,) at a certain ratio to a composition containing metals selected from Zn and Sn, S r Ti
We have found that it is possible to make a composition that uniformizes the growth of crystal grains of O, thereby producing a stable quality varistor with extremely little variation in varistor voltage, and a varistor with a large capacitance, leading to the present invention. Ta.

That is, in the present invention, 5rTiO:+ is 95.00 to 99
, 93 mol%, 0.0 in terms of Nb converted to Nb, O3
1 to 1.00 mol%, 5ift to 0.05 to 3゜00 mol%, Mn*, at least one metal selected from the group consisting of Zn, Sn, respectively, Mn0=, ZnO*
0.01 to 1.00 mol% in terms of S n Oz
This is a voltage nonlinear resistor ceramic composition (hereinafter simply referred to as the composition of the present invention) containing the present invention.

The method for producing the composition of the present invention will be explained below.

That is, 5rTiO as the main component is 95.00~
99.93 mol%, Nb as the second component is Nb2O,
o, oi to 1.00 mol% in terms of MnOz, ZnO, and at least one metal selected from the group consisting of Mn, Zn, and Sn as the third component.

S n Oz value converted to metal oxide is 0.01 to 1
．． 00 mol% and SiO□ as the fourth component from 0.05 to
At a composition ratio of 3°00 mol%, each is accurately weighed so that the total is 100 mol%. In this case, S “Tie,
For example, a mixture of 5rCOs and Tie may be used as a starting material, and Nbz 05 ,
Mn0z? Zno and 5not may use these metal elements, hydroxides, carbonates, etc. as starting materials.

The components mixed to have the above composition ratio are wet pulverized and mixed for 2 to 8 hours using a pulverizing mixer such as a ball mill, then filtered and dehydrated, and dried at about 100° C. to 150° C.

This dry mixture was then heated to 1000-1100 in the presence of air.
After calcining for 1 to 3 hours at a temperature of 1 to 3 hours, an organic binder such as polyvinyl alcohol is added to prepare a granulated powder of about 300 microns.

Next, the obtained granulated powder is pressure-molded at a pressure of about 0.5 to 3 tons/- to form a disk with a diameter of about 6 mm and a thickness of about 1.2 mm. is depied and reduced to about 135% in a reducing atmosphere (80-95% N + 5-20% H8).
After firing at a temperature in the range of 0 to 1500°C for 1 to 8 hours, the fired body was heated in the air at a temperature in the range of 900 to 1300°C for 1 to 8 hours.
The composition of the present invention is obtained by reoxidation treatment for ~5 hours.

The varistor element is obtained by forming conductive metal film electrodes made of silver or the like to form ohmic contact on both surfaces of the obtained disk-shaped sintered body by a conventional method.

〔Example〕

Various varistor elements were manufactured by the above-described method by changing the composition ratio of each compounded component, and the initial characteristics were measured.The results are shown in the following table.

In the table, ■1° is the voltage across the varistor element when a current of 10e^ is passed through the varistor element, and the voltage nonlinearity index α is the voltage across the varistor element when a current of 10e^ and 1mA is passed through the varistor element, respectively. From the ratio of the voltages VIO and V at both ends, α-1/log (V r o / V + )
It is shown as the value obtained from the formula. Also, the capacitance CA is LCR
This is a value measured using a meter at a measurement frequency of IKHz. Furthermore, the coefficient of variation (%) is expressed as the ratio of the standard deviation and the average value, representing a variation of 1°. These characteristic values are based on a reoxidation temperature of 1000' during the manufacture of the varistor.
The value when C is shown. In addition, the sample number in the left column of the table with an asterisk (*) indicates a control example.

[For production]

In the composition of the present invention, Nb2O5 is blended for the purpose of promoting semiconductor formation, and when the content is in the range of 0.01 to 1.00 mol%, the varistor voltage is 1. is low (, a varistor element with a large voltage non-linearity index α can be obtained. However, if 0.01
When it is less than mol % or exceeds 1.00 mol %, the value of 1° becomes large, and conversely α becomes small, which is not preferable.

Although the above example shows the case where Nb2O5 is added as the second component, tantalum (T a ) is also a homologous element to niobium (Nb), and its ionic radius and chemical properties are almost the same. Ta, O in place of part or all of Nb□OS.

It can be easily inferred that a varistor element with similar characteristics can be obtained even if .

Furthermore, as is clear from the results in the table above, the addition of SiO to the composition of the present invention increases the capacitance of the varistor element in the range of 0.05 to 3.0 mol%, and also increases the varistor voltage v10. It has the effect of reducing the coefficient of variation. However, when SiO□ is less than 0.05 mol%, the value of V+O increases and the coefficient of variation increases, while when it exceeds 3.00 mol%, α decreases and the coefficient of variation increases, which is not preferable. .

It is believed that such effects due to the addition of S i Oz are mainly due to uniform growth of crystal grains of 5rTiO+, which is the main component.

Incidentally, the composition of the present invention (S
The micrograph in Figure 1 (1000x magnification) showing the crystal structure of iOx (0.5 mol% addition) and sample number 16
Control composition shown in (addition of 0°0.01 mol% Si)
Comparison with the micrograph in Figure 2 (1000x magnification) showing the crystal structure of SrTiO3 shows that in the control composition, SrTiO3
In contrast, in the composition of the present invention, the growth of SrTiO3 crystals is uniform, whereas in the composition of the present invention, the growth of SrTiO3 crystals is not uniform, and there are particles that have grown abnormally among the fine particles. It can be seen that the particles have grown into uniformly sized particles. Therefore, it is thought that the formation of the insulating layer of 5rTiO and the metal oxide at the grain boundaries becomes uniform, and the variation in the characteristic values is reduced. In addition, instead of Sing,
Even if nitrides such as i, N, etc. are used, the same effect as 5iOz can be obtained.

Furthermore, the addition of MnO, ZnO, and Snow mainly has the effect of increasing α, but if it is less than 0.01 mol%, the effect is small, so it is not preferable.
When it exceeds 1°, the varistor voltage ■1° is high and the capacitance C
A becomes small, and the coefficient of variation of the varistor voltage also becomes large, making it impossible to obtain a stable varistor element.

Figure 3 is a graph showing the relationship between the reoxidation temperature after sintering and ■1° and α for the composition of the present invention, Sample No. 22 in the previous table. By adjusting the oxidation temperature, vl.

Since the values of and α can be controlled, the same −
Varistors with various characteristics can be manufactured with elements of the same size and composition. In addition, although the composition of sample number 22 is the case where 0.2 mol% of MnO is added as the third component, the same tendency as in the case of FIG. 3 can be obtained when ZnO and 5not are added. was confirmed.

〔Effect of the invention〕

According to the composition of the present invention, as is clear from the above examples and effects, the composition has high quality and reliability, having various varistor voltages with a small coefficient of variation (dispersion) of 1° and a voltage non-linearity index α. It is possible to obtain a varistor element with high performance. In addition, this varistor has a larger capacitance than conventional varistors, so it can be used to suppress overvoltage, remove sparks, and absorb noise in various electronic devices, such as eliminating sparks that occur between commutator pieces and brushes in small motor circuits. It can also be used as a multifunctional element having the functions of a varistor and a capacitor at the same time, for applications such as noise absorption and noise filters for microcomputer control equipment.

[Brief explanation of drawings]

Figure 1 is a photomicrograph showing the crystal structure of an example of the composition of the present invention, Figure 2 is a photomicrograph showing the crystal structure of a control composition, and Figure 3 is an example of the composition of the present invention. reoxidation temperature and V,. , α is a graph showing the relationship between α and α. Patent applicant: Ishizuka Electronics Co., Ltd. Figure 1

Claims (1)

[Claims] 95.00 to 99.93 mol% of SrTiO_3, N
0.01 to 1.00 when b is converted to Nb_2O_5
mol%, SiO_2 0.05-3.00 mol%, Mn
, Zn, and Sn at 0.01 to 1.00 mol% in terms of MnO_2, ZnO, and SnO_2, respectively. thing.