JPH06302407A - Voltage non-linear resistor ceramic composition - Google Patents

Abstract

PURPOSE:To acquire a voltage non-linear resistor ceramic composition wherein coefficient of variation of a varistor voltage and change rate of electrostatic capacity of a varistor voltage can be reduced in a varistor of a low varistor voltage. CONSTITUTION:In the title composition, 0.01 to 2.0 mole % of at least one kind of metallic oxide selected from Gd2O3, Tb4O7 and Yb2O3 and 0.01 to 2.0 mole % of at least one kind of metallic oxide selected from NiO and Cr2O3 are incorporated in a main composition which contains 70.0 to 99.9 mole % of SrTiO3 and whose remaining element consists of MgTiO3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage non-linear resistor (hereinafter simply referred to as a varistor) which is used when absorbing an abnormal voltage, that is, a surge generated in various electric and electronic devices and absorbing noise. The present invention relates to a strontium titanate porcelain composition for a varistor element having a voltage-dependent nonlinear resistance characteristic and a dielectric characteristic.

[0002]

2. Description of the Related Art Conventionally, a SiC varistor or a varistor having a voltage-dependent non-linear resistance characteristic used for absorbing surges of various electric and electronic devices, eliminating noise, and eliminating sparks is used. A ZnO based varistor was used. The voltage-current characteristic of such a varistor is approximately expressed by the following relational expression.

I = (V / C) ^{α In the} above equation, I is a current, V is a voltage, and C is a varistor-specific constant determined by the characteristics of the varistor material. Further, α is a voltage non-linearity index showing voltage non-linearity. Generally, the voltage between the varistor element terminals when a current of 10 mA is applied to the varistor is measured, and this voltage is referred to as varistor voltage V10, which is used as a measure of voltage-current characteristics.

Conventionally used SiC varistor has an α value of about 2 to 4, and ZnO varistor has an α value of 2
Since it is about 0 to 60, these varistor has excellent performance for absorbing a relatively high voltage such as surge. However, since these varistors have a low dielectric constant and a small electrostatic capacitance, almost no noise absorbing effect can be obtained.

Therefore, SrTiO _{3 is used} as a varistor having excellent surge absorption characteristics and noise absorption characteristics.
A varistor made from a series of semiconductor porcelain was developed. An example of this type of varistor is Japanese Patent Publication No. 58-2180.
As disclosed in Japanese Patent Publication No. 6, SrTiO ₃ or Sr
_The main component is _(1-x) Ca _x TiO _3, and the main component is, for example, Na ₂ O ₅ , T
was added _{a 2 O 3, La 2 O} 3 , etc., and metal oxides for improving the non-linearity, eg CuO, MnO
It is known that a composition containing ₂ or the like is used. A varistor using such a material has a high dielectric constant, so it has a function as a capacitor in addition to the original function of the varistor, and it has excellent performance in suppressing surge voltage and eliminating noise. There is.

[0006]

However, the varistor manufactured using the above composition has a problem that the coefficient of variation of the varistor voltage V ₁₀ is large and the yield is deteriorated. Further, the varistor has a varistor voltage of V ₁₀ especially when the varistor is left in a wet state in an uncoated state.
Therefore, there is a problem that it is extremely difficult to suppress the rate of change in capacitance to within ± 2%.

The problem that the coefficient of variation of the varistor voltage V ₁₀ becomes large is considered to be due to the fact that the above composition is easily affected by minute variations in the conditions of the manufacturing process. That is, in the case of producing a varistor porcelain using the above composition, the molded body is first fired in a neutral or reducing atmosphere to produce a semiconductor porcelain. After that, the semiconducting porcelain is heat-treated in the air to be re-oxidized to form an insulating layer at the grain boundary, or PbO, Bi ₂ O ₃ or Na is used.
_An insulating layer forming paste containing ₂ O is applied to the surface of a semiconductor porcelain and heat treated to diffuse the above components to form an insulating layer at a crystal grain boundary, which has varistor characteristics and capacitor characteristics. Obtained semiconductor porcelain. In the conventional composition, due to a minute change in firing conditions during semiconductorization in the above manufacturing process or a minute change in heat treatment conditions during reoxidation or diffusion of the components of the insulating layer forming paste, It is considered that the difference in the degree of formation of the insulating layer causes a large variation coefficient of the varistor voltage V ₁₀ . It should be noted that this minute change in the condition is a change that necessarily occurs in the normal manufacturing process, and it is difficult to reduce the change in the condition. Further, the large rate of change in the value of the varistor voltage V ₁₀ and the capacitance after being left in humidity is considered to be due to the identity of the components of this composition.

Therefore, even when the manufacturing conditions are changed, the selection range of the mixing ratio of each component can be widened and the coefficient of variation of the varistor voltage V ₁₀ can be reduced, and the composition is left to stand in a humid environment. There is a demand for a novel composition having good moisture resistance which does not increase the rate of change of the varistor voltage V ₁₀ and the capacitance afterward.

The object of the present invention is to provide such a novel composition.

[0010]

In order to solve the above-mentioned problems, the nonlinear resistor ceramic composition of the present invention is SrTiO 3.
70.0-99.9 mol% ₃ and the remaining component is Mg
Gd ₂ O ₃ , Tb ₄ O _{7 is} added to the main composition of TiO _3.
And 0.01 to 2.0 mol% of at least one metal oxide selected from Yb ₂ O ₃ and NiO and Cr ₂ O ₃
0.01 to at least one metal oxide selected from
It is composed of 2.0 mol%.

[0011]

This type of composition is not invented on the basis of theoretical grounds, but is confirmed by experiments whether or not desired performance can be obtained by selecting materials from various materials. While being developed, it is general. Therefore,
It is obvious to those skilled in the art that it is often not possible to clearly explain what action each material component used has, and what is the basis for limiting the mixing ratio of each component to a predetermined range. Ah Further, in this type of composition, the desired performance is not obtained as a result of a simple set of the action of each component, but rather a complex result of the components interacting with each other to obtain the desired result. It will be apparent to those skilled in the art that it is possible.

Since the present invention was also invented by the above-mentioned general development method, it is not possible to clearly explain the action of each component. Explained. In the present invention, 70.0-
It is considered that MgTiO ₃ which constitutes the main composition together with 99.9 mol% of SrTiO ₃ is a component which facilitates the formation of a semiconductor. From the experimental results, if MgTiO ₃ is less than 0.1 mol%, it becomes difficult to form a semiconductor, and 3
It has been confirmed that when the content is more than 0 mol%, the variation coefficient of the varistor voltage V10 becomes large due to the change in the condition generated during the heat treatment.

Also, 0.01 to 0.01 added to the above main composition.
2.0 mol% of Gd ₂ O ₃ , Tb ₄ O ₇ and Yb ₂ O ₃
The at least one metal oxide selected from (first addition component) affects the value of the voltage non-linearity index α. If this component is less than 0.01 mol%, the voltage non-linearity index α becomes too small. When this component is more than 2 mol%, the change rate of the varistor voltage V ₁₀ and the capacitance in wet becomes large due to the change of the condition generated during the heat treatment.

At least one metal oxide (second additive component) selected from NiO and Cr ₂ O ₃ mainly affects the sinterability. If this component is out of the range of 0.01 mol% to 2.0 mol%, the rate of change of the varistor voltage V ₁₀ and the electrostatic capacitance when left in the wet becomes large.

According to the present invention, the porcelain composition for a varistor having a low varistor voltage V ₁₀ is obtained as a result of setting the above-mentioned main composition, the first additive component and the second additive component in a predetermined component ratio.
The variation coefficient of the varistor voltage V ₁₀ can be reduced to about 10% or smaller even with respect to minute changes in firing conditions and heat treatment conditions that occur in a normal manufacturing process.
Further, a varistor porcelain composition capable of significantly suppressing the rate of change of the varistor voltage V ₁₀ and the electrostatic capacity in the humidity can be obtained.

[0016]

EXAMPLES Examples of the present invention will be described below.

First, a method for producing a test varistor for measuring the characteristics of the porcelain composition of the present invention will be described. First, 70.0-99.9 mol%
SrTiO ₃ and MgTiO ₃ are mixed to form a main composition. And this main composition, Gd ₂ O ₃ , Tb ₄ O ₇
And at least one metal oxide selected from Yb ₂ O ₃ (first addition component) and at least one metal oxide selected from NiO and Cr ₂ O ₃ (second addition component) have a predetermined composition ratio. After weighing so as to enter, wet mixing is performed for 10 to 16 hours using a pulverizing and mixing machine such as a ball mill. After mixing, after drying with a drier, the mixture is placed in a predetermined container and calcined at a temperature of 1000 to 1150 ° C. in an air atmosphere. After calcination, 1 again using a crushing mixer such as a ball mill
Wet mix for 0 to 16 hours and dry. Next, about 2% by weight of a binder such as polyvinyl alcohol is added to the dried material for granulation, and the granulated powder is added for 0.5 to 1.5 t /
10mm diameter and 1.2mm thickness when compressed with a pressing pressure of cm ^2.
To form a disk-shaped molded body.

Then, the disk-shaped molded body was subjected to about 1300 in a reducing atmosphere (80 to 97% N ₂ , 3-20% H ₂ ).
After firing at a temperature in the range of -1450 ° C for 1-6 hours,
A disc-shaped fired body is obtained by heat-treating this fired body in an air atmosphere at a temperature in the range of 900 to 1250 ° C. for 1 to 8 hours and reoxidizing it. Further, a varistor is completed by forming a conductive metal film electrode of silver or the like that forms ohmic contact on both surfaces of this fired body by a known method.

[Measurement Results] Tables 1 and 2 below show the varistor elements produced by the above method by changing the composition ratio of each compounding component of the porcelain composition using MgTiO ₃ as a mixed material of the main composition. The measurement result of is shown. The voltage non-linearity index α in each table is the voltage V across the varistor element when currents of 1 mA and 10 mA are applied to the varistor element.
It is a value obtained from the equation of α = 1 / log (V ₁₀ / V ₁ ) using ₁ and V ₁₀ . The capacitance is a value measured using an LCR meter with a measurement frequency of 1 KHz and a measurement voltage of 10 mV. Further variation coefficient of varistor voltage V ₁₀ (%) is intended to represent the variation of the V _10, there is shown a ratio between the average value and the standard deviation of the V ₁₀ in percentage. The rate of change in varistor voltage V10 and capacitance due to being left in humidity is measured by measuring the varistor voltage and capacitance after leaving the uncoated varistor element in an atmosphere of 95% humidity and 60 ° C. for 240 hours. The value is shown as a percentage with respect to the initial value.

The characteristic values in Tables 1 and 2 show the case where the reoxidation temperature is 1100 ° C. In addition, the “•” mark in front of the sample number in each table indicates that it is a comparative example.

[0021]

[Table 1]

[Table 2] As can be seen from the results of Tables 1 and 2 above, 70.0-9
₃₀ to 0.1 mol% of M in 9.9 mol% of SrTiO _3.
The main composition containing gTiO ₃ contains Gd ₂ O ₃ , Tb
0.01 to 2.0 mol% of at least one metal oxide selected from ₄ O ₇ and Yb ₂ O ₃ , and NiO and Cr.
_At least one metal oxide selected from ₂ O ₃
Compositions containing 01 to 2.0 mol% (Sample Nos. 1 to 2)
In the case of using 5), even if each component is selected in a wide range, the change in the conditions naturally occurring in the manufacturing process
The variation coefficient of the varistor voltage V10 falls within the range of 4.9 to 13.8%. In addition, the measurement results were obtained in which the varistor voltage and the electrostatic capacity when left in the humidity were within ± 2%. Therefore, according to the present invention, excellent properties can be obtained as compared with the conventional composition. Generally, the composition used for this varistor element is about 10 mol% of MgTiO ₃ ,
It is preferable that each of the first and second additive components is 1 mol% or less. It is needless to say that the varistor can be manufactured by using a composition of an appropriate blending component depending on the characteristic condition of the varistor.

Sample numbers 26 to 28 do not contain the second additive component, and sample numbers 29 and 30 do not contain the first additive component. As can be seen by comparing the two, the rate of change in the characteristics due to being left in the humidity increases when the second additive component is absent, and the voltage nonlinear index α decreases significantly when the first additive component is absent. Further, sample numbers 31 to 33 show the case where any of the components is out of the preferable component range. As can be seen from these, when any of the components is out of the preferable component range, the capacitance and the voltage non-linearity index α become small, the coefficient of variation of the varistor voltage becomes large, and the characteristics of the characteristics due to being left in the humidity are increased. The rate of change increases.

[0023]

With the composition of the present invention, the ceramic composition for a low varistor voltage V ₁₀ varistor, it is possible to reduce the variation coefficient of varistor voltage V _10,
The product yield can be increased. Further, by using the composition of the present invention, it is possible to obtain a varistor element having various characteristics and a small change rate of the varistor voltage V ₁₀ and the electrostatic capacitance in the humidity, so that the reliability of the varistor element is improved. Can be significantly improved.

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[Procedure amendment]

[Submission date] June 17, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

I = (V / C) ^{α In the} above equation, I is a current, V is a voltage, and C is a varistor-specific constant determined by the characteristics of the varistor material. Further, α is a voltage non-linearity index showing voltage non-linearity. Generally, the voltage between the varistor element terminals when a current of 10 mA is applied to the varistor is measured, and this voltage is referred to as varistor voltage V ₁₀ and is used as a measure of voltage-current characteristics.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

The problem that the coefficient of variation of the varistor voltage V ₁₀ becomes large is considered to be due to the fact that the above composition is easily affected by minute variations in the conditions of the manufacturing process. That is, in the case of producing a varistor porcelain using the above composition, the molded body is first fired in a neutral or reducing atmosphere to produce a semiconductor porcelain. After that, the semiconducting porcelain is heat-treated in the air to be re-oxidized to form an insulating layer at the grain boundary, or PbO, Bi ₂ O ₃ or Na is used.
_An insulating layer forming paste containing ₂ O is applied to the surface of the semiconductor porcelain and heat treated to diffuse the above components to form an insulating layer at the crystal grain boundaries, which has varistor characteristics and capacitor characteristics. Obtained semiconductor porcelain. In the conventional composition, due to a minute change in firing conditions during semiconductorization in the above manufacturing process or a minute change in heat treatment conditions during reoxidation or diffusion of the components of the insulating layer forming paste, and a difference occurs to the extent of forming an insulating layer, is considered that the variation coefficient of varistor voltage V ₁₀ is increased. It should be noted that this minute change in the condition is a change that necessarily occurs in the normal manufacturing process, and it is difficult to reduce the change in the condition. Further, the large rate of change in the value of the varistor voltage V ₁₀ and the capacitance after being left in humidity is considered to be due to the identity of the components of this composition.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

Since the present invention was also invented by the above-mentioned general development method, it is not possible to clearly explain the action of each component. Explained. In the present invention, 70.0-
It is considered that MgTiO ₃ which constitutes the main composition together with 99.9 mol% of SrTiO ₃ is a component which facilitates the formation of a semiconductor. From the experimental results, if MgTiO ₃ is less than 0.1 mol%, it becomes difficult to form a semiconductor, and 3
It has been confirmed that when the content is more than 0 mol%, the variation coefficient of the varistor voltage V ₁₀ becomes large due to the change of the condition generated during the heat treatment.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction content]

[Measurement Results] Tables 1 and 2 below show the varistor elements produced by the above method by changing the composition ratio of each compounding component of the porcelain composition using MgTiO ₃ as a mixed material of the main composition. The measurement result of is shown. The voltage non-linearity index α in each table is the voltage V across the varistor element when currents of 1 mA and 10 mA are applied to the varistor element.
It is a value obtained from the equation of α = 1 / log (V ₁₀ / V ₁ ) using ₁ and V ₁₀ . The capacitance is a value measured using an LCR meter with a measurement frequency of 1 KHz and a measurement voltage of 10 mV. Further variation coefficient of varistor voltage V ₁₀ (%) is intended to represent the variation of the V _10, there is shown a ratio between the average value and the standard deviation of the V ₁₀ in percentage. The rate of change of the varistor voltage V ₁₀ and the capacitance due to being left in the humidity is measured by measuring the varistor voltage and the capacitance after leaving the uncoated varistor element in an atmosphere of 95% humidity and 60 ° C. for 240 hours. , The value is shown as a percentage of the initial value.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Ishiwari 3158 Shimookubo, Osawano-cho, Kamishinagawa-gun, Toyama Prefecture Hokuriku Electric Industry Co., Ltd. Industry Co., Ltd.

Claims (1)

[Claims] 1. A include SrTiO ₃ 70.0 to 99.9 mol%, the main composition and the remaining components consisting of MgTiO _3, at least selected from _{Gd 2 O 3, Tb 4 O} 7 and Yb ₂ O ₃ 0.01 to 2.0 mol% of one metal oxide
When, at least one metal oxide nonlinear resistor ceramic composition characterized that it contained 0.01 to 2.0 mol% of any one selected from NiO and Cr ₂ O _3.