JPH0828287B2 - Voltage-dependent nonlinear resistor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to voltage-dependent nonlinear resistors.

(Prior Art) Conventionally, as this type of voltage-dependent non-linear resistor, so-called varistor, a composition containing strontium titanate (SrTiO ₃ ) as a main component has been known, and there is a demand for improving performance of electronic devices and the like. In order to improve the non-linear resistance coefficient of a voltage-dependent non-linear resistor used in electronic devices, a part of strontium titanate which is the main component of the composition is replaced with calcium titanate. .

(Problems to be Solved by the Invention) The composition in which a part of the strontium titanate is replaced with calcium titanate has a varistor voltage E ₁₀ having a negative temperature characteristic, and therefore generates heat when electric power is applied. Due to this, the varistor voltage E ₁₀ decreases and the current value increases accordingly. As a result, when the rush power to the voltage-dependent nonlinear resistor is about 1 W or less, the current value gradually increases with the passage of time as shown by the curve B in FIG. The value converges and holds the constant value, but when the rush power to the voltage-dependent nonlinear resistor exceeds approximately 1 W, the current value is constant with time as shown by the curve C in FIG. Even if the value is reached, it does not converge and continues to increase, so there is a problem that the connecting portion between the electronic device and the voltage-dependent nonlinear resistor is overheated and the connecting solder is melted.

It is an object of the present invention to provide a voltage-dependent nonlinear resistor having a positive varistor voltage change rate that solves the above problems.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides the following formula: [SrTiO ₃ ] _x · [CaTiO ₃ ] _y · [BaTiO ₃ ] _{z where} x + y + z = 1 0.325 <x < 0.475 0.225 <y <0.375 as a main component, and at least one of Nb, La, and Ta oxides of 0.05 to 0.50 mol% and Cu, M
At least one of oxides of o, Fe, Mn, and Si is 0.05 to 0.
The varistor voltage change rate formed by adding 50 mol% is positive.

The value of x in the composition ratio (x + y + z = 1) of SrTiO ₃ used in the present invention is 0.325 to 0.475 because the value of x is 0.325.
If it is smaller, the non-linear resistance coefficient [α] value decreases to 0.475.
If it is larger, the varistor voltage change rate [(ΔE ₁₀ (% /
℃]] becomes negative, and the value of y in the composition ratio of CaTiO ₃ is set to 0.225 to 0.375. If the value of y is out of this range, the varistor voltage change rate becomes negative, .
This is because if it is larger than 375, the nonlinear resistance coefficient value further decreases.

The reason why the amount of at least one of Nb, La, and Ta oxides added to the composition is set to 0.05 to 0.50 mol% is that the specific linear resistance coefficient value decreases if it is out of this range. And C added at the same time as the above-mentioned additive
The addition amount of at least one kind of oxides of u, Mo, Fe, Mn, and Si is set to 0.05 to 0.50 mol% when the content is less than 0.05 mol%, the non-linear resistance coefficient value decreases and 0.50 mol% This is because the varistor voltage varies when the value is larger than the above value.

(Operation) The voltage-dependent nonlinear resistor with the above composition shows a temperature characteristic in which the varistor voltage change rate [(ΔE ₁₀ (% / ° C)] has a positive temperature characteristic, and is obtained when inrush power of 1 W or more is applied. However, the current does not increase beyond a certain value.

(Example) Next, the voltage-dependent nonlinear resistor of the present invention will be described based on examples.

First, each metal titanate powder of SrTiO ₃ , CaTiO ₃ , and BaTiO ₃ and at least one of oxide powders of Nb, La, and Ta,
At least one of the oxide powders of Cu, Mo, Fe, Mn, and Si was weighed so that the composition ratios and addition amounts shown in the table were obtained,
This was mixed by a wet ball mill for 15 hours to obtain a mixture. Next, the resulting mixture was dried in air at a temperature of 150 ° C., and then polyvinyl alcohol as a binder was added thereto.
Part by weight was added, mixed and granulated to obtain a raw material powder.

Furthermore, this raw material powder is used in a dry press in a mold to produce 1,500 kg /
A ring-shaped molded body having an outer diameter of 12 mm, an inner diameter of 6 mm, a thickness of 0.9 mm, and a molded body density of 3.0 g / cm ³ was molded with a pressure of cm ² .

Subsequently, the ring-shaped compact was heated at a temperature of 1,350 in a mixed gas atmosphere containing 96% by volume of nitrogen gas and 4% by volume of hydrogen gas.
A sintered body was obtained by firing at 3 ° C. for 3 hours.

Further, this sintered body was heat-treated in air at a temperature of 1,000 ° C. for 3 hours to prepare voltage-dependent nonlinear resistors, which were used as samples 1 to 30.

Next, as shown in FIG. 3, after the silver electrode (2) material was applied to the upper surface of each sample (1) prepared by the above method, the temperature was changed to 18
It was dried at 0 ° C. for 10 minutes and then baked at a temperature of 780 ° C. for 10 minutes to form a silver electrode.

When the nonlinear resistance coefficient and the varistor voltage of each of Samples 1 to 30 were examined, the results shown in the table were obtained.

To measure the non-linear resistance coefficient and the rate of change of varistor voltage, connect a sample to a DC constant current source, connect an ammeter between the DC constant current source and the sample, and connect a voltmeter in parallel with the sample. Was connected and only the sample was immersed in a constant temperature bath.

 The non-linear resistance coefficient [α] was calculated by the following equation.

However, the varistor voltages E ₁ and E ₁₀ are 1 mA and 10 m, respectively, for the sample.
It is the voltage value when the current of A is passed.

The rate of change in varistor voltage [ΔE ₁₀ (% / ° C)] was calculated by the following equation.

As is clear from the table, the composition ratio of each metal titanate and the addition amount of the additive are within the range of the present invention.
Had positive temperature characteristics. On the other hand, the composition ratio of each metal titanate and the amount of the additive added are outside the scope of the present invention.
The temperature characteristics of 26 to 30 were negative.

In addition, the voltage-dependent nonlinear resistor of sample 9
The rate of change of the varistor voltage at each temperature was examined while changing the temperature to 125 ° C., and the result is shown as curve A in FIG. Similarly, the rate of change of the varistor voltage at each temperature of the voltage-dependent nonlinear resistor of sample 26 was examined, and the results were
It is shown as a curve B in the figure.

The rate of change of the varistor voltage at each temperature was measured according to the method of measuring the rate of change of the varistor voltage.

As is apparent from FIG. 1, it was confirmed that the temperature characteristics of the varistor voltage of Sample 9 in which the composition ratio of each metal titanate and the amount of the additive added were within the range of the present invention were positive.
On the other hand, the temperature characteristics of the varistor voltage of the sample 26 in which the composition ratio of each metal titanate and the addition amount of the additive were out of the range of the present invention were negative.

The change of the current with the passage of time was examined while applying 1.2 W of inrush power to the voltage-dependent nonlinear resistor of Sample 9, and the result is shown as curve A in FIG. Similarly, the sample
The change in current with time of the 26 voltage-dependent nonlinear resistors was investigated, and the result is shown as a curve C in FIG.

The change in current with the passage of time was indirectly measured by measuring the terminal voltage of the resistor connected in series to the sample.

As is clear from FIG. 2, the sample 9 in which the composition ratio of each metal titanate and the addition amount of the additive are within the range of the present invention is
It was confirmed that the current does not increase beyond a certain value even when an inrush power of 1 W or more is applied. On the other hand, in Sample 26 in which the composition ratio of each metal titanate and the addition amount of the additive were out of the range of the present invention, the current increased with the passage of time when the inrush power of 1 W or more was applied.

(Effects of the Invention) As described above, according to the present invention, when the varistor voltage change rate, that is, the temperature characteristic of the varistor voltage becomes positive and the rush power to the voltage-dependent nonlinear resistor exceeds 1 W, Also, since the current value does not increase more than a certain value, it is possible to prevent overheating of the connection portion with the electronic device or the like, and it is possible to prevent trouble such as melting of the connection solder at the connection portion.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the temperature of the voltage-dependent nonlinear resistor and the rate of change of the varistor voltage at each temperature, and FIG. 2 is the time when a constant voltage is applied to the voltage-dependent nonlinear resistor. FIG. 3 is a characteristic diagram showing the relationship with the current, FIG. 3 shows a sample having a silver electrode formed on the upper surface, A is a plan view thereof, and B is a sectional view taken along the line BB of A. (1) …… Sample, (2) …… Silver electrode

Claims (1)

[Claims] 1. A composition represented by the general formula [SrTiO ₃ ] _x. [CaTiO ₃ ] _y. [BaTiO ₃ ] _{z, where} x + y + z = 1 is expressed as 0.325 <x <0.475 0.225 <y <0.375. At least one of Nb, La, and Ta oxides is added to the composition as 0.05 to 0.50 mol% and Cu, M
At least one of oxides of o, Fe, Mn, and Si is 0.05 to 0.
A voltage-dependent nonlinear resistor having a positive varistor voltage change rate formed by adding 50 mol%.