JPH06333707A - Barista - Google Patents

Abstract

(57) [Summary] [Purpose] A low-voltage varistor used for surge absorption in electrical circuits including semiconductor devices, which has good nonlinear resistance characteristics, low leakage current in the low-current region, and is suitable for voltage application. The aim is to stabilize it. [Structure] Bi, Co, Mn, Sb, Sn, Ni, C which has varistor characteristics when added to the main component zinc oxide
In addition to oxides such as r and Si, titanium oxide, gallium oxide, and indium oxide are added at the same time for low voltage, so that the rising voltage of current-voltage characteristics is low,
It is possible to obtain a varistor having a high non-linear resistance coefficient, stable to a voltage load for a long time, and having good non-linear resistance characteristics in both the high current region and the low current region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a varistor used for absorbing surge in an electric circuit.

[0002]

2. Description of the Related Art In recent years, varistors have been used in a wide range of electric circuits and have greatly contributed to the industrial world. A zinc oxide varistor whose main component is zinc oxide (hereinafter referred to as ZnO) is a ZnO bismuth oxide (hereinafter referred to as Bi ₂ O).
₃ ) ・ Manganese oxide (hereinafter referred to as MnO ₂ ) ・
It is composed of a sintered body to which a basic additive of cobalt oxide (hereinafter referred to as CoO) is added and further various oxides are added to improve performance. The low voltage varistor is used for the purpose of protecting semiconductor elements from various surges in electronic circuits including semiconductors, and the high voltage varistor is used for purposes such as protecting the transmission and distribution line system from lightning surges.

A varistor has a high resistance when the applied voltage is low, but a current flows rapidly when the voltage reaches a certain value (called a varistor voltage). When a current I flows through the varistor. , The voltage between the electrodes of the varistor element is V ₁
It is represented by Amp. It is not preferable for an element that a current flows though the applied voltage is small. Such leakage current is evaluated by a method called a voltage ratio, and the voltage ratio is expressed by V ₁ mA / V ₁ μA or V ₁ mA / V ₁₀ μA.

Further, a varistor is often required to absorb a high current. ZnO itself, which is the main component of the zinc oxide varistor, has resistance, and heat is generated when a high current is applied, so low resistance is desired in the high current region. The limiting voltage ratio is evaluated by V ₅ A / V ₁ mA or the like in a low voltage varistor. ZnO
Since a small amount of gallium forms a solid solution in the steel, the electric resistance decreases. Therefore, an invention in which gallium oxide (hereinafter referred to as Ga ₂ O ₃ ) is added as a means for improving the nonlinear resistance characteristic in the high current region and improving the limiting voltage ratio is There is (JP-A-58-122703)
(See the official gazette).

[0005] Various zinc oxide varistors have a problem to be solved for both high voltage varistor and low voltage varistor. It is known that in a zinc oxide varistor, the rising voltage is almost determined by the number of grain boundaries existing between two electrodes, and at that time, a rising voltage of 3 to 4 V per grain boundary is shown. In the zinc oxide varistor, the current flows through the path having the smallest number of grain boundaries existing between the electrodes, and the rising voltage is also determined by the minimum number of grain boundaries. Therefore, if the particle size of the ZnO microcrystals in the sintered body varies, the current concentrates and flows only in a part of the sintered body, and the variation in particle size greatly deteriorates the performance of the zinc oxide varistor. In particular, zinc oxide varistors for low voltage are manufactured so that the size of ZnO microcrystals in the sintered body is increased in order to lower the rising voltage, but the promotion of grain growth often causes abnormal grain growth. As a result, variations in particle size are likely to occur. That is,
The conventional sintering technology does not achieve sufficient grain size control, and it is several tens of μ.
It is difficult to produce a sintered body of a uniform size having a particle size of m or more, and when Ga ₂ O ₃ is added, the voltage ratio in the low current region decreases and the leak current increases. was there.

[0006]

As described above, the conventional configuration has a problem that the resistance is lowered too much in the low current region, the voltage ratio is increased, and the leak current is increased.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a varistor having good non-linear resistance characteristics, a small leak current in a low current region, and stable against voltage application. To do.

[0008]

In order to achieve this object, the varistor of the present invention comprises ZnO and titanium oxide (hereinafter Ti).
O ₂ ) and a gallium component and an indium component are added at the same time, and a sintered body is obtained by firing a compact of a calcined powder.

[0009]

In this structure, the nonlinear resistance characteristics in the low current region and the high current region are both improved, the stability with respect to the pulse is increased, and the leakage current is reduced.

[0010]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below.

With respect to 100 mol of ZnO, 0.5 mol of Bi ₂ O _{3 and} 1.0 mol of CoO were added as additives.
Mix by a wet method by adding a mixture of 0.5 mol of MnO, 0.5 mol of nickel oxide (hereinafter referred to as NiO), 0.1 mol of chromium oxide (hereinafter referred to as Cr ₂ O ₃ ) and 0.5 mol of TiO _2. After crushing and drying, 25 × 10 ⁻⁴ mol of indium nitrate and Ga ₂ O converted to indium oxide (hereinafter referred to as In ₂ O ₃ )
Each aqueous solution of gallium nitrate of 25 × 10 ⁻⁴ mol converted to ₃ was added, pressure-molded, calcined at 600 ° C., and then pulverized to obtain calcined powder. Using this calcined powder, a molded body of a predetermined shape is formed, which is fired at a high temperature in the air atmosphere (heating rate 10
The temperature is raised at 0 ° C / hour, held at 1250 ° C for 2 hours, and then lowered at a temperature lowering rate of 100 ° C / hour) to a thickness of 1.2 m.
A disc-shaped sintered body having a diameter of 14 mm was prepared.

As shown in FIG. 1, gallium electrodes 2 are applied to both surfaces of a sintered body 1 by a thermal spraying method, and then copper is sprayed thereon, and lead wires 3 are connected by soldering, followed by coating. The varistor of (1) was created.

The varistor voltage of the varistor of sample number (1) is V ₁ mA / mm (voltage for 1 mm thickness between both terminals when a current of ₁ mA is applied), voltage ratio V ₁ mA / V _0.01 m
A, and the measured value of the limiting voltage ratio V ₅ A / V ₁ mA and the stability of the varistor against voltage application were measured with 8 ×.
Change rate of varistor rising voltage V ₁ mA (surge change rate) ΔV ₁ by two pulses of 20 μsec and 1 kA
The measured value of mA / V ₁ mA is shown in (Table 2).

Composition of this example for comparison with this example
From TiO₂, In₂O₃, Ga ₂O₃Out of three
Sample number (2) of (Table 1) excluding one or two of
The composition shown in the sample No. (8) is the same as that of the above embodiment.
Create varistor of sample number (2) to (8) by the method
The measured values of the electrical characteristics are shown in (Table 2).

[0015]

[Table 1]

[0016]

[Table 2]

The current-voltage characteristic of the varistor preferably has a high non-linear resistance characteristic even in a low current region and a high current region. Generally, a varistor having a high characteristic in a low current region has a high electric current characteristic. Insufficiency in the current region, and those having excellent characteristics in the high current region tend to be insufficient in the low current region, and it is difficult to obtain those having excellent properties in both the high and low current regions. Therefore, (Table 1) and (Table 2) above
As is clear from this, in the present embodiment in which TiO ₂ , Ga ₂ O ₃ , and In ₂ O ₃ are simultaneously added to ZnO shown in Sample No. (1), the varistor voltage is low and both the voltage ratio and the limiting voltage ratio are high. In addition to satisfying the above requirements, the surge resistance is superior to the comparative examples (Sample Nos. (2) to (8)) in which three kinds are not added at the same time.

Although not shown in (Table 2), the α value,
Excellent results were obtained in comparison with the comparative examples, such as variations in characteristics and results of load life tests.

As described above, according to this embodiment,
ZnO to TiO₂, G₂O₃, In ₂O₃At the same time
By using a sintered body that has
Low shear voltage, high non-linear resistance coefficient, long-term voltage
Stable against load and in both high and low current range
As a result, a varistor having good nonlinear resistance characteristics can be obtained.

(Second Embodiment) A second embodiment of the present invention will be described below. ZnO 100 mol, as an additive, Bi ₂ O ₃ 0.7 mol, CoO 1.0 mol
1, manganese carbonate (hereinafter referred to as MnCo ₃ ) 0.55
mol, TiO ₂ 0.7 mol, In ₂ O ₃ 2-3
Mixing a mixture consisting of 000 × 10 ⁻⁴ mol by a wet method
After crushing and drying, pressure molding, calcination at 600 ℃,
25 × 10 ⁻⁴ mol of gallium in terms of Ga ₂ O ₃ was added with an aqueous solution of gallium acetate to obtain a molded body of a predetermined shape, which was treated in the same manner as in Example 1 above to obtain a varistor of the same size and shape. Sample No. (1) was prepared and the measured values of the electrical characteristics similar to those of Example 1 were used and the amount of In ₂ O ₃ added was changed.
2) to 18), comparative examples are shown in (Table 3) and (Table 4) with sample numbers (11) and (19).

[0021]

[Table 3]

[0022]

[Table 4]

As is clear from (Table 3) and (Table 4), a varistor having an In ₂ O ₃ addition amount of 3 × 10 ⁻⁴ mol to 2000 × 10 ⁻⁴ mol with respect to 100 mol of ZnO has good characteristics. Is. The amount of In ₂ O ₃ added is 3 × 10
When it does not reach ^-4 mol, the voltage ratio becomes 2.0 or more, and the change rate Δ of the rising voltage V ₁ mA with respect to the surge is Δ.
Since the absolute value of V ₁ mA / V ₁ mA is 10% or more and the stability is insufficient, the amount of In ₂ O ₃ added is 3000 × 10
^-4 mol or more, the limiting voltage ratio becomes 2.0 or more,
Rate of change of rising voltage V ₁ mA with respect to surge ΔV ₁
The absolute value of mA / V ₁ mA becomes 10% or more and becomes unstable.

As described above, In ₂ O ₃ was added in an amount of 0.0003 m.
By adding ol% to 0.2 mol%, a varistor having excellent electric characteristics can be obtained.

(Third Embodiment) A third embodiment of the present invention will be described below.

With respect to 100 mol of ZnO, 0.7 mol of Bi ₂ O _{3 and} 1.0 mol of CoO were added as additives.
MnCO ₃ 0.55 mol, NiO 0.40mo
1, antimony oxide (hereinafter referred to as Sb ₂ O ₃ ) 0.2
A mixture of 0 mol and 0.70 mol of TiO ₂ was mixed and pulverized by a wet method, dried, and then pressure-molded to obtain 60
Calcinated at 0 ° C and converted to Ga ₂ O _{3 2} to 150 x 10
^-4 mol gallium was added with an aqueous solution of gallium nitrate,
50 × 10 ⁻⁴ mol of indium in terms of In ₂ O ₃ was added with an aqueous solution of indium nitrate and pulverized to obtain a shaped product of the same shape, which was then treated in the same manner as in Example 1 described above to obtain the same size and same size. Samples Nos. (22) to (28) were prepared in the same manner as in Example 1 except that the measured values of the electrical characteristics were changed by changing the amount of Ga ₂ O ₃ added. 21) and (29) are shown in (Table 5) and (Table 6).

[0027]

[Table 5]

[0028]

[Table 6]

As is clear from (Table 5) and (Table 6), a varistor in which Ga ₂ O ₃ is added in an amount of 2 × 10 ⁻⁴ mol to 150 × 10 ⁻⁴ mol per 100 mol of ZnO is good. It is a characteristic. The addition amount of Ga ₂ O ₃ is 1 × 1
When the content is 0 ⁻⁴ mol or less, the value of the limiting voltage ratio becomes 2 or more, which is not preferable, and the amount of Ga ₂ O ₃ added is 300 × 1.
When it is 0 ^-4 mol or more, the rising voltage is significantly increased, which is not suitable for low voltage, and the limiting voltage ratio is 2 or more, which is not preferable. In each of the comparative examples, the rate of change of the rising voltage V ₁ mA with respect to the surge ΔV ₁ mA / V ₁ m
The absolute value of A exceeds 10% and becomes unstable.

As described above, the amount of Ga ₂ O ₃ was 0.0002 m.
By adding ol% to 0.015 mol%,
A varistor with excellent electrical characteristics can be obtained.

(Embodiment 4) A fourth embodiment of the present invention will be described below.

With respect to 100 mol of ZnO, 0.7 mol of Bi ₂ O _{3 and} 1.0 mol of CoO were added as additives.
MnCO ₃ 0.55 mol, NiO 0.40mo
1, Sb ₂ O ₃ is 0.20 mol, TiO ₂ is 0.03
~ 3.0 mol of the mixture is mixed and pulverized by a wet method, dried, pressure-molded, calcined at 600 ° C, and Ga ₂
In terms of O ₃ was added to gallium 15 × 10 ^-4 mol with an aqueous solution of gallium nitrate, 15 × in terms of In ₂ O ₃
After 10 ⁻⁴ mol of indium was added with an aqueous solution of indium nitrate and pulverized, a molded body having a predetermined shape was formed, and the varistor having the same size and shape was prepared by the same process as in Example 1 described above. sample No. (32) to the present embodiment for changing the addition amount of TiO ₂ measurements of similar electrical characteristics and 1 (3
In 8), comparative examples are shown in (Table 7) and (Table 8) with sample numbers (31) and (39).

[0033]

[Table 7]

[0034]

[Table 8]

As is clear from (Table 7) and (Table 8), the varistor in which the amount of TiO ₂ added to ZnO 100 mol is 0.05 mol to 2.5 mol has good characteristics. If the added amount of TiO ₂ is 0.03 mol or less, the varistor voltage becomes high and it is not suitable for low voltage. Moreover, the value of the limiting voltage ratio becomes 2 or more, which is not preferable, and the change of the rising voltage V ₁ mA with respect to the surge. Rate ΔV ₁ mA / V
The absolute value of ₁ mA becomes 10% or more and becomes unstable. When the amount of TiO ₂ added was 3.0 mol or more, firing failure occurred, a good sintered body could not be obtained, and electrical characteristics could not be measured.

As described above, 0.05 mol% of TiO ₂ was added.
A varistor having excellent electric characteristics can be obtained by adding the addition of 2.5 to 2.5 mol%.

[0037]

As is apparent from the above description, according to the present invention, a calcined powder compact obtained by simultaneously adding three kinds of additives of TiO ₂ , Ga ₂ O ₃ , and In ₂ O _{3 to} ZnO is fired. With the configuration including the sintered body described above, it is possible to realize an excellent varistor that has good non-linear resistance characteristics, has a small leak current in a low current region, and is stable against voltage application.

[Brief description of drawings]

FIG. 1 is an external perspective view of a varistor according to a first embodiment of the present invention before a coating process.

[Explanation of symbols]

 1 Sintered body 2 Electrode 3 Lead wire

Claims (6)

[Claims] 1. A varistor of a sintered body containing zinc oxide as a main component and having a varistor voltage of 5 to 100 V, which comprises Bi, C
o, Mn, Sb, Cr, Pb, Ba, Ni, Sn, Si
Addition of an oxide of an element selected from the group consisting of 0.05 mol% to 2.5 mol in the sintered body.
% Added titanium oxide and 0.0005 mol% to 0.015 mol% in terms of Ga ₂ O ₃ in the sintered body.
A varistor comprising an added gallium component and an indium component added to the sintered body in an amount of 0.0003 mol% to 0.2 mol% in terms of In ₂ O ₃ . 2. The gallium component is a gallium salt solution,
The varistor according to claim 1, wherein the indium component is an indium salt solution. 3. The varistor according to claim 2, wherein the gallium salt solution is a gallium nitrate solution, and the indium salt solution is an indium nitrate solution. 4. The gallium component is a gallium salt solution,
The varistor according to claim 1, wherein the indium component is indium oxide. 5. The varistor according to claim 4, wherein the gallium salt solution is a gallium nitrate solution. 6. The varistor according to claim 4, wherein the gallium salt solution is a solution of gallium acetate.