JP2985384B2 - Stacked varistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated varistor in which a plurality of internal electrodes are laminated via a varistor characteristic portion in a sintered body, and more particularly to a varistor characteristic portion sandwiched between internal electrodes. The present invention relates to a multilayer varistor in which a voltage is reduced and reliability is improved by changing a density of a sintered body portion and a density of a sintered body portion of an outer layer.

[0002]

2. Description of the Related Art A varistor is widely used as a surge absorbing element or a voltage stabilizing element, and its electrical characteristics are represented by the following equation (1).

[0003]

(Equation 1)

[0004] formula (1), I is the current through the varistor, V is the applied voltage, V _i is the voltage between the terminals when the current iA flows through the device, a value of usually 1 mA, the varistor voltage V _It is called _1mA . α is called a voltage nonlinear coefficient, and indicates the degree of voltage control when the varistor is incorporated in an electric circuit. The larger α is, the better the voltage controllability is. In recent years, in the field of electronic devices such as communication devices, miniaturization and integration have been rapidly progressing, and accordingly, varistors have also been responding to ultra-miniaturization or integration to realize high-density mounting. There is a growing demand for lower voltage. In response to such a demand, a multilayer varistor has been proposed (Japanese Patent Publication No. 58-58).
No. 23921).

In the multilayer varistor, the number of grain boundaries between the electrodes can be reduced without causing the semiconductor crystal grains to grow in a huge manner, so that the operating voltage can be easily reduced. On the other hand, although not yet known, a multilayer varistor having a structure in which a non-connection type internal electrode is arranged between internal electrodes has been proposed as an improvement of the above-mentioned multilayer varistor (Japanese Patent Application No. 1-302496). . In this improved laminated varistor, the number of crystal boundaries interposed between the internal electrodes or the non-connected internal electrodes is set to 2 or less, and the varistor characteristics are obtained at the interface between the electrode and the crystal. Voltage variations are reduced,
In addition, it is possible to obtain a large surge withstand voltage while operating at a low varistor voltage of 4 to 16 V.

[0006]

Problems to be Solved by the Invention Japanese Patent Publication No. 58-2392
In the multilayer varistor disclosed in Japanese Patent Application Publication No. 01-30, the varistor characteristic is obtained at the zinc oxide crystal grain boundary.
In the multilayer varistor disclosed in No. 2496, varistor characteristics are obtained at the interface between the electrode and the zinc oxide crystal. The varistor voltage per zinc oxide crystal grain boundary is about 2
The varistor voltage at the interface between the electrode and the zinc oxide crystal is unipolar and is about 4V. Therefore, when trying to obtain a varistor voltage of 4V,
In the above two types of laminated varistors, the number of zinc oxide crystal grain boundaries sandwiched between the electrodes is desirably zero. Therefore, when the distance between the electrodes is 20 μm, it is desirable that the zinc oxide crystal be grown to at least 20 μm or more. In addition, when the distance between the electrodes is reduced, it is not necessary to grow zinc oxide crystals, but the processing becomes more difficult as the distance between the electrodes is reduced. Therefore, it is necessary to grow the zinc oxide crystal to a grain size of 20 μm or more as described above.

However, when the zinc oxide crystal grows large, the density of the sintered body decreases, and a large number of pores are formed. As a result, the environmental resistance, particularly the moisture resistance, is degraded by the large number of holes. As a method for improving the moisture resistance, a technique of coating the surface of a sintered body with glass is known. However, in this method, a glass paste must be applied to each of the sintered bodies and baked so that the sintered bodies do not fuse with each other or between the sintered bodies and the pod. Therefore,
This is very time-consuming and increases the cost of the stacked varistor.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive laminated varistor which can not only lower the varistor voltage but also has excellent environmental characteristics.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on a method for preventing a decrease in environmental characteristics when zinc oxide crystals are grown to reduce the varistor voltage. Considering that it is not necessary to make the crystal grain size of the sintered body portion sandwiched between the internal electrodes and the crystal grain size of the sintered body of the outer layer portion not sandwiched between the internal electrodes necessarily the same, Thus, the present invention has been accomplished.

[0010] ZnO as a main component and less as an auxiliary component
In a sintered body made of a raw material containing both Sb, the grain boundaries of the sintered body
To Zn₇Sb_TwoO₁₂A spinel crystal represented by
You. The inventors of the present application have proposed the addition of Sb added as a sub-component.
This Zn₇Sb _TwoO₁₂Are grains of zinc oxide crystals
Inhibit growth, conversely promote grain growth, or
Almost independent of grain growth of zinc oxide crystals
I found that. That is, Sb is replaced with Zn₇Sb_TwoO₁₂
When added in the form of
Inhibits the grain growth of crystals,_TwoO_ThreeSb in the form of
If added, the particle size of the zinc oxide crystals depends on the amount added.
Changes little or is added in large amounts
Found that they tended to promote grain growth
did. Therefore, zinc oxide crystal grains due to the addition form of Sb
By taking advantage of the difference in growth effects,
The particle size of the sintered body that functions as the
Increase the value to lower the varistor voltage, and
By suppressing grain growth in the outer layer
It is thought that a union can be obtained, and
Was.

That is, the present invention provides a laminated type including a sintered body obtained by using a raw material containing ZnO as a main component and at least Sb as a subcomponent, and a plurality of internal electrodes arranged in the sintered body. The varistor has the following configuration. The sintered body portion of the outer layer not sandwiched between the internal electrodes is composed of a raw material obtained by calcining and pulverizing a mixed powder containing ZnO as a main component and at least Sb ₂ O ₃ as a subcomponent. On the other hand, the sintered body portion sandwiched between the internal electrodes contains ZnO as a main component,
It is characterized by being constituted by using a raw material obtained by calcining and pulverizing a mixed powder containing at least Zn ₇ Sb ₂ O ₁₂ as an accessory component.

The second invention of the present application is directed to a sintered body obtained by using a raw material containing ZnO as a main component and at least Sb as a subcomponent, and a plurality of internal electrodes arranged in the sintered body. A multilayer varistor including at least one non-connection type internal electrode disposed between the internal electrodes and formed so as not to be electrically connected to the outside has the following configuration. That is, in the second invention, the sintered body portion of the outer layer not sandwiched between the internal electrode and the non-connection type internal electrode has ZnO as a main component and at least Sb ₂ as a subcomponent.
It is constituted by using a raw material obtained by calcining and pulverizing a mixed powder containing O ₃ , while a sintered body portion sandwiched between internal electrodes and / or non-connected internal electrodes is made of ZnO. It is composed of a raw material obtained by calcining and pulverizing a mixed powder containing at least Zn ₇ Sb ₂ O ₁₂ as a main component and as a sub-component.

In the first and second aspects of the present invention, S
b ₂ O ₃ and Zn ₇ Sb ₂ O ₁₂ are converted to Sb ₂ O ₃ by 0.01 so as to have the same ratio as Sb.
It is desirable to add about 0.5 mol%. Sb ₂ O ₃ and Zn ₇ Sb ₂ O ₁₂ are added in the same amount in terms of Sb because Sb is easily diffused along its concentration gradient. That is, Sb of the sintered body portion of the varistor characteristic portion and Sb of the sintered body portion of the outer layer
If the concentration is different, Sb diffuses to the lower concentration, and the target crystal grain size distribution cannot be realized.

Next, the reason why the addition amount of Sb ₂ O ₃ and Zn ₇ Sb ₂ O ₁₂ is desirably 0.01 to 0.5 mol% in terms of Sb ₂ O ₃ will be described. First, Sb ₂
When O ₃ is added, as shown in FIG. 1, the zinc oxide crystals do not grow to 5 μm or more, regardless of the amount of addition. On the other hand, as is clear from FIG. 1, Zn ₇ Sb ₂ O
_{When 12} is added, the larger the amount of addition, the more the grain growth of zinc oxide crystals is suppressed. However, when the amount of addition is small, the grain growth is promoted and a large crystal is obtained. The grain growth is Zn
Most promoted when the added amount of ₇ Sb ₂ O ₁₂ is 0.1 mol% in terms of Sb ₂ O ₃ , crystals of 10 μm or more are obtained in the range of 0.01 to 0.5 mol%. Therefore, Zn ₇ S
b ₂ O ₁₂ was converted to Sb ₂ O ₃ , and the raw material added in the range of 0.01 to 0.5 mol% was added to the varistor characteristic portion as Sb ₂ O 3.
_If the raw material to which ₃ is added in the range of 0.01 to 0.5 mol% is used for the outer layer, the crystal grain size of the varistor characteristic portion is 10 μm.
As described above, the crystal grain size of the outer layer portion is 5 μm or less. As a result, the varistor voltage in the varistor characteristic part is lowered,
Further, the sintered body portion of the outer layer is formed of a dense sintered body having few pores. At this time, S in the varistor characteristic portion and the outer layer portion
Since the b content is the same ratio, Sb does not diffuse into each other. Therefore, the particle size distribution of the zinc oxide crystals can be as designed above.

[0015]

The sintered body portion sandwiched between the internal electrodes and / or the non-connection type internal electrodes is a calcined mixed powder in which Sb is added in the form of Zn ₇ Sb ₂ O _{12 to} ZnO as a main component. ,
Since the varistor is composed of the crushed raw material, the varistor voltage is reduced. On the other hand, the sintered body portion of the outer layer not sandwiched between the internal electrode and / or the non-connection type internal electrode is obtained by calcining and pulverizing a material containing ZnO as a main component and adding Sb in the form of Sb ₂ O _3. As a result, the sintered portion of the outer layer is densified, and the environmental characteristics are improved.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be clarified by describing non-limiting embodiments of the present invention. Example 1 ZnO (96.9 mol%), CoO (1.0 mol%),
MnO (1.0 mol%), Sb ₂ O ₃ (0.1 mol%), and Cr ₂ O ₃ (1.0 mol%) in mixing the ceramic material formed in a molar ratio in parenthesis, B ₂ O ₃ ,
10% by weight of a glass powder composed of SiO ₂ , PbO and ZnO was added, water was added, and the mixture was pulverized by a ball mill to obtain a slurry. The slurry thus obtained was dehydrated, dried, calcined at a temperature of 780 ° C. for 2 hours, and then pulverized by a ball mill to prepare a raw material A.

On the other hand, ZnO and Sb_TwoO_ThreeTo 7: 1 mole
Mix at a temperature of 1200 ° C.
Treated with Zn₇Sb_TwoO₁₂Was synthesized. Next, ZnO
(96.9 mol%), CoO (1.0 mol%), MnO
(1.0 mol%), Zn₇Sb _TwoO₁₂(0.1 mol%
(Sb_TwoO_ThreeConversion)), and Cr_TwoO_Three(1.0 mol
%) In a molar ratio in parentheses
For material, B_TwoO_3,SiO_Two, PbO and ZnO
10% by weight of glass powder, and water
And a slurry was obtained. Like this
After dehydrating and drying the obtained slurry, the temperature of 780 ° C.
For 2 hours, then pulverize with a ball mill
Material B was prepared.

An organic binder was added to each of the two types of calcined raw materials A and B, and ethyl alcohol was further added as a solvent to form a slurry. Using these slurries,
Green sheets each having a thickness of 20 μm were obtained by a reverse roll coater. The obtained two types of green sheets were punched into a predetermined size and shape, and FIG.
The ceramic green sheets 1 to 6 shown in FIG. Here, green sheets 1 and 6 are made of raw material A, and green sheets 2 to 5 are made of raw material B.

On the upper surfaces of the ceramic green sheets 2 to 5, a conductive paste containing Ag and Pd is applied so as to have a weight ratio of Ag: Pd = 7: 3.
0 was formed. Ten ceramic green sheets identical to the green sheets 1 or 6 were laminated on the upper and lower sides of the ceramic green sheets 1 to 6, respectively, and pressed under a pressure of 2 ton / cm ² . The molded body obtained in this way is
It was fired at a temperature of 00 ° C. for 2 hours to obtain a sintered body 11. Next, a conductive paste containing Ag and Pd in a weight ratio of Ag: Pd = 7: 3 is printed on the side surfaces 11a and 11b of the sintered body 11 and baked at a temperature of 800 ° C. for 10 minutes to form an external electrode. 12a and 12b were formed. FIG. 3 shows a state in which the external electrodes are formed.

Example 2 The same raw material A and raw material B as used in Example 1 were prepared, and a green sheet having a thickness of 20 μm composed of raw material A and raw material B was obtained in the same manner as in Example 1. Was. Next, the obtained two types of ceramic green sheets were punched out into predetermined sizes and shapes to obtain ceramic green sheets 13 to 21 shown in FIG. In FIG. 4, the ceramic green sheets 13 and 21 are made of a raw material A, and the ceramic green sheets 14 to 20 are made of a raw material B.

Ceramic green sheets 14, 16, 1
A conductive paste containing Ag and Pd was applied to the upper surfaces of 8, 20 so as to have a weight ratio of Ag: Pd = 7: 3 to form internal electrodes 22, 24, 26, 28. On the upper surfaces of the ceramic green sheets 15, 17, and 19, a conductive paste containing Ag and Pd is applied so as to have a weight ratio of Ag: Pd = 7: 3, and the non-connection type internal electrodes 23, 25, and 27 was formed. Ten ceramic green sheets identical to the green sheets 13 or 21 were laminated on the upper and lower sides of the ceramic green sheets 13 to 21, respectively, and pressed under a pressure of 2 ton / cm ² .

The thus obtained molded body was subjected to 1000
Calcination was performed at a temperature of 2 ° C. for 2 hours to obtain 2 g of a sintered body. Next, Ag and Pd are applied to the side surfaces 29a and 29b of the sintered body 29, respectively.
The external electrodes 30a and 30b were formed by printing a conductive paste containing g: Pd at a weight ratio of 7: 3 and baking at a temperature of 800 ° C. for 10 minutes. FIG. 5 shows a state where the external electrodes are formed.

Example 3 ZnO ((97.0-x) mol%), CoO (1.0 mol%), MnO (1.0 mol%), Sb ₂ O ₃ (x mol%), and Cr ₂ B ₂ O ₃ and Si are added to a ceramic material obtained by mixing O ₃ (1.0 mol%) in the above molar ratio.
Glass powder composed of O ₂ , PbO and ZnO 10% by weight
Was added thereto, and water was added thereto, and the mixture was pulverized by a ball mill to obtain a slurry. The slurry thus obtained was dehydrated, dried, calcined at a temperature of 780 ° C. for 2 hours, and then pulverized by a ball mill to prepare a raw material A.

On the other hand, ZnO and Sb ₂ O ₃ were mixed in a molar ratio of 7: 1, and this was heat-treated at a temperature of 1200 ° C. to synthesize Zn ₇ Sb ₂ O ₁₂ . Next, ZnO
((97.0-x) mol%), CoO (1.0 mol%), MnO (1.0 mol%), Zn ₇ Sb ₂ O ₁₂ (x
Mol% (in terms of Sb ₂ O ₃ )) and Cr ₂ O ₃ (1.0
Mol%) in the above molar ratio, a glass powder composed of B ₂ O ₃ , SiO ₂ , PbO and ZnO is added at 10% by weight, water is added thereto, and the mixture is pulverized by a ball mill. Obtained. The slurry thus obtained was dehydrated, dried, calcined at a temperature of 780 ° C. for 2 hours, and then pulverized by a ball mill.
Raw material B was produced.

An organic binder was added to each of the two types of calcined raw materials A and B, and ethyl alcohol was further added as a solvent to form a slurry. Using these slurries,
Green sheets each having a thickness of 20 μm were obtained by a reverse roll coater. Next, the obtained two types of ceramic green sheets were punched into a predetermined size and shape, and the ceramic green sheets 1 shown in FIG.
~ 6. Next, the above ceramic green sheets 1
6, the laminated varistor shown in FIG. 3 was produced in exactly the same manner as in Example 1.

Evaluation of Examples 1 to 3 The varistor voltage of the laminated varistor manufactured in Example 1 and a corresponding conventional varistor and the DC voltage of 50% of the varistor voltage in an environment of a relative humidity of 95% and 60 ° C. Table 1 shows the varistor voltage change rate ΔV _{1 mA} after continuous application for 1000 hours.
Shown in

[0027]

[Table 1]

The varistor voltage of the laminated varistor manufactured in Example 2 and the corresponding varistor of the related art were set to a relative humidity of 95.
%, The change rate of the varistor voltage after continuously applying a DC voltage of 50% of the varistor voltage for 1000 hours in an environment of 60 ° C.
Table 2 shows _V1mA .

[0029]

[Table 2]

In obtaining the laminated varistor of the third embodiment,
Various laminated varistors were obtained by changing the contents of Zn ₇ Sb ₂ O ₁₂ and Sb ₂ O ₃ . Table 3 shows the average particle size of the varistor characteristic portion, the average particle size of the outer layer portion, the varistor voltage, and the voltage nonlinear coefficient of each of the obtained laminated varistors. In Table 3, Sb ₂ O ₃ marked with * = 0 mol% and 0.7 mol%
Are examples of Sb ₂ O ₃ and Zn ₇ S converted to Sb ₂ O _3.
The amount of b ₂ O ₁₂ added is outside the desired range.

[0031]

[Table 3]

[0032]

According to the multilayer varistor of the present invention, the sintered portion of the outer layer which is not sandwiched between the internal electrode and / or the non-connection type internal electrode has ZnO as a main component and Sb in the form of Sb ₂ O ₃ . Therefore, the sintered body portion of the outer layer is densified, and therefore, the environmental resistance, particularly, the moisture resistance is enhanced. The varistor characteristic portion, that is, the sintered body portion sandwiched between the internal electrode and / or the non-connection type internal electrode has ZnO as a main component and Sb as a subcomponent added in the form of Zn ₇ Sb ₂ O _12. The varistor voltage is also effectively reduced because of the use of the mixed powder.

Therefore, according to the present invention, it is possible to provide a laminated varistor having a low varistor voltage and excellent environmental characteristics, and perform a complicated operation such as coating a glass on a sintered body surface as in the conventional method. It can be omitted. Therefore, a laminated varistor exhibiting the above-described low varistor voltage and excellent reliability can be provided at low cost.

[Brief description of the drawings]

FIG. 1 shows the particle diameter of ZnO crystal and Sb ₂ O ₃ or Zn ₇
Is a diagram showing the relationship between the mixing ratio of Sb ₂ O _12.

FIG. 2 is an exploded perspective view illustrating a ceramic green sheet prepared in Example 1 and an electrode pattern formed thereon.

FIG. 3 is a cross-sectional view showing the multilayer varistor manufactured in Example 1.

FIG. 4 is an exploded perspective view illustrating a shape of a ceramic green sheet prepared in Example 2 and an electrode pattern formed thereon.

FIG. 5 is a cross-sectional view showing a multilayer varistor manufactured in Example 2.

[Explanation of symbols]

 1 to 6, 13 to 21 Ceramic green sheet 7 to 10, 22, 24, 26, 28 Internal electrode 23, 25, 27 Non-connection type internal electrode 11, 29 Sintered body

Continuation of the front page (72) Inventor Yukio Sakabe 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Murata Manufacturing Co., Ltd. (56) References JP-A-3-30401 (JP, A) JP-A-3-83846 (JP, A) JP-A-3-161901 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01C 7/02-7/22

Claims (2)

(57) [Claims] 1. A multilayer varistor comprising: a sintered body obtained by using a raw material containing ZnO as a main component and at least Sb as an auxiliary component; and a plurality of internal electrodes arranged in the sintered body. The outer layer sintered body portion not sandwiched between the internal electrodes,
ZnO as a main component and at least Sb ₂ O as a sub component
₃ is constituted by using a raw material obtained by calcining and pulverizing a mixed powder containing ₃ in which a sintered body portion sandwiched between the internal electrodes has ZnO as a main component and at least Zn ₇ Sb as a subcomponent. calcining a mixed powder containing ₂ O _12, the multilayer varistor, characterized in that it is constructed using the raw material obtained by grinding. 2. A sintered body obtained by using a raw material containing ZnO as a main component and at least Sb as a sub-component, a plurality of internal electrodes disposed in the sintered body, and a plurality of internal electrodes disposed between the internal electrodes. And a laminated varistor comprising at least one non-connection type internal electrode arranged so as not to be electrically connected to the outside, wherein the firing of an outer layer not sandwiched between the internal electrode and the non-connection type internal electrode is performed. The bound portion is formed using a raw material obtained by calcining and pulverizing a mixed powder containing ZnO as a main component and at least Sb ₂ O ₃ as a subcomponent, and the internal electrode and / or the non-connected The sintered body portion sandwiched between the mold internal electrodes is formed using a raw material obtained by calcining and pulverizing a mixed powder containing ZnO as a main component and at least Zn ₇ Sb ₂ O ₁₂ as a sub-component. Is characterized by Multilayer varistor.