JPH0273605A - Laminated type varistor - Google Patents

Abstract

PURPOSE:To prevent lack of oxygen at the time of baking, to reduce a leakage current and to improve reliability by alternately laminating varistor layers and inner electrodes, and adding glass powder into the electrodes. CONSTITUTION:Varistor layers 2 made of ZnO ceramics and inner electrodes 3 made of Ag-Pd alloy mixed with glass powder are alternately laminated. It is integrally sintered as a sintered material 4, and outer electrodes 5 are formed at the left and right end faces 4a, 4b. One end faces 3a of the electrodes 3 are alternately exposed with the end faces 4a, 4b of the sintered material 4 to be connected to the electrodes 5, and the other parts are sealed in the material 4. Thus, the glass powder is mixed with the electrodes 3 to avoid a decrease in oxygen concentration at the time of baking and temperature fall, to decrease a leakage current, and to improve reliability.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a multilayer varistor that functions as a voltage nonlinear resistor, and in particular reduces leakage current due to a decrease in oxygen concentration in the region near the internal electrode, thereby improving the performance of components. It relates to a structure that can improve the credibility of the system.

[Conventional technology]

Generally, a varistor is a resistor element whose resistance value changes non-linearly depending on an applied voltage, and is used as a surge absorption element to prevent overvoltage from being applied to an electronic circuit. Conventionally, as such a varistor, there is a rectangular parallelepiped laminated type varistor as shown in Fig. 4 (Japanese Patent Publication No. 58
-23921), this multilayer varistor 10 has varistor layers 11 and internal electrodes 12 alternately stacked and integrally sintered, and left and right end surfaces 13a of the sintered body 13.
.

An external electrode 14 is formed on 13b.

Further, this external electrode 14 has a portion on the left side of the sintered body 13 .

Internal electrodes 12 alternately exposed on right end surfaces 13a and 13b
One end surface 12a of the two is connected.

[Problem that the invention seeks to solve]

By the way, in a laminated varistor, it is necessary to supply oxygen into the varistor layer during the temperature-lowering process during firing. However, in the conventional varistor described above, the varistor layer and the internal electrode layer are in a laminated state, and this combined with the condition that the thickness of the varistor layer is thin leads to a problem that the oxygen concentration in the region near the internal electrode of the varistor layer decreases. There is a point.

As a result, leakage current increases, power consumption increases, and thermal runaway occurs. The thinner the material, the greater the rate of oxygen depletion, which increases the leakage current.

The purpose of the present invention is to prevent oxygen deficiency during firing,
An object of the present invention is to provide a multilayer varistor that can reduce leakage current and improve reliability.

[Means for solving problems]

The inventors of the present invention have conducted various studies to avoid the oxygen deficiency during the temperature drop, and have found that it is sufficient to include a substance in the internal electrode that can prevent the diffusion of the electrode. We have found that a glass component is the most suitable material. It is known that when a glass component is added to a multilayer ceramic capacitor, it diffuses into the ceramic portion and has an adverse effect such as lowering the dielectric constant. From this point of view, even in the case of a laminated type varistor, it is thought that mixing and adding a glass component to the internal electrodes would cause some adverse effects, and therefore, conventionally there was no idea of adding a glass component to the internal electrodes. However, after repeated studies by the inventors of the present invention, it was found that even if glass components were used in the above-mentioned laminated varistor, there would be no adverse effect.
It has also been found that diffusion of the internal electrodes can be prevented, and the present invention has been completed thereby.

Therefore, the present invention is a multilayer varistor in which varistor layers and internal electrodes are alternately stacked, and is characterized in that glass powder is added to the internal electrodes.

Here, as the glass powder, B, Si, Pb, Bl
It is desirable to use a glass powder containing at least two types of , Zn, and the amount of the glass powder added is 0.1 to 20 w with respect to the metal used for the internal electrode.
A range of t% is desirable because below the above range it is difficult to obtain the effect of reducing leakage current, and adding more than this will result in a decrease in the nonlinear coefficient.

[Effect]

According to the multilayer varistor according to the present invention, since glass powder is mixed into the internal electrodes, a decrease in oxygen concentration during firing and cooling can be avoided. That is, since the glass powder has a softening temperature lower than the firing temperature, the glass powder wraps the metal of the internal electrode in an extremely thin film during firing. Therefore,
In the temperature cooling process, the glass powder gives oxygen to the electrode metal, so that the metal does not deprive the ceramic of oxygen (as a result, the ceramic grain boundary phase is prevented from being reduced, and this prevents the varistor layer from being reduced). The supply of oxygen to the fuel cell is compensated, and oxygen deficiency can be avoided.As a result, leakage current can be reduced, and problems such as power consumption thermal runaway can be avoided.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 to 3 are diagrams for explaining a multilayer varistor according to an embodiment of the present invention.

In the figure, numeral 1 denotes the multilayer varistor of this embodiment, which has a rectangular parallelepiped shape and includes a varistor layer 2 made of ZnO-based ceramics and an internal electrode 3 made of an Ag-Pd alloy mixed with glass powder. External electrodes 5 are provided on the left and right end surfaces 4a and 4b of the sintered body 4, which is formed by laminating the layers alternately and sintering them together.
It is composed of Further, one end surface 3a of the internal electrode 3 is alternately exposed to both end surfaces 4a and 4b of the sintered body 4 and connected to the external electrode 5, and the other portion is enclosed within the sintered body 4. has been done.

Next, a method for manufacturing the multilayer varistor 1 of this embodiment will be described.

■ First, Z n O (96,0+mo 11%),
B l x Os (1°5-01%), Mn0 (1,
0moj! %), Co t 0s (0+5 n.

Bt Os , S loz , P
A glass component consisting of bO and ZnO was added at 5 wt% as a raw material, and an organic binder was mixed with this to form a green sheet with a thickness of 30μ by a doctor blade method.The green sheet was then cut into rectangular shapes. , a large number of varistor layers 2 are created.

■ On the other hand, baset made by mixing PT with vehicle,
An electrode paste is created by adding glass powder such as Bt 0s=S i Ox. Next, the varistor layer 2
The internal electrode 3 is formed by screen printing this electrode paste on the upper surface of the . In this case, one end surface 3a of the internal electrode 3
Only one end face extends to the outer edge of the varistor layer 2, and the other end face is located inward.

■Next, as shown in FIG. 3, the varistor layers 2 and internal electrodes 3 are alternately overlapped, and
The varistor layer 2 is laminated so that a is alternately exposed on both end faces of the varistor layer 2, and further on top of this laminate.

Ceramics JW7 as a dummy is layered on the lower surface, and this is pressed and bonded with a press to form a laminate.

Then, as shown in FIG. 1, only one end surface 3a of the internal electrode 3 is exposed to the outside of the left and right side surfaces of the laminate.
The remaining portion will be completely buried within the varistor layer 2.

■ Then, the above laminate was placed in the air at a temperature of 900-1300
C. to obtain a sintered body 4. In this firing process, the glass powder in the internal electrode 8i+3 is softened and the electrode 3
Therefore, when the temperature falls, the metal particles do not take away oxygen from the ceramics, thereby compensating the supply of oxygen to the ceramics and preventing deterioration of the area near the internal electrodes 3. That will happen.

■ After that, one end surface 3 of the internal electrode 3 of the sintered body 4 is
External electrodes 5 are formed by applying a paste mainly composed of Ag and adding Pd to the left and right end surfaces 4a and 4b where the portion a is exposed, and then baking the paste.

Next, the effects of this embodiment will be explained.

According to the multilayer varistor 1 of this embodiment, the internal electrode 3 is mixed with glass powder that prevents the reduction of the ceramic grain boundary phase by metal particles when the temperature decreases, so it is possible to prevent a decrease in oxygen concentration, and as a result, leakage can be prevented. The current can be significantly reduced, an increase in power consumption can be avoided, and the risk of thermal runaway can be reduced.

Next, we will discuss the effects of this embodiment on f! We will explain the results of experiments conducted to confirm this.

In this experiment, as shown in Table 1, BtOsSiOz
PbO-based (column 1 A), BtO.

5tot BitOs system (second column B), B, ○.

-3i Ox -P bo-B it○, system (third column C
), Bx Os Sioz ZnO system (column 4 D
), and each of these glass powders was added to the above PT paste at 0.01 to 30 w.
A multilayer varistor was produced by the above-mentioned manufacturing method by adding within the range of t%. Then, V+ of each laminated varistor
−A (varistor voltage of the element itself), nonlinear coefficient α
(α-1/1ogCVl@A/V@, IIIA
), and leakage current (D, C, current value that flows when 3V is applied) was measured. Further, for comparison, similar measurements were performed on a conventional multilayer varistor in which no glass powder was added to the internal Ti.

The results are shown in Table 2.As is clear from the table,
In the conventional sample, although the original characteristics of VIIIA+α are obtained, the leakage current is as large as 2 μA.

Also, in samples A to D of this example, when the amount of glass powder added was as small as 0.01 wt%, the leakage current was 2 μA.
However, when this addition amount exceeds 0.1 wt%, the leakage current is significantly reduced to 0.5 μ8 or less in all Example samples A-D. I understand that. On the other hand, the above addition amount is 3Qwt
%, the leakage current reduction effect is obtained, but α is reduced to 10 to 15. Therefore, from this experiment, the amount of the glass powder added is 0.1 to 20 IIlt%.
It can be said that it is desirable to keep it within the limits.

〔Effect of the invention〕

As described above, according to the multilayer varistor of the present invention, since glass powder is added to the internal electrode, it is possible to prevent oxygen depletion during cooling during firing, reduce leakage current, and improve reliability. be.

No. table

[Brief explanation of the drawing]

1 to 3 are for explaining a multilayer varistor according to an embodiment of the present invention, FIG. 1 is a sectional view thereof, FIG. 2 is a perspective view thereof, and FIG. 3 is an exploded perspective view thereof. 4 are cross-sectional views showing a conventional multilayer varistor. In the figure, 1 is a multilayer varistor, 2 is a varistor layer, and 3 is a multilayer varistor.
is the internal electrode.

Claims (1)

[Claims] (1) Consisting of alternating layers of varistor layers and internal electrodes,
A multilayer varistor that functions as a voltage nonlinear resistor, characterized in that glass powder is added to the internal electrode.