JPS60233801A - Voltage nonlinear resistor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is directed to a method in which the zinc oxide grain boundary segregated phase in a sintered body containing zinc oxide as a main component and having voltage nonlinearity is mainly composed of a bismuth titanate layered compound. This invention relates to a voltage nonlinear resistor that has low rise voltage and thermal stability.

[Technical pre-invention JQI In recent years, with the rapid development of semiconductor devices and circuits such as ICs, L-transistors, and thyristors, and their applications,
Control 2 The use of semiconductors and semiconductor circuits in communication equipment and power equipment has become widespread, and these equipment are rapidly becoming smaller and more sophisticated. However, on the other hand, with such progress, the withstand voltage, surge resistance, and noise resistance of these devices and their components cannot be said to be sufficient. Therefore, it is necessary to protect these devices and parts from abnormal surges and noise.
Alternatively, it is necessary to stabilize the circuit voltage. Until now, SiC and Si varistors have been widely used for these purposes. Recently, varistors have been developed that use zinc oxide as a main component and add additives to it. However, in recent years, as semiconductors and semiconductor circuits have become more dense and highly integrated, semiconductors and semiconductor circuits have become increasingly low-voltage and low-power. In order to protect these semiconductors and semiconductor circuits, or to stabilize @IBM pressure, varistors that work at even lower voltages have become necessary.

The voltage-current characteristics of a varistor are generally expressed by the following relational expression (1). Here, V is the voltage applied to the varistor body, and ■ is the current flowing through the varistor body. Further, C is a constant corresponding to the voltage when a given current is passed. α-1 is an ordinary resistor that follows Ohm's law, and the larger α is, the better the nonlinearity is.

Here, instead of expressing the varistor characteristics by C and α, it is expressed by the rising voltage V 1 mA and α when a current is passed through 1m8 at a current density of cffl. SiC varistors, which are a typical sintered body with voltage nonlinearity, are made by baking SiC particles with a ceramic binder, and the nonlinearity is due to the SiC varistor.
This is due to the voltage dependence of the contact resistance of C particles. If the thickness of the varistor body is 1 mm, the rise voltage when a current of 1 m^/cM flows is V 1 mA/cocoon, then SiC
Varistors can be manufactured from a few square meters to several thousand V by controlling the grain size and element thickness of the SiC particles, but because the nonlinear coefficient α is as small as 3 to 7, Not ten. Further, there is a zinc oxide varistor whose sintered body itself has nonlinearity like the SiC varistor. This is mainly composed of zinc oxide and contains small amounts of bismuth oxide, cobalt oxide, manganese oxide, antimony oxide, etc. as additives. The nonlinearity coefficient of the zinc oxide varistor is approximately 20 to 50, and exhibits extremely superior nonlinearity compared to the SiC varistor. For this reason, they are very suitable for protecting semiconductors and semiconductor circuits, but the voltage used by semiconductors and semiconductor circuits is becoming increasingly lower.

[Problems with the background technology] Conventional zinc oxide varistors have a low voltage varistor (VlmA of about 20μ) that supports the above-mentioned low voltage.
was extremely difficult to manufacture. The reason for this is that, as shown in Figure 1, the fine pattern of zinc oxide-based varistors consists of low-resistance zinc oxide crystal grains (1) surrounded by high-resistance grain boundary layers (2) that exhibit nonlinearity. It is. (3) in the diagram
is an electrode, and (4) is a terminal. Therefore, the thickness of the sintered body is 11
11Il^/mm per Wn is determined by the number of grain boundary layers (2) present in the thickness direction of the element body. In zinc oxide varistors, the rising voltage per grain boundary layer is approximately 2.5
■It's Cheng Gua.

When zinc oxide mixed with bismuth oxide, cobalt oxide, manganese oxide, etc. is sintered at a humidity of 1100 to 1300°C, the particle size of the zinc oxide crystal grains (1) in the sintered body is about 30 to 40 μm. It is. Therefore, V 1 mA/
mm is 40V or more. In order to manufacture a varistor with a voltage of VlmA-20V, it is necessary to make an element body with a thickness of 0.5 m. This platform microstructure has a form in which ten zinc oxide crystal grains (1) are connected in series and eight grain boundary layers (2) are present between the grains. As a method for manufacturing an element body with a thickness of 0.5 mm, there is a method of polishing a sintered body to obtain a predetermined thickness. However, the mechanical strength of the sintered body is weak because the zinc oxide crystal grains (1) are surrounded by grain boundary layers (2) mainly made of bismuth oxide. For this reason, during polishing, the zinc oxide crystal grains (1) fall off and microcracks occur, resulting in locally low voltage defective areas.

Another method is to mold the sintered body into a thin plate shape, taking into consideration the shrinkage rate after sintering so that the sintered body has a predetermined thickness. In this case, considering the shrinkage rate, it is 0.6 to 0.7
It must be molded to a thickness of mm. However, the mechanical strength of the molded product is very low, and cracks and chips occur, making it extremely difficult to handle the molded product.

In order to eliminate these defects, the grain size of the zinc oxide crystal grains (1) of the sintered body should be grown to about 100 μm, and the element thickness should be about 1.0a*rV 1111A=20V (7) It is necessary to increase the strength of the molded body. Recently, as a method of manufacturing zinc oxide-based low voltage varistors, there is a method of using zinc oxide crystal grains (1) having a grain size of about 100 μm, as proposed in, for example, Japanese Patent Laid-Open No. 140995/1983. During the sintering process, zinc oxide crystal grains (
Since it is difficult to grow 1) to a size of about 100 μm, zinc oxide crystal grains (1) grown to a large size from the beginning are used as part of the main component, zinc oxide.

However, in order to obtain large zinc oxide crystal grains (1), a mixture of zinc oxide and barium carbonate or strontium carbonate is molded and sintered, and this sintered body is boiled in pure water. 13a and S surrounding the crystal grain (1)
It is necessary to dissolve r in water and decompose the sintered body. Further, the grain size of the raw materials other than the zinc oxide crystal grains (1) is several μm or less. Therefore, during the sintering process, a difference in shrinkage rate occurs between the zinc oxide crystal grain (1) portion and the other raw material powder portions, making the sintered body porous.

Therefore, in order to obtain a dense element body with a low V 1 mA/mm, zinc oxide crystal grains (sintering temperature 2 grain size, addition ratio) should be used.

The selection of conditions such as the composition of raw materials other than crystal nuclei becomes complicated.

Another disadvantage of zinc oxide varistors that contain bismuth oxide as an additive is the heat treatment conditions for the sintered body (including the electrode baking process).
It can be said that the life characteristics change greatly depending on the condition. This is because the grain boundary layer (2) that exhibits non-σ line property is mainly composed of bismuth oxide. The bismuth oxide crystal phase in the sintered body before heat treatment includes at least one of an α phase, a β phase, and a δ phase. By heat-treating this sintered body, all bismuth oxide is converted into the γ phase. It is thought that the life characteristics change greatly due to this process of change to the γ phase.

In this way, manufacturing low voltage varistors using a composition system containing zinc oxide as the main component and bismuth oxide as an additive had the disadvantage of requiring a very large number of steps (and the selection and management of conditions were complex). .

[Object of the invention] The present invention has zinc oxide as the main component, and the zinc oxide grain boundary segregated phase is mainly composed of a bismuth titanate layered compound instead of bismuth oxide, so that the zinc oxide crystal particles in the sintered body are
It is an object of the present invention to provide a low voltage voltage nonlinear resistor grown to a thickness of 00 μm or more.

[Summary of the Invention] The voltage nonlinear resistor of the present invention is a voltage nonlinear resistor 1 whose main component is zinc oxide and whose sintered body itself has voltage nonlinearity. The phase is mainly 2+.

(B i 202) (B + 2T i 3010)
It consists of a bismuth layered compound shown in the following.

[Embodiments of the Invention] The details of the present invention will be described below. In other words, the fine structure of the varistor in which the zinc oxide grain boundary segregated phase is mainly composed of bismuth titanate layered compound is similar to that of conventional bismuth oxide, and the grain boundary layer that exhibits nonlinearity is composed of bismuth titanate layered compound. It is. This has made it possible to eliminate crystal phase changes in the grain boundary layer during the heat treatment process. As described above, the present invention provides a highly reliable, low-voltage nonlinear resistor obtained by having the zinc oxide crystal grain boundary segregated phase mainly composed of a bismuth titanate layered compound instead of bismuth oxide.

Next, embodiments of the present invention will be described. Zinc oxide 9,
Bismuth oxide, bismuth titanate layered compound, cobalt oxide, manganese oxide, and nickel oxide were weighed as starting materials to the composition ratios shown in Table 1.

After mixing, drying, granulation, and molding, the mixture was sintered at a temperature of 1100 to 1300°C to obtain a sintered body having a diameter of 15 #I and a thickness of 1.0 am. A 1.0 cd electrode showing ohmic contact was formed on this, and VIIIA/s and nonlinear coefficient α were measured. Table 1 shows the results. Examples of the present invention are composition Nos. 5 to 8 marked with O, and these were sintered at a temperature of 1220° C. for 2 hours.

(The following is a blank space) In Table 1, composition No. 11 to 4 are reference examples in which the amount of bismuth oxide was changed, and composition No. 5 to 8 are examples in which M in the bismuth titanate compound was changed.

From Table 1, composition Nos. 5 to 8 of Examples have the highest V 1
It can be seen that the mA/wear becomes low and the non-linear coefficient α is also high, so the effect is remarkable. Also, the VI of the sintered body for each added amount of bismuth oxide and bismuth titanate compound
FIG. 2 shows the change in IIIA/m, and FIG. 3 shows the change in the nonlinear coefficient α. In FIGS. 2 and 3, curve A shows the case of bismuth oxide, and curve B shows the case of bismuth titanate compound.

From FIG. 2 and FIG. 3, the example of curve B in which bismuth titanate layered compound is added is compared with the reference example of curve A in which bismuth oxide is added. I know it will grow significantly. Figure 4 shows the life characteristics with respect to heat treatment temperature.
Rate of change in rising voltage V 1 mA when a current of 1 m^/d is applied for 1000 hours in an atmosphere of 5°C ΔV l m
Curve A2 shows the case of Reference Example 1 with composition NQ2, and curve B6 shows the case of Example with composition N06. It can be seen from FIG. 4 that the example of curve B6 containing a bismuth titanate layered compound as the zinc oxide grain boundary segregated phase is not affected by the heat treatment temperature. Further, if the amount of the hismuth titanate layered compound added is less than 0.05 mol %, it is not sufficient to grow zinc oxide crystal grains and V111A/m becomes high, which is not suitable. In addition, if the amount exceeds 3.0 mol%, it will be more than the required amount and will cause problems such as precipitation on the surface of the sintered body and fusion of the sintered body.
In addition, V 1 mA/mm also increases, and the nonlinear coefficient α also begins to decrease, which is not appropriate.

In addition to the additives used in the above examples, Sb, C
r', Sn, AI, MO, 8a, B, Si.

Nonlinearity can be further improved by adding a small amount of oxides of Pb, Fe, and Sr.

[Effects of the Invention] As described in detail above, the present invention uses zinc oxide as the main component and contains bismuth titanate layered compound in the form of B f 4 Ti 3012 as the zinc oxide grain boundary segregated phase at 1%! By containing 0.05 to 3.0 mol% in total, zinc oxide crystal grains can be grown to 100 μm or more, and there is no crystal phase change in the grain boundary layer during the heat treatment process, resulting in high reliability and stable properties. It is possible to provide a voltage nonlinear resistor with a high voltage.

[Brief explanation of drawings]

Fig. 1 is an enlarged cross-sectional view showing a zinc oxide-based varistor with a fine IIm structure, and Figs. 2 to 4 show a comparison of characteristics between an example of the present invention and a reference example. FIG. 3 is a curve diagram showing the change in V1fflA/Irm with respect to the addition amount, FIG. 3 is a curve diagram similarly showing the change in the nonlinear coefficient α, and FIG. 4 is a curve diagram showing the rate of change in V 1 mA with respect to the heat treatment temperature. (1)...Zinc oxide crystal grains (2)...Grain boundary layer (3)...Electrode (4)...Terminal patent patented Applicant Marcon Electronics Co., Ltd. Figure 1 Figure 2 Power cI Tatami (Moruso) Figure 3 0.030.05 0. S D, II 3.0 η
O no Karo 1k (7l%) Figure 4 @ Buried 4g (-C)

Claims (2)

[Claims] (1) In a voltage nonlinear resistor whose main component is zinc oxide and whose sintered body itself has voltage nonlinearity, the zinc oxide grain boundary segregation phase of the sintered body is mainly 2+, 2− (BI 202 ) (B l 2T f 301o
) A voltage nonlinear resistor characterized in that it is made of a layered compound coated with SUMAS. (2) 8 bismuth layered compounds! 4T! 30
12. The voltage nonlinear resistor according to claim 1, wherein the voltage nonlinear resistor contains 0.05 to 3.0 mol% of type 12.