JPS606522B2 - semiconductor composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has zinc oxide as its main component, and additives such as praseodymium (Pr), lanthanum (La), and cobalt (
The present invention relates to a semiconductor ceramic composition (hereinafter referred to as a ceramic varistor) containing voltage nonlinear resistance characteristics containing Co) and silicon (Si).

In recent years, ceramic varistors, which are mainly composed of zinc oxide and have excellent voltage nonlinear resistance characteristics, have been widely used as electronic components to protect circuits and prevent malfunctions. There is a growing demand for varistors with excellent voltage non-linear resistance characteristics even on the large current side. As shown in FIG. 1, the voltage-current characteristics of a varistor are such that the current changes non-linearly with respect to the voltage. Therefore, the voltage-current characteristics are usually expressed by the following empirical formula. 1:(ki)Q Here, 1 is the current flowing through the element, and V is the applied voltage at that time.

The voltage when a current of 1 A normally flows is called the varistor voltage. C is a constant corresponding to resistance. Further, Q is commonly used as an index indicating the degree of nonlinearity. However, over a wide current range, Q itself changes depending on the voltage, so if nonlinearity is exhibited over a wide range, the ratio of the voltage on the low current side to the voltage on the high current side (for example, as shown in Figure 1) It is more reasonable to express it by the ratio of A of VI shown to V5M). In this case, the voltage ratio is 4.0, and the voltage nonlinear resistance characteristics are excellent. In recent years, ceramic varistors whose main component is zinc oxide include bismuth (Bi), antimony (Sb), manganese (Mn), and cobalt (Co).
) and varistors in which electrodes are provided on porcelain containing oxides such as chromium (Cr) as additives have been developed. This type of ceramic varistor has the advantage that its voltage nonlinear resistance characteristic is caused by the crystalline structure itself, and its nonlinearity is very stable over a wide current range. However, on the other hand, since it contains substances such as bismuth and antimony that are extremely prone to evaporation under the high temperatures required when firing varistors, it is difficult to fire large quantities of varistors with the same characteristics at a high yield. This method requires special measures and has the disadvantage of being relatively expensive to manufacture. On the other hand, ceramic varistors whose main component is zinc oxide include praseodymium (Pr), cobalt (Co), chromium (Cr), and potassium (K).
Porcelain containing oxides such as oxides as additives and provided with electrodes has been developed (Japanese Patent Application Laid-Open No. 53-114093
).

It does not contain components that easily evaporate, such as bismuth or antimony, and has good voltage nonlinear resistance characteristics, but it is essential to add potassium and chromium to improve the voltage nonlinear resistance characteristics in the large current region. ing. However, the addition of potassium causes problems in moisture resistance, which is extremely important for electronic components. For this reason, when this element is actually used, it is necessary to protect the surface of the fired element by covering it with fused glass, which increases the number of manufacturing steps and increases manufacturing costs. . Also,
Since it is necessary to use a relatively large amount of highly purified praseodymium, which is a scarce resource, this method has the disadvantage of being uneconomical. In contrast, the present invention aims to solve the above-mentioned drawbacks of ceramic burrs outer shells containing zinc oxide as a main component.

That is, by discovering the following fact in a ceramic varistor whose main component is zinc oxide and which also contains praseodymium, lanthanum, and cobalt, the above-mentioned drawbacks have been successfully solved. That is, according to the present invention,
By adding silicon element, it is possible to obtain excellent voltage nonlinear resistance characteristics in a large current region without using an alkali metal element such as potassium. ceramic.

Although there are still many aspects of the role of silicon as an additive outside the burr that have not been fully elucidated, the inventors believe the following. That is, the microstructure of a ceramic varistor whose main component is zinc oxide is estimated as follows.

That is, zinc oxide crystals with low resistivity are surrounded by grain boundaries or grain boundary layers with high resistivity. The smaller the resistance of the crystal, the better. On the other hand, the larger the resistance near the grain boundaries, the better for non-linear resistance characteristics. A trace amount of camphor element settles into the zinc oxide crystal, lowers the specific resistance of the crystal, and improves the voltage nonlinear resistance characteristics. but,
When the silicon content increases, the silicon element also lowers the specific resistance near the grain boundaries, which contributes to the development of nonlinear resistance, so that the nonlinearity actually decreases. Therefore, if the distribution of the borosilicate element is non-uniform within one element body, non-uniformity will occur in the distribution of resistance and the distribution of voltage non-linear resistance characteristics within one element body. Therefore, when an electric field is applied to such an element, a current is generated in a part of it,
The disadvantage is that the temperature of that part increases and it breaks down. However, the advantage of silicon element is that its ionic radius is small and it is easily diffused, so the distribution within a single element body tends to be extremely uniform. For this reason, the use of silicon element has the advantage that breakdown phenomena due to the causes mentioned above are less likely to occur and it is easier to obtain an element that is resistant to current surges. From these facts, it is considered that by containing an appropriate amount of silicon element, it is possible to obtain an element that has excellent voltage nonlinear resistance characteristics and is resistant to current surges. The present invention solves the above-mentioned problems by incorporating silicon by the above-described method without using any alkali metal elements such as potassium.

Furthermore, since the distribution of silicon tends to be uniform, it has become possible to obtain a fired body made of crystals with uniform grain size, which is also excellent in terms of reliability. Furthermore, in order to add silicon in this way, it is preferable that the amount of praseodymium or lanthanum be extremely small, and because of the parentheses, resources are saved and it is also economically advantageous. The composition according to the invention is as follows.

In other words, when converting zinc oxide into the form of Zn○, it is 99.87
99-84.88 hol%, praseodymium oxide and lanthanum oxide in R203 (however, R is Pr and La
) in the form of 0.01 to 0.038 ho1, respectively.
%, 0.1 to 15 in terms of cobalt oxide in Coo form
hol% and silicon oxide are converted to Si02 form and are 0.
It has a composition of 0001 to 0.08 hol%. The present invention will be explained below with reference to Examples.

Examples Commercially available zinc oxide, praseodymium oxide, lanthanum oxide,
Cobalt oxide and silicon oxide were weighed to a predetermined ratio and mixed using a ball mill.

After drying the mixture, mix it with PVA solution and make it into neck granules.
It was press-molded into a disc of 5 m long and 1.5 mt. The molded samples were fired for 2 hours at a temperature of 1250-1500 qo. A 11.5 mm Ag electrode was attached to the fired sample to measure the voltage nonlinear resistance characteristics. Representative examples of the results are shown in Table 1.

Sample No. in Table 1. 1~No. 7 is a sample according to the present invention.

Sample No. &No.9 is a comparative example in which silicon was not added. As can be seen from Table 1, all of the samples of the present invention have an o of around 15 or more and a voltage ratio of V5/Vi.
It exhibits excellent voltage non-linear resistance characteristics from the low current region to the high current region, with mA of 2 or less, and is clearly very useful in practice.

This voltage nonlinear resistance characteristic is due to the bulk characteristics of the sintered body itself, so the varistor voltage can be easily set to the desired value depending on the application by changing the sample thickness, firing conditions, etc. realizable. The reasons for limiting each additive are as follows.

If the amount of braceodymium oxide and lanthanum oxide is less than 0.01 mol%, the effect will be small and 0.01 mol%.
When it exceeds 0.3 ol%, the resistance decreases and the voltage non-linear resistance characteristics in the low current region deteriorate.

If the amount of cobalt oxide is less than 0.1 mol %, the effect will be small, and if it exceeds 15 hol %, voltage nonlinearity in a large current region will deteriorate. The amount of silicon oxide is 0.0001 mol%
If the amount is less than 0.05 mol %, there is no effect, while if it exceeds 0.05 mol %, the voltage nonlinearity in the low current region deteriorates rapidly.
Incidentally, it goes without saying that the characteristics will be further improved if a differential powder is used as much as possible as the silicon raw material. Even better results are obtained if wet mixed with other raw materials in the form of a solution.

Further, in the examples, oxides were used as raw materials, but equivalent characteristics can be obtained from carbonates, nitrates, hydroxides, chlorides, etc., which can be converted into oxides during firing.

For other manufacturing methods, ordinary ceramic methods are sufficient.

Concerning the preliminary conditions, there will be no particular problem as long as the pulverization after calcining is carried out sufficiently. The main firing conditions are normally air or oxygen, but by creating an appropriate oxygen partial pressure with a neutral gas such as kiln or argon,
It is also possible to realize something with even better performance.
The electrode may be in ohmic contact with the fired body or in non-ohmic contact, and the electrodes may be applied using any of the following methods: grating, plating,
Any method such as thermal spraying, vapor deposition, or sputtering is possible.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the voltage nonlinear resistance characteristics of a ceramic varistor. Figure 1

Claims (1)

[Claims] 1 Zinc oxide converted to ZnO form: 99.8799~
84.88 mol%, praseodymium oxide and lanthanum oxide in R_2O_3 (R is Pr and La)
0.01 to 0.035 mol% each in terms of
, 0.1 to 15 m in terms of cobalt oxide in the form of CoO
ol% and silicon oxide in the form of SiO_2 are 0.
A semiconductor composition having a composition of 0001 to 0.05 mol%.