JPH0362003B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing semiconductor ceramics for voltage nonlinear resistors. In recent years, resistors with nonlinear voltage-current characteristics, so-called varistors, have been developed that use strontium titanate-based semiconductor ceramics as an element body.
This type of voltage nonlinear resistor is manufactured by (a) applying a paste containing metal oxides such as Mn, Zn, and Co to the surface of semiconductor porcelain made by converting strontium titanate into a semiconductor, and The element body is an insulating layer formed on the crystal grain boundaries of the semiconductor porcelain by heat treatment at a temperature of 1200 to 1300°C in an atmosphere, and an electrode is attached to this, or (b) a main body made of strontium titanate. Ingredients include metal oxides for promoting semiconductor formation, such as Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ ,
CeO ₂ , Nd ₂ O ₃ , WO _{3 ,} etc., and V ₂ O ₅ , Cr ₂ O ₃ , CuO, which are metal oxides for improving voltage-current nonlinear characteristics.
It is known to have an element body containing CuO ₂ , MoO ₃ , MnO _{2 ,} etc., and to which electrodes are attached. This voltage nonlinear resistor has a perovskite crystal structure and exhibits ferroelectricity, so it functions not only as a varistor but also as a capacitor. It has the advantage of being able to absorb voltage (surge) and stabilize voltage. however,
In the case of conventional strontium titanate-based semiconductor ceramics, for example, in (a) above, metal oxides such as Mn, Zn, Co, etc. are applied to the surface of the small semiconductor ceramics in order to insulate the grain boundaries. The manufacturing process is complicated and involves processes that are difficult to control, such as the need for coating, and the need for heat treatment to uniformly diffuse the oxide into the grain boundaries of the semiconductor porcelain, and the characteristics may vary depending on the manufacturing conditions. There was a drawback that characteristics such as the nonlinear index (α) and the threshold voltage (Vth) of the voltage nonlinear resistor varied widely due to the fact that the voltage was easily influenced. In addition, in the latter (b), when firing in a neutral or reducing atmosphere, the metal oxide for improving voltage-current nonlinear characteristics becomes metallized and evaporates, causing damage to the furnace materials of the firing furnace. However, it is difficult to obtain a desired composition, and there are also disadvantages in that characteristics such as nonlinear index (α) and threshold voltage (Vth) vary. The present invention has been made in view of these drawbacks, and is intended to prevent the characteristics and composition from greatly varying depending on manufacturing conditions, and to create a voltage with small variations in characteristics such as threshold voltage and nonlinear index. The purpose is to enable manufacturing of semiconductor ceramics for non-linear resistors. The gist of the present invention is the general formula: (Sr _1-xy Ca _{x Bay} ) (Ti _1-z Zr _z )O ₃ (where x, y, z are the mole fractions of each component, 0.03
≦x≦0.30, 0.03≦y≦0.30, x+y≦0.50, 0
≦z≦0.20) 99.0 to 99.9 mol% of the main component, and 0.1 to 1.0 mol% of at least one kind of semiconducting agent selected from the group consisting of oxides of rare earth elements, Nb, W, and Ta. The main component raw material of semiconductor porcelain and the semiconducting agent are mixed so that
After forming the obtained mixture into a predetermined shape, it is fired in a neutral or reducing atmosphere to obtain semiconductor porcelain, and the semiconductor porcelain is heat-treated in a natural atmosphere or an oxidizing atmosphere to form crystal grains of the semiconductor porcelain. The present invention provides a method for manufacturing semiconductor ceramics for a voltage nonlinear resistor, which is characterized by insulating the field. In one embodiment of the invention, the composition contains up to 5 mol% of SiO ₂ and/or Al ₂ O ₃ as a mineralizing agent. In other embodiments, 1 mol% or less
Inclusion of MnO ₂ etc. is carried out. The content of these components is limited as described above because if the content exceeds the above, the properties will be adversely affected. The reason why the composition of the semiconductor ceramic according to the present invention is limited as described above is as follows. In other words, if the mole fraction x of Ca in the main component is less than 0.03, the nonlinear index (α) will be too small to be practical;
If it exceeds 0.30, the threshold voltage becomes high, so
x was within the above range. Also, the molar fraction y of Ba is
If it is less than 0.03, the nonlinear index becomes small, and if it exceeds 0.30, the threshold voltage becomes high, so y was set in the above range. In addition, x+y≦0.5 is set as x+y
This is because if exceeds 0.5, the threshold voltage becomes too high to be practical. Zr in principal component
The mole fraction Z is set to 0 to 0.20 because if Z exceeds 0.20, the threshold voltage becomes too high. The reason why the semiconducting agent was set at 0.1 to 1.0 mol% was because
This is because if the amount of the semiconducting agent is less than 0.1 mol%, the threshold voltage will be high or the material will not be made into a semiconductor, and if it exceeds 1.0 mol%, it will be difficult to obtain varistor characteristics. The semiconductor ceramic for a voltage nonlinear resistor according to the present invention is prepared by mixing the main component and a semiconducting agent, mixing and pulverizing in a ball mill, drying, mixing an appropriate amount of an organic binder, granulating, and then molding. It can be produced by firing it at 1350-1400℃ in a neutral or reducing atmosphere and then heat-treating it at 1000-1200℃ in a natural atmosphere or oxidizing atmosphere. Electrodes are placed on the surface of the resulting semiconductor porcelain. By forming this, a voltage non-linear resistor can be obtained. Examples of the present invention will be described below. Example Using SrCO ₃ , CaCO ₃ , BaCO ₃ , TiO ₂ and ZrO ₂ as raw materials, these were mixed in the composition ratio shown in Table 1, wet mixed in a ball mill for 10 hours, dried, and heated in air at The main components (Sr _1-xy Ca _x Ba _y ) (Ti _1-z Zr _z ) O ₃ were prepared by calcining at 1250°C for 2 hours, and mixed with the semiconducting agent in the proportions shown in Table 1. The compositions were prepared in such a way that the composition ratios shown in the same table were obtained. 6% by weight of an organic binder was added to this mixed raw material, thoroughly wet-mixed in a ball mill, dehydrated and dried, and then molded into a disk shape by applying a pressure of 2000 Kg/cm ² . This molded product was heated to 1150℃ in a natural atmosphere.
Pre-calcined for an hour and then in a reducing atmosphere (95% N2 ₎
+5% H ₂ ) at 1350 to 1400° C. for 2 hours to obtain a semiconductor porcelain disk with a diameter of 8 mm and a wall thickness of 1 mm. Next, this disk was heat-treated at 1000 to 1200° C. in a natural atmosphere to form an insulating layer at the grain boundaries, thereby obtaining a semiconductor ceramic disk for a voltage nonlinear resistor. Silver paste was printed and coated on the opposite surfaces of this disk and baked at 800°C in a natural atmosphere to form electrodes and obtain a voltage nonlinear resistor. The threshold voltage (Vth) and nonlinear index (α) of the voltage nonlinear resistor thus obtained were determined. The results are also shown in Table 1. 1st
In the table, samples with numbers marked with an x-mark are outside the scope of the present invention, and Vth is 10mA to the voltage nonlinear resistor.
It is the voltage (V ₁₀ ) when flowing, and α is the voltage (V _{10 )}
This is the value obtained from the following formula from and the voltage (V ₁ ) when 1mA is applied. α=1/log( _V10 / _V1 )

[Table] Comparative example SrTiO ₃ 99.3 mol%, Y ₂ O ₃ 0.2 mol%, CuO 0.5 mol% were weighed, 6% by weight of an organic binder was added to the mixture, thoroughly wet mixed in a ball mill, dehydrated, and dried. After that, a pressure of 2000 Kg/cm ² was applied to form it into a disk shape. Next, this molded product was pre-fired at 1150°C in a natural atmosphere for 1 hour, then fired at 1380°C in a reducing atmosphere (95% N ₂ + 5% H ₂ ) for 2 hours, and then heat treated at 1100°C in a natural atmosphere. A semiconductor ceramic disk having a diameter of 8 mm and a wall thickness of 1 mm was obtained with an insulating layer formed at the grain boundaries, and electrodes were formed thereon in the same manner as in the examples to obtain a voltage nonlinear resistor. Threshold voltage (Vth) and nonlinear index before and after applying a pulse voltage of 300 V for the voltage nonlinear resistors of sample numbers 3 and 6 obtained in the example and the voltage nonlinear resistor obtained in the comparative example (α) was calculated. The results are shown in Table 2. Note that Table 2 also shows the average value ( ) and deviation value (σ) for 100 samples.

[Table] As is clear from the results in Tables 1 and 2, according to the present invention, it is possible to manufacture a voltage nonlinear resistor with a large nonlinear index in the region of low threshold voltage, and in addition, compared to Compared to the conventional one shown in the example,
It is possible to manufacture a voltage nonlinear resistor with less variation in characteristics, in which each deviation value of threshold voltage and nonlinear index is less than half. Further, in the voltage nonlinear resistor according to the present invention, even when a pulse voltage is applied, the threshold voltage and the nonlinear index do not decrease much,
On the contrary, the variation is decreasing. As is clear from the above description, the present invention eliminates the disadvantage of large variations in characteristics in conventional voltage nonlinear resistors made of strontium titanate-based semiconductor ceramic, and has a threshold voltage of several volts. It is possible to manufacture a voltage nonlinear resistor that has a large nonlinearity index from a low voltage region to a high voltage region of about 100 volts and has small variations in characteristics, and it also enables the production of a voltage nonlinear resistor with an insulating layer at the grain boundaries. There is no need for the process of applying metal oxides and thermally diffusing them to form them, and in addition, there is almost no chance that the components will metalize and evaporate during the reduction process to convert them into semiconductors. Therefore, manufacturing is easy and yields are low. It has excellent effects such as not damaging the firing furnace.

Claims (1)

[Claims] 1 General formula: (Sr _1-xy Ca _{x Bay} ) (Ti _1-z Zr _z ) O ₃ (where x, y, z are the mole fractions of each component, 0.03
≦x≦0.30, 0.03≦y≦0.30, x+y≦0.50, 0
≦z≦0.20) 99.0 to 99.9 mol% of the main component, and 0.1 to 1.0 mol% of at least one kind of semiconducting agent selected from the group consisting of oxides of rare earth elements, Nb, W, and Ta. The main component raw material of semiconductor porcelain and the semiconducting agent are mixed so that
After forming the obtained mixture into a predetermined shape, it is fired in a neutral or reducing atmosphere to obtain semiconductor porcelain, and the semiconductor porcelain is heat-treated in a natural atmosphere or an oxidizing atmosphere to form crystal grains of the semiconductor porcelain. A method for manufacturing semiconductor ceramic for voltage nonlinear resistor, characterized by insulating the field.