JPH0362004B2 - - 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 non-linear voltage-current characteristics, so-called varistors, whose element bodies are made of strontium titanate-based semiconductor ceramics have been developed.
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 applying it in air or in a nitrogen atmosphere. Inside
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, and an electrode is attached to this, or (b) a semiconductor is formed as the main component of strontium titanate. Metal oxides for promoting chemical reaction, 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 (surge) and stabilize voltage. However, with conventional strontium titanate-based semiconductor ceramics, for example,
In order to insulate the grain boundaries, Mn,
The manufacturing process is complicated, as metal oxides such as Zn and Co must be coated on the surface of small semiconductor porcelains, and heat treatment is required to uniformly diffuse the oxides into the grain boundaries of the semiconductor porcelains. In addition to involving difficult processes, there are large variations in characteristics such as the nonlinear index (α) and threshold voltage (Vth) of the voltage nonlinear resistor due to the fact that the characteristics are easily influenced by manufacturing conditions. There was a drawback. 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 makes it possible to easily manufacture semiconductor ceramics for voltage nonlinear resistors whose composition and characteristics do not vary depending on manufacturing conditions and whose characteristics such as threshold voltage and nonlinear index have little variation. The purpose is to The gist of the present invention is the general formula: (Sr _1-x B _x ) (Ti _1-y Zr _y ) O ₃ (where x and y are the mole fractions of each component, and 0.03≦x
≦0.30, 0.02≦y≦0.20) and 99.0 to 99.9 mol% of the main component, and 0.1 to 1.0 mol% of at least one semiconductor forming 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 a semiconductor-forming agent are mixed to have a composition consisting of mol%, the resulting mixture is molded into a predetermined shape, and then fired in a neutral or reducing atmosphere to produce semiconductor porcelain. A method for manufacturing a semiconductor ceramic for a voltage nonlinear resistor, characterized in that the crystal grain boundaries of the semiconductor ceramic are insulated by heat-treating the semiconductor ceramic in a natural atmosphere or an oxidizing atmosphere. In one embodiment of the invention, the composition contains up to 5 mol% of SiO ₂ and/or as a mineralizer.
Al ₂ O ₃ may also be included. Moreover, as another embodiment, 1 mol% or less of MnO ₂ and other components may be contained. The reason why the content of these components is limited as described above is that if the content exceeds the above-mentioned content, the properties are adversely affected. The reason why the composition of the semiconductor ceramic according to the present invention is limited as described above is as follows. That is, if the molar fraction x of Ba in the main component is less than 0.03, the nonlinear index will be small, and if it exceeds 0.30, the threshold voltage will become high, which is not practical, so the above range was set.
The mole fraction y of Zr in the main component is set to 0.02 to 0.20 because if y is less than 0.02, the nonlinear index will be small, and if it exceeds 0.20, the threshold voltage will be high, and both are not practical. The content of the semiconducting agent was set at 0.1 to 1.0 mol% because the content was
This is because if it is less than 0.1 mol%, the threshold voltage is high, and if it exceeds 1.0 mol%, varistor characteristics cannot be obtained. According to the present invention, the voltage nonlinear resistor is obtained by mixing the main component of the strontium titanate-based ceramic composition with the above composition and a semiconductor agent in a predetermined ratio,
Add an appropriate organic binder to it, granulate it, and
After molding under pressure of 2500Kg/cm ² , in natural atmosphere
Pre-baked at 1000~1200℃, further fired at 1350~1400℃ in a neutral or reducing atmosphere to make a semiconductor, then 1000℃ in a natural atmosphere or an oxidizing atmosphere.
Heat treatment at ~1200°C results in semiconductor porcelain with insulated grain boundaries, which can be manufactured by forming electrodes on the surface of this semiconductor porcelain. The method for manufacturing semiconductor ceramics according to the present invention makes it possible to manufacture a voltage nonlinear resistor that has a large nonlinear index in a low threshold voltage region and has little variation in characteristics, and also has crystal grains. There is no need for the process of applying and diffusing metal oxide to form an insulating layer in the field, and in addition, there is almost no chance of the components becoming metallized and evaporating during the reduction treatment to convert them into semiconductors, making it easier to manufacture. It has excellent advantages such as being easy, having a high yield, and not damaging the firing furnace. Examples SrCO ₃ , BaCO ₃ , TiO ₂ and ZrO ₂ as raw materials
Weigh these to obtain the main components of the composition shown in Table 1, wet mix in a ball mill for 10 hours, dehydrate and dry, then heat in air at 1100 to 1250℃.
Calcined for 2 hours to obtain a strontium titanate ceramic composition having the composition shown in Table 1, which was mixed with each semiconductor agent shown in Table 1 in the composition ratio shown in the same table,
After thorough wet mixing in a ball mill and dehydration, 6% by weight of an organic binder was added and granulated, and a pressure of 2000 kg/cm ² was applied to form a disk. This molded product was pre-fired at 1150°C for 1 hour in a natural atmosphere, and then heated to 1350-1400°C in a reducing atmosphere (95% N ₂ + 5% H ₂ ).
C. for 2 hours to obtain a semiconductor porcelain having a diameter of 8 mm and a wall thickness of 1 mm, which was then heat treated at 1000 to 1200 DEG C. in a natural atmosphere to obtain a semiconductor porcelain whose grain boundaries were insulated. Silver paste was printed and coated on the opposing surfaces of this semiconductor porcelain 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 each voltage nonlinear resistor obtained in this manner were determined. The results are also shown in Table 1. 1st
In the table, the samples with numbers marked with 〓 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 flows. α=1/log( _V10 / _V1 )

[Table] Comparative examples SrTiO ₃ 99.3 mol%, Y ₂ O ₃ 0.2 mol% and
Weigh and mix 0.5 mol% of CuO, thoroughly wet mix in a ball mill, dehydrate and dry, add 6% by weight of an organic binder, granulate, and apply a pressure of 2000 kg/cm ² to form a disc. It was formed into a 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 porcelain with a diameter of 8 mm and a wall thickness of 1 mm with insulated grain boundaries was obtained, and electrodes were formed thereon in the same manner as in the example 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. In addition, Table 2 shows the average value (X) and deviation value (σ) for each 100 samples. In the column for each sample, the upper row shows the results before pulse application, and the lower row shows the results after pulse application. The results are shown below.

[Table] As is clear from the results in Tables 1 and 2, the voltage nonlinear resistor using the semiconductor ceramic composition according to the method of the present invention has a low threshold voltage and a large nonlinear index. Moreover, compared to the conventional one shown in the comparative example, the deviation values of the threshold voltage and nonlinear index are less than half, and the variation in characteristics is very small. As is clear from the above description, the present invention eliminates the disadvantage of large variations in characteristics in conventional voltage nonlinear resistors using strontium titanate-based semiconductor ceramic as an element body, and achieves low threshold voltage and It makes it possible to manufacture a voltage nonlinear resistor with a large nonlinearity index and little variation in characteristics, and also eliminates the need for the process of coating and diffusing metal oxide to form an insulating layer at grain boundaries. Moreover, during the reduction treatment, the components hardly evaporate, and therefore, it has excellent effects such as easy production, good yield, and no damage to the firing furnace.

Claims (1)

[Claims] 1 General formula: (Sr _1-x B _ax ) (Ti _1-y Zr _y ) O ₃ (where x and y are the mole fractions of each component, and 0.03≦x
≦0.30, 0.02≦y≦0.20)
99.0-99.9 mol%, rare earth elements, Nb, W and
The main component raw material of semiconducting ceramics and the semiconducting agent are mixed to have a composition consisting of 0.1 to 1.0 mol% of at least one type of semiconducting agent selected from the group consisting of oxides of Ta, and the resulting mixture is After forming 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 insulate the crystal grain boundaries of the semiconductor porcelain. A method for manufacturing semiconductor porcelain for a voltage nonlinear resistor, characterized by: