JPH09219336A - Manufacturing method for grain boundary insulating semiconductor ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain elements of strontium titanate grain boundary insulating semiconductor ceramic capacitor having few variations in performance. SOLUTION: Strontium titanate is made by mixing strontium carbonate and titanium oxide in equal mol., pre-burning in the air and being crushed (first step). After the strontium titanate obtained during the first step is added and mixed with silicon oxide and one material of tantalum oxide or niobium oxide and pre-heated farther in a higher temperature than that in the first step under a deoxidation circumstance, it is crushed (second step). Binder is added to material powder obtained during the second step and element which is made by pressurized forming is degreased and pre-heated (third step). Conductive paste is applied on the main surface of the pre-heated body by the third step, electrode baking is performed in the air or in oxygen circumstance and at the same time grain boundary of the pre-heated body is oxidized again (fourth step).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a grain boundary insulation type semiconductor ceramic capacitor.

[0002]

2. Description of the Related Art A conventional grain boundary insulation type semiconductor ceramic capacitor is a strontium carbonate, titanium oxide, etc., which is mixed with a raw material obtained by further adding a sintering accelerator and various additives of a semiconducting element, and calcined in air. A binder is added to the material powder obtained by pulverization and whose main component is strontium titanate, and the pressure-molded element is fired at a temperature of around 1200 ° C. in the atmosphere. The sintered body is further fired at a temperature of about 1250 ° C. in a reducing atmosphere. After that, a conductive paste is applied to the main surface of the sintered body, and the paste is applied in air or oxygen atmosphere to 800
In general, a manufacturing method in which the electrode is baked at a temperature around ℃ and the grain boundaries of the sintered body are reoxidized at the same time.

[0003]

However, with the conventional sintering and reduction methods, it is difficult to make the crystal grain size of the sintered body uniform, which causes variations in the electrical characteristics.

An object of the present invention is to provide an excellent grain boundary insulating type semiconductor ceramic capacitor having a uniform crystal grain shape of a sintered body and a small variation in electric characteristics.

[0005]

In order to achieve this object, the present invention forms uniform strontium titanate particles as the main component in the raw material process. By firing a molded body using this material at a low temperature, crystal grain growth of the sintered body is suppressed, and a grain boundary insulation type semiconductor ceramic capacitor having a uniform crystal grain shape can be obtained.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a grain boundary insulating type semiconductor capacitor according to claim 1 of the present invention comprises: equimolar mixing strontium carbonate and titanium oxide, calcining them in the air, pulverizing them and titanic acid. A first step of making strontium, strontium titanate obtained in the first step, and silicon oxide,
Further, the raw material obtained by adding and mixing any one of tantalum oxide and niobium oxide was again calcined in a reducing atmosphere at a temperature higher than that in the first step, and then pulverized. A binder is added to the material powder, and a third step of degreasing and pre-baking the pressure-molded element, and a conductive paste is applied to the main surface of the pre-baked body in the third step, and at the same time as electrode baking in air or oxygen atmosphere. It comprises a fourth step of reoxidizing the grain boundaries of the calcined body.

In the first step of calcination, the main component, strontium carbonate, is chemically reacted uniformly. The strontium titanate particles are reduced and crystal particles are grown in the second step of calcination, and the strontium titanate material having a uniform particle shape is prepared by pulverization. Since the above materials are molded and fired at a temperature at which grain growth does not occur in the third and fourth steps, a sintered body of a semiconductor ceramic capacitor having a uniform crystal grain size can be obtained.

According to the second aspect of the present invention, the calcination temperature of the first step is 1100 to 1200 ° C. and the calcination temperature of the second step is lower than 1250 ° C. and higher than the first step. The obtained material is molded, degreased and baked at a temperature lower than 600 ° C. in the third step, and reoxidized at a temperature of 700 to 800 ° C. in the fourth step.

Calcination temperature in the first step 1100 to 1200 ° C.
Defines the temperature range in which the chemical reaction of strontium titanate is completed, and the calcination temperature of the second step is higher than the temperature of the first step and lower than 1250 ° C. is the reduction of strontium titanate particles and The temperature range suitable for growth is set, the temperature of 600 ° C in the third step defines the temperature at which the binder removal of the molded body is completely burned, and the temperature of 700 to 800 ° C in the fourth step is the main component. The strontium titanate crystal grains do not grow, and the temperature at which an element body having a strength that can withstand use is obtained is determined, whereby a strontium titanate element body having a uniform crystal grain shape can be obtained.

(Embodiment 1) First, in order to obtain strontium titanate as a main component, 1: 1 equimolar amounts of strontium carbonate and titanium oxide were weighed, mixed in a ball mill for 22 hours, dehydrated and dried 1100. It is calcined at a temperature of ˜1250 ° C. for 4 hours, then pulverized in a ball mill for 75 hours and dehydrated and dried. Silicon oxide 0.1 mol% and niobium oxide 0.5 to strontium titanate after drying
Mol% was added, this was mixed in a ball mill for 22 hours, dehydrated and dried, and then 1200 in a reducing atmosphere of H ₂ : O ₂ = 10: 1.
Calcination is performed at a temperature of ˜1300 ° C. for 4 hours, then crushed by a ball mill for 4 hours, and dehydrated and dried.

A binder is added to the dried material powder to form a disk having a diameter of 20 mm and a thickness of 1 mm. The molded body was placed in an alumina sheath and degreased at a temperature of 600 ° C. for 4 hours. After that, a silver paste is applied to the surface of the fired body, and electrode baking is performed at a temperature of 800 ° C. for 1 hour in an oxygen atmosphere, and at the same time, grain boundaries of the fired body crystal particles are reoxidized. The electrical characteristics of the obtained strontium titanate element are shown in (Table 1).

[0012]

[Table 1]

As is clear from (Table 1), the manufacturing method of the present invention reduces variations in V _{0.1 mA} / mm and surge resistance of the element body, but it is clear that the effect is particularly exhibited in surge resistance. Further, if the calcination temperature in the first step is low, grain growth is less likely to occur in the calcination in the reducing atmosphere in the second step, and variations in surge withstand cannot be suppressed. On the other hand, if it is too high, the reduction reaction of the particles is insufficient and the variation of V _{0.1 mA} / mm is large. Further, when the calcination temperature in the second step is high, the reaction solidification of the particles progresses and the size of the particles cannot be controlled by pulverization.
The variation of _0.1mA / mm and surge tolerance tends to increase. Therefore, it is understood that the calcination temperature of the first step is about 1200 ° C. and the calcination temperature of the second step is about 1200 to 1250 ° C.

Although niobium oxide is used as a semiconductor-forming element in the first embodiment of the present invention, tantalum oxide may be used instead of strontium titanate. It has been confirmed that similar results can be obtained with a composition substituted with magnesium or the like.

[0015]

As described above, by controlling the crystal grain size of strontium titanate and the reduced state of the grains in the raw material process according to the present invention, it is possible to manufacture a grain boundary insulation type semiconductor ceramic capacitor with small variations.

Claims (2)

[Claims] 1. A first step in which equimolar amounts of strontium carbonate and titanium oxide are mixed, calcined in the air, and pulverized to obtain strontium titanate, strontium titanate obtained in the first step, and silicon oxide, and The second step of calcination of the raw material to which any one of tantalum oxide and niobium oxide is added and mixed in a reducing atmosphere at a temperature higher than the first step, and then pulverization, and the material powder obtained in the second step The third step of adding a binder to the material and pre-baking the press-molded element for degreasing, and applying a conductive paste to the main surface of the pre-baked body in the third step, and baking the electrodes simultaneously in air or in an oxygen atmosphere A method of manufacturing a grain boundary insulating semiconductor ceramic capacitor, comprising a fourth step of reoxidizing a grain boundary of a body. 2. The calcination temperature in the first step is 1100 to 120.
At 0 ° C., the calcination temperature of the second step is lower than 1250 ° C. and higher than that of the first step, and the degreasing calcination temperature of the third step is 60.
The temperature of the fourth step is 700 to 800 at a temperature lower than 0 ° C.
The method for producing a grain boundary insulation type semiconductor ceramic capacitor according to claim 1, wherein the temperature is 0 ° C.