JPS6057213B2 - Manufacturing method of grain boundary insulated semiconductor ceramic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a grain boundary insulated semiconductor ceramic capacitor that has a high dielectric constant, a high breakdown voltage, and small variations in breakdown voltage values.

Conventionally, barium titanate-based and strontium titanate-based porcelains have been prepared by adding at least one kind of valence control element such as rare earth elements and NbNWNSb, or heating them in a vacuum or a reducing atmosphere, or adding valence control elements to them. It is made into a semiconductor by adding at least one of them and heating in a neutral or reducing atmosphere. By applying a metal or its compound that turns the grain boundaries of the ceramic into an insulator to such semiconductor porcelain and heat-treating it, an insulating layer is formed at the grain boundaries and the apparent dielectric strength is lower than that of conventional porcelain capacitors. It is known that a capacitor with a large capacitance can be obtained, and is called a loose grain-boundary insulated semiconductor porcelain capacitor.

However, the conventional ones had the disadvantage that the breakdown voltage was low and its variation was large.

This invention eliminates the above-mentioned drawbacks, and aims to provide a grain boundary insulated semiconductor ceramic capacitor with a high dielectric constant, high breakdown voltage, and small variation in breakdown voltage. That is, the gist of the present invention is to add Bi to barium titanate-based or strontium titanate-based semiconductor porcelain. O. , a metal or its compound that turns the crystal grain boundaries of semiconductor ceramics into an insulator, such as CuO, is applied, first heat-treated in a neutral or reducing atmosphere, and then
This method is characterized in that the above-mentioned metal or its compound is applied to the semiconductor porcelain again and heat-treated in the atmosphere.
Here, the barium titanate-based or strontium titanate-based semiconductor porcelain includes the following types in addition to the conventionally well-known ones described above.

In other words, barium titanate-based semiconductor porcelain contains BaTi
One in which part of Ba in O3 is replaced with srNcaNp]), or one in which part of Ti is replaced with Zr or Sn, or? , Tj in which these partial substitutions are made simultaneously. In addition, in strontium titanate-based semiconductor ceramics, a part of Sr in SrTiO3 is added to Ca. ．． Ba. ．． P
b, or a part of T1 is replaced with Zr, . Those substituted with Sn or Sr, . There are some materials in which these partial substitutions are made for Ti at the same time. When TlO2 is added as an additive in each of the semiconductor ceramics described above, up to 5 mol% of TlO2 can be sintered at low temperatures and grain growth can be promoted.
It shows favorable results such as improved apparent dielectric constant.

Things that make the grain boundaries of semiconductor porcelain into insulators include:
In addition to BilCu, Pb. ．． Mn,. Fe,. Although there are metals such as B or compounds such as oxides of these metals, it is sufficient if the crystal grain boundaries can be made into an insulator after the treatment of the present invention is completed.

Further, although the amount of metal or its compound applied to semiconductor ceramics makes the characteristics constant over a fairly wide range, if the amount is outside the appropriate range, the characteristics will be adversely affected, such as dielectric loss worsening. Further, the amount applied varies depending on each metal or each compound. Furthermore, any method such as coating, dipping, spraying, vapor deposition, etc. can be used as a method of application. After applying the metal or its compound, heat treatment is performed in a neutral or reducing atmosphere, and the temperature range is 1100 to 140℃.
0'C is suitable.

If the temperature is lower than 1100°C, sufficient diffusion will occur to make the grain boundaries an insulator, but if the temperature exceeds 1400°C, grain growth will occur, which is undesirable.

In the next step, the semiconductor porcelain is coated with metal or its compound and then heat-treated in air. The degree range is 950
~1300°C. If the temperature is less than 950°C, oxidation will not be carried out sufficiently, and a material with a large apparent dielectric constant will not be obtained, and no improvement in insulation resistance will be observed.

Furthermore, if the temperature exceeds 1300°C, the metal or its compound will evaporate and will no longer diffuse to the grain boundaries! Ru. The temperature at which the heat treatment is performed in air is preferably lower than the temperature at which the heat treatment was performed in a neutral or reducing atmosphere in the previous step.

This is because superior values of apparent permittivity and insulation resistance can be obtained compared to treatments at the same temperature or higher. Further, the types of the metal and its compound applied the first time may be different from the types of the metal and its compound applied the second time.

This invention will be described in detail below with reference to Examples.

Examples BaTlO3, SrTiO3, CaTiO3, P
Main raw materials such as bsnO3, BazrO3, Y2O3,
Atomic control elements such as Ce2O3, WO3, TiO2 and SlO2, ZnO, . A mineralizing agent such as GeO2 was appropriately blended, pulverized and mixed in a wet ball mill, and then dehydrated and dried.

Next, about 10% by weight of vinyl acetate resin was added as a binder, and the particles were granulated and sized to about 50 mesh, and formed into a disk with a diameter of 10TKfn and a wall thickness of 0.5TI0fL using a hydraulic press. The formed disk was calcined in the atmosphere at 1200°C for 2 hours to remove the binder, and then heated with 2.5 to 1% hydrogen,
Firing was performed at 1400-1490°C for 2 hours in a reducing atmosphere consisting of 97.5% to 8% nitrogen solubility, resulting in a diameter of 8.
In this order, a barium titanate-based semiconductor ceramic sample and a strontium titanate-based semiconductor ceramic sample each having a wall thickness of 0.4 Tmm were obtained.

A metal oxide paste consisting of 2% by weight of B12O3, 23% by weight of Pb3O4, 4% by weight of CUO and 50% by weight of varnish was applied to the obtained sample.

The amount of coating was approximately 10 m9r. The ceramic sample coated with the paste was heat treated in nitrogen at 1200° C. for 5 hours to diffuse the metal oxide into the grain boundaries of the semiconductor ceramic.

Next, apply the above metal oxide paste again in an amount of 10
It was coated with W19r and heat treated in air at 1150° C. for 1 hour to transform the grain boundaries into an insulator.

Further, the silver paste was screen printed in a pattern of 6.5 TnIn in diameter and baked at 800'C for 2 hours to produce a capacitor.

Capacitance, dielectric loss (Tanδ) and breakdown voltage (BD■) of the semiconductor ceramic capacitor thus obtained
The results are shown in Table 2.

Capacitance and dielectric loss are +25℃, 1KH2-0.
Measurement was performed under the condition of 3V.

In addition, the breakdown voltage is the average value ('
X) and standard deviation value (δ). Reference Example 1 A barium titanate-based semiconductor porcelain sample and a strontium titanate-based semiconductor porcelain sample having the composition ratios shown in Table 1 were
The metal oxide paste used in the above example was applied in an amount of 5
It was coated with m9r and heat treated in air at 1150° C. for 1 hour to transform the grain boundaries into an insulator.

Further, a silver paste was screen printed in a pattern with a diameter of 6.5, and baked at 8000C for 2 hours to create a condenser, which was used as a reference example for comparison with the present invention. The characteristics of the obtained semiconductor ceramic capacitor were measured in the same manner as in the above examples, and the results are shown in Table 3.

Reference Example 2 A barium titanate-based semiconductor porcelain sample and a strontium titanate-based semiconductor porcelain sample having the composition ratios shown in Table 1 were
The metal oxide paste used in the above example was applied in an amount of 5
mgr and heat treated at 1200° C. for 5 hours in a nitrogen atmosphere to diffuse the metal oxide into the grain boundaries of the semiconductor porcelain.

Further, it was heat treated in air at 1150'C for 1 hour. Thereafter, the silver paste was screen printed in a pattern with a diameter of 6WL and baked at 800°C for 2 hours to produce a capacitor, which was used as a reference example for comparison with the present invention in the same manner as Reference Example 1. The characteristics of the obtained semiconductor ceramic capacitor were measured in the same manner as in the above-mentioned example, and the results are shown in Table 4.

As is clear from a comparison of Tables 2, 3, and 4, according to the present invention, a metal oxide paste is applied to the surface of the semiconductor ceramic, heat-treated in a neutral or reducing atmosphere, and then the semiconductor By applying metal oxide paste to the porcelain surface and heat-treating it in air, the breakdown voltage can be reduced to 100%.
(2) Although the standard deviation value remains almost the same, it has the effect of substantially reducing variation, and is of great practical value.

Claims (1)

[Claims] 1. A barium titanate-based or strontium titanate-based semiconductor porcelain is provided with a metal or a compound thereof that makes the crystal grain boundaries of the semiconductor porcelain an insulator, such as Bi_2O_3 and CuO, and is first placed in a neutral or reducing atmosphere. 1. A method for producing a grain boundary insulated semiconductor ceramic capacitor, which comprises heat-treating the capacitor in the atmosphere, then applying the metal or its compound to the semiconductor ceramic again, and heat-treating the semiconductor ceramic in the atmosphere. 2. A method for manufacturing a grain boundary insulated semiconductor ceramic capacitor according to claim 1, characterized in that the heat treatment temperature in the air is lower than the temperature at which the heat treatment is performed in a neutral or reducing atmosphere. 3. The method for manufacturing a grain boundary insulated semiconductor ceramic capacitor according to claim 1, characterized in that the heat treatment is performed at a temperature of 1100 to 1400°C in a neutral or reducing atmosphere. 4. The method for manufacturing a grain boundary insulated semiconductor ceramic capacitor according to claim 1, characterized in that the heat treatment is performed at a temperature of 950 to 1300°C in the atmosphere.