JPS6048897B2 - Composition for semiconductor ceramic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composition for semiconductor ceramic capacitors containing strontium titanate as a main component.

It is known that a capacitor having a large apparent dielectric constant can be obtained by forming electrodes on both sides of a semiconductor ceramic whose grain boundaries are insulators.

Conventionally, barium titanate-based materials have been used for this semiconductor porcelain, but although a large apparent dielectric constant of up to 69,000 can be obtained, the dielectric loss (tan δ) is on average 5 to 5.
As high as 6%, and -30℃ when compared to +20℃
In the temperature range from +85°C, the temperature characteristic of the apparent permittivity was as large as 40%. As a material which has improved the above-mentioned drawbacks, there is a material mainly composed of strontium titanate.

For example, strontium titanate contains silicon dioxide (SiO
2) There is a type of strontium titanate-based semiconductor porcelain obtained by adding manganese dioxide (MnO0) and firing, in which manganese oxide or copper oxide is diffused into the grain boundaries of the porcelain. Because it contains (SiO0), manganese oxide is unevenly distributed near the grain boundaries, which helps to make the grain boundaries an insulator, but the crystal grains become smaller and the apparent dielectric constant is as small as 20.000. , the dielectric loss (tan δ) also shows a value of 2% or more. Also, strontium titanate, niobium (Nb), tantalum (T)
a) By adding each oxide of tungsten (W) and firing it in a reducing atmosphere to make semiconductor porcelain, coating bismuth oxide (BiO0) on both sides and heat-treating them in an oxidizing atmosphere. , the crystal grain boundaries are made into insulators, and the apparent dielectric constant is 50.000 or more and the dielectric loss (t
an δ) is 1% or less, but the temperature characteristic of the apparent permittivity exceeds ±13% in the temperature range of -30°C to +85°C when +20°C is the standard, and the temperature characteristics are similar to those of fired porcelain. Tsuki was seen. This invention was discovered as a result of studying the various problems mentioned above, and has a high apparent permittivity, good temperature characteristics, low dielectric loss, and small change in characteristics due to changes in firing temperature. It is an object of the present invention to provide a composition for a semiconductor ceramic condenser having excellent properties such as the above. That is, the gist of this invention is strontium titanate or strontium titanate 97.7 to 99.8 in which a part of strontium is replaced with calcium or barium.
5% by weight manganese oxide (MnO.

)-0.05~0''wt% yttrium oxide (Y2O3
)-0.1 to 1.5% by weight of bismuth oxide or at least L species among bismuth oxide, manganese oxide, copper oxide, and lead oxide are diffused into the grain boundaries of the semiconductor ceramic, and the grain boundaries are an insulator. It is characterized by being Among the compositions of the semiconductor ceramic described above, strontium titanate is SrTizO.

can be expressed as , and thus Ti
Excessive or insufficient O2 has already been disclosed in Research and Practical Application Report Special Issue No. 28, published by 1932, pages 19 to 200. Here, Z is 0.97≦Z≦1.
It can be selected within the range of 03.

The reason why the value of Z can be changed within the above range is that the electrical characteristics are not impaired compared to the electrical characteristics of a semiconductor ceramic capacitor made of SrTiO3 where Z=1. Depends on something.

More specifically, SrTlO. When obtaining the semiconductor porcelain strontium composed of
By varying it in the range of 1.03, SrTiO3
(In this case, compared to the case where Z=1), the firing temperature can be lowered, and the firing cost can be reduced. The reason why the value of z is limited to the above range is because if the amount of Z is less than 0.97, the firing temperature becomes high and the dielectric loss deteriorates.

On the other hand, if the Z amount exceeds 1.03, the firing temperature will be high and the smudges between the fired porcelains will increase. Strontium titanate also includes strontium titanate in which a portion of strontium is replaced with calcium or barium.

Regarding strontium titanate substituted in this way, 3
It is also disclosed in Table 35 on page 21. If expressed as a general formula, it can be expressed as the following formula 1. (Srl-XAx
) TizO3...1 However, A: Ba, Ca4
．． O<X≦0.05, 0.97≦Z≦1.03 where,
What makes it possible to replace a part of Sr with Ba and Ca is Sr.
rTiO.

This is because the electrical characteristics are not impaired compared to the electrical characteristics of a semiconductor ceramic capacitor composed of. More specifically, partial substitution with Ba makes it possible to obtain a large dielectric constant by changing the Curie point, while partial substitution with Ca makes it possible to improve the breakdown voltage. In addition, Ba, Ca
Simultaneous replacement is also possible. Here, the reason why the amount of X is limited to the above range is because if the amount of X exceeds the upper limit value, the apparent dielectric constant becomes small.

Further, regarding the amount of z, the detailed explanation of the invention will be omitted here since the reason is the same as that already mentioned for SrTiZO3. Manganese oxide plays the role of a sintering aid that promotes sintering, and its content (MnO.

) is 0.05 to 0. It is sufficient if it is within the range of heel volume%. This means that if it is less than 0.05% by weight, the temperature characteristics of the apparent permittivity will be ±
This is because if the content exceeds 10%, and exceeds 0% by weight, firing becomes easy, but the dielectric loss exceeds 1%. Yttrium oxide promotes semiconductor formation, and its content (Y2
O3) may be in the range of 0.1 to 1.5% by weight.

This is because if the content is less than 0.1% by weight, the dielectric loss will exceed 1%, and if it exceeds 1.5%, the withstand voltage will decrease. Oxides such as V, Cr, Fe, and CO are already known as substances that make grain boundaries insulators, but in this invention, bismuth oxide, bismuth oxide, manganese oxide, and oxide are used. The results showed that good properties could be obtained for at least one of copper and lead oxide.

This invention will be described in detail below with reference to Examples. Example 1 In order to obtain semiconductor porcelain having the composition ratio shown in Table 1,
SrTiOa,. CaTiO3, BaTiOa, MnC
O3, Y2O.

Each raw material was prepared, weighed, and ground together with a vinyl acetate resin as a binder in a wet ball mill for 7 hours. After pulverizing, the mixture was granulated to about 50 mesh, and molded into a disk with a diameter of 10.0 mm and a thickness of 0.5 W8 nm using a hydraulic press. Next, the molded disk was heated in the atmosphere at 1150°C for 2 hours.
The binder was burned by calcination for a period of time.

After further cooling to room temperature, it was heated to 1350-1450'C in a reducing atmosphere consisting of m volume% hydrogen and 9% nitrogen.
It was baked for 2 hours. Subsequently, 10 mg of a paste made by kneading 90% by weight of bismuth oxide and w% by weight of copper oxide with varnish in a weight ratio of 1:1 was applied to the surface of the semiconductor porcelain, and heat treated in air at 1150°C for 1 hour to form crystal grains. The world has become an insulator.

Furthermore, silver paste was applied to both planes of the semiconductor porcelain, and
Three powders were baked at 0'C to form electrodes and create a capacitor. Apparent permittivity (E), dielectric loss (Tanδ), and insulation resistance (IR) of the capacitor thus obtained
, breakdown voltage (■/T!Un), and temperature characteristics of apparent dielectric constant were measured, and the results are shown in Table 1. In addition, the apparent permittivity and dielectric loss are +25°C1 frequency 1KHz
This is a value measured under the condition that one voltage is 0.3V. The insulation resistance is measured at +25°C when the sample is exposed to a DC voltage of 5 per unit thickness.
The figure shows the resistance value after 3 snails were applied with 0V. The breakdown voltage indicates the lower limit at which the current increases rapidly when the DC voltage applied to the sample is increased at +25°C. The temperature characteristic of the apparent permittivity represents the rate of change in the temperature range of -30°C to +85°C with +20°C as a reference. Items marked with * in the table are outside the scope of this invention, and all others are within the scope of this invention.

Furthermore, X and Z in Table 1 indicate the values of X and Z in equation 1. Example 2 Sample No. 4 of Example 1 was treated with manganese oxide, copper oxide, lead oxide, and bismuth oxide, which form an insulating layer at the grain boundaries, in the same manner as in Example 1 at the ratios shown in Table 2. , we created capacitors and measured their electrical characteristics.

The measurement results are also shown in Table 2.

In addition, those marked with * in Table 2 are outside the scope of this invention.

Among these, sample number 15 has a large Tan δ, and sample numbers 16 and 17 both have temperature characteristics exceeding +10%. Example 3 The electrical properties of Sample No. 1 and Sample No. 5 of Example 1 were measured while varying the firing temperature, and the results are shown in Table 3.

As is clear from the examples described above, according to the invention, a material having a large apparent dielectric constant of 40,000 or more can be obtained, and the dielectric loss is as small as 1% or less.

Claims (1)

[Claims] 1. Strontium titanate or strontium titanate in which a portion of strontium is replaced with calcium or barium - 97.7 to 99.85% by weight Manganese oxide (MnO_2) - 0.05 to 0.8% by weight
Bismuth oxide or bismuth oxide and at least one of manganese oxide, copper oxide, and lead oxide are diffused into the grain boundaries of semiconductor porcelain consisting of 0.1 to 1.5% by weight of yttrium oxide (Y_2O_3) to form crystal grains. A composition for a semiconductor ceramic capacitor, characterized in that the field is an insulator.