JPS6044816B2 - Composition for semiconductor ceramic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composition for a semiconductor ceramic capacitor that is based on strontium titanate semiconductor ceramic, has a high dielectric constant, flat dielectric constant temperature characteristics, and has excellent insulation resistance and dielectric loss. It is something.

Conventionally, Y and N have been added to strontium titanate-based compositions.
b, one or more valence control elements such as Dy, Ta, and W are added, or ZnO and GeO are added together with these valence control elements. Bismuth oxide (B1.O0) and lead oxide (P
By coating a metal oxide such as bO), diffusing the metal oxide into the grain boundaries of the porcelain to form an insulating layer at the grain boundaries, and providing electrodes on the surface of the porcelain, a large capacitor can be obtained. This is known. Among such capacitors, SrTiO. as the main ingredient, and Y as an additive.
. O. A composition with a composition ratio of 0.075 mol % of TiO2 and 0.5 mol % of TiO2 was calcined in the atmosphere at 1150°C for 2 hours, and then in a reducing atmosphere consisting of hydrogen % by volume and nitrogen by 8 mol %. A porcelain sample was prepared by firing at 1,400 to 14,300 C for 2 hours. Bi was added to the obtained sample. O. A metal oxide paste mixed with varnish and varnish was applied and baked at 900 to 13,000C in the air for 1 hour to form capacitors with electrodes, as shown in Figures 1 and 2.
The temperature characteristics of the apparent permittivity and the temperature characteristics of the dielectric loss were obtained as shown in the figures. As is clear from the figure,
This type of capacitor contains Bi at the grain boundaries of the porcelain. O. There is a close relationship between the heat treatment temperature when diffusing the capacitor and the characteristics of the resulting capacitor, and in particular, the temperature characteristic of the apparent dielectric constant is flatter when heat treated at a lower temperature. For example, when the heat treatment temperature is 1300℃, -30 to +
Based on the apparent dielectric constant at +25°C in a temperature range of 85°C, its temperature characteristics are +18 to -14.5%, but when heat treated at 900°C, it becomes +2.4 to -1.3. %
It becomes quite flat. However, even if the temperature characteristics of the apparent permittivity are flattened by lowering the heat treatment temperature, the second
As is clear from the figure, the dielectric loss has significantly deteriorated. In this way, even if the temperature characteristics of the apparent permittivity of conventional products are flat, the dielectric loss is poor and the insulation resistance is also deteriorated.Furthermore, as the applied voltage increases, the characteristics worsen, and The drawback was that it could only be used in

An object of the present invention is to provide a composition for a semiconductor ceramic capacitor which can be obtained from a capacitor having a large dielectric constant, flat temperature characteristics of apparent dielectric constant, and excellent insulation resistance and dielectric loss.

In particular, it is an object of the present invention to provide a composition for a semiconductor ceramic capacitor, which provides a capacitor with a small voltage dependence of dielectric loss. In other words, the gist of this invention is:
Bismuth oxide is converted into Bi2O3 at the grain boundaries of strontium titanate-based semiconductor porcelain, which is mainly composed of strontium titanate and is obtained by adding a valence control element consisting of Y and sintering it in a reducing atmosphere. te85.0~99
．． 9% by weight, copper oxide is 0.1-15 in terms of CuO
．． It is characterized in that a metal oxide consisting of 0% by weight is diffused and the grain boundaries are made into an insulator.

The reason for limiting the composition ratio of metal oxides is that pismuth oxide is 85%. When the saliva content is less than %, dielectric loss increases and its temperature characteristics deteriorate.

Also 99. If the heel weight exceeds %, the insulation resistance and dielectric loss will deteriorate, and the characteristics will be greatly affected by changes in the heat treatment temperature. Further, if copper oxide is less than 0.1% by weight, there is no effect of improving the voltage dependence of dielectric loss, and if it exceeds 15% by weight, dielectric loss, especially dielectric loss on the high temperature side, deteriorates. The amount of copper oxide is a problem among metal oxides as mentioned above, and the amount of copper oxide is 0.0% per weight of the main strontium titanate semiconductor ceramic. It is preferable that the dielectric loss is less than % of the heel weight, and dielectric loss exceeding this range deteriorates and it becomes difficult to obtain the desired characteristics.

Furthermore, the strontium titanate semiconductor ceramic herein means not only SrTiO3 but also one in which a part of SrTlO3 is replaced with Ca (30 atomic % or less) or Ba (10 atomic % or less). Here, Sr of SrTiO3
Strontium titanate-based semiconductor porcelain in which a portion of strontium titanate is substituted with Ca or Ba has already been disclosed in Research and Practical Application Report Special Issue No. 28, page 221, Table 35, published in 1932@. That is, the strontium titanate-based semiconductor ceramics containing these substitutional elements have lost the properties of the semiconductor ceramic capacitor composed of SrTiO3, and the characteristics have been individually improved by each substitutional element.

In this invention, a part of Sr is replaced with Ca of 30 atomic % or less.
When substituted with SrTiO3, the capacitance-temperature characteristics can be improved compared to SrTiO3. however,
If it exceeds 30 atom %, the capacity will become small, which is not preferable.
Also, is the amount of Sr less than 10 atomic %? When substituted with SrTiO3, the capacitance becomes larger and the antiseptic strength can be improved compared to SrTiO3, but when the content exceeds 10 atomic %, the dielectric loss deteriorates. Incidentally, in this strontium titanate-based semiconductor ceramic, the excessive inclusion of TiO2 is disclosed in, for example, Japanese Patent Application Laid-Open No. 12589-1989, and in this invention, too, if TiO2 is added in excess to less than 5 mol%. It shows favorable results such as being able to sinter at low temperatures, promoting grain growth, and improving the temperature characteristics of the apparent dielectric constant.

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

Example 1 In order to obtain a porcelain composition having a composition ratio as shown in Table 1, main raw materials such as SrTlO3, CaTiO3, BaTiO3, and each "raw material of a valence control element consisting of Y2O3" were appropriately blended and wet-processed. After pulverizing and mixing in a pot mill, the mixture was dehydrated and dried.

Next, about 1% by volume of vinyl acetate resin was added as a binder, and the particles were granulated into about 50 meshes, sized using a hydraulic press, and had a diameter of 12.5 mm and a wall thickness of 0.6 Tn. It was molded into a disc of n.
The molded disk was pre-fired at 1150°C for 2 hours in the air, and then primary fired at 1400-1430°C for 2 hours in a reducing atmosphere consisting of 1% hydrogen by volume and 8% nitrogen by volume, resulting in a diameter of 10w0n1 wall thickness. 0.5? A strontium titanate semiconductor ceramic sample was obtained.

A metal oxide paste consisting of bismuth oxide and copper oxide was applied to the obtained sample.

This metal oxide paste is a mixture of bismuth oxide, copper oxide, and varnish. The amount of paste to be applied to the sample is 1.5 in terms of metal oxide weight per weight of the sample.
This paste was applied to the entire surface of the sample to a uniform thickness, dried, and then baked in the air at 900 to 1300° C. for about 1 hour. Furthermore, a silver paste containing 4% by weight of bismuth lead borosilicate as a frit was applied to both sides of the sample in a circular shape with an outer diameter of 8WL, and
A capacitor was created by baking at 00°C to form an electrode.

For each capacitor, the apparent permittivity (εs) and dielectric loss (twist nζ) were measured at 25°C and 1KHz-0.3V.
Resistivity was measured at 25°C with an applied voltage of 50V per order,
Furthermore, the temperature change rate of apparent permittivity and dielectric loss (Ta
nζ) was measured. Table 2 shows the measurement results. In Tables 1 and 2, those marked with * are outside the scope of this invention, and all others are within the scope of this invention. Figure 3 shows sample number 1-1.
, 1-5, 1-7, and 1-14, the relationship between the heat treatment temperature and the apparent dielectric constant when a metal oxide is diffused into the grain boundaries of porcelain is shown.

Figure 4 is a diagram of the relationship between heat treatment temperature and dielectric loss, Figure 5 is a diagram of the relationship between heat treatment temperature and resistivity, and Figure 6 is a diagram of the relationship between heat treatment temperature and temperature change rate of apparent permittivity. be. In addition, Fig. 7 shows sample numbers 1-1, 1-5, 1-7, 1.
-14, 1KHz10.3Vr at 25℃
This figure shows the bias voltage dependence of the apparent permittivity and dielectric loss measured under the conditions of ms.

Next, Figure 8 shows the relationship between various electrical properties when the amount of copper oxide is varied for metal oxides consisting of bismuth oxide and copper oxide that diffuse into the grain boundaries of semiconductor porcelain. . The composition of the semiconductor ceramic is SrTlO3
99.85 mol%, Y2O3O. The diffusion heat treatment temperature of the metal oxide paste was 1100℃ using 15 mol%.
And so. Example 2 Various electrical characteristics were measured when varying the amount of TiO in the composition of semiconductor ceramics, and the results are shown in FIG.

At this time, Y2O3 was set to 0.15 mol%. As a metal oxide for insulating the grain boundaries of semiconductor porcelain, a metal oxide containing bismuth oxide and copper oxide in a ratio of 9% by weight: 4% by weight was used and thermally diffused at 1100°C. As described above, according to the present invention, a large dielectric constant can be obtained, the dielectric loss and resistivity are also good, and the temperature characteristics of the apparent dielectric constant and dielectric loss are also flat.

5 Furthermore, when the metal oxide is diffused into the grain boundaries of the porcelain, even if the heat treatment temperature changes, the variation in each property is smaller than in the conventional case.

Furthermore, the device of this invention exhibits a small dielectric loss even when a high voltage is applied, and can obtain sufficiently satisfactory characteristics not only when applying a low voltage but also when a high voltage is applied, and has a characteristic that bias voltage dependence is small. have.

[Brief explanation of the drawing]

Figure 1 is a temperature characteristic diagram of apparent permittivity of a conventional example, Figure 2 is a temperature characteristic diagram of dielectric loss of a conventional example, and Figure 3 is a diagram of the relationship between heat treatment temperature and apparent permittivity of metal oxide. , FIG. 4 is a diagram of the relationship between heat treatment temperature and dielectric loss, FIG. 5 is a diagram of the relationship between heat treatment temperature and resistivity, and FIG. 6 is a diagram of the relationship between heat treatment temperature and temperature change rate of apparent permittivity. Figure 7 shows the apparent permittivity,
Figure 8 is a diagram showing the relationship between dielectric loss and bias voltage, and Figure 8 is a diagram showing the relationship between each electrical characteristic when the amount of copper oxide is changed.
FIG. 9 is a diagram showing the relationship with each electrical characteristic when the amount of TiO2 is changed.

Claims (1)

[Claims] 1 Bismuth oxide changes to Bi_2O_3 in the grain boundaries of strontium titanate-based semiconductor porcelain obtained by adding a valence control element consisting of Y to strontium titanate and sintering it in a ring atmosphere. Converted to 85.
0 to 99.9% by weight, copper oxide converted to CuO, 0.
1 to 15.0% by weight of a metal oxide is diffused,
A composition for a semiconductor ceramic capacitor, characterized in that grain boundaries are made into an insulator.