JPH0524647B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a grain boundary insulated semiconductor ceramic capacitor in which a diffusion substance is attached to the surface of a semiconductor ceramic, the diffusion substance is thermally diffused into the grain boundary layer, and the grain boundary layer is reoxidized. Regarding the manufacturing method. [Prior art] Grain boundary insulated semiconductor ceramic capacitors are made by increasing the resistance of the crystal grain boundaries of semiconducting ceramic and using the crystal grain boundaries as a dielectric material. It depends on the state of the insulator layer, which is about several μm thick. Semiconductor porcelain is generally made of a composition whose main component is strontium titanate or barium titanate, and which contains one or more elements called valence control elements such as niobium, tantalum, antimony, or rare earth elements. It is obtained by molding and firing in a neutral or reducing atmosphere. Conventionally, methods for converting the grain boundaries of semiconductor ceramics obtained in this way into insulators include a method of re-oxidizing the grain boundary layer by heat treatment in the atmosphere, or a method of re-oxidizing the grain boundary layer, which is easily diffused into the grain boundaries. Grain boundary diffusion substances to be compensated, for example, one or more of elements such as copper, bismuth, lead, or manganese, are attached to the surface of the semiconductor porcelain by printing or other means, and then heat treatment is performed in the atmosphere,
A common method is to diffuse the grain boundary diffusion substance into the grain boundary layer and simultaneously re-oxidize the grain boundary layer. [Problems to be Solved by the Invention] However, in the grain boundary insulating step described above, in the method of reoxidizing the grain boundary layer by heat treatment in the atmosphere without using a diffusing substance, the insulation resistance value or It had the disadvantage of a low dielectric breakdown voltage value. On the other hand, in the thermal diffusion method using a diffusion substance such as copper, bismuth, lead, or manganese, the diffusion substance is thermally diffused into the grain boundary layer and the grain boundary layer is reoxidized at the same time, as described above. A long heat treatment was required to sufficiently diffuse the substance into the grain boundary layer.
As a result, the crystal grains near the surface of the semiconductor ceramic are reoxidized deeply, and the width of the insulating layer becomes thicker, leading to a decrease in capacitance or an increase in dielectric loss of the resulting capacitor. A problem had arisen. Furthermore, if the heat treatment is not performed sufficiently, the diffusion substance will not be uniformly diffused, resulting in the drawback that the resulting capacitor will have a low insulation resistance value or dielectric breakdown voltage value, similar to the above-mentioned method that does not use a diffusion substance. Ta. This was particularly noticeable when the semiconductor porcelain had a thick shape or a complicated shape. The present invention has been made in view of such circumstances, and in the step of forming a grain boundary insulator, after thermally diffusing a diffusion substance into semiconductor ceramics in a container whose pressure is reduced to less than atmospheric pressure, the container contains oxygen. By introducing gas to raise the pressure to above atmospheric pressure and cooling to reoxidize the grain boundaries, a small, large-capacity, grain-boundary insulated type with high capacitance, high insulation resistance, and high dielectric breakdown voltage is created. The object of the present invention is to provide a method for manufacturing a semiconductor ceramic capacitor. [Means for Solving the Problems] A method for manufacturing a grain boundary insulated semiconductor ceramic capacitor according to the present invention involves attaching a diffusing substance to the surface of semiconductor ceramic, thermally diffusing the diffusing substance into the grain boundary layer, and dispersing the grain. A method for manufacturing a grain boundary insulated semiconductor ceramic capacitor in which the boundary layer is reoxidized includes a thermal diffusion process in which the semiconductor ceramic and the diffusion material are placed in a container whose pressure is reduced to below atmospheric pressure, and heated, and oxygen is added to the container. The method is characterized in that it includes a reoxidation process in which a gas containing gas is introduced to bring the pressure above atmospheric pressure and the inside of the container is cooled. [Function] In the method of manufacturing a grain boundary insulated semiconductor ceramic capacitor of the present invention, the semiconductor ceramic and the diffusion material are placed in a container whose pressure is reduced to below atmospheric pressure and heated, thereby causing the evaporation of the diffusion material. is promoted, and the amount of the diffusion substance adhering to the semiconductor ceramic increases. Diffusion of the diffusion substance to the grain boundaries is promoted, and re-oxidation of the semiconductor ceramic is prevented at this time. Furthermore, after the diffusion substance has diffused into the grain boundaries, by introducing a gas containing oxygen into the container and cooling the container, excessive diffusion of the diffusion substance into the grain boundaries can be prevented. , the semiconductor porcelain is fully reoxidized. [Example] Hereinafter, the method for manufacturing a semiconductor ceramic capacitor of the present invention will be specifically explained based on the example. First, a method for manufacturing strontium titanate-based semiconductor porcelain will be described. Strontium carbonate, titanium oxide, and niobium pentoxide were weighed in a molar ratio of 100:100:0.2, wet mixed for 24 hours using a resin ball mill and a resin ball, and then evaporated and dried.
Calculate at 1200℃. Add 2.5% polyvinyl alcohol to the resulting powder
The mixture is then wet mixed and ground again for 24 hours using a resin ball mill and resin balls, and then evaporated and dried. Then, it is passed through a 60 mesh sieve and granulated.
Form into a disc shape of 10mmφ x 1.5mm using a pressure of 2ton/ ^cm2 . This molded body was heated at 1000°C for 2 hours to remove organic components, and a mixed gas flow of H ₂ and N ₂ (H ₂ :N ₂ =
1:9) for 6 hours at 1500°C to obtain a disk-shaped strontium titanate semiconductor ceramic. The semiconductor porcelain thus obtained had an average crystal grain size of 50 μm and exhibited almost uniform grain growth. In addition, the specific resistance value of this semiconductor porcelain is
It was 40 mΩcm, which was a sufficiently low value. Next, a method for converting the crystal grain boundaries of the semiconductor ceramic obtained above into an insulator will be described. Example 1 FIG. 1 is a schematic sectional view showing the configuration of an apparatus for carrying out the method of the present invention, and numeral 1 in the figure is a reaction vessel for converting the semiconductor ceramic into the insulator. The reaction vessel 1 is, for example, a cylindrical sealed vessel made of alumina, and is installed with its axial direction in the horizontal direction. A heater 6 is provided around the outside of the reaction container 1, and a support base 2 made of alumina and having a rectangular cross section is provided on the lower side inside the reaction container 1.
A sample holding container 3 made of alumina and having a U-shaped cross section is provided on the support base 2 in order to place a semiconductor ceramic 4a to which a diffusion substance, which will be described later, is attached. On the other hand, an insertion port 7a for a temperature sensor 7 is provided on one side wall of the reaction vessel 1.
By inserting the sample into the reaction container 1, the temperature near the semiconductor ceramic 4a placed in the sample holding container 3 is measured. Further, an exhaust pipe 8 connected to a vacuum pump (not shown) via an exhaust valve 8a is fixed at one end of the other side wall of the reaction vessel 1, and a compressor (not shown) is connected to the other end via a gas introduction valve 9a. Alternatively, a gas introduction pipe 9 connected to an oxygen cylinder is fixedly installed. Using a device having such a configuration, the grain boundaries of the semiconductor ceramic are made into an insulator by the following operations. First, on one or both surfaces of the semiconductor ceramic obtained above, grain boundary diffusion substances for valence compensation, such as bismuth oxide (BiO ₃ ), copper oxide (Cu ₂ O), and lead oxide (PbO), are applied. The molar ratio is 4:
Diffusion material paste mixed in a ratio of 2:4 is used as an element.
Apply at a rate of 10mg per gram. In the air,
Heat at 350℃ for 2 hours to burn off organic components,
Place it on the sample holding container 3 inside the reaction container 1. Next, after opening the exhaust valve 8a and reducing the pressure inside the reaction container 1 to 0.05 MPa using a vacuum pump,
The inside of the reaction vessel 1 is heated to 1150° C. using the heater 6, and this state is maintained for 1 hour. Thereafter, the gas introduction valve 9a is opened to introduce atmospheric air or oxygen gas from a compressor or an oxygen cylinder to return the inside of the reaction vessel 1 to atmospheric pressure, and when it is naturally cooled to room temperature, the grain boundary insulated semiconductor ceramic capacitor is formed. You get a body. Furthermore, In-Ga on both sides.
When an electrode is formed by applying the alloy, a grain boundary insulated semiconductor ceramic capacitor having a high capacitance value, high insulation resistance value, and high dielectric breakdown voltage value is obtained. Note that in this example, the semiconductor porcelain to which the diffusive substance was attached was thermally diffused under reduced pressure below atmospheric pressure. This is because the reoxidation reaction of the semiconductor ceramic progresses simultaneously with the diffusion of the substance to the grain boundaries, and as a result, the width of the insulator layer becomes thicker, making it impossible to obtain a high capacitance value. After the thermal diffusion treatment, air or oxygen gas is introduced into the container in a reduced pressure state to raise the pressure to above atmospheric pressure and the container is cooled. At the same time as the reoxidation of
This is because high capacitance cannot be obtained. In addition, it is important to introduce the atmosphere or oxygen gas at a pressure higher than atmospheric pressure into the container because if the pressure is lower than atmospheric pressure, the semiconductor ceramic will not be sufficiently reoxidized, resulting in the insulation resistance value and dielectric breakdown voltage value of the semiconductor ceramic capacitor. This is because the Example 2 Next, another example of the method of the present invention will be described. First, the semiconductor porcelain 4 obtained by applying the diffusion substance paste and removing the organic components in the same manner as described above.
A is placed on the sample holding container 3 in the reaction container 1 shown in FIG. Next, the pressure inside the reaction vessel 1 was reduced to 0.07 MPa using a vacuum pump, and after heating at 1150° C. for 1 hour, heating was stopped and cooling was started while the pressure was reduced. Then, when the temperature inside the reaction vessel 1 reaches 1000°C, air is introduced from the gas introduction pipe 9, and the inside of the reaction vessel 1 is returned to atmospheric pressure, and cooling is continued to bring the inside of the reaction vessel 1 to room temperature. A grain boundary insulated semiconductor ceramic capacitor body is obtained. After the thermal diffusion treatment, by controlling the temperature at which the atmosphere or oxygen gas is introduced into the reaction vessel 1, that is, after cooling it to a predetermined temperature under reduced pressure, the atmosphere or oxygen gas is introduced and the reaction is carried out. By returning the inside of the container 1 to atmospheric pressure and continuing cooling, the progress of reoxidation of the semiconductor ceramic 4a can be controlled. Further, when an In-Ga alloy is applied to both sides of the grain boundary insulated semiconductor ceramic capacitor body to form electrodes, a grain boundary insulated semiconductor ceramic capacitor having desired capacitance, insulation resistance, and dielectric breakdown voltage values can be obtained. A capacitor is obtained. Example 3 Next, a third example of the method of the present invention will be described. First, the semiconductor porcelain 4 obtained by applying the diffusion substance paste and removing the organic components in the same manner as described above.
A is placed on the sample holding container 3 in the reaction container 1 shown in FIG. Next, the pressure inside the reaction vessel 1 was reduced to 0.03 MPa using a vacuum pump, and after heating at 1150° C. for 1 hour, cooling was started under reduced pressure. Reaction vessel 1
When the temperature reaches 900°C, oxygen gas is introduced, the gas pressure inside the reaction vessel 1 is set to 0.2 MPa, and the temperature inside the reaction vessel 1 is maintained at 900°C for 30 minutes. Thereafter, the inside of the reaction vessel 1 is cooled down to room temperature by natural cooling to obtain a grain boundary insulated semiconductor ceramic capacitor body. In this way, by controlling the timing of introducing the atmosphere or oxygen gas into the reaction vessel 1 after the thermal diffusion treatment, in other words, the atmosphere or oxygen gas is introduced into the reaction vessel 1 which has been cooled to a predetermined temperature in a reduced pressure state to a predetermined pressure. The progress of reoxidation of the semiconductor ceramic 4a can be controlled by introducing oxygen gas, maintaining the temperature for a predetermined time, and then cooling it again. Further, when an In-Ga alloy is applied to both sides of the grain boundary insulated semiconductor ceramic capacitor body to form electrodes, a grain boundary insulated semiconductor ceramic capacitor having desired capacitance, insulation resistance, and dielectric breakdown voltage values can be obtained. A capacitor is obtained. Example 4 Furthermore, a fourth example of the method of the present invention will be described. FIG. 2 is a schematic cross-sectional view showing the structure of another apparatus for carrying out the method of the present invention, in which reference numeral 1 denotes a reaction vessel for converting the semiconductor ceramic into the insulator. The reaction vessel 1 is, for example, a cylindrical sealed vessel made of alumina, and is installed with its axial direction in the horizontal direction. A heater 6 is installed outside the reaction vessel 1.
are provided around the periphery, and on the lower side of the reaction vessel 1, support stands 2 made of alumina and having a rectangular cross section are arranged at predetermined intervals.
2 are provided respectively. A sample holding container 3 made of alumina and having an L-shaped cross section is provided on one side of the support stands 2, 2 to place the diffusion substance 5, and the other side is provided with a semiconductor sample holding container 3 on which the diffusion substance 5 is not attached. A sample holding container 3 made of alumina and also having an L-shaped cross section is provided in order to place the porcelain 4b thereon. On the other hand, a temperature sensor 7 is mounted on one side wall of the reaction vessel 1.
By inserting the temperature sensors 7, 7 into the reaction container 1, the temperature and diffusion near the semiconductor ceramic 4b placed in the sample holding container 3 can be measured. The temperature near each substance 5 is measured. Further, an exhaust pipe 8 connected to a vacuum pump (not shown) via an exhaust valve 8a is fixed at one end of the other side wall of the reaction vessel 1, and a compressor (not shown) is connected to the other end via a gas introduction valve 9a. Alternatively, a gas introduction pipe 9 connected to an oxygen cylinder is fixedly installed. Using a device having such a configuration, the grain boundaries of the semiconductor ceramic are made into an insulator by the following operations. First, the semiconductor ceramic 4b to which no diffusion substance is attached is placed on the sample holding container 3, and a diffusion substance for valence compensation, that is, bismuth oxide (BiO ₃ ), is placed on the sample holding container 3.
A diffusion substance made by mixing copper oxide (Cu ₂ O) and lead oxide (PbO) in a molar ratio of 4:2:4 is placed in the sample holding container 3 . And exhaust valve 8a
is opened and the inside of reaction vessel 1 is pumped using a vacuum pump.
After reducing the pressure to 0.01 MPa, the temperature near the diffusion material 5 is heated to 1200° C. and the temperature near the semiconductor ceramic 4 is heated to 1150° C. using the heater 6, and maintained for one hour. Thereafter, the gas introduction valve 9a is opened to introduce atmospheric air using a compressor, and the reaction vessel 1 is returned to atmospheric pressure and cooled to room temperature by natural cooling, thereby obtaining a grain boundary insulated semiconductor ceramic capacitor body. In this way, by controlling the heating temperature of the semiconductor ceramic 4b to be equal to or lower than the heating temperature of the diffusion material 5, the amount of the diffusion material 5 attached to the semiconductor ceramic 4b is increased, and the crystal grain boundaries of the diffusion material 5 are sufficient diffusion. Therefore, even if the semiconductor ceramic 4b is thick or has a complicated shape, a uniform and thin insulating layer can be formed. Furthermore, when an In-Ga alloy is applied to both sides of the grain boundary insulated semiconductor ceramic capacitor body to form electrodes, a grain boundary insulated semiconductor porcelain having high capacitance, high insulation resistance, and dielectric breakdown voltage can be produced. A capacitor is obtained. Note that the heating temperature of the semiconductor porcelain 4b is higher than that of the diffusion substance 5.
The reason why the heating temperature is controlled to be below the heating temperature is that if the heating temperature of the semiconductor porcelain 4b is higher than the heating temperature of the diffusion material 5, the diffusion material 5 will not be sufficiently supplied to the semiconductor porcelain 4b, and the insulation resistance value or dielectric breakdown voltage will decrease. This is because the value becomes lower. The electrical properties of the semiconductor ceramic capacitor obtained as described above, namely, the apparent permittivity ε _app and the dielectric loss
Table 1 shows the results of examining tan δ, insulation resistivity ρ, and dielectric breakdown voltage values. The apparent permittivity ε _app is the capacitance C measured under an AC voltage of 1 Vrms and 1 KHz, the thickness t of the element body,
It was obtained by substituting the electrode area S and the vacuum permittivity ε ₀ into equation (1). ε _app = Ct/ε ₀・S... (1) The above dielectric loss tan δ (%) is the result of measurement under an AC voltage of 1 Vrms, 1 KHz, and the above insulation resistivity ρ (Ωcm) is the result of measurement under a DC voltage of 50 V. After applying for 1 minute, the resistance value R, the element thickness t, and the electrode area S are expressed by formula (2).
It was obtained by substituting . ρ=R·S/t (2) The dielectric breakdown voltage value (V _DC /mm) is calculated by converting the value measured by applying a DC voltage per 1 mm thickness of the element. Further, Table 1 shows, as a comparative example, the electrical characteristics of a grain boundary insulated semiconductor ceramic capacitor manufactured outside the conditions of the method of the present invention. That is, Comparative Example 1 was obtained by placing semiconductor porcelain to which no diffusive substance paste was applied, placing it in the reaction vessel 1, reducing the pressure to 0.05 MPa, heating it at 1150°C for 1 hour, and then introducing air to naturally cool it. In Comparative Example 2, a semiconductor ceramic capacitor coated with a diffusion substance paste and from which organic components were removed was heated in the atmosphere at 1150°C for 1 hour without reducing the pressure in the reaction vessel 1, and then cooled naturally. A semiconductor porcelain capacitor obtained by

〔effect〕

As detailed above, in the method for manufacturing a grain boundary insulated semiconductor ceramic capacitor of the present invention, in the step of insulating the grain boundary layer of the semiconductor ceramic, the semiconductor ceramic and the diffusion material are placed in a container whose pressure is reduced to below atmospheric pressure. Since the method includes a process of thermally diffusing the diffusion substance to the grain boundaries by disposing the semiconductor ceramic and heating it, the amount of the diffusion substance attached to the semiconductor ceramic increases and sufficient diffusion is achieved. This prevents the capacitance value from decreasing, and
A uniform and thin insulating layer can be formed even on thick or complex-shaped semiconductor porcelain. After the above process, a gas containing oxygen is introduced into the container to make the pressure higher than atmospheric pressure, and the inside of the container is cooled to reoxidize the grain boundary layer, so that the crystals near the surface of the semiconductor ceramic are cooled. Excessive re-oxidation of the particles is prevented. Therefore, the present invention exhibits excellent effects such as obtaining a small, large-capacity, grain-boundary insulated semiconductor ceramic capacitor having a high capacitance value, high insulation resistance value, and high dielectric breakdown voltage value.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the configuration of an apparatus for implementing the method of the present invention, and FIG. 2 is a schematic cross-sectional view showing the configuration of another apparatus for implementing the method of the present invention. DESCRIPTION OF SYMBOLS 1... Reaction container, 2... Support stand, 3... Sample holding container, 4a... Semiconductor porcelain, 4b... Semiconductor porcelain, 5...
Diffusion substance, 6... Heater, 7... Temperature sensor.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a grain boundary insulated semiconductor ceramic capacitor in which a diffusion substance is attached to the surface of semiconductor ceramic, the diffusion substance is thermally diffused into the grain boundary layer, and the grain boundary layer is reoxidized, A thermal diffusion process in which the semiconductor porcelain and the diffusion material are placed in a container whose pressure is reduced to below atmospheric pressure and heated; A method for manufacturing a grain boundary insulated semiconductor ceramic capacitor, the method comprising: a reoxidation process of cooling the capacitor.