JPS6031097B2 - Method for firing semiconductor porcelain for capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for firing semiconductor porcelain for capacitors, in which a plurality of molded bodies are placed on a shell and fired in a reducing gas atmosphere.

As a capacitor material obtained by insulating the grain boundaries of a ceramic semiconductor, there are materials mainly containing barium titanate and strontium titanate.

These materials have extremely high electrical resistance and are insulators as they are, but they can be mixed with pentavalent metal compounds such as niobium oxide (
When a small amount of Nb2Q) or tantalum oxide (Ta205) is added and fired, it becomes a semiconductor based on the principle of valence control. However, this alone is usually insufficient to convert the material into a semiconductor, and it is common to sinter it in a reducing atmosphere, for example, a mixed atmosphere of hydrogen and nitrogen. The electrical resistance of the semiconductor porcelain thus obtained has a high conductivity below IQ-c. Therefore, it cannot be used as a capacitor as it is, so after firing, heat treatment is performed in air to re-oxidize the surface and near the grain boundaries, or copper oxide, manganese oxide, etc. are thermally diffused into the grain boundaries. Semiconductor porcelain with an apparent voltage of 20,000~
A semiconductor capacitor having a temperature of 7000 degrees Fahrenheit is obtained. The firing step in a reducing gas atmosphere in the manufacturing process of semiconductor capacitors as described above is an extremely important factor that influences electrical characteristics.

That is, the reducing gas atmosphere must be kept constant within the furnace, and for example, a method is used in which a mixed gas of nitrogen, hydrogen, etc. is caused to flow into the furnace at a constant rate and flow out at a constant rate. Usually, the molded body is placed on a box-shaped pod and placed in the firing furnace.

However, when the atmosphere firing is carried out using this method, there is a drawback that when the amount of the molded body packed in the mold increases, the electrical characteristics vary depending on the position within the mold, resulting in poor process accuracy. In particular, this tendency was more pronounced for materials with higher dielectric constants. The reason for this is thought to be that when a conventional box-shaped shell is installed in a furnace, the gas flow velocity differs locally, causing a positional difference in the reducing gas atmosphere. The method of the present invention eliminates the above-mentioned conventional drawbacks by changing the shape of the shell, and provides a manufacturing method in which uniform electrical characteristics can be obtained even when a large number of molded products are fired in an atmosphere at once. .

FIG. 1A shows a conventional sheath for manufacturing semiconductor ceramic elements, and has a shape in which side plates 2, 2', 3, and 3' are formed on four sides of a bottom plate 1.

FIG. 1B shows a sheath using the manufacturing method of the present invention, in which side plates 2 and 2' projecting upward are formed on both sides of the bottom plate 1. FIG. 1C shows another sheath used in the manufacturing method of the present invention, and the side plate 2 of the sheath shown in FIG. 1B,
2', a partition plate 4 parallel to the side plates 2, 2',
As shown in FIG. The molded body 5 is fired while a mixed gas of nitrogen and hydrogen is caused to flow in and out at a constant speed in a direction parallel to the side plates 2 and 2' of the shell. (Example) Strontium titanate (SrTi03) was added with 0.1 to 2 mol% of bismuth oxide (Bi203) and niobium oxide (N
Q05) Add in a range of 0.1 to 2 mol %, mix thoroughly, and then press-form into a disc shape of 15th side x 0.7th side.

This molded body is placed on the pod shown in Fig. 1 B or C, and the pod is placed in a furnace.
1370oo~14 in a reducing gas atmosphere consisting of 90%
Bake at 60 oo for 2-4 hours. Thereafter, a diffusion substance is applied to one side of the sintered body using a known suitable binder (for example, polyvinyl alcohol), and 1050CO
Heat treatment at ~1200 C for about 2 hours. Silver electrodes are provided on both sides of the sintered body thus obtained. Figure 3A,
B and C are respectively A and B in FIG. It is a figure showing the characteristic of the semiconductor ceramic element manufactured using the saw shown in C, and the state of its fluctuation.

As is clear from FIG. 3, in conventional method A, the characteristics vary greatly depending on the position, and there are many elements with a small dielectric constant, especially in the direction of the reducing gas outflow. Therefore, the amount that can be fired is limited.
Another disadvantage is that the process step is small.

On the other hand, according to methods B and C of the present invention, elements with uniform characteristics can be obtained almost regardless of the position of the element,
The amount that can be fired is increased and the process yield is improved. The reason for this is considered to be that the reducing gas was not uniformly supplied into the shell in the conventional shell, and it is thought that the reducing gas was uniformly supplied by the method of the present invention. As described above, the method of the present invention has the advantage that a large quantity of semiconductor ceramic elements with little variation in characteristics can be manufactured by simply using a sheath with side plates that block the flow of reducing gas removed.

In addition, in the examples, hydrogen 1 to 10% was used as the reducing gas.
Although a mixed gas consisting of 99 to 90% nitrogen was used, it goes without saying that the reducing gas may be any atmosphere that can sufficiently convert the sample into a semiconductor.

In addition, although strontium titanate is used as an example in the examples, similar effects can be obtained by the method of the present invention in systems mainly based on barium titanate or composite compounds thereof.

[Brief explanation of drawings]

FIG. 1A is a perspective view of a conventional sheath for manufacturing semiconductor porcelain for capacitors, and FIGS. 1B and C are perspective views of a sheath for manufacturing semiconductor porcelain for capacitors of the present invention, respectively.
Figure 2 is a top view showing the molded body placed on the shell shown in Figure 1A, and Figures 3A, B, and C are the views of Figure 1A, B, and C, respectively.
FIG. 4 is a diagram showing the relationship between the mounting position and the dielectric material of the element fired using the shavings shown in FIG. 1...Bottom plate, 2, 2'...Side plate, 4,
4'... Partition plate, 5... Molded body. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A plurality of molded bodies are placed on the bottom surface of a pod having upwardly protruding side plates on both sides of the bottom plate, the pod is housed in a furnace, and the pod is placed in a furnace. A method for firing semiconductor porcelain for capacitors, characterized in that the molded body is fired by supplying reducing gas in a direction parallel to the side plate of the pod. 2. A method for firing semiconductor porcelain for capacitors as set forth in claim 1, characterized in that a sheath is used in which partition plates parallel to the side plates are provided between the side plates.