JPS6110226A - Reduced reoxidized semiconductor capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention relates to a reduction and reoxidation type semiconductor capacitor in which a ceramic is heat-treated in a reducing atmosphere to become a semiconductor, and then heat-treated in an oxidizing atmosphere to form an insulating layer on the surface. Regarding.

(Prior art) For example, a ceramic green sheet mainly composed of barium titanate (BaTi03) is fired in air at around 1300°C, then heat-treated in a reducing atmosphere at 1000-1100°C to become a semiconductor, and then heated at 900-1000°C. Reduction-reoxidation type semiconductor capacitors are widely used, which have a surface oxidized by heat treatment in air at a temperature of 0.degree. C., and a silver electrode provided on the oxidized layer on the surface. Such a reduction and reoxidation type semiconductor capacitor is characterized by its small size and large capacity.

(Problems to be Solved by the Invention) In order to realize a larger capacity with a smaller size in such a reduction-reoxidation type semiconductor capacitor, a method such as making the surface oxidation layer thinner may be considered. However, if it is made too thin, problems arise in terms of reliability, and therefore there is a limit to increasing the capacity. That is, although a material that is easily reduced and easily reoxidized is selected as a material for such a semiconductor capacitor, it is difficult to form a surface oxidation layer uniformly and evenly and thinly during the reoxidation stage.

This is because the boundary between the semiconductor layer and the insulating layer is not clear. Currently realized, its areal capacitance is, for example, 500 to 600 nF/+IJI.

Therefore, the main object of the present invention is to provide a reduction and reoxidation type semiconductor capacitor that can further increase the capacity.

(Means for Solving the Problems) In the present invention, a porous ceramic portion is formed on at least one principal surface of a semiconductor ceramic plate made into a semiconductor by reduction treatment, using the same or a different ceramic material, and then reoxidized to form a porous ceramic portion. An insulating layer is formed on the surface of each ceramic particle of the porous ceramic portion, and an electrode is laminated on this surface insulating layer.

(Function) The area of the surface insulating layer formed by reoxidation treatment on the surface of each ceramic particle included in the porous ceramic part increases, and electrodes are laminated on the entire surface of the insulating layer, so the area that acts as a capacitor increases. The area also becomes larger.

(Effects of the Invention) According to the present invention, it is possible to obtain a capacitor that is smaller and has a larger capacity than the conventional capacitor. Specifically, the areal capacity can be increased to about 1.5 to 2 times that of the conventional method.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

(Embodiment) FIG. 1 is a sectional view showing a main part of an embodiment of the present invention. Figure 2 is a diagram showing the whole of this embodiment, and Figure 2 (
a) shows the plan view, and Fig. 2(b) shows the plan view of Fig. 2(a).
A cross-sectional view taken along line nB-11B is shown.

Reduction-reoxidation semiconductor capacitor 10 includes a semiconductor ceramic plate 12 . The semiconductor ceramic plate 12 is made of, for example, barium titanate or strontium titanate, and is made into a semiconductor by being reduced in the form of a ceramic green sheet by heat treatment in a reducing atmosphere. A porous ceramic layer 14.14 is formed on the main surface of this semiconductor ceramic plate 12. This porous ceramic r*tj is made of the same or different ceramic material as the semiconductor ceramic board 12, and when the semiconductor ceramic board is in the state of a ceramic green sheet, it is coated with particles of a certain particle size or more containing a binder such as varnish. It is formed by, for example, printing or applying a ceramic paste, and then scattering or evaporating the paste when the ceramic paste is fired integrally. A surface oxidation layer 16 is formed on the surface of each ceramic particle included in the porous layer 14 by heat treatment (reoxidation treatment) in an oxidizing atmosphere.

Then, the porous ceramic layer 14, that is, the surface oxidized layer 1
An electrode 18 is laminated over the entire surface of the electrode 6 by baking a silver paste, for example. This electrode 18 may be made of a metal other than silver, and its formation method can include not only baking but also wet plating such as electroless plating, dry plating such as sputtering, ion blasting, welding, or CVD. . A lead wire is attached to the electrode 18 as necessary.

Experimental example A ceramic green paste to be made into the semiconductor ceramic plate 12 is prepared by adding a binder to a composition mainly composed of BaTiO3 to prepare a ceramic paste, and by extrusion molding this ceramic paste or by a known method such as a doctor blade method. Get a sheet. The thickness of this green sheet was 400 μm. The ceramic green sheet is punched out into a disk shape as shown in FIG. On the other hand, a ceramic green sheet having the same composition is fired in air at 1330°C and classified to obtain powder (A) with a particle size of 30 to 90 μm. Separately, a calcined powder (B) mainly composed of BaTiO3 is obtained. In addition, the calcining salinity is 1150°C. Then,
A ceramic paste consisting of A=50%, B=10%, and face=40% is prepared, and printed and applied on both sides of a ceramic green sheet in a circular pattern as shown in FIG. After that, it was dried in air at 1330℃ for 2 hours.
Bake for an hour. Therefore, in this state, a dense semiconductor ceramic plate 12 and a porous ceramic portion 14 are formed. Next, in a reducing atmosphere of 90% N2 and 10% N2, heat treatment is performed at 1150° C. for 1 hour to perform reoxidation treatment, and as shown in FIG. was formed.

A silver paste was printed on the surface oxidation 1'i16 of the porous ceramic layer 14 and baked at 830° C. to form the electrode 18.

In this sample, the areal capacitance was 950 nF/cd, the dielectric loss was 3.5%, and the breakdown voltage was 250 ■.

Furthermore, lead wires were attached to the above-mentioned sample in the same manner as in the conventional method, and the surface was coated with resin to produce a densifier. Then, the capacitor thus obtained was heated at 85°C.
DC 25V was continuously applied at a high temperature of 40℃.
A test was conducted in which 18 V DC was continuously applied at a humidity of 95%. As a result, even after 3000 hours, 1
Out of 00 samples, not a single defect occurred.

Comparative Example The same ceramic green sheet as in the example was fired without forming a porous portion, and then a sample was prepared in exactly the same manner as in the example. As a result, the areal capacity is 580 n
F/ad, dielectric loss is 3.0%, breakdown voltage is 250■
Met.

In the above embodiment, the thickness of the porous portion 14 was approximately 50 μm. However, the thickness of this porous portion 14 may be arbitrarily set within the range of 20 μm to 100 μm.

According to the inventor's experiments, when the thickness of the porous portion is 20 μm or less, the effect of expanding the surface area of the surface insulating layer is small, while when it is 100 μm or more, the dielectric loss increases.

The porous portion 14 is preferably made of the same ceramic material as the semiconductor ceramic board 12 in view of stains with the semiconductor ceramic board 12.

In the example shown in FIG. 2, the overall shape is formed into a disk shape.

However, such an external shape may be any other shape such as a rectangular plate shape.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing essential parts of an embodiment of the present invention. Figure 2 is a diagram showing the entire embodiment of Figure 1, and Figure 2 (
a) is its plan view, and Fig. 2(b) is the line 1 of Fig. 2(a).
FIG. 1B is a cross-sectional view taken along line 1B-IIB. In the figure, 12 is a semiconductor ceramic plate, 14 is a porous portion, 16 is a surface oxidation layer, and 18 is an electrode. Patent applicant Murata Manufacturing Co., Ltd. Representative Patent attorney Oka 1) Kei Zen (and 1 other person)

Claims (1)

[Scope of Claims] 1. A dense semiconductor ceramic plate made into a semiconductor by reduction treatment, a porous ceramic portion formed on at least one main surface of the semiconductor ceramic plate, and the porous portion formed by the reoxidation treatment. A reduction and reoxidation type semiconductor capacitor, comprising: a surface insulating layer formed on the surface of each ceramic particle included in the semiconductor capacitor; and an electrode laminated on the surface insulating layer. 2. The semiconductor shellac board is formed by firing a ceramic green sheet, and the porous ceramic part is formed by printing a ceramic paste of a certain particle size or more on the main surface of the ceramic green sheet and integrally firing it, and then forming the ceramic paste into a ceramic paste. The reduction and reoxidation type semiconductor capacitor according to claim 1, which is formed by scattering the contained binder.