JPH01239826A - Manufacture of reduced reoxidized semiconductor ceramic capacitor - Google Patents

Abstract

PURPOSE:To manufacture a reduced reoxidized semiconductor capacitor with high yield by a method adapted for a mass production by laminating a molded sheet having a composition to which reduction resistant additive is added on the surface of the sheet containing the composition including as a main ingredient BaTiO3 and rare earth element oxide, sintering it, and then reducing it. CONSTITUTION:After a molded sheet 4 having a composition to which reduction resistant additive is added is laminated on the surface of the sheet 4 containing the composition including as a main ingredient BaTiO3 and rare earth element oxide, it is sintered to obtain a dielectric ceramic, the ceramic is reduced, reoxidized or merely reduced to form a surface dielectric layer 6. For example, a composition containing 88mol% of BaTiO3, 3mol% of Nd2O3 and 9mol% of TiO2 is of a composition 1, and the composition to which 1wt.% of CaTiO3 is added is of a composition 2. Five layers of the sheets 5 each containing the composition 1 are laminated on one layer of the sheet 4 containing the composition 2, one layer of the sheet 4 containing the composition 2 is laminated to be pressure thereon, and baked at 1300 deg.C in the air to obtain a dielectric ceramic. Then, it is reduced, reoxidized to form a surface dielectric 6, and electrodes 8 are then formed on both side faces thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method of manufacturing a reduction and reoxidation type semiconductor ceramic capacitor used in various electronic devices.

Conventional reduction-reoxidation type semiconductor ceramic capacitors have been put into practical use as small capacitors that can provide large capacitance. BaTiO
A composition in which the main component is 3 and rare earth element oxides, etc. is generally known, and a dense ceramic with a particle size of 1 to 2 μm is obtained.

The cross section of a conventional reduction and reoxidation type semiconductor capacitor is as shown in Fig. 4, where 1 is a surface dielectric layer, 2 is a semiconductor layer, and 3 is a surface dielectric layer.
is the counter electrode. The manufacturing method is as follows. An organic binder is added to a mixed raw material whose composition matches the characteristics of the capacitor, and the mixture is granulated, sized, and shaped. First, the molded body is fired in air to produce dielectric porcelain. Next, the entire structure is made into a semiconductor by heat treatment in a reducing atmosphere, and a thin dielectric layer is formed on the surface by further heat treatment in air. Finally, electrodes are applied to both sides to form a capacitor. The capacitance of a capacitor increases as the thickness of the dielectric layer decreases. Therefore, a reduction and reoxidation type semiconductor capacitor having a thin surface dielectric layer has a larger capacitance than a general ceramic capacitor.

However, this manufacturing method requires three heat treatments, and the characteristics of the capacitor are affected by all of them. In particular, variations in heat treatment conditions when forming the surface dielectric layer 1 have a large effect on its thickness, leading to variations in capacitance and a decrease in breakdown voltage.

SUMMARY OF THE INVENTION The present invention aims to improve the above-mentioned problems and to provide a method for manufacturing a reduction-reoxidation type semiconductor capacitor with a high yield by a method suitable for mass production.

Means for Solving the Problem In order to solve this problem, the present invention provides a surface of a molded sheet having a composition mainly composed of BaTiOs and containing a rare earth element oxide, and adding a reduction-resistant additive to this molded sheet composition. This method forms a surface dielectric layer by laminating molded sheets having the added composition and then sintering the resulting dielectric porcelain by subjecting it to reduction and reoxidation treatment or only reduction treatment. .

Effect: When dielectric ceramics with different compositions of the inside and surface layer of the ceramic are reduced, the reduction state will differ depending on the composition.If a reduction-resistant substance is added to the surface layer at that time,
That portion may not be completely converted into a semiconductor, or depending on the conditions, may remain as a dielectric surface layer. In addition, since the thickness of the surface layer can be set in advance as the thickness of the molded sheet, the thickness of the surface dielectric layer can be easily controlled, which suppresses variations in capacitance and reduces breakdown voltage. can also be prevented.

Example The present invention will be described in detail below based on Examples.

BaTiO388molti, Nd2O33moA/%,
The composition of TiO29 mortar is composition 1, and BaTiO3s
smolti, Nd 2053 mo/l/%, Ti02
A composition of 9-El% and 1wt% of CaTiO3 is defined as composition 2. Each raw material was weighed as in the composition of Composition 1, wet mixed in a ball mill, and then dried. This raw material contains 7 wt% polyvinyl butyral as an organic binder, 3 wt% dioctyl phthalate as a plasticizer, and acetic acid n as a solvent.
After adding 50 wt% of butyl and wet kneading, filtering and defoaming,
A sheet with a thickness of .mu.m was molded. Next, a sheet having a thickness of 20 μm was molded for Composition 2 in the same manner.

Each sheet was cut into a shape of 70 mm x 130 mm, six sheets of composition 1 were laminated on one layer of sheet of composition 2, and one layer of sheet of composition 2 was further laminated thereon. Next, these laminates were crimped and cut into a shape of 7 mm x 7 mm. Next, after removing the binder, these were fired in air at a temperature of 1300'C for 2 hours to obtain dielectric porcelain. Next, these dielectric ceramics were placed in a reducing atmosphere (N2:u
2=95:5) at 1000° C. for 4 hours, and then re-oxidized in air at 100° C. for 4 hours to form a surface dielectric layer. Next, silver paste was screen printed at predetermined positions on both sides and baked at 850'C to form electrodes. FIG. 2 shows a cross section of the obtained reduced and reoxidized semiconductor capacitor, and FIG. 1 shows a pressed body of the molded sheet. The portion of the molded sheet 4 of Composition 2 in FIG. 1 becomes the surface dielectric layer 6 of FIG. 2, and the portion of the molded sheet 6 of Composition 1 becomes the semiconductor layer 7. 8 is a counter electrode. Here, the characteristics as a capacitor are determined by the composition 2 forming the surface dielectric layer 6.

For comparison, a conventional reduction-reoxidation semiconductor capacitor having composition 1 was made and its characteristics were compared. Capacitance per unit area, dielectric loss (tanδ), breakdown voltage (BDV),
Table 1 shows the results of measuring the variation in capacitance. Capacitance and tan δ are 0.1'I, IKH
Measurements were made under conditions 2(7), and BD''/ was measured using a step-up breakdown method to measure the voltage immediately before a current of 1 mA or more flows between the two poles of the capacitor.

Table 1 As is clear from Table 1, the manufacturing method of the present invention reduces variations in capacitance and other properties while keeping them the same as in the conventional method, and also prevents a decrease in BD'/. I was able to do that.

Note that in this example, Nd2O3 was used as the rare earth element oxide.
was used, but other rare earth elements (e.g. La.

Ca, Pr, Sm, Eu, Gd, Dy, etc.) may be used,
As the reduction-resistant additive, ζMgTiO3, human β203, etc. may be used.

Furthermore, by laminating the molded sheet 4 of composition 2 on only one side, a reduction and reoxidation type semiconductor ceramic capacitor as shown in FIG. 3 can be easily manufactured.

Effects of the Invention As described above, according to the present invention, a reduction resistant additive is added to the surface of a molded sheet having BaTi05 as a main component and a rare earth element oxide. After laminating the molded sheets, the dielectric ceramic obtained by sintering is subjected to reduction/reoxidation treatment or only reduction treatment to form a surface dielectric layer, so that the thickness of the surface dielectric layer can be adjusted in advance. can be set, reducing variations in capacitance and preventing a drop in breakdown voltage.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a crimped body according to the method for manufacturing a reduction and reoxidation type semiconductor ceramic capacitor of the present invention, and FIG. 2 is a sectional view of a reduction and reoxidation type semiconductor ceramic capacitor according to an embodiment of the present invention.
FIG. 3 is a sectional view of another example of the reduction and reoxidation type semiconductor ceramic capacitor according to the embodiment of the present invention, and FIG. 4 is a sectional view of a conventional reduction and reoxidation type semiconductor ceramic capacitor. 4... Molded sheet of composition 2, 5...
Molded sheet of composition 1, 6...surface dielectric layer,
7... Semiconductor layer, 8... Counter electrode.

Claims (1)

[Claims] A dielectric obtained by laminating a molded sheet having a composition in which a reduction-resistant additive is added to the above composition on the surface of a molded sheet having a composition mainly composed of BaTiO_3 and containing a rare earth element oxide, and then sintering the molded sheet. A method for manufacturing a reduction and reoxidation type semiconductor ceramic capacitor, characterized in that a surface dielectric layer is formed by subjecting body ceramic to reduction and reoxidation treatment or only reduction treatment.