Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
1999-02-09
2001-05-08
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S321500, C361S322000
Reexamination Certificate
active
06229686
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to monolithic capacitors having internal electrodes composed of base metals, which are suitable for middle- to high-voltage use requiring a high withstand voltage.
2. Description of the Related Art
Recently, surface mounting of electronic units has been in progress to satisfy the miniaturization of electronic device. As a result more compact electronic units have been used making it necessary to prove more compact monolithic capacitors with higher capacitance.
On the other hand, middle- to high-voltage capacitors with high withstand voltage have been used, for example, in back lights and switching power sources of liquid crystal displays. Requirements for such middle- to high-voltage capacitors are high withstand voltage, further miniaturization, and inexpensiveness.
In conventional middle- to high-voltage monolithic capacitors, suppression of discharge from the outer surfaces of the capacitors is an essential factor for achieving high withstand voltage. Various types of monolithic capacitors having high withstand voltage have been disclosed in, for example, Japanese Utility Model Application Laid-Open Nos. 60-76028, 62-120333, and 58-56431, and Japanese Patent Application Laid-Open No. 62-210612.
For example, in a proposed middle- to high-voltage monolithic capacitor with high withstand voltage, thick ceramic layers are provided above and below the capacitance extraction section composed of a plurality of overlapping internal electrodes, in order to suppress discharge from the top and bottom faces of a sintered ceramic body.
Japanese Patent Application Laid-Open No. 62-210612 discloses a monolithic capacitor with high withstand voltage in which ceramic layers with a relatively low dielectric constant are disposed above and below the capacitance extraction section including overlapping internal electrodes. The ceramic layers suppress flashover above and below the sintered body.
In these conventional middle- to high-voltage monolithic capacitors, thick ceramic layers are disposed above and below the capacitance extraction section; hence the monolithic capacitors are inevitably large, and do not satisfy the requirement for miniaturization and particularly lower heights.
Since these monolithic capacitors and a middle- to high-voltage monolithic capacitor disclosed in Japanese Patent Application Laid-Open No. 62-210612 have internal electrodes composed of noble metals, such as silver and silver-palladium, these are disadvantageous with regard to material costs.
On the other hand, conventional monolithic capacitor configurations capable of reducing material costs use base metals, such as nickel and copper, as internal electrode materials. Since base metals are readily oxidizable, a ceramic material having high reduction-resistant characteristics must be used in the production of monolithic capacitors by a monolithic ceramic firing technology. All the conventional monolithic capacitors are not suitable for middle- to high-voltage use and the ceramic materials used in these monolithic capacitors do not have high reduction-resistant characteristics capable of enhancing withstand voltage.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a monolithic capacitor which is free from disadvantages in conventional middle- to high-voltage monolithic capacitors.
It is another object of the present invention to provide a compact and inexpensive monolithic capacitor having high withstand voltage.
A monolithic capacitor in accordance with the present invention comprises a sintered ceramic body comprising a sintered ceramic matrix, a plurality of internal electrodes deposited in the thickness direction in the sintered ceramic body, separated by the sintered ceramic matrix, and alternately extending to opposing first and second side faces of the sintered ceramic body, and top and bottom ceramic layers provided above and below the sintered ceramic matrix, wherein the sintered ceramic matrix comprises a reduction-resistant ceramic comprising BaTiO
3
, the top and bottom ceramic layers comprise a reduction-resistant ceramic comprising CaZrO
3
, and the plurality of internal electrodes comprise a base metal.
Since the reduction-resistant ceramic layers comprising CaZrO
3
have a low dielectric constant compared with the reduction-resistant ceramic matrix comprising BaTiO
3
, these layers are suitably used for formation of low-dielectric layers in a middle- to high-voltage monolithic capacitor. When these ceramic elements are fired in a reduction-resistant atmosphere, these are firmly bonded to each other due to interdiffusion therebetween. Accordingly, such a configuration allows the use of internal electrodes composed of an inexpensive base metal.
In the monolithic capacitor in accordance with the present invention, the side faces of the sintered ceramic matrix are preferably covered with a reduction-resistant ceramic comprising CaZrO
3
.
REFERENCES:
patent: 4607316 (1986-08-01), Wada et al.
patent: 5117326 (1992-05-01), Sano et al.
patent: 0312817 (1988-09-01), None
patent: 0690462 (1996-01-01), None
patent: 193059 (1923-02-01), None
patent: 743700 (1952-10-01), None
patent: 2303488 (1997-02-01), None
patent: 58-56431 (1983-04-01), None
patent: 60-76028 (1985-05-01), None
patent: 62-120333 (1987-07-01), None
patent: 62-210612 (1987-09-01), None
European Search Report (in English) issued Dec. 1, 1999 in a related application.
Shimahara Yutaka
Takeuchi Shozo
Dinkins Anthony
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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