Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2001-02-15
2003-09-02
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S312000, C428S469000
Reexamination Certificate
active
06614644
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a multilayer ceramic capacitor and a method for the manufacture thereof; and, more particularly, to a miniaturized large capacitance multilayer ceramic capacitor with an improved reliability and an increased operating life, and a method for manufacturing same, wherein the improvement of reliability and operating life is achieved by employing ceramic particles having greater electrical resistance in forming dielectric layers and the improvement of size and capacitance is achieved by scaling down the thickness of such dielectric layers and stacking a greater number of thus scaled down layers.
BACKGROUND OF THE INVENTION
In general, a multilayer ceramic capacitor
40
includes a ceramic body
42
having a pair of external electrodes
44
respectively formed at two opposite end portions thereof. The ceramic body
42
is fabricated by sintering a laminated body formed of alternately stacked dielectric layers
46
and internal electrodes
48
. Each pair of neighboring internal electrodes
48
faces each other with a dielectric layer
46
intervened therebetween and is electrically coupled to different external electrodes
44
, respectively, as shown in FIG.
4
.
The dielectric layer is made of a reduction resistive ceramic material including, e.g., barium titanate (BT) as a major component, and an oxide of rare-earth metal and/or a compound of such acceptor type element as Mn, V, Cr, Mo, Fe, Ni, Cu, Co. The term “reduction resistive ceramic material” used herein represents a ceramic material not being readily deoxidized in a non-oxidative atmosphere but easily oxidized by firing in an oxidative atmosphere. The internal electrodes are formed by sintering a conductive paste whose main component is, for example, Ni metal powder.
The ceramic body is formed by: forming a chip-shaped laminated body with alternately stacked ceramic green sheets and patterned internal electrodes; removing a binder off the chip-shaped laminated body; sintering the binder removed laminated body in a non-oxidative atmosphere at a high temperature ranging from 1200° C. to 1300° C.; and finally re-oxidizing the sintered laminated body in the oxidative atmosphere.
Recent trend for ever more miniaturized and dense electric circuits demands for a further scaled down multilayer ceramic capacitor with higher capacitance. Keeping up with such demand, there has been made an effort to fabricate thinner dielectric layers and to stack a greater number of the thus produced dielectric layers.
However, when the dielectric layers of the multilayer ceramic capacitor are thinned out, dielectric breakdown in the layers between internal electrodes can easily occur since the electric field intensity per unit thickness increases. Accordingly, the operating life of the multilayer ceramic capacitor becomes shortened and the reliability in the electrical characteristic of the capacitor is also deteriorated.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a multilayer ceramic capacitor of a highly miniaturized size and lengthened operating life by increasing the electrical resistance of ceramic grains formed in dielectric layers.
It is another object of the present invention to provide a method for manufacturing same.
In accordance with one aspect of the present invention, there is provided a multilayer ceramic capacitor, comprising: a plurality of dielectric layers; a multiplicity of internal electrodes alternately stacked with the dielectric layers; and a pair of external electrodes connected to the internal electrodes, wherein the dielectric layers includes ceramic grains, the ceramic grains having a main component and one or more additive elements, the additive elements being non-uniformly distributed in the ceramic grains.
In accordance with another aspect of the present invention, there is provided a method for manufacturing a multilayer ceramic capacitor, comprising the steps of: preparing a ceramic material having a main substance and one or more additive elements, the additive elements being distributed inside of the main substance; forming ceramic green sheets by using the prepared ceramic material; coating internal electrode patterns on the ceramic green sheets; stacking the ceramic green sheets including the internal electrode patterns; dicing the stacked ceramic green sheets to form chip-shaped laminated bodies; and sintering the chip-shaped laminated bodies.
REFERENCES:
patent: 5225960 (1993-07-01), Kishi et al.
patent: 5335139 (1994-08-01), Nomura et al.
patent: 5668694 (1997-09-01), Sato et al.
patent: 5790367 (1998-08-01), Mateika et al.
patent: 5977006 (1999-11-01), Iguchi et al.
patent: 6078494 (2000-06-01), Hansen
patent: 6292354 (2001-09-01), Kobayashi et al.
Chazono Hirokazu
Kishi Hiroshi
Shizuno Hisamitsu
Reichard Dean A.
Taiyo Yuden Co. Ltd.
Thomas Eric
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