Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2000-07-06
2001-09-25
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S321400, C501S137000, C501S138000
Reexamination Certificate
active
06295196
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to monolithic ceramic electronic components, such as a monolithic ceramic capacitor provided with internal electrodes composed of a base metal, for example, nickel or a nickel alloy.
2. Description of the Related Art
Various types of monolithic ceramic electronic components provided with a plurality of ceramic layers and internal electrodes formed between the ceramic layers have been commercially available. A typical example thereof is a monolithic ceramic capacitor in which a ceramic dielectric material is used for the ceramic layers.
Conventionally, a noble metal such as palladium or platinum or an alloy thereof is used for internal electrodes in such a monolithic ceramic capacitor because the dielectric material must be fired in air at a temperature as high as approximately 1,300° C. However, such materials for electrodes are very expensive, resulting in an increase in production cost.
In order to reduce the production cost, the use of base metals as materials for internal electrodes in monolithic ceramic capacitors has been implemented, and various types of nonreducing dielectric materials which can be fired in a neutral or reducing atmosphere in order to prevent the electrodes from oxidizing during firing have been developed. Examples of the base metal used for internal electrodes include cobalt, nickel and copper. In view of cost and oxidation resistance, nickel is predominantly used.
There is now a demand for further reduction in size and larger capacitance with respect to monolithic ceramic capacitors, and an increase in dielectric constant and a decrease in thickness have been studied with respect to ceramic dielectric materials, and simultaneously, a decrease in thickness has been studied with respect to materials for electrodes.
In general, internal electrodes of monolithic ceramic capacitors are formed by a printing method, such as screen-printing, using a paste containing a metallic powder. When nickel powder is used as the metallic powder to be incorporated in such a paste, a nickel powder having an average particle diameter of more than 0.25 &mgr;m, which is produced by a liquid phase method or a chemical vapor method, is used in many cases. However, with such a large particle size, it is difficult to decrease the thickness of internal electrodes.
When a nickel powder having an average particle diameter as large as 0.25 &mgr;m is used, in order to make the dielectric ceramic exhibit dielectric properties, the thickness of the electrodes must be set at 0.8 &mgr;m or more.
Although a decrease in the thickness of the ceramic dielectric layer is the most effective means to increase the capacitance of the monolithic ceramic capacitor, for example, if the thickness of the ceramic layer is 3 &mgr;m or less against the thickness of 0.8 &mgr;m of the internal electrode, delamination, which is a fatal structural defect in the monolithic capacitor, frequently occurs due to a difference in shrinkage factor between the electrode and the ceramic.
With respect to high dielectric constant type monolithic ceramic capacitors satisfying F-level and E-level characteristics and temperature-compensating type monolithic ceramic capacitors satisfying SL-level and CG-level characteristics stipulated in the Japanese Industrial Standard (JIS), if the thickness of the ceramic layer is as thin as 3 Mm or less, the electrical characteristics may degrade, resulting in difficulty in obtaining a high-performance monolithic ceramic capacitor.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a monolithic ceramic electronic component, such as a monolithic ceramic capacitor, in which the thickness of inner electrodes and ceramic layers can be decreased without the occurrence of structural defects, enabling miniaturization and high reliability.
A monolithic ceramic electronic component in accordance with the present invention includes a laminate including a plurality of ceramic layers obtained by sintering a ceramic raw material powder, and a plurality of internal electrodes located between the ceramic layers and obtained by sintering a metallic powder. The ceramic layers have a thickness of about 3 &mgr;m or less and contain ceramic grains having an average particle diameter of more than about 0.5 &mgr;m. The particle diameter of the ceramic grains in the thickness direction of the ceramic layers is smaller than the thickness of the ceramic layers. The internal electrodes have a thickness of about 0.2 to 0.7 &mgr;m.
Preferably, the monolithic ceramic electronic component further includes an external electrode formed on each of the opposing ends of the laminate, the ceramic layers are composed of a ceramic dielectric material, and each of the plurality of internal electrodes is formed with an edge being exposed to either one of the opposing ends of the laminate so as to be electrically connected to either one of the external electrodes to form a monolithic ceramic capacitor.
Preferably, the internal electrodes are formed of a paste containing the metallic powder, and the metallic powder in the paste has an average particle diameter of about 10 to 200 nm.
Preferably, the metallic powder is composed of a base metal, and the base metal preferably contains nickel.
Preferably, the internal electrodes are formed by a method including a step of applying the paste containing the metallic powder by a printing method.
Preferably, the ceramic raw material powder before sintering has an average particle diameter of about 25 to 250 nm.
Preferably, each of the ceramic grains constituting the ceramic layers has a uniform composition and a uniform crystal system, and the individual ceramic grains have the same composition and the same crystal system.
Preferably, each of the ceramic grains constituting the ceramic layers has a uniform composition and a uniform crystal system, and the ceramic layers are composed of at least 2 types of ceramic grains having different compositions.
REFERENCES:
patent: 4283753 (1981-08-01), Burn
patent: 6043174 (2000-03-01), Maher et al.
patent: 6205015 (2001-03-01), Wada et al.
Hamaji Yukio
Nakamura Takanori
Wada Nobuyuki
Yamana Tsuyoshi
Dinkins Anthony
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen
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