Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1999-03-03
2001-08-07
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C428S472000, C428S701000, C428S702000, C156S089140, C361S313000, C361S321200
Reexamination Certificate
active
06270906
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a monolithic ceramic electronic component such as a monolithic ceramic capacitor, and more particularly to an improvement in an inner electrode of the same.
2. Description of the Related Art
Conventionally, dielectric ceramic materials such as barium titanate, strontium titanate, calcium titanate, and the like, having a perovskite-type structure have been widely used as capacitor materials, due to their high dielectric constants. With the recent tendency that electronic components are small-sized, capacitors, which are passive components, are required to have a high electrostatic capacitance and also to be miniaturized.
For monolithic ceramic capacitors containing ceramic dielectric materials in their dielectric layers, it is necessary to bake the dielectric ceramic materials at high temperatures, for example, at about 1300° C. in the atmosphere. Therefore, as the inner electrodes, noble metals such as palladium, platinum, and the like, and their alloys were used. However, these electrode materials are very expensive, and the material cost occupied a large part of the product cost. Thus, it was difficult to reduce the product cost.
To solve the above-mentioned problems, it has been attempted to use base metals as a material for the inner electrodes of the monolithic ceramic capacitors. As a result, there have been developed a variety of dielectric ceramic materials which have such anti-reduction properties that they can be baked in a neutral or reducing atmosphere, which prevents the electrodes thereof from being oxidized. Such base metals as the inner electrode material include cobalt, nickel, copper, and the like. In the viewpoint of the cost and the anti-oxidation properties, nickel is mainly used.
At present, there is still a need to develop still smaller-sized and higher-capacitance monolithic ceramic capacitors. For this reason, investigation has been made on dielectric ceramic materials having a higher dielectric constant and on thinner ceramic layers made of dielectric ceramic materials. Furthermore, examination has been made on thinner electrodes.
In general, the inner electrodes of the monolithic ceramic capacitors are formed by printing, such as screen-printing, of pastes containing metal powders. For example, in most cases, nickel powders for use as the metal powder to be contained in such pastes, formed by liquid phase method or chemical vapor deposition method, have a mean particle size exceeding 0.25 &mgr;m. However, since the particle size is large, it is difficult to form the thin inner electrodes.
When the nickel powder having a mean particle size of about 0.25 &mgr;m were used, the thickness of the inner electrode was required to be at least 0.8 &mgr;m to realize the dielectric characteristics of the dielectric ceramic materials.
For the purpose of enhancing the electrostatic capacitance of the monolithic ceramic capacitors, one of the most effective means is to provide a thin ceramic layer between the inner electrodes. However, if the ceramic layer has a thickness of 3 &mgr;m or less when the inner electrodes each have a thickness of 0.8 &mgr;m, delamination is often caused due to the difference in shrinkage between the inner electrode material and the ceramic. This is one of fatal defects of the monolithic ceramic capacitors.
In the case that the nickel power and/or the ceramic raw material powder has a large mean particle size, large concavities and convexities at the interfaces between the inner electrodes and the ceramic layers are formed. When the powders are baked, this causes the problem that the coverage (effective electrode areas) of the inner electrodes is reduced (with an increase in the frequency of electrode breaking). Thus, this brings the reduction in reliability of the 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 which has no structural defects, of which the inner electrodes and ceramic layers can be thinned, and which has high performances such as high capacitance, is small in size, and has a high reliability.
The present invention is intended for a monolithic ceramic electronic component equipped with a laminate including plural laminated ceramic layers each made of a sintered ceramic raw material powder layer, and an inner electrode made of a sintered metal powder and positioned along a predetermined interface between the ceramic layers. To solve such technical problems as described above, the monolithic ceramic electronic component is characterized in that the ceramic layers each have a thickness of up to about 3 &mgr;m, and the ceramic grains of said ceramic layers after sintering have a mean particle size of up to about 0.5 &mgr;m, and the inner electrode has a thickness of from about 0.2 &mgr;m to 0.7 &mgr;m.
Preferably, according to the present invention, the monolithic ceramic electronic component further contains an outer electrode formed on the respective opposite end faces of the laminate, the ceramic layer is made of a ceramic dielectric material and the plural inner electrodes are so formed that one edge of each inner electrode is exposed out of one of the end faces of the laminate with the outer electrode electrically connected with the exposed inner electrodes, whereby a monolithic ceramic capacitor is formed.
Preferably, according to the present invention, a paste containing the metal powder is used to form the inner electrode, the metal powder in the paste has a thickness of from about 10 nm to 200 nm. In this case, as the metal powder, a base metal, more preferably, powder made of a metal containing nickel such as nickel or a nickel alloy is used.
Preferably, according to the invention, the paste containing the metal powder is applied by printing to form the inner electrodes.
According to the present invention, it is preferable that the ceramic raw material powder before sintering to form the ceramic layers has a mean particle size of up to about 500 nm.
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Miyazaki Takaharu
Nakamura Takanori
Wada Nobuyuki
Yamana Tsuyoshi
Jones Deborah
McNeil Jennifer
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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