Monolithic ceramic electronic component

Details Monolithic ceramic electronic component Monolithic ceramic electronic component

1999-12-20

2002-10-29

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrostatic capacitors

Fixed capacitor

C361S312000, C361S309000, C361S301400

Reexamination Certificate

active

06473292

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a monolithic ceramic electronic component, and more particularly to a large monolithic ceramic electronic component for use in a middle and high voltage range.
Further, the present invention relates to a monolithic ceramic electronic component, and more particularly to a monolithic ceramic electronic component which includes plural internal electrodes disposed so as to be opposed to each other through ceramic layers in a ceramic element.
2. Description of the Related Art
Conventionally, as a smoothing condenser for electric cars, electrolyte condensers and film capacitors have been used. The electrolyte condensers have high ESR, and heat is evolved when a large current flows. To prevent the evolution of heat, it is necessary to provide a high capacitance capacitor with a capacitance of fifty to sixty thousand &mgr;F. In general, the smoothing condenser comprises about 4 condensers each having an outside diameter of 8*15 cm and a capacitance of about 3000 &mgr;F. Thus, the smoothing condenser has the problem that it is very large in size. Further, the electrolyte condenser has the problem that periodic maintenance is required, since the dry up of an electrolyte occurs. On the other hand, the film capacitor has a smaller ESR than the electrolyte condenser, and the capacitance is in the rage of 400 to 1000 &mgr;F. However, since films are used as dielectric, the dielectric constant is low. Accordingly, the film capacitor comprises about two capacitors each having a size of 8*15 cm, which causes the problem that it is large in size. Further, since the film capacitor has a low resistance to heat, it is necessary further to increase the size of the film capacitor, when a large capacitance is rendered to the film capacitor.
FIGS. 3A and B
are plan and front views each showing a monolithic ceramic capacitor
1
which is one example of a conventional monolithic ceramic electronic components interesting to the present invention.
As shown in
FIGS. 3A and 3B
, the monolithic ceramic capacitor
1
comprises a capacitor body
2
having a rectangular shape specified by a longitudinal dimension L, a widthwise dimension W, and a thickness-wise dimension T, and first and second external electrodes
3
and
4
formed on the opposite end-faces in the longitudinal direction of the capacitor body
2
.
The capacitor body
2
comprises plural dielectric layers
5
which are laminated in the state that they are extended in parallel to the plane specified by the longitudinal dimension L and the widthwise dimension W, and plural sets of internal electrodes
6
which are opposed to each other through specific one of the dielectric layers
5
, respectively.
As to the plural sets of internal electrodes
6
, the internal electrodes electrically connected to the first external electrodes
3
and the internal electrodes electrically connected to the second external electrode
4
are alternately disposed. The internal electrode
6
shown by exploding a part of the capacitor body
2
in
FIG. 3A
is electrically connected to the first external electrodes which is seen in it's profile shown by the broken line. The internal electrode
6
electrically connected to the second external electrode
4
is symmetrical with the illustrated internal electrode
6
.
Conventionally, in general, such a monolithic ceramic capacitor
1
is designed so that the capacitor body has a dimensional relation between the longitudinal dimension L, the widthwise dimension W, and the thickness-wise dimension T of L>W and W≦2T.
The recent market demands that such monolithic ceramic capacitors
1
as described above should have a high capacitance and be suitable for high voltage uses.
As means for meeting the above demand, it is suggested that for the monolithic ceramic capacitor
1
, the lamination number of the internal electrodes
6
and the thickness of the dielectric layers
5
should be increased.
However, if such a means is employed, the dielectric layers
5
each need to have a thickness of 20 &mgr;m or more, so that the monolithic ceramic capacitor
1
may be made suitable for use in a middle and high voltage range of a rated voltage of 250V or higher. Therefore, to attain a large capacitance of 1 &mgr;F or more, the lamination number of the internal electrodes
6
becomes very large, and thereby, the thickness-wise dimension T of the capacitor body
2
has to be remarkably increased.
Therefore, when fired to produce the capacitor body
2
, ceramics constituting the dielectric layers
5
are insufficiently sintered or are unstable. That is, pores are ready to be formed in the dielectric layers
5
, the internal electrodes
6
are insufficiently sintered, and the sintering state of the internal electrodes
6
tends to have dispersions. As a result, the initial characteristics of the obtained monolithic ceramic capacitor
1
are deteriorated. That is, possibly, delamination occurs, the breakdown voltage (BDV) is reduced, and cracks are readily caused, due to the electrostriction. Also, in some cases, the reliability such as the high temperature service-life or the like may be reduced.
As means for rendering a high capacitance to the monolithic ceramic capacitor
1
, it is proposed that the effective area of the internal electrodes
6
is increased by increasing the longitudinal dimension L and the widthwise dimension W of the capacitor body
2
.
However, even though the effective area of the internal electrodes
6
is increased by relatively increasing the longitudinal dimension L and the widthwise direction W of the capacitor body
2
as described above, this means only taken is the same that practically no measures for improving the BDV of the monolithic ceramic capacitor
1
are taken. Accordingly, the monolithic ceramic capacitor
1
when it is applied in a middle and high voltage range encounters problems of BDV or the like.
Chip monolithic ceramic capacitors, which are typical monolithic ceramic electronic components, are produced as follows. Plural internal electrodes
52
are disposed so as to be opposed to each other through ceramics (ceramic layers)
51
, and the one-ends of the internal electrodes
52
are led-out alternately to the different end-faces of the ceramic element
54
. On the opposite end faces of the ceramic element
54
, a pair of external electrodes
53
,
53
are disposed so as to be connected to the internal electrodes
52
, as shown in
FIG. 9
,
FIGS. 10A
,
10
B, and
10
C, for example.
In the case that the monolithic ceramic capacitor having a structure as shown in
FIGS. 9 and 10
, which is a product for use in a middle and high voltage range, it is not necessarily easy to secure high withstanding voltage properties. It is needed to develop monolithic ceramic capacitors with a high reliability, having a high breakdown voltage and excellent withstanding voltage properties.
The above-description, not limited to monolithic ceramic capacitors, are also true of monolithic ceramic electronic components such as varistors, inductors, and so forth.
For the purpose of enhancing the breakdown voltages of such monolithic ceramic electronic components as described above, the following methods are ordinarily suggested.
(1) a method of increasing the thickness of the element (the distance between the opposed electrodes through the ceramic layers(thickness-wise distance)), and
(2) a method of rendering the internal electrodes such an electrode structure that plural series connection capacitances are formed.
However, the breakdown voltage has the tendency that it is dominated by the degree of electric fields concentrated onto the edge portions (
52
a
in
FIG. 10A
) of the internal electrodes
52
. In the case of the above-described methods (1) and (2) applied, it is practically difficult to enhance the breakdown voltage sufficiently, since the electric fields are concentrated onto the edge portions (peripheries and corners) of the internal electrodes
52
.
Accordingly, to relax the electric field concentration onto th

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