Multilayer ceramic capacitor

Details Multilayer ceramic capacitor Multilayer ceramic capacitor

2000-12-12

2002-03-26

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrostatic capacitors

Fixed capacitor

C361S321600, C361S306100, C361S303000, C361S310000, C029S025420

Reexamination Certificate

active

06362947

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a multilayer ceramic capacitor; and, more particularly, to a novel structure of conductive layers therein.
BACKGROUND OF THE INVENTION
Referring to
FIG. 1
, there is illustrated a partial cutaway perspective view of a conventional multilayer ceramic capacitor. The multilayer ceramic capacitor
100
, as shown in
FIG. 1
, includes a laminated body
103
having alternately stacked ceramic dielectric layers
101
and conductive layers
102
and a pair of external electrodes
104
-
1
,
104
-
2
respectively disposed at two opposite end portions of the laminated body
103
. The conductive layers
102
are alternately connected to the external electrodes
104
-
1
,
104
-
2
: that is, the external electrode
104
-
1
is connected to every second conductive layer and the external electrode
104
-
2
is coupled with the remaining conductive layers not connected to the external electrode
104
-
1
. The ceramic dielectric layers
101
and the conductive layers
102
have flat surfaces. Further, the thickness of the conductive layers
102
is spatially uniform without local variation. When a voltage is applied between the external electrodes
104
-
1
,
104
-
2
, the multilayer ceramic capacitor
100
stores electric charges in the conductive layers
102
, thereby producing electric fields between every two neighboring conductive layers.
Nowadays, multilayer ceramic capacitors are required to be further scaled down but with higher capacitance. Such tasks, however, may not be successfully achieved with the capacitor
100
. Accordingly, different types of multilayer ceramic capacitors have been proposed for that purpose. In
FIG. 2
, there is illustrated a cutaway perspective view of one of such improved prior art multilayer ceramic capacitors. A multilayer ceramic capacitor
100
a
shown in
FIG. 2
differs from the conventional multilayer ceramic capacitor
100
, in that the conductive layers
102
a
of the capacitor
100
a
are corrugated. As a result, the contact area between the conductive layers
102
a
and the ceramic dielectric layers
101
a
in capacitor
10
a
becomes larger than that in the capacitor
100
and, therefore the capacitance of the capacitor
100
a
increases.
Since, however, it is relatively difficult to make the corrugated conductive layers very thin, the ability to realize the miniaturization of multilayer ceramic capacitors with large capacitance by employing an increased number of such corrugated layers is inherently limited. Further, the corrugated conductive layers
102
a
require the use of a greater amount of conductive paste than the flat conductive layers
102
. Generally, the conductive paste used in forming the conductive layers contributes to a large portion of the manufacturing cost of a multilayer ceramic. Therefore, the use of corrugated conductive layers would lead to an increased manufacturing cost.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a miniaturized large capacitance multilayer ceramic capacitor with a low manufacturing cost.
In accordance with one aspect of the present invention, there is provided a multilayer ceramic capacitor, comprising:
a laminated body formed by alternately stacked ceramic dielectric layers and conductive layers,
wherein the interfaces between the ceramic dielectric layers and the conductive layers are corrugated and the conductive layers have a nonuniform thickness.
The conductive layers are provided with interrupted regions devoid of a conductive material and the boundary portions of the conductive layers close to the interrupted regions are curved upward or downward along the stacking direction of the ceramic dielectric layers and the conductive layers.
In accordance with another aspect of the present invention, there is provided a method for forming a multilayer ceramic capacitor, comprising the steps of:
stacking ceramic green sheets having a conductive paste coated thereon; and
pressing the stacked ceramic green sheets with a die having grooves on a pressing surface thereof, wherein an average depth of the grooves is between about 10 and 30% of an average thickness of a ceramic green sheet.


REFERENCES:
patent: 3617834 (1971-11-01), Charles
patent: 4471406 (1984-09-01), Sawairi
patent: 5251094 (1993-10-01), Amano et al.
patent: 6043174 (2000-03-01), Maher et al.
patent: 6124769 (2000-09-01), Igarashi et al.
patent: 6134098 (2000-10-01), Kuroda et al.
patent: 6141846 (2000-11-01), Miki
patent: 6143109 (2000-11-01), Sano et al.
patent: 6254715 (2001-07-01), Okazaki et al.

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