Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2002-12-05
2004-04-13
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S306100, C361S306300
Reexamination Certificate
active
06721163
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a stacked ceramic body, including ceramic layers and internal electrode layers that are alternately stacked with one another, that can be utilized as a piezoelectric device or a stacked ceramic capacitor.
2. Description of the Related Art
A stacked ceramic body produced by alternately stacking ceramic layers, containing a piezoelectric material and a dielectric material, and internal electrode layers, containing an electrode material, with one another can be widely utilized as a piezoelectric device and a stacked ceramic capacitor.
FIG. 19
of the accompanying drawings shows an example of a known stacked ceramic body. Ceramic layers
91
and
93
and internal electrode layers
92
and
94
are alternately stacked with one another as shown in the drawing. In this stacked ceramic body
9
, right and left end faces
920
and
940
of the internal electrode layers
92
and
94
are respectively exposed on the right and left side surfaces
901
and
902
. Dummy layers
99
are respectively stacked on the upper and lower ends in the stacking direction.
The stacked ceramic body
9
includes a right side surface electrode
941
electrically connected to the internal electrode layer
92
exposed on the right side surface
901
, and a lead wire
95
connected to the right side surface electrode
941
through an electrically conductive paste
950
. The stacked ceramic body
9
includes also a left side surface electrode
942
electrically connected to the internal electrode layer
94
exposed on the left side surface
902
, and a lead wire
94
connected to the left side surface electrode
902
through the conductive paste
950
. When the lead wires
95
are connected to an external power source (not shown in the drawing), voltages are applied to each ceramic layer
91
,
93
.
The stacked ceramic body
9
described above is produced in the following way.
A print portion for the internal electrode layer is printed on a green sheet for the ceramic layer either rightward (having a right end portion exposed on the right side surface after stacking) or leftward (having a left end portion exposed on the left side surface after stacking). A predetermined number of green sheets are stacked to give an unsintered stacked body.
The unsintered stacked body is introduced into a press-bond jig and is heated at 80° C. to mutually press-bond the green sheet for the ceramic layer and the print portion for the internal electrode layer. Thereafter, degreasing, sintering, machining into a predetermined size, fitting of side surface electrodes, insulation, and so forth, are carried out to give the stacked ceramic body
9
shown in FIG.
19
.
In a multi-stacked ceramic body having as many as hundreds of stacked layers, however, a difference of thickness reaching several millimeters occurs in some cases between each Y portion at which ceramic layers
91
and
93
are adjacent to each other in the stacking direction and an X portion at which the ceramic layers
91
and
93
are adjacent to each other through the internal electrode layers
92
and
94
as shown in FIG.
19
.
Assuming that the number of the ceramic layers
91
and
93
is 500 and the thickness of the internal electrode layers
92
and
94
are 5 &mgr;m, the difference of the thickness between the X portion and the Y portion is as great as 2.5 mm.
The difference of the thickness between the X portion and the Y portion has been absorbed in the past by inter-layer press-bonding of the green sheet and the print portion at the time of the unsintered stacked body. However, when the number of ceramic layers is as great as several hundred, inter-layer press-bonding cannot sufficiently absorb the difference.
In the stacked ceramic body sintered while inter-layer adhesion of the green sheet and the print portion is not sufficient, de-lamination (inter-layer peeling) is likely to develop.
Particularly in the case of a thin, stacked ceramic body having hundreds of thin ceramic layers stacked on one another, vigorous de-lamination such as cleavage of the ceramic layers from the side surface of the stacked ceramic body occurs.
It may be possible to employ a method that elevates the pressure in the press-bonding operation of the unsintered stacked body to prevent de-lamination, but the green sheet is likely to be broken. When the unsintered stacked body containing the damaged green sheet is sintered, cracks may develop inside the stacked ceramic body.
SUMMARY OF THE INVENTION
In view of the problems with the prior art technologies, this invention aims at providing a stacked ceramic body in which de-lamination (inter-layer peeling) does not easily occur, and a production method thereof.
According to a first aspect of the invention, there is provided a stacked ceramic body comprising a predetermined number of unit layers, each of the unit layers including a ceramic layer, an internal electrode layer stacked on at least a part of a surface of the ceramic layer, a spacer stacked on a surface of the ceramic layer at which the internal electrode layer is not formed, and having substantially the same thickness as the internal electrode layer, and adhesive layers stacked on a surface of the internal electrode layer and on a surface of the spacer.
Next, the operation and effect of the invention will be explained.
In the stacked ceramic body according to the first invention, the internal electrode layer and the spacer each having substantially the same thickness are stacked on the ceramic layer, and the adhesive layers are stacked on both the internal electrode layers and the spacers. Other ceramic layers are then stacked through the adhesive layers.
Therefore, the stacked ceramic body has a uniform thickness as a whole, and a partial difference of thickness does not easily occur. The adhesive layer ensures bonding between the ceramic layers. The adhesive layer can also absorb the difference of thickness between the internal electrode layer and the spacer.
The first invention described above can provide a stacked ceramic body in which de-lamination (inter-layer peeling) does not easily occur.
According to a second aspect of the invention, there is provided a method for producing a stacked ceramic body by stacking a predetermined number of unit layers, each of the unit layers including a ceramic layer, an internal electrode layer stacked on at least a part of a surface of the ceramic layer, a spacer stacked on a surface of the ceramic layer at which the internal electrode layer is not formed, and having substantially the same thickness as the internal electrode layer, and adhesive layers stacked on a surface of the internal electrode layer and on a surface of the spacer, the method comprising the steps of preparing slurry for a ceramic layer, containing a ceramic material and a binder, slurry for an internal electrode layer, containing an electrode material and a binder, slurry for a spacer, containing a spacer material and a binder, and slurry for an adhesive layer, containing an adhesive layer material and a binder; a binder content in the slurry for the adhesive layer being higher than a binder content in the slurry for the ceramic layer; forming a green sheet for a ceramic layer from the slurry for the ceramic layer; forming a print portion for the internal electrode layer on the green sheet for the ceramic layer by use of the slurry for the internal electrode layer; forming a print portion for the spacer by use of the slurry for the spacer; forming and stacking a print portion for the adhesive layer on the print portions for the internal electrode layer and for the spacer by use of the slurry for the adhesive layer to give an unsintered unit; stacking a predetermined number of the unsintered units to give an unsintered stacked body; and pressing and bonding the unsintered stacked body and then sintering the unsintered stacked body.
According to a third aspect of the invention, there is provided a method for producing a stacked ceramic body by stacking a predetermined number of unit layer
Ito Tetuji
Iwase Akio
Takeuchi Yukihisa
Denso Corporation
Dinkins Anthony
Nixon & Vanderhye P.C.
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