Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2000-02-09
2001-07-24
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S306100, C361S308100, C361S303000
Reexamination Certificate
active
06266229
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-layer capacitor and, more particularly, to a multi-layer capacitor which can be advantageously used in high frequency circuits.
2. Description of the Related Art
Conventional multi-layer capacitors include those described in Japanese Unexamined Patent Publication No. H2-256216 in which a multi-layer capacitor
1
, as shown in
FIGS. 15 through 17
of the present application, is disclosed.
FIG. 15
is a plan view of the external appearance of the multi-layer capacitor
1
.
FIG. 16
is a plan view of a first section of the multi-layer capacitor
1
showing a first electrode
10
located on one surface of one internal dielectric layer
9
of the capacitor
1
.
FIG. 17
is a plan view of a second section of the multi-layer capacitor
1
showing a second electrode
11
located on one surface of a differential internal dielectric layer
9
of the capacitor
1
.
Referring to
FIGS. 15-17
, the multi-layer capacitor
1
includes a capacitor main body
8
in the form of a rectangular parallelpiped having two principal surfaces
2
and
3
in a face-to-face relationship with each other and four side surfaces
4
,
5
,
6
and
7
connecting the principal surfaces
2
and
3
. The capacitor main body
8
includes a plurality of dielectric layers
9
(
FIGS. 16-17
) made of, for example, a ceramic dielectric material. Each of the dielectric layers is generally planar in shape and lies generally parallel to the principal surfaces
2
and
3
. At least a pair of first and second internal electrodes
10
and
11
are provided on respective surfaces of the dielectric layers
9
in a face-to-face relationship with each other, with a dielectric layer
9
interposed therebetween to form a capacitor unit.
The first internal electrode
10
is formed with four lead electrodes
12
,
13
,
14
and
15
which extend to two opposing side surfaces
4
and
6
, as shown.
Each lead electrode
12
,
13
,
14
and
15
is coupled to a respective external terminal electrode
16
,
17
,
18
and
19
provided on the side surfaces
4
and
6
of the capacitor main body
8
. Specifically, the lead electrodes
12
and
13
are connected to the external terminal electrodes
16
and
17
, respectively, which are located on the side surface
4
, and the lead electrodes
14
and
15
are connected to the external terminal electrodes
18
and
19
, respectively, which are located on the side surface
6
.
Referring to
FIG. 17
, the second internal electrode
11
is also formed with four lead electrodes
20
,
21
,
22
and
23
which extend to the side surfaces
4
and
6
, respectively. More specifically, the lead electrodes
20
and
21
extend to positions on the side surface
4
which are different from the positions to which the lead electrodes
12
and
13
extend, and the lead electrodes
22
and
23
extend to positions on the side surface
6
of the main body
8
which are different from the positions to which the lead electrodes
14
and
15
extend.
The lead electrodes
20
through
23
are electrically coupled to external terminal electrodes
24
,
25
,
26
and
27
, respectively. External terminal electrodes
24
and
25
are located on the side surface
4
at positions which are different from those of the external terminal electrodes
16
and
17
. External terminal electrodes
26
and
27
are located on the side surface
6
at positions which are different from the positions of the external terminal electrodes
18
and
19
.
Thus, the plurality of first external terminal electrodes
16
through
19
and the plurality of second external terminal electrodes
24
through
27
are arranged on the two side surfaces
4
and
6
such that they alternate adjacently to each other.
FIG. 18
illustrates current flowing through the multi-layer capacitor
1
as viewed in plan view corresponding to FIG.
17
. In
FIG. 18
, first internal electrode
10
and second internal electrode
11
, shown with broken and solid lines, respectively, are shown in an overlapping relationship.
In
FIG. 18
, the arrows indicate typical current paths and directions. In the state illustrated, current flows from each of the external terminal electrodes
24
through
27
to each of the external terminal electrodes
16
through
19
. Because an alternating current is used, the direction of current flow will reverse periodically.
When the currents flow, magnetic flux is induced. The direction of the flux is determined by the direction of the currents to produce self-inductance components. Since the currents flow in various directions at central regions
28
(indicated by circles) of the internal electrodes
10
and
11
, the induced magnetic flux generated by the various currents is canceled and substantially no net magnetic flux is produced in those regions.
The current in the vicinity of each of the external terminal electrodes
16
through
19
and
24
through
27
tends to flow toward each of the external terminal electrodes
16
through
19
and away from each of the external terminal electrodes
24
through
27
. There are currents that flow to the left and right as viewed in
FIG. 18
to spread at an angle of about 180 degrees. As a result, a major part of magnetic flux is canceled and there is no significant generation of net magnetic flux in these areas.
Therefore, in the multi-layer capacitor
1
shown in
FIGS. 15 through 17
, the generation of self-inductance is suppressed in the areas points described above to reduce equivalent series induction (hereinafter “ESL”).
However, currents flow substantially in the same direction in the vicinity of each of the side surfaces
5
and
7
on which no external terminal electrodes are provided, i.e., at each of the left and right edge portions indicated by hatching in FIG.
18
. This results in substantially no cancellation of magnetic flux in these areas and significant net self-inductance is created. Therefore, the measures taken to reduce ESL in the multi-layer capacitor
1
shown in
FIGS. 15 through 17
are less than desirable.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide a multi-layer capacitor which more effectively reduces ESL.
In accordance with a preferred embodiment the present invention, a multi-layer capacitor includes a capacitor body including top and bottom surfaces and opposed side surfaces which have continuously flat surfaces and are disposed between the top and bottom surfaces and opposed end surfaces disposed between the top and bottom surfaces and the opposed side surfaces, the capacitor body including a plurality of first electrode plates and a plurality of second electrode plates, the first and second electrode plates being interleaved with each other in opposed and spaced apart relation, a dielectric material located between each opposed set of the first and second electrode plates, the first and second electrode plates each including a main electrode portion and a plurality of spaced apart lead structures extending therefrom, respective lead structures of the first electrodes plates being located adjacent respective lead structures of the second electrode plates in an interdigitated arrangement, and a plurality of electrical terminals located on each of the opposed side surfaces of the capacitor body, corresponding lead structures of the first electrode plates and corresponding lead structures of the second electrode plates being electrically connected together by respective ones of the electrical terminals to define a plurality of first polarity electrical terminals and a plurality of second polarity electrical terminals, respectively, located on the capacitor body; wherein each of the first polarity terminals is disposed opposite to another of the first polarity terminals across the capacitor body and each of the second polarity terminals is disposed opposite to another of the second polarity terminals across the capacitor body and at least one of the lead structures of the first and
Kondo Takanori
Kuroda Yoichi
Murata Michihiro
Naito Yasuyuki
Taniguchi Masaaki
Dinkins Anthony
Keating & Bennett LLP
Murata Manufacturing Co. Ltd
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