Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2001-03-13
2002-08-06
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S306100, C361S308100
Reexamination Certificate
active
06430025
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multilayer capacitor and, more particularly, to a multilayer capacitor which can be advantageously used in high frequency circuits.
2. Description of the Related Art
Conventional multilayer capacitors include that described in Japanese Unexamined Patent Publication No. H2-256216 in which a multilayer capacitor
1
, as shown in
FIGS. 15 through 17
, is disclosed.
FIG. 15
is a plan view of the external appearance of the multilayer capacitor
1
.
FIG. 16
is a plan view of a first section of the multilayer 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 multilayer 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 multilayer 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 dielectrical 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
or 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 multilayer 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 multilayer 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 multilayer capacitor
1
shown in
FIGS. 15 through 17
is less than desirable.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a multilayer capacitor which more effectively reduces ESL.
In accordance with one aspect of the present invention, a multilayer capacitor, comprises:
a capacitor main body having a generally rectangular parallelpiped shape with two principal surfaces in a face-to-face relationship with each other and four side surfaces connecting said principal surfaces;
m capacitor units formed in said capacitor main body, m being an integer greater than or equal to one, each of said capacitor units being formed by a respective pair of first and second internal electrodes disposed in said main body in a face-to-face relationship with a dielectric material layer interposed therebetween to form a capacitor unit;
n first external electrodes, n being an integer greater than 2, each of said first external electrodes being located on a respective one of said side surfaces of said capacitor main body, at least one of said first external electrodes being located on each of at least three of said side surfaces;
said first internal electrode having n first lead electrodes, each of said first lead electrodes extending to and being electrically coupled to a respective one of said first external electrodes;
p second external electrodes, p being an integer greater than 1, each of said second external electrodes being located on a respective one of said side surfaces of said capacitor main body; and
said second internal electrode having p second lead electrodes, each of said second lead electrodes extending to and being electrically coupled to a respective one of said second external electrodes.
The internal and lead electrodes are preferably arranged in such a manner that when currents of different polarity are applied to said first and second internal electrodes, the net induced inductance in the area of all four of said side surfaces is substantially zero.
In one embodiment of the present invention, the first internal electrode is formed with at
Kondo Takanori
Kuroda Yoichi
Naito Yasuyuki
Taniguchi Masaaki
Dinkins Anthony
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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