Multilayer capacitor

Details Multilayer capacitor Multilayer capacitor

2000-09-28

2002-04-09

Dinkins, Anthony (Department: 2831)

Electricity: electrical systems and devices

Electrostatic capacitors

Fixed capacitor

C361S306300, C361S309000, C361S313000

Reexamination Certificate

active

06370011

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
FIG. 7
shows a schematic sectional view of a typical prior art multilayer capacitor
1
which includes a main body
5
having a plurality of ceramic dielectric material layers
2
stacked one on top of the other. A set of first internal electrodes
3
and a set of second internal electrodes
4
are arranged alternately, with a respective dielectric material layer
2
located between adjacent pairs of electrodes
3
and
4
to form a plurality of capacitor units.
Each of the first internal electrodes
3
is electrically coupled to a first external terminal electrode
8
formed on a first end face
6
of the main body
5
. Each of the second internal electrodes
4
is electrically coupled to a second external electrode
9
formed on a second end surface
7
of main body
5
. As a result, the electrostatic capacities respectively provided by the plurality of capacitor units are connected in parallel by the first and second external terminal electrodes
8
and
9
.
The multilayer capacitor
1
shown in
FIG. 7
exhibits a problem which is discussed below.
FIG. 9
is a schematic sectional plan view showing one of the electrodes
3
of FIG.
7
. In this figure, arrows indicate the path and direction of typical currents
22
which flow in each of the first internal electrodes
3
of the multilayer capacitor
1
. In the state shown (the directions of the currents alternate over time when an AC signal is applied to the capacitor), the currents
22
flow from the second external electrode
9
to the second internal electrodes
4
(not shown in FIG.
9
), vertically to the first internal electrodes
3
through the dielectric material layers
2
and then to the first external terminal electrode
8
through the first internal electrodes
3
. There is a general flow of currents in both internal electrodes
3
and
4
from right to left, i.e., in the same direction, as seen in FIG.
9
.
As is well known, the current
22
induces a magnetic flux in a direction determined by the direction of the current
22
, thereby producing a self-inductance component. Since the currents
22
flow in the longitudinal direction of the internal electrodes
3
, the multilayer capacitor
1
produces relatively high equivalent series inductance (ESL) and may fail to function properly in a high frequency band when it is used as a decoupling capacitor or bypass capacitor.
This problem is partly overcome using the structure shown schematically in FIG.
8
. This structure is described in Japanese unexamined patent publication No. H7-201651.
Like the multilayer capacitor
1
shown in
FIG. 7
, the multilayer capacitor
11
includes a main body IS having a plurality of dielectric material layers
12
stacked one on top of the other. A plurality of first internal electrodes
13
and a plurality of second internal electrodes
14
are arranged on respective dielectric material layers
12
to form pairs of overlapping electrodes, each pair of overlapping electrodes being separated by a respective dielectric material layer
12
such that a plurality of capacitor units are formed.
In this multilayer capacitor
11
, first and second external terminal electrodes
18
and
19
are formed, respectively, on first and second principal surfaces
16
and
17
extending in parallel with the internal electrodes
13
and
14
.
A plurality of first connection portions
20
, which are electrically isolated from second internal electrodes
14
, are provided to electrically connect the first internal electrodes
13
to both the first external terminal electrode
18
and to each other.
A plurality of second connection portions
21
, which are electrically isolated from first internal electrodes
13
, are provided to electrically connect the second internal electrodes
14
to both the second external terminal electrode
19
and each other.
Thus, the electrostatic capacities provided by the plurality of the capacitor units formed by the respective pairs of internal electrodes
13
and
14
are coupled in parallel by the connection portions
20
and
21
and are combined at external terminal electrodes
18
and
19
, respectively.
Compared to the prior art capacitor of
FIG. 7
, the multilayer capacitor
11
shown in
FIG. 8
reduces the equivalent series inductance (ESL) and is suitable for use in a high frequency band.
In
FIG. 10
, the arrows indicate the path and direction of typical currents
23
which flow in, for example, the first internal electrodes
13
of the multilayer capacitor
11
. In the state shown (the directions of the currents alternate over time when an AC signal is applied to the capacitor), the currents
23
flow from the second internal electrodes
14
(not shown in
FIG. 10
) in a face-to-face relationship with the first internal electrodes
13
to the first internal electrodes
13
through the second connection portions
21
. Then, most of the currents flow to the nearest first connection portion
20
and further to the first external terminal electrode
18
through the first connection portion
20
.
When such a flow of the currents
23
is viewed with attention to the area around the connection portions
20
or
21
, since the currents
23
flow in various directions, components of magnetic flux produced by the currents
23
are advantageously canceled by each other to suppress the generation of net magnetic flux. Further, since the lengths of the paths of the currents
23
flowing through the internal electrodes
13
or
14
are limited to the intervals between adjacent connection portions
20
and
21
, the lengths of each of the current paths is relatively short and, therefore, the self-inductance components produced are reduced.
However, the reduction of the ESL in the multilayer capacitor
11
is achieved only for components of magnetic flux induced by the currents
23
in the direction in which the internal electrodes
13
and
14
extend.
FIG. 11
is an enlarged view of a part of the multilayer capacitor
11
shown in
FIG. 8
, in which currents
24
and
25
flowing respectively through the connection portions
20
and
21
of the multilayer capacitor
11
are indicated by the dashed arrows.
Referring to
FIG. 11
, when currents flow, for example, from the second external terminal electrode
19
to the first external terminal electrode
18
, upwardly directed currents
24
,
25
flow through both the first connection portions
20
and through the second connection portions
21
, respectively.
The currents
24
flowing through the first connection portion
20
and the currents
25
flowing through the second connection portion
21
produce respective components of magnetic flux
26
and
27
, as shown in FIG.
12
. The currents flowing through the respective connection portions
20
and
21
flow from the back side to the front side of the plane of
FIG. 12
(i.e., they flow out of the page). The direction of the resultant components of magnetic flux
26
and
27
oppose one another in the areas between the connection portions
20
and
21
. As a result, the magnetic flux is canceled between the connection portions
20
and
21
.
The magnetic flux
28
that surrounds the components of magnetic flux
26
and
27
, however, is not cancelled. Rather, the magnetic flux
28
tends to be greater than each individual magnetic flux
26
,
27
and, therefore, increases the ESL.
As a result, the components of magnetic flux
26
and
27
produced by the currents
24
and
25
flowing through the connection portions
20
and
21
are not effectively canceled and increase the self-inductance of the capacitor
11
. Thus, the ESL is not sufficiently reduced and high frequency performance is not sufficiently improved.
SUMMARY OF THE INVENTION
In order to solve the above-described technical problems, a multilayer capacitor according to the present invention comprises a cap

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