Inductor devices – Coil or coil turn supports or spacers – Printed circuit-type coil
Reexamination Certificate
2000-04-12
2003-08-05
Enad, Elvin (Department: 2832)
Inductor devices
Coil or coil turn supports or spacers
Printed circuit-type coil
C336S083000, C336S212000, C336S218000
Reexamination Certificate
active
06603382
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inductive element such as a thin-film inductor or a thin-film transformer. More particularly, the invention relates to an inductive element which has a magnetic layer formed of a plurality of magnetic films in lamination, can avoid concentration of magnetic fluxes from a coil layer to the magnetic film the closest to the coil layer, or more preferably, can improve high frequency characteristic by ensuring formation of a uniform magnetic flux distribution for all the magnetic layers.
2. Description of the Related Art
For example, a thin-film inductor comprises a first magnetic layer formed on a substrate, a coil layer formed via an insulating layer on the first magnetic layer, and a second magnetic layer formed via another insulating layer on the coil layer.
The above-mentioned thin-film inductor, which is used, for example, in a micro DC-DC converter, has a problem in that, when the magnetic layers composing the thin-film inductor are formed by single layers having a large thickness, eddy-current loss increases in a high frequency band, thus making it impossible to obtain a satisfactory high frequency characteristic.
In a conventional art, therefore, a thin-film inductor
1
comprising magnetic layers
3
and
5
formed into a multi-layer structure was devised as shown in FIG.
10
. This permits maintenance of inductance at above a certain level and reduction of eddy-current loss, thus improving high frequency characteristic.
As shown in
FIG. 10
, a coil layer
4
is provided between a first magnetic layer
5
and a second magnetic layer
3
, and each of the magnetic layer
5
and
3
comprises a plurality of magnetic films
5
a
to
5
c
or
3
a
to
3
c
in lamination.
Also as shown in
FIG. 10
, all the magnetic films composing the magnetic layers
5
and
3
are formed with the same width t
1
, the same thickness h
1
and the same magnetic permeability &mgr;
1
.
However, if all the magnetic films forming the magnetic layers
5
and
3
are formed with the same width t
1
, the same thickness h
1
and the same magnetic permeability t
1
, a magnetic film closer to the coil layer
4
would have concentration of magnetic fluxes from the coil layer
4
. This prevents formation of a uniform magnetic flux density distribution throughout the entire magnetic films, thus making it impossible to cause all the magnetic films to perform the same functions.
Because all the magnetic films forming the magnetic layer
4
are formed into the same thickness h
1
, the magnetic films
5
a
and
3
a
the closest to the coil layer
4
have an increased magnetic flux density within the magnetic films caused by fluxes generated from the coil layer
4
, thus making it easier to reach the magnetic saturation state. When the magnetic films
5
a
and
3
a
become magnetization-saturated, the magnetic films
5
a
and
3
a
no more substantially function as magnetic films but are in a state similar to air-core state.
More specifically, it was the conventional practice to reduce eddy-current loss by forming the magnetic layer through lamination of thin magnetic films. However, if all the magnetic films are formed with the same thickness h
1
and the same magnetic permeability &mgr;
1
, magnetic fluxes from the coil layer
4
are concentrated more on a magnetic film closer to the coil layer
4
, and the magnetic film approaches the saturated state more along with the increase in amplitude of excitation current or in superposed DC current, thus posing problems such as a decrease in inductance.
Magnetic fluxes from the coil layer
4
concentrate more on a magnetic film closer to the coil layer
4
, thus preventing obtaining a uniform magnetic flux distribution for the individual magnet films. This is proved also from equivalent resistance of the individual magnetic films as described below.
FIG. 11
is a graph illustrating the relationship between frequency and equivalent resistance of the individual magnetic films. In all frequency bands, as shown in
FIG. 11
, equivalent resistance is the largest in the magnetic films
5
a
and
3
a
the closest to the coil layer
4
, followed by equivalent resistance of the magnetic films
5
b
and
3
b
, and equivalent resistance is smaller in the magnetic films
5
c
and
3
c
the most distant from the coil layer
4
.
The differences in equivalent resistance as described above between the magnetic films are attributable to different amounts of magnetic flux induced from the coil layer
4
to the magnetic films. More magnetic fluxes generated from the coil layer
4
are induced into the magnetic film closer to the coil layer
4
. A magnetic film closer to the coil layer
4
would have therefore a larger equivalent resistance.
As described above, when the magnetic films
5
a
and
3
a
the closest to the coil layer
4
reach the magnetically saturated state, the function to be performed by the magnetic films
5
and
3
is accomplished by only the magnetic films
5
b
,
3
b
,
5
c
and
3
c
, and this results in substantially decrease in the thickness of the magnetic films
5
and
3
. This in turn leads to a decrease in inductance and a deterioration of superposed DC current characteristic.
When the magnetic films
5
a
and
3
a
reach the magnetically saturated state, fluxes generated from the coil layer
4
are concentrated on the magnetic films
5
b
and
3
b
which are closer to the coil layer
4
next to the magnetic films
5
a
and
3
a
, and the magnetic films
5
b
and
3
b
become susceptible to magnetic saturation as in the case of the magnetic films
5
a
and
3
a
, and this forms another factor causing a deterioration of superposed DC current characteristic.
SUMMARY OF THE INVENTION
The present invention was developed to solve these problems and has an object to provide an inductive element which has a magnetic layer formed of a plurality of magnetic films in lamination, can avoid concentration of magnetic fluxes from a coil layer to the magnetic film the closest to the coil layer, or more preferably, can improve high frequency characteristic by ensuring formation of a uniform magnetic flux distribution for all the magnetic layers.
A first aspect of the invention provides an inductive element comprising a coil layer, and a magnetic layer covering the coil layer via an insulating layer; the magnetic layer being formed of at least two superposed magnetic layers; and inductive element including a combination of magnetic films in which, for any two magnetic films forming the magnetic layer, the value of product of multiplication of magnetic permeability and thickness of a magnetic film closer to the coil layer is smaller than the value of product of multiplication of magnetic permeability and thickness of a magnetic film more distance from the coil layer.
When forming a magnetic layer into a multi-layer configuration, it is the conventional practice to form a plurality of magnetic films with the same magnetic permeability and the same thickness. As a result, fluxes from the coil layer are concentrated more on a magnetic film closer to the coil layer, thus preventing formation of a uniform magnetic flux distribution for all magnetic films, and the individual magnetic films cannot equally display their functions. Particularly, the magnetic film the closest to the coil layer becoming in magnetically saturated state and cannot substantially function as a magnetic layer, leading to decreased superposed DC current characteristic and inductance. The present circumstances are therefore that the effect of using a multi-layer magnetic layer is not sufficiently displayed.
In the first aspect of the invention, in contrast, concentration of magnetic fluxes on a magnetic film close to the coil layer can be avoided by using, for any two magnetic films forming the magnetic layer, a value of product of multiplication of magnetic permeability and thickness of a magnetic film closer to the coil layer smaller than the value of product of multiplication of magnetic permeability and thickness o
Komai Eiichi
Ogawa Kazushi
Sasaki Yoshito
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Enad Elvin
Poker Jennifer A.
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