Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-08-09
2004-11-30
Cao, Allen (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06826022
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to CPP (current-perpendicular-to-plane) type magnetic sensors or magnetic sensors using the tunnel effect, which are mounted on magnetic reproducing devices, such as a hard disc device, or other magnetic sensing devices. In particular, the present invention relates to a magnetic sensor capable of improving reproducing output and changing rate of resistance, and to a manufacturing method therefor.
2. Description of the Related Art
FIG. 11
is a partial cross-sectional view of a conventional CPP (current-perpendicular-to-plane) type magnetic sensor (spin-valve type thin-film magnetic element) when it is viewed from an opposing face opposing a recording medium.
Reference numeral
1
indicates a first electrode layer, and on this first electrode layer
1
, a laminate
9
is provided which is composed of an antiferromagnetic layer
2
formed of a Pt—Mn alloy or the like, a fixed magnetic layer
3
formed of an Ni—Fe alloy or the like, a nonmagnetic material layer
4
formed of copper (Cu), and a free magnetic layer
5
formed of an Ni—Fe alloy or the like.
As shown in
FIG. 11
, insulating layers
6
composed of Al
2
O
3
or the like are formed on two sides of the laminate
9
in the track width direction (X direction in the figure) and on the first electrode layer
1
, and in addition, a hard bias layer
7
formed of a Co—Pt alloy or the like is formed on each of the insulating layers
6
.
In addition, a second electrode layer
8
is formed continuously on the hard bias layers
7
and the free magnetic layer
5
.
The magnetization of the fixed magnetic layer
3
is fixed in the height direction (Y direction in the figure) by an exchange coupling magnetic field generated between the fixed magnetic layer
3
and the antiferromagnetic layer
2
, and on the other hand, the magnetization of the free magnetic layer
5
is aligned in the track width direction (X direction in the figure) by a longitudinal bias magnetic field from the hard bias layer
7
.
In the CPP type magnetic sensor shown in
FIG. 11
, a sensing current is allowed to flow through each layer forming the laminate
9
in the direction (Z direction in the figure) perpendicular thereto.
Concomitant with the trend toward miniaturization of element size due to increasingly higher recording density in the future, it has been expected that CPP type magnetic sensors in which a sensing current is allowed to flow through individual films in the direction perpendicular thereto more effectively improve reproducing output than CIP (current-in-plane) type magnetic sensors in which a sensing current is allowed to flow through the films in the direction parallel thereto.
In addition,
FIG. 23
is a partial cross-sectional view of a conventional magnetic sensor (tunnel type magnetoresistive element) using the tunnel effect when it is viewed from an opposing face opposing a recording medium.
Reference numeral
1
indicates a first electrode layer, and on this first electrode layer
1
, a laminate
9
is provided which is composed of an antiferromagnetic layer
2
formed of a Pt—Mn alloy or the like, a fixed magnetic layer
3
formed of a Ni—Fe alloy or the like, an insulating-barrier layer
400
formed of Al
2
O
3
or the like, and a free magnetic layer
5
formed of a Ni—Fe alloy or the like.
As shown in
FIG. 23
, insulating layers
6
composed of Al
2
O
3
or the like are formed on two sides of the laminate
9
in the track width direction (X direction in the figure) and on the first electrode layer
1
, and in addition, a hard bias layer
7
formed of a Co—Pt alloy or the like is formed on each of the insulating layers
6
.
In addition, a second electrode layer
8
is formed continuously on the hard bias layers
7
and the free magnetic layer
5
.
The magnetization of the fixed magnetic layer
3
is fixed in the height direction (Y direction in the figure) by an exchange coupling magnetic field generated between the fixed magnetic layer
3
and the antiferromagnetic layer
2
, and on the other hand, the magnetization of the free magnetic layer
5
is aligned in the track width direction (X direction in the figure) by a longitudinal bias magnetic field from the hard bias layer
7
.
The magnetic sensor shown in
FIG. 23
has the structure which is called a tunnel type magnetoresistive element, and the features of this structure are that a layer provided between the fixed magnetic layer
3
and the free magnetic layer
5
is the insulating barrier layer
400
, which is an insulating layer, and that the electrode layers
8
and
1
are formed on the top and the bottom of the laminate
9
, respectively.
In the tunnel type magnetic sensor shown in
FIG. 23
which generates change in resistance using the tunnel effect, when the magnetizations of the fixed magnetic layer
3
and the free magnetic layer
5
are antiparallel to each other, it is most difficult for a tunnel current to flow through the insulating barrier layer
400
, so that the resistance becomes a maximum. On the other hand, when the magnetizations of the fixed magnetic layer
3
and the free magnetic layer
5
are parallel to each other, it is most easy for a tunnel current to flow through the insulating layer
400
, so that the resistance becomes a minimum.
By using this principle, when the magnetization of the free magnetic layer
5
varies by the influence of an external magnetic field, change in electrical resistance is detected as change in voltage, thereby sensing a leakage magnetic field from the recording medium.
However, in a magnetic sensor having the structure shown in
FIG. 11
or
23
, problems described below have occurred.
Concomitant with the trend toward higher recording density in the future, when the track width Tw which is defined by the width dimension in the track width direction of the upper surface of the free magnetic layer
5
is decreased, the size of the free magnetic layer
5
itself is decreased, and hence, even when a longitudinal bias magnetic field is supplied from the hard bias layer
7
to the free magnetic layer
5
, the free magnetic layer
5
is difficult to be appropriately placed in a single domain state in the track width direction (X direction in the figure). In addition, since the influence of a demagnetizing field of the free magnetic layer
5
is enhanced, the stability of reproducing properties is degraded.
In order to solve the problems described above, a method in which the film thickness of the hard bias layer
7
is increased so as to supply an intense longitudinal bias magnetic field to the free magnetic layer
5
may be considered; however, in the method described above, since the magnetization of the free magnetic layer
5
formed in a very small area tends to be fixed, and the magnetization change cannot be performed sensitively in response to an external magnetic field, a problem of degradation of reproducing output may arise in some cases.
Next, as shown in
FIG. 23
, the insulating layers
6
are provided on two sides of the laminate
9
in the track width direction. The insulating layers
6
are provided so that a current flowing from the electrode layer
1
or
8
through the laminate
9
flows effectively.
However, since the hard bias layer
7
is formed on the insulating layer
7
, a part of the current flowing from the electrode layer
1
or
8
through the laminate
9
is shunted to the hard bias layer
7
. The current thus shunted flows into the insulating barrier layer
400
, the fixed magnetic layer
3
, or the like not through the free magnetic layer
5
.
That is, in addition to a regular route through which a current flows from the electrode layer
1
or
8
in the laminate
9
, an additional current route through which a part of the current is shunted to the hard bias layer
7
not through the free magnetic layer
5
is formed, resulting in shut loss. Accordingly, decrease in changing rate of resistance (&Dgr;R/R) occurs.
In order to solve the problems described above, as shown in
FIG. 24
(a partial cross-sectional view sho
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Cao Allen
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