Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-03-20
2004-03-16
Chen, Tianjie (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06707649
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a CPP (current perpendicular to the plane) type magnetic sensing element, and particularly to a magnetic sensing element permitting a decrease in the effective element size while maintaining the large optical element size, and permitting effective and easy improvement in reproduced output, and a method of manufacturing the same.
2. Description of the Related Art
FIG. 13
is a partial sectional view showing the structure of a conventional magnetic sensing element, as viewed from the side facing a recording medium.
In
FIG. 13
, reference numeral
1
denotes an underlying layer of Ta or the like, on which an antiferromagnetic layer
2
of PtMn or the like is formed. Furthermore, a pinned magnetic layer
3
made of NiFe or the like is formed on the antiferromagnetic layer
2
, a nonmagnetic intermediate layer
4
made of Cu or the like is formed on the fixed magnetic layer
3
, and a free magnetic layer
5
made of NiFe or the like is formed on the nonmagnetic intermediate layer
4
. Also, a protecting layer
6
made of Ta or the like is formed on the free magnetic layer
5
. A multilayer film
9
ranges from the underlying layer
1
to the protecting layer
6
.
Magnetization of the pinned magnetic layer
3
is pinned in the Y direction shown in the drawing by an exchange anisotropic magnetic field with the antiferromagnetic layer
2
.
Magnetization of the free magnetic layer
5
is oriented in the X direction shown in the drawing by a longitudinal bias magnetic field from each of hard bias layers
7
formed on both sides of the free magnetic layer
5
in the track width direction (the X direction shown in the drawing).
As shown in
FIG. 13
, electrode layers
8
are formed on the hard bias layers
7
. The track width Tw is determined by the length of the upper surface of the free magnetic layer
5
in the track width direction (the X direction).
In the magnetic sensing element shown in
FIG. 13
, the direction of a current flow is referred to as a “CIP (current in the plane) type” in which the current flows in substantially parallel to the film plane of each of the layers of the multilayer film
9
. This type is schematically shown in FIG.
14
.
As shown in
FIG. 14
, in a multilayer film ranging from an antiferromagnetic layer to a free magnetic layer, the width of the upper surface of the free magnetic layer is the track width Tw, the thickness of the multilayer film is T, and the length of the multilayer film in the height direction (the Y direction shown in the drawing) is MRh.
When the current density (J=I/(MRh×T)) and the thickness T are constant, and the track width Tw and the height length MRh are reduced to 1/S, the resistance value R of the multilayer film is constant, and thus the change in resistance &Dgr;R is also constant. However, the sensing current I is reduced to 1/S, and thus output &Dgr;V (=&Dgr;R×I) is also reduced to 1/S.
On the other hand, when the track width Tw and the height length MRh are reduced to 1/S with a constant heating value P, the resistance value R of the multilayer film is constant, and thus the change in resistance &Dgr;R is also constant. The sensing current I is also constant, and thus output &Dgr;V is a constant value.
In a CPP (current perpendicular to the plane) type magnetic sensing element in which the sensing current flows perpendicularly to the film plane of each of the layers of the multilayer film, the output &Dgr;V changes as follows:
FIG. 15
is a schematic drawing of a CPP type magnetic sensing element. Like in
FIG. 14
, in
FIG. 15
, the track width determined by the width of the upper surface of a free magnetic layer of a multilayer film is denoted by Tw, the thickness of the multilayer film is T, and the length of the multilayer film in the height direction (the Y direction shown in the drawing) is MRh.
Like in the CIP type, when the current density (J=I/(Tw×MRh)) and the thickness T are constant, and the track width Tw and the height length MRh are reduced to 1/S, the resistance value R of the multilayer film is increased S
2
times, and thus the change in resistance &Dgr;R is also increased S
2
times. However, the sensing current I is reduced to 1/S
2
, and thus output &Dgr;V (=&Dgr;R×I) is constant.
On the other hand, when the track width Tw and the height length MRh are reduced to 1/S with a constant heating value P, the resistance value R of the multilayer film is increased S
2
times, and thus the change in resistance &Dgr;R is also increased S
2
times. The sensing current I is reduced to 1/S, and thus output &Dgr;V is increased S times.
In this way, as narrowing of the element size advances, reproduced output V of the CPP type can be more increased than the CIP type. Therefore, the CPP type is expected to appropriately comply with narrowing of the element size with increases in the recording density in the future.
However, it was found that unless the track width Tw and the height length MRh are 0.1 &mgr;m or less (i.e., the element area is 0.01 &mgr;m
2
or less), the CPP type magnetic sensing element cannot effectively produce higher reproduced output than the CIP type.
The element size will possibly gradually decrease with future increases in the recording density. However, with the accuracy of the present photolithography techniques, it is very difficult to form a magnetic sensing element having a 0.1 &mgr;m square element area. Also, with an excessively small element size, a leakage magnetic field from a recording medium cannot be effectively sensed by the magnetic sensing element, thereby possibly causing deterioration in reproduced output and deterioration in stability of a reproduced waveform.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been achieved for solving the above problem of the conventional technique, and an object of the present invention is to provide a magnetic sensing element permitting a decrease in the effective element size while maintaining the large optical element size, and permitting effective and easy improvement in reproduced output, and a method of manufacturing the magnetic sensing element.
The present invention provides a magnetic sensing element comprising a multilayer film comprising an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic intermediate layer and a free magnetic layer, wherein a current flows perpendicularly to the film plane of each of the layers of the multilayer film, and a current limiting layer comprising a mixture of an insulating portion and a conductive portion is provided on at least one of the upper and lower surfaces of the free magnetic layer directly or through another layer.
The magnetic sensing element of the present invention is a CPP type in which a sensing current flows perpendicularly to the film plane of each of the layers of the multilayer film.
Therefore, the sensing current perpendicularly flows in the current limiting layer. However, in the present invention, the current limiting layer provided on at least one of the upper and lower surfaces of the free magnetic layer comprises a mixture of the insulating portion and the conductive portion, and thus the sensing current flows only in the conductive portion.
Therefore, the sensing current flowing from an electrode layer to the free magnetic layer through the current limiting layer locally flows only in a portion of the free magnetic layer corresponding to the conductive portion to locally increase the current density in this portion.
Therefore, in the present invention, even when the element area (referred to as an “optical element area”) of the free magnetic layer in the direction parallel to the film planes is formed in the same large size as a conventional element, the element area (referred to as an “effective element area”) in which the sensing current actually flows in the free magnetic layer to contribute to a magnetoresistive effect can be decreased. Thus, even when a magnetic sensing element having a large optical el
Hasegawa Naoya
Hayakawa Yasuo
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Chen Tianjie
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