Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-10-31
2004-07-20
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C360S324120
Reexamination Certificate
active
06764778
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a so-called thin film magnetic element, in which electric resistance changes according to the relation between the magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer affected by an external magnetic field, and particularly to a thin film magnetic element adaptable for track narrowing.
2. Description of the Related Art
FIG. 18
, designated “PRIOR ART,” is a sectional view of the structure of a conventional thin film magnetic element as viewed from the air bearing surface (ABS) side.
The thin film magnetic element shown in
FIG. 18
is referred to as a “spin valve thin film magnetic element” which is one of GMR (giant magnetoresistive) elements utilizing a giant magnetoresistive effect, for detecting a recording magnetic field from a recording medium such as a hard disk or the like.
The spin valve thin film magnetic element comprises a multilayer film
9
comprising an underlying layer
6
, an antiferromagnetic layer
1
, a pinned magnetic layer
2
, a nonmagnetic conductive layer
3
, a free magnetic layer
4
, and a protecting layer
7
, which are laminated in turn from the bottom. A pair of hard bias layers
5
are formed on both sides of the multilayer film
9
, and a pair of electrode layers
8
are formed on the hard bias layers
5
. Each of the underlying layer
6
and the protecting layer
7
comprises a Ta (tantalum) film or the like. The track width Tw is determined by the width dimension of the-upper surface of the multilayer film
9
.
Generally, the antiferromagnetic layer
1
comprises a Fe—Mn (iron-manganese) alloy film or a Ni—Mn (nickel-manganese) alloy film, each of the pinned magnetic layer
2
and the free magnetic layer
4
comprises a Ni—Fe (nickel-iron) alloy film, the nonmagnetic conductive layer
3
comprises a Cu (copper) film, the hard bias layers
5
comprise a Co—Pt (cobalt-platinum) alloy film, and the electrode layers
8
comprise a Cr (chromium) film.
As shown in
FIG. 18
, magnetization of the pinned magnetic layer
2
is put into a single magnetic domain state in the Y direction (the direction of a leakage magnetic field from a recording medium; height direction) by an exchange anisotropic magnetic field with the antiferromagnetic layer
1
. Magnetization of the free magnetic layer
4
is oriented in the X direction by the influence of a bias magnetic field from the hard bias layers
5
.
Namely, the magnetization direction of the pinned magnetic layer
2
is set to be perpendicular to the magnetization direction of the free magnetic layer
4
.
In the spin valve thin film magnetic element, a sensing current is supplied to the pinned magnetic layer
2
, the nonmagnetic conductive layer
3
and the free magnetic layer
4
from the electrode layers
8
respectively formed on the hard bias layers
5
. The movement direction of the recording medium such as a hard disk or the like coincides with the Z direction. When a leakage magnetic field is applied from the recording medium in the Y direction, the magnetization direction of the free magnetic layer
4
is changed from the X direction to the Y direction. As a result, the electric resistance changes based on the relation between the change in the magnetization direction of the free magnetic layer
4
and the pinned magnetization direction of the pinned magnetic layer
2
(this is referred to as the “magnetoresistive effect”), and thus the leakage magnetic field from the recording medium is detected by a voltage change based on the change in the electric resistance value.
However, the conventional thin film magnetic element shown in
FIG. 18
has the following problems.
As described above, the magnetization direction of the pinned magnetic layer
2
is put into the single magnetic domain state and pinned in the Y direction, but the hard bias layers
5
magnetized in the X direction are provided on both sides of the pinned magnetic layer
2
. Therefore, particularly, magnetization at either end of the pinned magnetic layer
2
is not pinned in the Y direction due to the influence of the bias magnetic fields of the hard bias layers
5
.
Namely, the magnetization direction of the free magnetic layer
4
put into the single magnetic domain state in the X direction is not perpendicular to the magnetization direction of the pinned magnetic layer
2
due to magnetization of the hard bias layers
5
in the X direction, particularly, in the vicinities of the side ends of the multilayer film
9
. The reason for setting the magnetization directions of the free magnetic layer
4
and the pinned magnetic layer
2
to be perpendicular to each other is that magnetization of the free magnetic layer
4
can be easily changed with a small external magnetic field to greatly change the electric resistance, thereby improving reproduction sensitivity. The other reason is that the perpendicular relation permits the formation of an output waveform having good symmetry.
Furthermore, in the thin film magnetic element shown in
FIG. 18
, the side surfaces of the multilayer film
9
are inclined, and the inclination angle e of the side surfaces of the multilayer film
9
readily varies with the product. A variation in the inclination angle causes a variation in the length of the free magnetic layer
4
in the track width direction. Namely, the width dimension Ew of the sensitive zone E
A
exhibiting the magnetoresistive effect also varies to cause the problem of causing a variation in magnetic field sensitivity of the thin film magnetic element.
In the multilayer film
9
, the central zone excluding the dead zones D
A
is a sensitive zone E
A
which substantially contributes to reproduction of the recording magnetic field and which exhibits the magnetoresistive effect. The width of the sensitive zone E
A
is shorter than the track width Tw set at the time of formation of the multilayer film
9
by an amount corresponding to the width of the dead zones D
A
.
In this way, in the magnetoresistive element, the dead zones D
A
which less contributes to reproduced output are formed in the multilayer film
9
near the both sides thereof, and thus the dead zones D
A
are only zones in which the DC resistance value (DCR) is increased.
In recent years, the track width Tw of the thin film magnetic element has been further decreased with a further increase in recording density of a magnetic recording medium, and thus the track width Tw has been required to be decreased to 0.5 &mgr;m or less. However, the width dimension Dw of the dead zones D
A
is about 0.1 &mgr;m, and with a track width Tw of 0.5 &mgr;m or less, the ratio of the width dimension Dw of the dead zones to the track width Tw is increased to cause difficulties in accurately controlling the width dimension Ew of the sensitive zone E
A
. When the ratio of the width dimension Dw of the dead zones D
A
to the track width Tw is increased, reproduced output is also decreased.
Furthermore, in the thin film magnetic element shown in
FIG. 18
, the side surfaces of the multilayer film
9
are inclined, and the inclination angle &thgr; of the side surfaces of the multilayer film
9
readily varies with the product. A variation in the inclination angle causes a variation in the length of the free magnetic layer
4
in the track width direction. Namely, the width dimension Ew of the sensitive zone E
A
exhibiting the magnetoresistive effect also varies to cause the problem of causing a variation in magnetic field sensitivity of the thin film magnetic element.
FIG. 44
, designated as “PRIOR ART,” is a sectional view showing the structure of another thin film magnetic element manufactured by a conventional manufacturing method, as viewed from the ABS side.
The thin film magnetic element shown in
FIG. 44
is called a spin valve thin film magnetic element which is one of GMR (giant magnetoresistive) elements utilizing the giant magnetoresistive effect, for detecting a recording magnetic field from a recording medium such as a hard disk or the like.
The
Hasegawa Naoya
Ide Yosuke
Kuriyama Toshihiro
Saito Masamichi
Tanaka Ken'ichi
Alps Electric Co. ,Ltd.
Thibodeau Paul
Uhlir Nikolas J.
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