Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2002-08-27
2004-09-14
Le, N. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S260000, C428S692100
Reexamination Certificate
active
06791320
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic detection device used primarily with a hard disk drive, a magnetic sensor, or the like. More particularly, the invention relates to a magnetic detection device that permits proper control of the magnetization of a free magnetic layer even in a design with narrower tracks, and exhibits excellent reproducing characteristics, and a manufacturing method for the same.
2. Description of the Related Art
FIG. 35
is a partial sectional view of the structure of a conventional magnetic detection device observed from a surface opposing a recording medium.
In
FIG. 35
, a multilayer film
8
formed on a substrate
1
includes an antiferromagnetic layer
2
, a pinned magnetic layer
3
, a nonmagnetic material layer
4
, and a free magnetic layer
5
. Hard bias layers
6
are formed on both sides of the multilayer film
8
, and electrode layers
7
are formed on the hard bias layers
6
.
The magnetization of the pinned magnetic layer
3
is fixed in a direction Y in the drawing by an exchange coupling magnetic field generated between itself and the antiferromagnetic layer
2
. On the other hand, the magnetization of the free magnetic layer
5
is pinned in a direction X in the drawing by a longitudinal bias magnetic field from the hard bias layer
6
.
As shown in
FIG. 35
, a track width Tw is restricted by the width dimension in the direction of the track width (in the direction X in the drawing) of the free magnetic layer
5
. With a higher recording density in the future, the dimension of the track width Tw will be further reduced.
The tracks that are becoming increasingly narrower have been preventing the structure of the magnetic detection device shown in
FIG. 35
from properly controlling the magnetization of the free magnetic layer
5
.
First, according to the structure illustrated in
FIG. 35
, as the width dimension of the free magnetic layer
5
is reduced to accommodate narrower tracks, the region subjected to the influences of an intense longitudinal bias magnetic field from the hard bias layer
6
takes up more percentage in the free magnetic layer
5
. The area affected by the intense longitudinal bias magnetic field turns into a dead region that is magnetically less responsive to an external magnetic field. With narrower tracks, the dead region grows larger, resulting in degraded reproduction sensitivity.
Second, the hard bias layer
6
and the free magnetic layer
5
are apt to develop magnetic discontinuity. This trend is especially true if a foundation layer formed of Cr or the like lies between the hard bias layer
6
and the free magnetic layer
5
.
Such magnetic discontinuity causes enhanced influences of the diamagnetic fields of the end portions of the free magnetic layer
5
in the width direction, frequently leading to a phenomenon known as the “buckling phenomenon” in which the magnetization of the free magnetic layer
5
is disturbed. The buckling phenomenon tends to take place in a wider region of the free magnetic layer
5
as the tracks become narrower. This reduces the stability of the reproduced waveforms.
Third, with a narrower gap, a part of the longitudinal bias magnetic field from the hard bias layer
6
escapes to a shielding layers (not shown) formed on the top and bottom of the magnetic detection device shown in FIG.
35
. This disturbs the magnetization of the shielding layers and weakens the longitudinal bias magnetic field to be supplied to the free magnetic layer
5
, preventing effective control of the magnetization of the free magnetic layer
5
.
To overcome the problem described above, the exchange bias method has recently been used. According to the method, the magnetization control of the free magnetic layer
5
is attained using an antiferromagnetic layer formed on the free magnetic layer.
The magnetic detection device using the exchange bias method is fabricated according to the manufacturing process illustrated in, for example, FIG.
36
and
FIG. 37
, which are partial sectional views of the magnetic detection device observed from its surface opposing a recording medium.
In the process illustrated in
FIG. 36
, the antiferromagnetic layer
2
made of, for example, a PtMn alloy is formed on the substrate
1
. Then, the pinned magnetic layer
3
, the nonmagnetic material layer
4
, and the free magnetic layer
5
made of a magnetic material are deposited thereon. A Ta film
9
is formed on the free magnetic layer
5
to prevent the latter from being oxidized when its surface is exposed to the atmosphere.
Subsequently, a liftoff resist layer
10
is formed on the Ta film
9
shown in FIG.
36
. The portion of the Ta film
9
exposed on both sides in the track width direction or the direction X in the drawing that is not covered by the resist layer
10
is then completely removed by ion milling. The free magnetic layer
5
under the Ta film
9
is also partly removed, as indicated by the dotted lines in the drawing.
In the step illustrated in
FIG. 37
, ferromagnetic layers
11
, second antiferromagnetic layers
12
formed of an IrMn alloy or the like, and electrode layers
13
are deposited in this order on the portions of the free magnetic layers
5
that are exposed on both sides of the resist layer
10
. Removing the resist layer
10
shown in
FIG. 37
completes the exchange bias type magnetic detection device.
In the magnetic detection device shown in
FIG. 37
, the track width Tw can be restricted in terms of the interval in the track width direction (in the direction X in the drawing) of the ferromagnetic layers
11
. The ferromagnetic layers
11
are firmly fixed by the exchange coupling magnetic field generated between themselves and the second antiferromagnetic layers
12
. This causes both ends A of the free magnetic layers
5
, which are positioned under the ferromagnetic layers
11
, to be firmly fixed in the direction X in the drawing by the ferromagnetic coupling between themselves and the ferromagnetic layers
11
. Thus, it has been believed that a central portion B of the free magnetic layer
5
in the area of the track width Tw is formed into a weak single domain so it is able to magnetically respond to an external magnetic field.
The use of an exchange bias type magnetic detection device has been expected to provide a solution to the problems described above.
However, the magnetic detection device formed according to the manufacturing process illustrated in FIG.
36
and
FIG. 37
poses the following shortcomings.
First, during the ion milling step in the process illustrated in
FIG. 36
, a part of the free magnetic layer
5
formed under the Ta film
9
is inevitably removed while removing the Ta film
9
. In addition, an inert gas used for ion milling, such as Ar, is apt to enter through the exposed portion of the free magnetic layer
5
. The damage caused by the ion milling set forth above tends to destroy the crystal structure of surface portions
5
a
of the free magnetic layer
5
, or to the occurrence of lattice defects (mixing effect). This frequently results in the degradation of the magnetic characteristics of the surface portions
5
a
of the free magnetic layer
5
.
Ideally, only the Ta film
9
is removed in the ion milling step of the process illustrated in
FIG. 36
, leaving the free magnetic layer
5
intact. In reality, it is difficult to achieve such degree of milling control.
The reason underlying the difficulty in achieving ideal milling control is due to the thickness of the Ta film
9
formed on the free magnetic layer
5
. The Ta film
9
is formed to have a thickness in the range of between about 30 angstroms to about 50 angstroms. This film thickness is necessary to adequately protect the free magnetic layer
5
from oxidation.
The Ta film
9
is, however, oxidized by being exposed to air or during annealing in a magnetic field to produce an exchange coupling magnetic field between the pinned magnetic layer
3
or the ferromagnetic layers
11
and the antiferromagnetic layers
2
or
12
. The thicknes
Hasegawa Naoya
Umetsu Eiji
Alps Electric Co. ,Ltd.
Aurora Reena
Brinks Hofer Gilson & Lione
Le N.
LandOfFree
Magnetic detection device adapted to control magnetization... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic detection device adapted to control magnetization..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic detection device adapted to control magnetization... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3273522