Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1998-12-08
2003-02-25
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S322000, C360S327310
Reexamination Certificate
active
06525912
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thin-film magnetic heads mounted in, for example, hard disk drives. Specifically, the present invention relates to a thin-film magnetic head and to a method that is capable of production of the thin-film magnetic head having a highly precise planar shape.
2. Description of the Related Art
FIG. 5
is an enlarged cross-sectional view away from a recording medium of a conventional thin-film magnetic head. This thin-film magnetic head is a reading head using magnetoresistive effects, and is provided at the side face, lying at the trailing edge, of a slider of a floating head. An inductive magnetic head for writing may also be disposed on the reading head.
A lower shielding layer
1
is formed of an alloy, e.g. sendust or permalloy (a Ni—Fe alloy). A lower gap layer
2
composed of a nonmagnetic material, e.g. alumina (Al
2
O
3
), is formed on the lower shielding layer
1
, and a magnetoresistive layer
15
is deposited thereon. The magnetoresistive layer
15
comprises a giant magnetoresistive (GMR) element, such as an anisotropic magnetoresistive (AMR) element or a spin-valve film. The magnetoresistive layer
15
senses leakage magnetic fluxes from a recording medium as a change in resistance and outputs them as a change in voltage. The magnetoresistive layer
15
has a width T
4
in the direction of the track width (the transverse direction in the drawing), and the width T
4
is slightly larger than the track width Tw.
Hard magnetic bias layers
4
are formed as a longitudinal bias layer at both sides of the magnetoresistive layer
15
, and electrode layers
5
that are composed of an electrically conductive nonmagnetic material, such as chromium or tantalum are formed on the hard magnetic bias layers
4
. An upper gap layer
7
composed of a nonmagnetic material such as alumina is formed on the electrode layers
5
, and an upper shielding layer
8
composed of, for example, permalloy is formed on the upper gap layer
7
.
A method for making the magnetoresistive layer
15
shown in
FIG. 5
will now be described with reference to
FIGS. 6A
to
6
C and
7
A to
7
B. The drawings at the left sides and the right sides of
FIGS. 6A
to
6
C and
FIGS. 7A
to
7
B are cross-sectional views and plan views, respectively, of the thin-film magnetic head in each production step. The cross-sectional view shown in
FIG. 6A
is taken from a transverse line at the central region of the magnetoresistive layer
15
in the width T
6
in the plan view. The same relationship holds for the other drawings.
The lower gap layer
2
is deposited on the lower shielding layer
1
, and then a magnetoresistive layer
15
′ is deposited on the entire lower gap layer
2
. As shown
FIG. 6A
, a resist layer
20
is formed on the magnetoresistive layer
15
′ . Since the resist layer
20
is of a lift-off type, indentations
20
a
are formed at both bottom sides of the resist layer
20
. As shown in the plan view of
FIG. 6A
, the resist layer
20
is formed on the entire magnetoresistive layer
15
′ other than at two windows
20
b
. Thus, the magnetoresistive layer
15
′ is exposed at the windows
20
b.
The width of the resist layer
20
between the windows
20
b
is set to T
5
. The resist layer
20
is provided to determine the width of the magnetoresistive layer
15
′ in the track width direction, hence the width of the resist layer
20
is made substantially equal to the width T
4
of the completed magnetoresistive layer
15
(refer to FIG.
5
).
The regions of the magnetoresistive layer
15
′ exposed from the resist layer
20
are removed by etching to expose the lower gap layer
2
, as shown in FIG.
6
B. The hard magnetic bias layers
4
and the electrode layers
5
are then formed on the exposed regions of the lower gap layer
2
, as shown in
FIG. 6C. A
stripping solution is penetrated into the interface of the resist layer
20
and the magnetoresistive layer
15
′ though the indentations
20
a
, and then the resist layer
20
is removed.
As shown in
FIG. 7A
, a resist layer
21
is formed on the magnetoresistive layer
15
″ and the electrode layers
5
. Since the resist layer
21
is not of a lift-off type, it has no indentations at the bottom sides. The resist layer
21
has a length L
3
in the depth direction in order to define the length of the magnetoresistive layer
15
″ in the depth direction. Thus, the length L
3
of the resist layer
21
is substantially equal to the length (not shown in the drawing) of the completed magnetoresistive layer
15
shown in FIG.
5
.
The exposed region of the magnetoresistive layer
15
″ which is not covered with the resist layer
21
is removed by etching. The magnetoresistive layer
15
is thereby formed on the lower gap layer
2
, and the hard magnetic bias layers
4
and the electrode layers
5
are formed on both sides of the magnetoresistive layer
15
.
As described above, in the formation of the magnetoresistive layer
15
, the width T
4
of the magnetoresistive layer
15
in the track width is first determined by the lift-off-type resist layer
20
, the hard magnetic bias layers
4
and the electrode layers
5
are formed, and then the length of the magnetoresistive layer
15
in the depth direction is determined by the resist layer
21
.
The method for making the magnetoresistive layer
15
, however, has the following disadvantages. In
FIG. 6C
, the total thickness of the hard magnetic bias layer
4
and the electrode layer
5
is larger than the thickness of the magnetoresistive layer
15
″. Thus, as shown in
FIG. 7A
, the thickness h
1
of the resist layer
21
on the magnetoresistive layer
15
″ is larger than the thickness h
2
on the electrode layers
5
. Such a difference in the thickness causes random scattering in the exposure step due to improper focusing. As a result, the planar shape of the resist layer
21
in the transverse direction of the drawing or the track width direction is not linear as shown in the plan view of
FIG. 7A
, but is instead curved in the air bearing surface (ABS) direction and the depth direction, which is the reverse direction of the ABS direction.
Thus, the planar shape of the magnetoresistive layer
15
completed by etching the exposed region is also curved in the ABS face direction and the depth direction, by following the shape of the resist layer
21
, as shown in FIG.
8
A. Since the side in the ABS direction is polished in a subsequent step to planarize it as shown in
FIG. 8B
, the curvature is not substantially disadvantageous. The face in the depth direction is, however, not subjected to any treatment in the subsequent steps; hence the curved face of the magnetoresistive layer
15
in the depth direction remains.
In the step shown in
FIG. 7A
, the resist layer
21
is post-baked to enhance etching resistance of the resist layer
21
prior to the etching of the exposed region. The resist layer
21
is deformed by post-baking from the rectangular shape as shown in
FIG. 7A
to a rounded shape. A modified layer
21
′ is formed on the resist layer
21
due to the effects of argon during ion-milling etching, as shown in
FIG. 9
(a longitudinal cross-sectional view of the thin-film magnetic head having the resist layer
21
). Since the modified layer
21
′ is not removed by the resist stripping solution, it must be removed by an oxygen-plasma dry etching process.
The oxygen-plasma dry etching process, however, also etches the surfaces of the magnetoresistive layer
15
in the depth direction and the ABS direction that adjacent to the modified layer
21
′. Thus, an indented section is formed on these surfaces. Since the surface in the depth direction is not subjected to any treatment in the subsequent steps as described above, the indented section of the magnetoresistive layer
15
in the depth direction remains, although the indented section in the ABS section is polished (see FIG.
8
B).
With a narrowing trend of the track width for
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Renner Craig A.
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