Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making named article
Reexamination Certificate
2000-11-28
2002-06-25
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making named article
C430S312000, C430S315000, C430S319000, C430S394000, C029S603070
Reexamination Certificate
active
06410212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thin-film magnetic heads provided with a coil layer formed between core layers. In particular, the present invention relates to a thin-film magnetic head which has an upper core layer having an improved shape and can meet trends towards narrow tracks, and relates to a method for making the same.
Also, the present invention relates to a thin-film magnetic head which is provided with a coil layer formed between core layers and has satisfactory NLTS (nonlinear transition shift) characteristics and OW (overwrite) characteristics.
2. Description of the Related Art
FIG. 10
is a longitudinal cross-sectional view of a conventional thin-film magnetic head. The left end of the thin-film magnetic head in the drawing faces recording media. This thin-film magnetic head is a so-called “composite thin-film magnetic head” having a reading head hi using a magnetoresistive effect and an inductive head h
2
for writing signals onto recording media, such as a hard disk. The inductive head h
2
is deposited on the reading head h
1
. This thin-film magnetic head is provided at the end of the trailing side of a slider of a floating-type magnetic head.
The reading head hi h as a lower core layer
1
composed of a magnetic material having high permeability, for example, a Fe—Ni alloy (permalloy). The lower core layer
1
also functions as an upper shielding layer of the reading head h
1
by means of the magnetoresistive effect.
A gap layer
2
composed of a nonmagnetic material, such as alumina (Al
2
O
3
), is provided on the lower core layer
1
. As shown in
FIG. 10
, an insulating layer
3
composed of a resist or an organic resin is formed on the gap layer
2
. Furthermore, a spiral coil layer
4
composed of a highly conductive material such as copper is formed on the insulating layer
3
so as to surround a base section
6
b
of an upper core layer
6
. In
FIG. 10
, the coil layer
4
can be partially seen.
An insulating layer
5
composed of a resist or an organic resin is formed on the coil layer
4
. The upper core layer
6
is formed by plating a magnetic material such as permalloy on the insulating layer
5
. A front end section
6
a
of the upper core layer
6
is bonded to the lower core layer with the gap layer
2
provided therebetween to form a magnetic gap having a gap length Gl
1
. The base section
6
b
of the upper core layer
6
is magnetically coupled with the lower core layer
1
through cavities formed in the gap layer
2
and the insulating layer
3
.
FIG. 11
is a plan view of the thin-film magnetic head shown in FIG.
10
. The upper core layer
6
consists of a leading region A having a constant width and a trailing region B gradually spreading from the leading end region. The leading region A of the upper core layer
6
is slender and has a width which is equal to the track width T
W
.
In the inductive head h
2
for writing, recording currents flowing in the coil layer
4
induce recording magnetic fields in the lower core layer
1
and the upper core layer
6
. Leakage magnetic fields from the magnetic gap section between the lower core layer
1
and the front end section
6
a
of the upper core layer
6
record magnetic signals on recording media, such as a hard disk.
As shown in
FIG. 10
, the reading head h
1
includes a lower shielding layer
7
composed of a magnetic material, a magnetoresistive element layer
9
formed on the lower shielding layer
7
with a lower gap layer
8
provided therebetween
8
, and an upper shielding layer or lower core layer
1
formed on the magnetoresistive element layer
9
with an upper gap layer
10
provided therebetween.
NLTS characteristics and OW characteristics, as important recording characteristics, greatly depend on the shape of the leading region A of the upper core layer
6
. Herein, the NLTS (nonlinear transition shift) characteristics mean the phase lead caused by non-linear distortion of the leakage magnetic field, generated in the magnetic gap between the upper core layers
1
and the lower core layer
6
of the inductive head h
2
in
FIG. 10
by the leakage magnetic field from the magnetic recording signals which are just recorded on a recording medium towards the head.
The OW (overwrite) characteristics mean a difference in output of recorded signals at a low frequency between the initial output before overwriting at a high frequency and the decreased output after the overwriting.
When the leading region A of the upper core layer
6
is slender, as shown in
FIG. 11
, the length L
1
of the leading region A is considered to be preferably in a range of approximately 4 &mgr;m to 10 &mgr;m. Such a length L
1
, however, causes deterioration of OW characteristics although it contributes to improvement in NLTS characteristics.
The upper core layer
6
of the thin-film magnetic head is formed by a frame plating process, as shown in FIG.
12
. In this-process, the coil layer
4
is formed and is covered with the insulating layer
5
. An underlying layer
7
composed of a magnetic material such as a NiFe alloy is formed over the gap layer
2
, exposed in the vicinity of the end, and the insulating layer
5
. After a resist layer
8
is formed on the underlying layer
7
, the resist layer
8
is exposed and developed to form a pattern of the shape of the upper core layer
6
. A magnetic layer (upper core layer
6
) is plated on the exposed underlying layer
7
. The residual resist layer
8
is removed to form the upper core layer
6
. The thin-film composite is cut along line Z—Z in
FIG. 12
to form the thin-film magnetic head shown in
FIG. 10
, wherein the cut surface along line Z—Z faces the recording media.
Production of the upper core layer
6
of a conventional thin-film magnetic head has the following problems.
FIG. 13
is a plan view when a resist layer
38
is formed on the underlying layer
7
and a pattern
39
of the upper core layer
6
is formed on the resist layer
38
. As shown in
FIG. 13
, the pattern
39
of the upper core layer
6
consists of the leading region A having a track width T
W
at the left side in the drawing and the trailing region B spreading towards the right side. The current track width T
W
, approximately 2 to 3 &mgr;m, of the leading region A must be decreased to 1 &mgr;m or less in order to meet current high-density recording trends.
The pattern
39
is formed by exposing and developing the resist layer
38
. In conventional processes, the slender leading region A and the spreading trailing region B are simultaneously exposed using short-wavelength light (g-line to i-line) at a low NA (numerical aperture) of 0.2 to 0.3 for achieving a large depth of focus. For example, the upper limit of the resolution is 1.0 &mgr;m for a combination of the i-line and a numerical aperture NA of 0.2 to 0.3. Thus, a track width T
W
of less than 1.0 &mgr;m is not achieved in conventional processes.
When the resist layer
38
on the leading region A is removed in the development step after the formation of the pattern
39
for the upper core layer
6
, a developing solution barely penetrates into the resist layer
38
in the pattern
39
for the slender leading region A having a small width (track width T
W
). Thus, the resist layer
38
in the leading region A may be not completely removed. Accordingly, this process is not applicable to an upper core layer having a smaller track width T
W
.
In addition, the leading region A of the resulting thin-film magnetic head has a small track width T
W
and a large length L
1
. Thus, OW characteristics are decreased by damping of the magnetic flux density in the leading region A. It is known that the OW characteristics of the upper core layer
6
having the leading region A with the track width T
W
decrease as the length L
1
of the leading region A increases.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a thin-film magnetic head having an improved leading edge of an upper core layer to meet narrow track width requirement without deterioration o
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
McPherson John A.
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