Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-09-11
2003-01-07
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S319000
Reexamination Certificate
active
06504686
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composite thin-film magnetic head comprising a reproducing head and a recording head and to a method of manufacturing such a thin-film magnetic head.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as surface recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite head is made of a layered structure including a recording head having an induction-type magnetic transducer for writing and a reproducing head having a magnetoresistive (MR) element for reading.
It is required to increase the track density on a magnetic recording medium in order to increase recording density among the performance characteristics of a recording head. To achieve this, it is required to implement a recording head of a narrow track structure wherein a track width, that is, the width of top and bottom poles sandwiching the recording gap layer measured in the air bearing surface, is reduced down to microns or the submicron order. Semiconductor process techniques are utilized to implement such a structure.
Reference is now made to
FIG. 16A
to FIG.
19
A and
FIG. 16B
to
FIG. 19B
to describe an example of a method of manufacturing a composite thin-film magnetic head as an example of a related-art method of manufacturing a thin-film magnetic head.
FIG. 16A
to
FIG. 19A
are cross sections each orthogonal to an air bearing surface of the head.
FIG. 16B
to
FIG. 19B
are cross sections of a pole portion of the head each parallel to the air bearing surface.
In the manufacturing method, as shown in FIG.
16
A and
FIG. 16B
, an insulating layer
102
made of alumina (Al
2
O
3
), for example, and having a thickness of about 5 to 10 &mgr;m is deposited on a substrate
101
made of aluminum oxide and titanium carbide (Al
2
O
3
—TiC), for example. On the insulating layer
102
a bottom shield layer
103
made of a magnetic material is formed for making a reproducing head.
Next, on the bottom shield layer
103
, alumina, for example, is deposited to a thickness of 100 to 200 nm through sputtering to form a bottom shield gap film
104
as an insulating layer. On the bottom shield gap film
104
an MR element
105
for reproduction having a thickness of tens of nanometers is formed. Next, a pair of electrode layers
106
are formed on the bottom shield gap film
104
. The electrode layers
106
are electrically connected to the MR element
105
.
Next, a top shield gap film
107
is formed as an insulating layer on the bottom shield gap film
104
and the MR element
105
. The MR element
105
is embedded in the shield gap films
104
and
107
.
Next, on the top shield gap film
107
, a top-shield-layer-cum-bottom-pole-layer (called a bottom pole layer in the following description)
108
having a thickness of about 3 &mgr;m is formed. The bottom pole layer
108
is made of a magnetic material and used for both a reproducing head and a recording head.
Next, as shown in FIG.
17
A and
FIG. 17B
, on the bottom pole layer
108
, a recording gap layer
109
made of an insulating film such as an alumina film whose thickness is 0.2 &mgr;m is formed. Next, a portion of the recording gap layer
109
is etched to form a contact hole
109
a
to make a magnetic path. On the recording gap layer
109
in the pole portion, a top pole tip
110
made of a magnetic material and having a thickness of 0.5 to 1.0 &mgr;m is formed for the recording head. At the same time, a magnetic layer
119
made of a magnetic material is formed for making the magnetic path in the contact hole
109
a
for making the magnetic path.
Next, as shown in FIG.
18
A and
FIG. 18B
, the recording gap layer
109
and the bottom pole layer
108
are etched through ion milling, using the top pole tip
110
as a mask. As shown in
FIG. 18B
, the structure is called a trim structure wherein the sidewalls of the top pole portion (the top pole tip
110
), the recording gap layer
109
, and a part of the bottom pole layer
108
are formed vertically in a self-aligned manner.
Next, an insulating layer
111
made of an alumina film, for example, and having a thickness of about 3 &mgr;m is formed on the entire surface. The insulating layer
111
is then polished to the surfaces of the top pole tip
110
and the magnetic layer
119
and flattened.
Next, on the flattened insulating layer
111
, a first layer
112
of a thin-film coil is made of copper (Cu), for example, for the induction-type recording head. Next, a photoresist layer
113
is formed into a specific shape on the insulating layer
111
and the first layer
112
. Heat treatment is then performed at a specific temperature to flatten the surface of the photoresist layer
113
. On the photoresist layer
113
, a second layer
114
of the thin-film coil is then formed. Next, a photoresist layer
115
is formed into a specific shape on the photoresist layer
113
and the second layer
114
. Heat treatment is then performed at a specific temperature to flatten the surface of the photoresist layer
115
.
Next, as shown in FIG.
19
A and
FIG. 19B
, a top pole layer
116
is formed for the recording head on the top pole tip
110
, the photoresist layers
113
and
115
, and the magnetic layer
119
. The top pole layer
116
is made of a magnetic material such as Permalloy. Next, an overcoat layer
117
of alumina, for example, is formed to cover the top pole layer
116
. Finally, lapping of the slider is performed to form the air bearing surface
118
of the thin-film magnetic head including the recording head and the reproducing head. The thin-film magnetic head is thus completed.
FIG. 20
is a top view of the thin-film magnetic head shown in FIG.
19
A and FIG.
19
B. The overcoat layer
117
and the other insulating layers and insulating films are omitted in FIG.
20
.
In
FIG. 19A
, ‘TH’ indicates the throat height and ‘MR-H’ indicates the MR height. The throat height is the length (height) of the pole portions, that is, the portions of the two magnetic pole layers facing each other with the recording gap layer in between, the length between the air-bearing-surface-side end and the other end. The MR height is the length (height) between the air-bearing-surface-side end of the MR element and the other end. In
FIG. 19B
, ‘P
2
W’ indicates the pole width, that is, the track width of the recording head (hereinafter called the recording track width). In addition to the factors such as the throat height and the MR height, the apex angle as indicated with &thgr; in
FIG. 19A
is one of the factors that determine the performance of a thin-film magnetic head. The apex is a hill-like raised portion of the coil covered with the photoresist layers
113
and
115
. The apex angle is the angle formed between the top surface of the insulating layer
111
and the straight line drawn through the edges of the pole-side lateral walls of the apex.
As the reproducing output of the reproducing head increases, noise such as Barkhausen noise increases, and variations in output increase, with regard to the composite thin-film magnetic head wherein the bottom pole layer of the recording head also functions as the top shield layer of the reproducing head as shown in FIG.
19
A and
FIG. 19B
, the composite head being capable of attaining surface recording density as high as 20 gigabits per square inches or 30 gigabits per square inches. A variation in output may be represented by COV (%), that is, a value obtained by dividing the standard deviation of the output by the mean value of the output, the standard deviation being obtained by measuring the output 100 consecutive times, and multiplying the result by 100. In this case, a variation in output is great if the COV is great.
One of the factors that cause an increase in noise and an increase in output variation of the reproducing head as mentioned above is residual magnetism and variations therein that are produced in the recording
Evans Jefferson
Oliff & Berridg,e PLC
TDK Corporation
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