Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2003-04-02
2004-08-31
Loney, Donald J. (Department: 1772)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S693100, C428S900000, C428S928000, C360S322000, C360S324000, C360S324120, C029S603070, C029S603180, C029SDIG002, C204S192100, C204S192110, C204S192150, C204S192340, C216S072000
Reexamination Certificate
active
06783874
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magnetic sensors in which electrode layers are formed to overlap a multilayer film, and more particularly, relates to a magnetic sensor in which overlap electrode layers at the left and right sides can be precisely formed so that the film thicknesses thereof are equivalent to each other.
2. Description of the Related Art
FIG. 21
is a partly cross-sectional view of a related magnetic sensor (spin-valve type thin-film element) viewed from an opposing face side opposing a recording medium.
Reference numeral
1
indicates a first antiferromagnetic layer composed of a PtMn alloy or the like, and on this first antiferromagnetic layer
1
, a fixed magnetic layer
2
formed of a NiFe alloy or the like, a nonmagnetic material layer
3
formed of Cu or the like, and a free magnetic layer
4
formed of a NiFe alloy or the like are provided to form a laminate structure.
As shown in
FIG. 21
, on the free magnetic layer
4
, second antiferromagnetic layers
5
with a track width Tw provided therebetween in the track width direction (X direction in the figure) are formed, and on these second antiferromagnetic layers
5
, electrode layers
6
are provided.
In the embodiment shown in
FIG. 21
, exchange coupling magnetic fields are generated in regions in which the second antiferromagnetic layers
5
are provided on the free magnetic layer
4
, the magnetizations of the free magnetic layer
4
in the regions described above are fixed in the X direction shown in the figure, and the free magnetic layer
4
in the track width Tw is put in a weak single domain state so that the magnetization reverse may occur with respect to an external magnetic field.
In the related example shown in
FIG. 21
, there have been the following two problems. The first problem is that element resistance cannot be satisfactory decreased. The reason for this is that the second antiferromagnetic layer
5
is formed of a material such as a PtMn alloy having a high resistivity, and that sense current flows from the electrode layer
6
to the free magnetic layer
4
side through this second antiferromagnetic layer
5
(the flow of the sense current is shown by the arrows). The PtMn alloy mentioned above has a resistivity of an approximately 170 &mgr;&OHgr;·cm or more, and on the other hand, the electrode layer
6
is formed of a material such as Au having a very low resistivity of approximately 2 to 6 &mgr;&OHgr;·cm. Hence, even when a material having a low resistivity is used for the electrode layer
6
, according to the structure of the magnetic sensor shown in
FIG. 21
, the sense current must flow once through the second antiferromagnetic layer
5
having a high resistivity, and as a result, decrease in element resistance cannot be achieved. In addition, since the element height has been decreased concomitant with recent trend toward higher recoding density, the element resistance is also increased.
The second problem is side reading. As described above, since flowing toward the free magnetic layer
4
side through the second antiferromagnetic layer
5
, the sense current spreads wider than the track width Tw and then flows toward the free magnetic layer
4
side. In this step, since the magnetization of the free magnetic layer
4
in the vicinity of the track width Tw is not tightly fixed with the second antiferromagnetic layer
5
and varies to some extent with respect to an external magnetic field, a so-called effective track width tends to be larger than the track width Tw (this track width Tw is also referred to as “optical track width” in some cases) shown in the figure. Consequently, the side reading is liable to occur in that external signals are read at positions apart from the track width Tw.
In order to solve the above two problems, the structure in which the electrode layers
6
overlaps the free magnetic layer
4
in the track width Tw has been researched.
FIGS. 22 and 24
are views showing steps of manufacturing a magnetic sensor in which electrode layers form an overlap structure. The views showing the manufacturing steps, described above, are partly cross-sectional views each showing a magnetic sensor in the manufacturing step when viewed from an opposing face side opposing a recording medium.
In the step shown in
FIG. 22
, the first antiferromagnetic layer
1
, the fixed magnetic layer
2
, the nonmagnetic material layer
3
, and the free magnetic layer
4
are formed in that order from the bottom, and in addition, on the free magnetic layer
4
, the second antiferromagnetic layers
5
are formed with a predetermined space T1 provided therebetween in the track width direction (X direction in the figure). For the formation of the second antiferromagnetic layers
5
, as shown in
FIG. 22
, for example, a solid second antiferromagnetic film
5
is first formed over the entire surface of the free magnetic layer
4
, resist layers
8
with a predetermined space therebetween in the track width direction are formed on the solid second antiferromagnetic film
5
, part of the solid second antiferromagnetic film
5
which is not covered with the resist layers
8
is removed by etching, and the resist layers
8
are then removed, thereby forming the second antiferromagnetic layers
5
.
In the step shown in
FIG. 23
, a solid electrode film
6
is formed on the second antiferromagnetic layers
5
and the free magnetic layer
4
, and on the solid electrode film
6
, a resist film
7
is formed. In the step shown in
FIG. 23
, a space for the track width Tw is formed in the resist film
7
in the track width direction (X direction in the figure), thereby forming the resist layers
7
. The track width Tw is smaller than the space T1 formed between the second antiferromagnetic layers
5
.
In the step shown in
FIG. 24
, part of the solid electrode film
6
which is not covered with the resist layers
7
is removed by ion milling or reactive ion etching, thereby exposing the upper surface of the free magnetic layer
4
. Since the other parts of the solid electrode film
6
, which are not removed and which form the electrode layers
6
, overlap the upper surfaces of the second antiferromagnetic layers
5
and the free magnetic layer
4
, and sense current tends to flow easily from the electrode layers
6
to the free magnetic layer
4
side (the flow of the sense current is indicated by the arrows in FIG.
24
), it has been anticipated that the problems described above, that is, the increase in element resistance and the side reading, can be simultaneously solved.
In recent years, the track width TW has been decreased concomitant with the trend toward higher recording density. When the track width Tw is decreased, dead regions (regions which do not directly contribute to reproduction) positioned under the second antiferromagnetic layers
5
and in the very vicinity of both sides of the track width tend to have a larger ratio of the whole area, and as a result, decrease in reproduction output cannot be prevented. However, when the structure is formed so that the electrode layers
6
overlap the free magnetic layer by the manufacturing steps shown in
FIGS. 22
to
24
, the dead regions can be decreased to some extent as compared to those of the magnetic sensor shown in
FIG. 22
since the space between the second antiferromagnetic layers
5
can be increased, and hence it has been expected that the reproduction output can be effectively improved by the structure described above.
In addition, in the structure in which the electrode layers
6
overlap the free magnetic layer
4
while the track width Tw is decreased, as is the magnetic sensor shown in
FIG. 24
, widths T2 and T3 (hereinafter referred to as “overlap length”) of the overlap portions in the track width direction are approximately {fraction (1/100)}&mgr;m, and hence the alignment accuracy becomes important when the electrode layers
6
are formed.
However, in the manufacturing steps shown in
FIGS. 22
to
24
, the second antiferromagnetic layers
5
each having a predeter
Hasegawa Naoya
Ishibashi Naohiro
Oshima Masahiro
Umetsu Eiji
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Loney Donald J.
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