Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-03-27
2003-12-16
Cao, Allen (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06665156
ABSTRACT:
This application is based on Japanese Patent Application 2000-88874 filed on Mar. 28, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a magnetoresistive head, a manufacture method thereof, and a magnetic recording/reproducing apparatus with such a magnetic head.
b) Description of the Related Art
Magnetic recording/reproducing apparatus such as hard disk drives are rapidly reducing their sizes and increasing recording densities. The recording track width of a recording medium is becoming narrower than ever to improve the recording density.
In order to compensate for a reproduction output level lowered by a narrower width of a recording track, a magnetoresistive head (hereinafter abbreviated to “MR head”) having a high sensitivity has been developed. Recently, an MR head capable of obtaining a large output signal by utilizing a giant magnetoresistance effect (hereinafter abbreviated to “GMR”) is practically used.
An MR head utilizing GMR uses a multi-layer magnetic film (spin valve film) formed, for example, by sequentially stacking a ferromagnetic layer (free layer) whose magnetization direction is changed with an external magnetic field, a non-magnetic conductive layer, a ferromagnetic layer (pinning layer) whose magnetization direction is pinned down, and an antiferromagnetic layer for pinning the magnetization direction of the pinning layer.
It is important to suppress Barkhausen noises of an MR head using a spin valve film to be generated by discontinuous motion of magnetic domain walls in the free layer. The structure of efficiently applying a longitudinal magnetic field to the free layer has been adopted to suppress Barkhausen noises.
Typical examples of the longitudinal magnetic field applying structure are an abutted junction structure such as disclosed in JP-B-7-122925 and a gull wing structure such as disclosed in JP-A-11-86237 in which this structure is called an overlaid structure.
FIG. 13
shows an MR head having the abutted junction structure shown in JP-B-7-122925.
An MR head
40
shown in
FIG. 13
has an MR film
43
and a pair of hard magnets for applying a longitudinal magnetic field to the MR layer
43
. The MR film
43
is formed on a lower gap layer
42
formed on a lower shield film
41
on a substrate (not shown). Each hard magnet is constituted of a magnet film
44
formed on the lower gap layer
42
and an electrically conductive film
45
formed on the magnetic film
44
.
This MR head
40
constructed as above is manufactured in the following method. An MR film is deposited and a mask is formed on the MR film to remove an unnecessary portion thereof by milling and form the MR film
43
. Then, the magnet film
44
is deposited on the exposed surface of the lower gap layer
42
and the conductive film
45
is deposited. Lastly, the mask is removed by lift-off. A reading track width TW is equal to the space between opposite ends of the pair of hard magnets of the MR head
40
.
The MR film
43
of the MR head
40
formed by milling has a forward tapered side wall
43
a
depending upon a milling angle and a shadowing effect of oblique milling. Therefore, the side wall
44
a
of the magnet film
44
for applying a longitudinal magnetic field to the MR film
43
has a backward tapered shape. In order to narrow a reading track, the ferromagnetic layer (free layer) of the MR film
43
is formed to have the upper narrowed tapered portion, and the MR film
43
becomes in contact with the magnet film
44
only at its side walls
43
a.
Therefore, the magnet film
44
gives the MR film
43
a magnetic effect only or dominantly of a static magnetic field. This poses the problem that a single domain cannot be formed efficiently in the MR film
43
. Another problem is unstable electrical conduction between the MR film
43
and conductive film
45
because they contact only at the side walls
43
a
. Another problem is burs formed on the edges of the magnet film
44
or conductive film
45
when the mask used for milling is lifted off. Burs near the free layer make the gap thickness of the MR head irregular. Therefore, signal separation between adjacent bits in a recording medium becomes imperfect, or at the worst, the magnet film
44
and an upper shield layer to be formed at a later process may be short-circuited.
FIG. 14
shows an MR head having the gull wing structure such as shown in JP-A-11-86237.
An MR head
50
shown in
FIG. 14
has a lower shield film
51
formed on a substrate (not shown), a lower gap layer
52
formed on the film
51
, a pair of hard magnets formed on the lower gap layer
52
and an MR film
55
. Each of the hard magnets is constituted of a magnet film
53
formed on the lower gap layer
52
and an electrically conductive film
54
formed on the magnet film
53
. The magnet film
53
applies a longitudinal magnetic field to the MR film
55
.
In manufacturing the MR head
50
constructed as above, a magnet film and a conductive film are laminated and portions thereof corresponding to the reading track width TW are removed by milling to form the magnet film
53
and conductive film
54
. Thereafter, an MR film is deposited and an unnecessary portion thereof is removed to form the MR film
55
. The reading track width TW is equal to the width of a contact region of the MR film
55
with the lower gap layer
52
.
Since the MR film
55
of the MR head
50
manufactured by this method is in surface contact with the magnet film
53
and conductive film
54
, electrical conduction therebetween is more reliable than the MR head
40
having the abutted junction structure. Since the side walls of the magnet film
53
on the MR film
55
side have the forward tapered shape, a single domain can be formed in the MR film
55
by positively using not only the static magnetic field applied by the magnet film
53
but also exchange coupling at the interface between the magnet film
53
and MR film
55
.
For mass production of MR heads, generally a number of MR heads are formed at a time on a single large area substrate, and each MR head together with a partial region of the large area substrate is cut from the substrate.
With this method, a variation in thicknesses of each film formed on the whole area of the large area substrate becomes a variation in reading track widths TW of MR heads
50
under mass production. The reason for this will be described with reference to
FIGS. 15A
to
15
C.
FIGS. 15A
to
15
C are schematic cross sectional views illustrating the manufacture processes for the MR films
55
of the MR heads
50
.
A film to be used for the magnet films
53
is formed, for example, by depositing a CoCrPt alloy layer (60 nm in thickness) on an underlying film (20 nm in thickness) of Cr. A film to be used for the conductive films
54
is formed, for example, by depositing a Ta alloy layer (200 nm in thickness) on an underlying film (20 nm in thickness) made of Ti. The thickness of the magnetic film
53
and conductive film
54
(a thickness of as great as 300 nm in total) formed on the lower gap layer
52
has inevitably a variation.
FIG. 15A
shows a thin portion X and a thick portion Y of a laminated film of the magnet film
53
and conductive film
54
.
A variation in film thicknesses is generated because of different film forming rates in each area of a large area substrate. For example, a variation in film forming rates is suppressed by rotating a substrate relative to the target in a sputtering system. However, there is no film forming system for mass production which has the same film forming rate in the whole area of a large area substrate. A film thickness difference in the whole area of a large area substrate becomes larger as the thickness of a film becomes greater.
As shown in
FIG. 15B
, when the conductive film
54
and magnet film
53
in the thin portion X is trenched by milling and the low gap layer
52
is exposed, the lower gap layer
52
in the thick portion Y is not still exposed. In
FIG. 15B
, reference symbol
54
Miyazawa Kenichi
Sawada Shuichi
Wakui Yukio
Cao Allen
Dickstein Shapiro Morin & Oshinsky LLP.
Yamaha Corporation
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