Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-08-10
2003-01-28
Tupper, Robert S. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06512661
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic recording technology, and more particularly to a giant magnetoresistive read head which is capable of being used at high magnetic recording densities and which has reduced noise.
BACKGROUND OF THE INVENTION
Magnetoresistive (“MR”) heads are currently used in read heads or for reading in a composite head.
FIGS. 1A and 1B
depict a conventional MR head
10
which uses a MR sensor
30
, preferably a spin valve.
FIG. 1A
depicts a side view of the conventional MR head
10
. For clarity, only a portion of the conventional MR head
10
is depicted. Also shown is the surface of the recording media
40
. Thus, the air-bearing surface (ABS) is shown. Depicted in
FIG. 1A
are the first shield
14
, the second shield
22
, the MR sensor
30
and the leads
19
a
and
19
b.
Also shown is the height of the MR sensor
30
, also known as the stripe height (h).
FIG. 1B
depicts the conventional MR head
10
as viewed from the ABS. The MR head
10
includes a first shield
14
formed on a substrate
12
. The MR head
10
also includes a first gap
16
separating a MR sensor
30
from the first shield
14
. The MR head
10
also includes a pair of hard bias layers
18
a
and
18
b.
The hard bias layers
18
a
and
18
b
magnetically bias layers in the MR element
30
. The MR head
10
also includes lead layers
19
a
and
19
b,
which conduct current to and from the MR sensor
30
. A second gap
20
separates the MR sensor
30
from a second shield
22
. When brought in proximity to a recording media (not shown), the MR head
10
reads data based on a change in the resistance of the MR sensor
30
due to the field of the recording media. Thus, the current through the MR sensor flows across the ABS, for example from left to right, or vice-versa, in both
FIGS. 1A and 1B
.
Giant magnetoresistance (“GMR”) has been found to provide a higher signal for a given magnetic field. Thus, GMR is increasingly used as a mechanism for conventional higher density MR sensors
30
. One MR sensor
30
which utilizes GMR to sense the magnetization stored in recording media is a conventional spin valve.
FIG. 1C
depicts one conventional GMR sensor
30
, a conventional spin valve. The conventional GMR sensor
30
typically includes a seed layer
31
, a pinning layer that is typically an antiferromagnetic (“AFM”) layer
32
, a pinned layer
34
, a spacer layer
36
, a free layer
38
, and a capping layer
39
. The seed layer is used to ensure that the material used for the AFM layer
32
has the appropriate crystal structure and is antiferromagnetic in nature. The spacer layer
36
is a nonmagnetic metal, such as copper. The pinned layer
34
and the free layer
38
are magnetic layers, such as CoFe. The magnetization of the pinned layer
34
is pinned in place due to an exchange coupling between the AFM layer
32
and the pinned layer
34
. The magnetization of the free layer
38
is free to rotate in response to the magnetic field of the recording media
40
. However, note that other conventional GMR sensors, such as conventional dual spin valves, conventional synthetic spin valves, and spin filters, are also used.
More recently, another configuration for conventional MR heads has been disclosed.
FIG. 2
depicts a side view of a conventional MR head
50
in which current is driven perpendicular to the ABS. Also depicted is the recording media
40
. The MR head
50
utilizes the MR sensor
30
. Thus, the MR head
50
typically uses some sort of spin valve as the MR sensor
30
. However, the MR head
50
could use another type of MR sensor (not shown), such as an AMR sensor. Regardless of the type of MR sensor used, the MR head
50
uses a vertical sensor, through which current is driven perpendicular to the ABS. As viewed from the ABS, the MR sensor
30
would generally appear as shown in FIG.
1
C.
Referring back to
FIG. 2
, the MR head
50
also includes the first shield
52
, the first gap
54
, a conductor
56
that connects the MR sensor
30
to the first shield
52
, the lead
58
, the second gap
60
and the second shield
62
. Also shown is the stripe height of the MR sensor
30
, h, and the read gap
64
. Current is driven through the MR sensor
30
between the first shield
52
and the lead
58
. Thus, current is either parallel or antiparallel to the current direction
66
depicted in FIG.
2
.
The conventional MR head
50
has advantages over the conventional MR head
10
. In particular, the conventional MR head
50
may be more suitable for reading higher areal density media because of the direction of current flow through the MR head
50
. The desired resistance of the MR sensor
30
can be provided in the MR head
50
by adjusting the stripe height, h. At the same time, the width of the MR sensor
30
, as seen from the air-bearing surface (left to right in FIG.
1
B), can be made small enough to be used with recording media
40
having a smaller track width. Thus, the conventional MR head
50
is of interest for high areal density recording applications.
Although the conventional MR head
50
functions, one of ordinary skill in the art will readily realize that there are drawbacks to the conventional MR head
50
. Referring to
FIGS. 1A-C
and
2
, the MR sensor
30
of the conventional MR head
50
is subject to noise due to domain wall motion. In contrast to the MR head
10
, the MR sensor
30
does not magnetically bias the free layer
38
of the MR sensor
30
. The materials used to magnetically bias the free layer
38
in the MR head
10
are typically conductive hard magnetic layers
18
a
and
18
b
that are placed adjacent to the free layer
38
as viewed from the ABS. These hard magnetic layers are typically materials such as CoCrPt and CoPt, which are conductive. However, if such hard magnetic layers
18
a
and
18
b
are placed at the sides of the free layer
38
in the conventional MR head
50
, the hard magnetic layers
18
a
and
18
b
will shunt current away from the MR sensor
30
. The signal from the MR sensor
30
would thus be lowered, which is undesirable.
In order to prevent the shunting of current away from the MR sensor
30
in the conventional MR head
50
, no hard magnetic layers are used. However, this results in a free layer
38
of the MR sensor
30
that may have multiple domains. When the free layer
38
is subject to an external field, for example from the recording media
40
, the magnetization of the free layer
38
changes in response to the external field. The walls between the domains in the free layer
38
move to change the magnetization of the free layer
38
. The domains which form and the ways in which the domain walls move is not repeatable. Thus, the formation of a multi-domain state in the free layer
38
leads to domain wall movement, thereby producing non-linearity and noise in the sensor signal. Such non-linearity and noise are undesirable in the MR head
50
during operation.
There is an additional limiting factor to the height of the conventional MR sensor
30
. As magnetic flux travels up the conventional MR sensor
30
, away from the recording media
40
, flux leaks out of the conventional MR sensor
30
. The shield
14
and
22
and the shields
52
and
62
are significantly larger than the conventional MR sensor
30
. Thus, magnetic flux leaks out of the conventional MR sensor
30
and into the shields
14
,
22
,
52
and
62
. The height at which virtually all of the magnetic flux has leaked out of the conventional MR sensor
30
is defined as the flux decay length. If the conventional MR sensor
30
is made longer than the flux decay length, the additional height of the conventional MR sensor
30
will contribute to the resistance in the MR head
50
, but not to the magnetoresistance. Any additional height of the conventional MR sensor
30
will, therefore, be a source of parasitic resistance and thus be wasted.
Accordingly, what is needed is a system and method for providing a MR head which is capable of reading information stored on magnetic recording media at higher den
Read-Rite Corporation
Sawyer Law Group LLP
Tupper Robert S.
Watko Julie Anne
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