Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-02-04
2002-07-09
Hudspeth, David (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06417999
ABSTRACT:
BACKGROUND
Computer storage devices, such as disk drives, use read/write heads to store and retrieve data. A write head stores data by utilizing magnetic flux to set the magnetic moment of a particular area on a magnetic media. The state of the magnetic moment is later read by a read head which senses the magnetic fields.
Conventional thin film read heads employ magnetoresistive material, generally formed in a layered structure of magnetoresistive and non-magnetoresistive materials, to detect the magnetic moments of the data bits on the media. The data bits are positioned in concentric tracks on the storage media. Decreasing the width of these tracks allows an increase in the storage capacity of the media (more tracks per inch). However, the width of the tracks are limited by how narrow both the read and write reads can be made.
The width of conventional read heads have been limited by their method of fabrication. One such method is shown in
FIGS. 1
a-e.
The first step of this process is shown in
FIG. 1
a
and involves depositing a sensor material
20
on top of a layer of alumina
10
. The senor material is typically a multi-layered anisotopic magneto-resistive (AMR) or spin valve material.
Next, as shown in
FIG. 1
b
, a bi-layer photoresist layer
30
is applied directly on top of the sensor material
20
. The bi-layer photoresist
30
has a soft base layer
32
and a hardened overhanging image layer
34
. The bi-layer photoresist
30
is positioned directly above the desired position of the sensor element
22
(not shown). As will be further explained, the width of the sensor
22
, and thus of the readable track, is limited by the height h
b
of the base layer
32
of the photoresist
30
.
FIG. 1
c
shows the next step of etching the sensor material
20
. During this step sensor material
20
on either side of the sensor element
22
is etched away by an ion beam etch. As can be seen, the ion beam etch removes the sensor material
20
which is not under or immediately adjacent the bi-layer photoresist
30
. During this step the shadow of the overhang
36
of the image layer
34
of the photoresist is used with the ion beam set at an angle to define the sensor element
22
with slanted sides
24
. Some of the etched sensor material
20
′ will deposit itself over the photoresist
30
.
In the next step, a hard bias
40
and lead material
50
are deposited. This is shown in
FIG. 1
d
. The hard bias
40
is deposited over the alumina
10
arid the sides
24
of the sensor
22
up to near the base layer
32
of the photoresist
30
. After the hard bias
40
is deposited, the lead material
50
is deposited over the hard bias
40
and up against the side walls
33
of the base layer
32
.
The last step of this process is shown in
FIG. 1
e
. During this step the bi-layer photoresist
30
is lifted off (removed) from the top of the sensor element
22
. The resulting structure is a read sensor which has the sensor element
22
biased by the hard bias
40
and which a sensing current can be passed through the sensor element
22
by way of the leads
50
.
One problem with this existing method of fabrication is that due to a geometric limitation inherent in a bi-layer overhang structure, the width of the sensor cannot be made less than a certain minimum amount. This limitation in turn limits the minimum width of the data track used. Specifically, the problem is that the bi-layer photoresist must be kept above a certain minimum to avoid fencing which can cause shorting. Fencing is a build-up of material ejected during the etch of the sensor material
20
along the side walls
33
of the photoresist
30
. When fencing occurs the later removal of the photoresist will leave a spike of ejected material. This spike of material can contact other elements of the device and cause shorting.
Fencing can be avoided by maintaining an aspect ratio (the width w
o
of the overhang
36
relative to the height h
b
of the base layer
32
) of at least 2. This allows the ejected material sufficient room to collect under the overhang
36
and not on the sides
33
which would cause fencing. Another geometric limitation is due to the thickness h
b
of the base layer
32
. The base layer
32
must be thick enough to avoid the ejected material
20
′ and the later deposited material
40
′ and
50
′, which collect on the photoresist
30
, from extending far enough from the photoresist
30
to come in contact with the sensor
22
. Clearly, with a bridge of material between the photoresist and the sensor, the hard bias
40
and lead material
50
will be improperly deposited. As such, to avoid such material bridging, it has been found that the base layer
32
must be thicker than a minimum of about 0.1 &mgr;m.
Therefore, because of the necessary minimum thickness of the base layer h
b
(about 0.1 &mgr;m) and the required minimum aspect ratio of the overhang
36
(about twice the thickness of the base layer, w
0
about 0.2 &mgr;m), the photoresist
30
typically cannot be narrower then about 0.5-0.6 &mgr;m. Thus, the minimum track widths of the media used with read sensors made by this conventional method are limited to a minimum of about 0.5-0.6 &mgr;m.
Additional problems with the conventional method include low film density and poor composition control of the multi-element materials deposited to create the read head. With the existing method, the hard bias material is sputter deposited over the sensor
22
. The shadowing effect of the overhang
36
causes an uneven composition as the lighter mass element, such as cobalt, which can be deposited at higher angles (relative to the vertical), will be deposited in greater amounts under the overhang
36
. The area under the overhang
36
will likewise have lesser amounts of the heavier elements such as platinum and tantalum. As a result, near the sensor junction there will exist low film density and varied material composition. Which in turn results in poor magnetic properties (e.g. H
c
, and M
r
T) of the hard bias layer.
Therefore, a method is sought which will allow fabrication of apparatuses with significantly narrower read sensors, such that an increase in data storage can be achieved through the use of narrower data tracks. The method must fabricate the sensor in a manner which will avoid fencing and which will not result in low film density and poor composition control. Also, the method must perform these tasks while minimizing the cost and time of fabrication.
SUMMARY
The method of the present invention is embodied in a method for fabricating a magnetoresistive head structure with a narrow read sensor.
In at least one embodiment of the method, the steps include obtaining a lead and magnetic bias layer, applying a photoresist layer over the lead and magnetic bias layer and about a desired position of a sensor (such that the desired position of the sensor is substantially free of the photoresist layer), etching the lead and magnetic bias material substantially at the desired position of the sensor, depositing a sensor at the desired position of the sensor, and removing the photoresist.
The step of obtaining a lead and magnetic bias layer can include depositing a lead layer and depositing a magnetic bias layer over the lead layer. It is preferred that the lead layer is deposited as a layering which includes a first tantalum layer about 50 Å thick, a gold layer about 300 Å thick positioned over the first tantalum layer, and a second tantalum layer about 50 Å thick positioned over the gold layer. The magnetic bias layer can be a hard bias layer or an exchange layer. It is preferred that the hard bias layer is deposited as a layering which includes an underlayer of chromium about 50-200 Å thick and a permanent magnet layer over the underlayer of cobalt chromium and platinum about 500 Å thick.
With the magnetic bias layer being an exchange layer, the method further includes a step of annealing to set the exchange. This step occurs after the step of obtaining the lead and magnetic bias layers. It is preferre
Barr Ronald A.
Knapp Kenneth E.
Lai Chih-Huang
Rottmayer Robert
Carr & Ferrell LLP
Castro Angel
Read-Rite Corporation
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