Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-09-18
2003-10-21
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324000
Reexamination Certificate
active
06636400
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to magnetic transducers for reading information signals from a magnetic medium and to methods of making the same.
2. Description of the Related Art
Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks are commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive read (MR) sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which the MR element resistance varies as the square of the cosine of the angle between the magnetization of the MR element and the direction of sense current flow through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers.
GMR sensors using only two layers of ferromagnetic material (e.g., nickel-iron, cobalt, or nickel-iron-cobalt) separated by a layer of nonmagnetic material (e.g., copper) are generally referred to as spin valve (SV) sensors manifesting the SV effect. In an SV sensor, one of the ferromagnetic layers, referred to as the pinned layer, has its magnetization typically pinned by exchange coupling with an antiferromagnetic (e.g., nickel-oxide or iron-manganese) layer.
The magnetization of the other ferromagnetic layer, referred to as the free layer, however, is not fixed and is free to rotate in response to the field from the information recorded on the magnetic medium (the signal field). In the SV sensors, SV resistance varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the free layer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in direction of magnetization in the free layer, which in turn causes a change in resistance of the SV sensor and a corresponding change in the sensed current or voltage. In addition to the magnetoresistive material, the MR sensor has conductive lead structures for connecting the MR sensor to a sensing means and a sense current source. Typically, a constant current is sent through the MR sensor through these leads and the voltage variations caused by the changing resistance are measured via these leads.
To illustrate,
FIG. 1
shows a prior art SV sensor
100
comprising end regions
104
and
106
separated by a central region
102
. A free layer (free ferromagnetic layer)
110
is separated from a pinned layer (pinned ferromagnetic layer)
120
by a non-magnetic, electrically-conducting spacer
115
. The magnetization of pinned layer
120
is fixed by an antiferromagnetic (AFM) layer
121
, which is formed on a gap layer
123
residing on a substrate
180
. Cap layer
108
, free layer
110
, spacer layer
115
, pinned layer
120
, and AFM layer
121
are all formed in central region
102
.
Conventionally, hard magnets are formed in end regions
104
and
106
in order to stabilize free layer
110
. These hard magnets are typically formed of a cobalt-based alloy which is sufficiently magnetized and perhaps shielded so that the magnetic fields of the media and/or the write head do not effect the magnetism of the hard magnets. To perform effectively, the hard magnets should have a high coercivity, a high MrT (magnetic remanence×thickness), and a high in-plane squareness on the magnetization curve. A preferred cobalt-based alloy for the hard magnet is cobalt-platinum-chromium.
Thus, as illustrated in
FIG. 1
, hard bias layers
130
and
135
are formed in end regions
104
and
106
, respectively, and provide longitudinal bias for free layer
110
. Leads
140
and
145
are formed over hard bias layers
130
and
135
, respectively. Hard bias layers
130
and
135
and lead layers
140
and
145
abut first and second side edges of the read sensor in a connection which is referred to in the art as a “contiguous junction”. A sensor tail at the contiguous junction is formed from materials such as tantalum, nickel-iron, cobalt-iron, copper, platinum-manganese and ruthenium.
Leads
140
and
145
provide electrical connections for the flow of the sensing current I@s from a current source
160
to the MR sensor
100
. Sensing means
170
connected to leads
140
and
145
sense the change in the resistance due to changes induced in the free layer
110
by the external magnetic field (e.g., field generated by a data bit stored on a disk). One material for constructing the leads in both the AMR sensors and the SV sensors is a highly conductive material, such as a metal.
As illustrated in the graph of
FIG. 2
, the preferred hard magnet material (i.e., cobalt-platinum-chromium) on gap alumina or glass exhibits favorable properties for sensor biasing purposes. As shown, however, these properties degrade when deposited on materials forming the sensor tail in the contiguous junction region (e.g., tantalum, nickel-iron, cobalt-iron, copper, ruthenium, etc.). Unfortunately, if the sensor tail is too long, magnetic instability will result.
Referring ahead to
FIG. 9
, a close-up view is shown of SV sensor
100
with a contiguous junction
906
and a sensor tail
908
. Sensor tail
908
exposes several layers and materials including cobalt-iron
920
, ruthenium
922
, cobalt-iron
924
, copper
926
, cobalt-iron
928
, nickel-iron
930
, tantalum
932
, as well as platinum-manganese, iridium-manganese, and nickel-oxide in AFM layer
121
and other materials of a sensor seed layer
918
.
FIG. 9
illustrates more particularly one approach that was taken to improve the hard magnet properties of hard bias layer
135
, which was to include a bi-layer seed layer
910
underneath it. Bi-layer seed layer
910
included a first seed layer
902
consisting of tantalum and a second seed layer
904
consisting of chromium.
Although improved hard magnet properties were exhibited with use of bi-layer seed layer
910
of
FIG. 9
, relatively thick seed layers (e.g., approximately 30 Angstroms of tantalum and 35 Angstroms of chromium) were required in order to achieve them. Such thick seed layers are undesirable because they increase the spacing between the hard magnet and the free layer, thereby decreasing the effectiveness of the hard magnet.
Accordingly, what are needed are methods and apparatus for improving hard magnet properties in magnetoresistive read heads that do not require the use of thick seed layers.
SUMMARY OF THE INVENTION
We have discovered that by utilizing a bi-layered seed layer consisting of oxidized tantalum and chromium over a contiguous junction region of a
Freitag James Mac
Pinarbasi Mustafa
Evans Jefferson
International Business Machines - Corporation
Oskorep John J.
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