Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-06-07
2004-01-20
Heinz, A. J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06680828
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetoresistive read (MR) sensors for reading signals recorded in a magnetic storage medium, and more particularly, this invention relates to improving the design of an MR sensor.
BACKGROUND OF THE INVENTION
Computer systems generally utilize 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 is 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 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 an 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 flowing through the MR element. Recorded data can be read from a magnetic storage medium because the external magnetic field from the recorded magnetic storage 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 separated by a layer of non-magnetic electrically conductive material are generally referred to as spin valve (SV) sensors manifesting the GMR effect (SV effect). In a spin valve 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., NiO, FeMn, PtMn) 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 recorded magnetic storage medium (the signal field).
In spin valve sensors, the spin valve effect 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 storage medium because the external magnetic field from the magnetic storage medium causes a change in the direction of magnetization in the free layer, which in turn causes a change in resistance of the spin valve sensor and a corresponding change in the sensed current or voltage.
FIG. 1
shows a typical spin valve sensor
100
(not drawn to scale) comprising end regions
104
and
106
separated by a central region
102
. The central region
102
has defined edges and the end regions are contiguous with and abut the edges of the central region. 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 the pinned layer
120
is fixed through exchange coupling with an antiferromagnetic (AFM) layer
125
. An underlayer
126
is positioned below the AFM layer
125
.
The underlayer
126
, or seed layer, is any layer deposited to modify the crystallographic texture or grain size of the subsequent layers, and may not be needed depending on the substrate. A variety of oxide and/or metal materials have been employed to construct underlayer
126
for improving the properties of spin valve sensors. Often, the underlayer
126
may be formed of tantalum (Ta), zirconium (Zr), hafnium (Hf), or yttrium (Y). Ideally, such layer comprises NiFeCr in order to further improve operational characteristics.
Free layer
110
, spacer
115
, pinned layer
120
, the AFM layer
125
, and the underlayer
126
are all formed in the central region
102
. Hard bias layers
130
and
135
formed in the end regions
104
and
106
, respectively, provide longitudinal bias for the free layer
110
. Leads
140
and
145
formed over hard bias layers
130
and
135
, respectively, provide electrical connections for the flow of the sensing current I
s
from a current source
160
to the MR sensor
100
. Sensor
170
is connected to leads
140
and
145
senses 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). IBM's U.S. Pat. No. 5,206,590 granted to Dieny et al. and incorporated herein by reference, discloses an MR sensor operating on the basis of the spin valve effect.
Another type of spin valve sensor is an anti-parallel (AP)-pinned spin valve sensor.
FIG. 2A
shows an exemplary AP-Pinned spin valve sensor
200
(not drawn to scale). Spin valve sensor
200
has end regions
202
and
204
separated from each other by a central region
206
. AP-pinned spin valve sensor
200
comprises a Ni—Fe free layer
225
separated from a laminated AP-pinned layer
210
by a copper spacer layer
220
. The magnetization of the laminated AP-pinned layer
210
is fixed by an AFM layer
208
, or pinning layer, which is made of NiO. Again, beneath the AFM layer
208
is an underlayer
209
.
The laminated AP-pinned layer
210
includes a first ferromagnetic layer
212
(PF
1
) of cobalt and a second ferromagnetic layer
216
(PF
2
) of cobalt separated from each other by a ruthenium (Ru) anti-parallel coupling layer
214
. The AMF layer
208
, AP-pinned layer
210
, copper spacer
220
, free layer
225
and a cap layer
230
are all formed sequentially in the central region
206
. Hard bias layers
235
and
240
, formed in end regions
202
and
204
, provide longitudinal biasing for the free layer
225
. Electrical leads
245
and
250
are also formed in end regions
202
and
204
, respectively, to provide electrical current from a current source (not shown) to the spin valve sensor
200
.
In use, the GMR effect depends on the angle between the magnetizations of the free and pinned layers. More specifically, the GMR effect is proportional to the cosine of the angle &bgr; between the magnetization vector of the pinned layer (MP) and the magnetization vector of the free layer (MF) (Note FIGS.
2
B and
2
C). In a spin valve sensor, the electron scattering and therefore the resistance is maximum when the magnetizations of the pinned and free layers are antiparallel, i.e., majority of the electrons are scattered as they try to cross the boundary between the MR layers. On the other hand, electron scattering and therefore the resistance is minimal when the magnetizations of the pinned and free layers are parallel; i.e., of electrons are not scattered as they try to cross the boundary between the MR layers.
In other words, there is a net change in resistance of a spin valve sensor between parallel and antiparallel magnetization orientations of the pinned and free layers. The GMR effect, i.e., the net change in resistance, exhibited by a typical prior art spin valve sensor is about 6% to 8%.
In order to effect the necessary pinning of at least one of the ferromagnetic layers to afford proper operation, it is necessary to include the hard bias layers in the con
Castro Angel
Heinz A. J.
International Business Machines - Corporation
Kotab Dominic M.
Silicon Valley IP Group PC
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