Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-02-04
2004-05-11
Ometz, David (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S322000
Reexamination Certificate
active
06735058
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates generally to a current-perpendicular-to-plane (CPP) read head for magnetic recording and, in particular, to a CPP read head with an amorphous magnetic bottom shield layer and an amorphous nonmagnetic bottom lead layer.
2. The Relevant Art
Computer systems generally utilize auxiliary memory storage devices having magnetic read/write heads and a magnetic medium. Data can be written on the magnetic medium by the magnetic write head and can be read from the magnetic medium by the magnetic read head. A direct access storage device, such as a disk drive, incorporating rotating magnetic disks is commonly used for data in magnetic media on the disk surfaces. Data are written on concentric, radially spaced tracks on the magnetic media, and are read from the tracks on the magnetic media.
In high capacity disk drives, a current-in-plane (CIP) read head, in which a sense current flows in a direction parallel to film interfaces, is now extensively used to read data from the tracks on the magnetic media. This CIP read head comprises a giant magnetoresistance (GMR) sensor, a longitudinal bias (LB) stack, and conductor leads. The GMR sensor typically comprises two ferromagnetic films separated by an electrically conducting nonmagnetic film. The resistance of this GMR sensor varies as a function of the spin-dependent transmission of conduction electrons between the two ferromagnetic films and the accompanying spin-dependent scattering which takes place at interfaces of the ferromagnetic and nonmagnetic films.
In the conventional GMR sensor, one of the ferromagnetic films, referred to as a transverse pinned (or reference) layer, typically has its magnetization pinned by exchange coupling with an antiferromagnetic film, referred to as a transverse pinning layer. The magnetization of the other ferromagnetic film, referred to as a free (or sense) layer is not fixed, however, and is free to rotate in response to signal fields from the magnetic medium. In this GMR sensor, a GMR effect varies as the cosine of the angle between the magnetization of the reference layer and the magnetization of the sensing layer. Data can be read from the magnetic medium because the external magnetic field from the magnetic medium rotates the magnetization of the sense layer, which in turn changes the resistance of the GMR sensor and correspondingly changes a readout voltage.
FIG. 1
shows a typical prior art CIP read head
100
. A GMR sensor portion
101
is fabricated in a central region
102
, while LB (longitudinal bias) stacks and conductor lead layers
126
are fabricated in two end regions
103
and
105
. Various films of the GMR sensor are deposited on a bottom gap layer
118
, which is previously deposited on a bottom shield layer
120
. The bottom shield layer
120
is deposited on a wafer.
Photolithographic patterning and ion milling are applied to define the central region
102
and the two end regions
103
and
105
. In the GMR sensor
101
, a ferromagnetic sense layer
106
is separated from a ferromagnetic reference layer
108
by an electrically conducting nonmagnetic spacer layer
110
. The magnetization of the reference layer
108
is fixed through exchange coupling with an antiferromagnetic transverse pinning layer
114
. The depicted GMR sensor
101
also comprises seed layers
116
and cap layers
112
. The seed layers
116
facilitate the growth of the transverse pinning, reference, spacer and sense layers with preferred crystalline textures during depositions so that desired improved GMR properties are attained. The cap layer
112
protects the underlying films from oxidation during subsequent annealing operations.
The LB stacks and conducting lead layers
126
are deposited in the end regions
103
and
105
. The films deposited in the central and end regions are sandwiched between electrically insulating nonmagnetic films, one referred to as a bottom lead layer
118
and the other referred to as a top lead layer
124
.
To ensure proper sensor operation, exchange coupling between the transverse pinning layer
114
and the reference layer
108
must be sufficiently high to rigidly pin the magnetization of the reference layer
108
in a transverse direction perpendicular to the air bearing surface (the surface being viewed in FIG.
1
). An inadequate exchange coupling may cause canting of the magnetization of the reference layer from the preferred transverse direction, thus causing malfunction of the GMR sensor. This ferromagnetic/antiferromagnetic exchange coupling is typically characterized by a unidirectional anisotropy field (H
UA
) induced by this exchange coupling. This H
UA
field thus must be sufficiently high to rigidly pin the magnetization of the reference layer for proper sensor operation.
To ensure optimal biasing of GMR responses, another exchange coupling between the ferromagnetic reference layer and the ferromagnetic sense layers must be optimized in order to orient the magnetization of the sense layer in a longitudinal direction parallel to the air bearing surface. The ferromagnetic/ferromagnetic exchange coupling is typically characterized by a ferromagnetic field (H
F
) induced by the exchange coupling. The H
F
field thus must be very well controlled in order to balance two other fields in the sense layer, a demagnetizing field induced by the magnetization of the reference layer, and a current-induced field. A non-optimal or high H
F
may cause the magnetization of the sense layer to deviate from the preferred longitudinal direction, thus leading to non-linear, low GMR responses.
The disk drive industry has been engaged in an on-going effort to fabricate a narrower GMR sensor for increasing disk drive track density, and to sandwich the CIP read head into thinner gap layers for increasing linear density. It is crucial for the narrower GMR sensor to exhibit a higher GMR coefficient, and for the thinner gap layer to prevent current shorting between the CIP read head and shield layers. The GMR coefficient of the GMR sensor is expressed as &Dgr;R
G
/R
//
, where R
//
is a resistance measured when the magnetizations of the sense and reference layers are parallel to each other, and &Dgr;R
G
is the maximum giant magnetoresistance (GMR) measured when the magnetizations of the sense layer
106
and the reference layer
108
are antiparallel to each other. A higher GMR coefficients leads to higher signal sensitivity.
A new challenge will be posed when increasingly narrow GMR sensors cannot be made to exhibit higher GMR coefficients for further increasing the track density, and when increasingly thinner gap layers cannot be made to prevent current shorting between the CIP read head and shield layers. To solve these issues, a current-perpendicular-to-plane (CPP) read head, which also comprises layers of deposited films but in which the sense current flows in a direction perpendicular to the film interfaces, has been developed.
CPP read heads typically also comprise a GMR sensor, a LB stack, and conductor leads, but all these films are confined in the central region only. The conducting spacer layer separating the reference and sensing layers is, in the CPP read head, used as a conducting barrier layer across which the sense current flows. Typically, the GMR sensor of the CPP read head exhibits a GMR coefficient that is about 40% higher than a similar GMR sensor of the CIP read head. In addition, the GMR sensor can be replaced by a tunneling magnetoresistance (TMR) sensor by replacing the conducting barrier layer with an insulating barrier layer. Typically, the TMR sensor exhibits a tunneling magnetoresistance (TMR) coefficient higher than the GMR sensor of the CPP read head. The TMR coefficient of the TMR sensor is expressed as &Dgr;R
T
/R
//
, where R
//
is a resistance measured when the magnetizations of the sense and reference layers are parallel to each other, and &Dgr;R
T
is the maximum tunneling magnetoresistance (TMR) measured when the magnetizations of the sense and reference layers are ant
Lin Tsann
Mauri Daniele
International Business Machines - Corporation
Kunzler & Associates
Ometz David
LandOfFree
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