Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-09-20
2004-05-04
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06731477
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates generally to spin-valve sensors for reading data from a magnetic media and, more particularly to novel structures and processes of spin-valve sensors, and to magnetic recording systems which incorporate such spin-valve sensors
2. The Relevant Art
Computer systems generally utilize auxiliary memory storage devices having magnetic media on which data can be written and from which data can be read for later uses. A direct access storage device, such as a disk drive, incorporating rotating magnetic disks, is commonly used for storing data in a magnetic form on the disk surfaces. Data are written on concentric, radially spaced tracks on the disk surfaces. Magnetic read/write heads are then used to read data from the tracks on the disk surfaces.
FIG. 1
shows one example of a disk drive
100
embodying the present invention. As shown in
FIG. 1
, the disk drive
100
comprises at least one rotatable magnetic disk
112
supported on a spindle
114
and rotated by a disk drive motor
118
. The magnetic medium on each magnetic disk
112
is in the form of concentric, annular data tracks (not shown).
At least one slider
113
is positioned on the disk
112
. Each slider
113
supports one or more magnetic read/write heads
121
incorporating one or more read sensors of the present invention. As the magnetic disk rotates, the slider
113
is moved radially in and out over the disk surface
122
so that the magnetic read/write heads
121
may access different portions of the magnetic disk
112
where desired data are written. Each slider
113
is attached to an actuator arm
119
by means of a suspension
115
. The suspension
115
provides a slight spring force which biases the slider
113
against the disk surface
122
. Each actuator arm
119
is attached to an actuator
127
. The actuator
127
as shown in
FIG. 1
may be a voice coil motor (VCM). The VCM comprises a coil movable within a fixed magnetic field, and the direction and speed of the coil movements are controlled by the motor current signals supplied by a controller
129
.
During operation of the disk storage system, the rotation of the magnetic disk
112
generates an air bearing between the surface of the slider
113
(which includes the surface of the head
121
) referred to as an air bearing surface (ABS), and the surface
122
of the disk
112
. This air bearing exerts an upward force or lift on the slider
113
, and thus counter-balances the slight spring force of the suspension
115
and supports the slider
113
off and slightly above the disk surface by a small, substantially constant spacing during normal operation.
The various components of the disk storage system are controlled in operation by control signals generated by the control unit
129
. The control signals include access control signals and internal clock signals. Typically, the control unit
129
comprises logic control circuits, storage means, and a microprocessor. The control unit
129
generates control signals to control various system operations such as drive motor control signals on a line
123
and head position and seek control signals on a line
128
. The control signals on the line
128
provide the desired current profiles to optimally move and position the slider
113
to the desired data track on the disk
112
. Read and write signals are communicated to and from the read/write heads
121
by means of a recording channel
125
. In the depicted embodiment, the read/write heads
121
incorporate the read sensor of the present invention.
Two types of read sensors have been extensively explored for magnetic recording at ultrahigh densities (≧20 Gb/in
2
). One is a current-in-plane (CIP) spin-valve sensor
200
in which a sense current
218
flows in a direction parallel to interfaces of a plurality of films, as depicted in FIG.
2
. The other is a current-perpendicular-to-plane (CPP) magnetic-tunnel-junction sensor
300
in which a sense current
318
flows in a direction perpendicular to the interfaces of a plurality of films. Greater details will be given to the CPP read sensor of the present invention below with reference to FIG.
3
.
In high capacity disk drives, a giant magnetoresistance (GMR) head carrying the CIP spin-valve sensor is now extensively used to read written data from the tracks on the disk surfaces. This CIP spin-valve sensor typically comprises two ferromagnetic films separated by an electrically conducting nonmagnetic film. Due to a GMR effect, the resistance of this CIP spin-valve 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 this CIP spin-valve sensor, one of the ferromagnetic films, referred to as a transverse pinned layer, typically has its magnetization pinned by exchange coupling with an antiferromagnetic film (e.g., Ni—Mn, Pt—Mn, Ir—Mn, etc.) used as a transverse pinning layer. The magnetization of the other ferromagnetic film, referred to as a sense or “free” layer, however, is not fixed and is free to rotate in response to the signal field from written data on the magnetic medium. In this CIP spin-valve sensor, the GMR effect varies as the cosine of the angle between the magnetizations of the sense and transverse pinned layers. The written data can be read from the magnetic medium because the external magnetic field from the written data causes a change in the direction of magnetization in of the sense layer, which in turn causes a change in the resistance of the CIP spin-valve sensor and a corresponding change in the sensed current or voltage. It should be noted that an anisotropy magnetoresistance (AMR) effect is also present in the sense layer and tends to reduce the overall GMR effect.
The CIP spin-valve sensor
200
is formed with deposition methods, such as DC magnetron sputtering, ion beam sputtering, etc, onto a wafer and is confined in a central region with two end regions (not shown) that abut the edges of the central region. Seed layers
202
are deposited on the wafer. These seed layers have a face-centered-cubic crystalline structure, which orients the crystalline structures of subsequently deposited films so that the closest packed planes of these films are parallel to the wafer surface. These closest packed planes are believed to play a crucial role in improving GMR properties of the CIP spin-valve sensor
200
.
A transverse pinning layer made of an antiferromagnetic film
204
is deposited above the seed layer
202
. A keeper layer made of a ferromagnetic film
206
is separated from a reference layer also made of a ferromagnetic film
210
by a ruthenium (Ru) spacer layer
208
. The magnetizations of the keeper layer
206
and the reference layer
210
(both of which are used as transverse pinned layers) are fixed through antiferromagnetic/ferromagnetic coupling between the transverse pinning layer
204
and the keeper layer
206
, and through ferromagnetic/ferromagnetic coupling across the Ru spacer layer
208
. The reference layer
210
is separated by a copper (Cu) spacer layer
212
from a sense layer also made of a ferromagnetic film
214
. The cap layer
216
is deposited above the sense layer
214
.
The other, more recently explored CPP magnetic-tunnel-junction sensor is shown in FIG.
3
. This CPP magnetic-tunnel-junction sensor
300
has a similar sensor structure as that of the CIP spin-valve sensor
200
. The primary difference between the two sensors is that the Cu spacer layer used in the CIP spin-valve sensor
200
is replaced by an Al—O barrier layer in the magnetic-tunnel-junction sensor
300
.
The disk drive industry has been engaged in an ongoing effort to increase the recording density of the disk drive, and correspondingly to increase the overall signal sensitivity to permit the currently used CIP spin-valve sensor in the disk drive to read smaller changes in magnetic fields. The major p
Lin Tsann
Mauri Daniele
Evans Jefferson
Hitachi Global Storage Technologies - Netherlands B.V.
Kunzler & Associates
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