Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-10-12
2003-07-29
Cao, Allen (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06600636
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to computer disk drive transducer heads. In particular, the present invention relates to transducer heads having an inductive write head and a magnetoresistive or a giant magnetoresistive read head.
BACKGROUND OF THE INVENTION
Computer disk drives store information on magnetic disks. Typically, the information is stored on each disk in concentric tracks, divided into sectors. Information is written to and read from a disk by a transducer head, mounted on an actuator arm capable of moving the transducer head radially over the disk. Accordingly, the movement of the actuator arm allows the transducer head to access different tracks. The disk is rotated by a spindle motor at a high speed, allowing the transducer head to access different sectors on the disk.
A typical computer disk drive is illustrated in FIG.
1
. The disk drive, generally identified by reference numeral
20
includes a base
24
and magnetic disks
28
(only one of which is shown in FIG.
1
). The magnetic disks
28
are interconnected to the base
24
by a spindle motor (not shown) mounted within or beneath the hub
32
, such that the disks
28
can be rotated relative to the base
24
Actuator arm assemblies
36
(only one of which is shown in
FIG. 1
) are interconnected to the base
24
by bearings
40
, such that they can be moved radially with respect to the magnetic disks
28
. The actuator arm assemblies
36
include transducer heads
44
(only one of which is illustrated in
FIG. 1
) at a first end, to address each of the surfaces of the magnetic disks
28
. A voice coil motor
48
pivots the actuator arm assemblies
36
about the bearings
40
, to radially position the transducer heads
44
across the surfaces of the magnetic disks
28
. The voice coil motor
48
is operated by a controller
52
that is in turn operatively connected to a host computer (not shown). By changing the radial position of the transducer heads
44
with respect to the magnetic disks
28
, the transducer heads
44
can access different data tracks or cylinders
56
on the magnetic disks
28
.
A typical transducer head contains functionally separate write and read heads, or elements, that are integrated into a unitary, thin film structure. A conventional thin film transducer head
100
is illustrated in
FIGS. 2 and 3
, and generally includes a write head
104
and a read head
108
.
The write head
104
is usually what is known as an inductive head. Where such heads are constructed from ferrite material, they are known as ferrite heads. The write head
104
generally includes a yoke of magnetically conductive material formed from a write pole
112
and a shared shield
116
. A coil of electrically conductive wire
118
is wrapped about a portion of the yoke, and the ends of that coil are connected to a current source (not shown). During a write operation, current is introduced to the coil in a first direction. The electrical current through the coil produces a magnetic field within the yoke. At a gap
120
formed between an end of the write pole
112
and an end of the shared shield
116
, the magnetic field spreads out because the magnetic permeability of the gap is less than that of the yoke itself. The gap
120
is positioned so that it is in close proximity to the magnetic disk, allowing some of the magnetic field to pass through the disk and magnetize a portion of the disk in a particular direction. In a typical disk drive for use in a digital computer, a “one” is coded by reversing the direction in which the disk is magnetized from one portion of a track to the next. This is done by reversing the direction of the current in the coil. A zero is indicated by the absence of a change in magnetic polarity. Of course, these conventions could be reversed.
The read head
108
in a disk drive operates by sensing the magnetic flux transistions encoded in the disk by the write operation. One method of sensing such transistions is with a magnetoresistive head. Such a head is comprised of material that changes its electrical resistance when it is exposed to a magnetic field. Magnetoresistive heads have come into wide use in disk drive systems because they are capable of providing high signal output. High signal output is important, because the magnetic fields produced in the disks by the write operation are very small. In addition, the high signal output of the magnetoresistive head allows the data on the disk to be densely packed, allowing the disk drive to have a high storage capacity.
Magnetoresistive read heads generally include a strip of magnetoresistive material
124
held between two magnetic shields. In the conventional transducer head illustrated in
FIGS. 2 and 3
, the magnetic shields are formed from the shared shield
116
and a read shield
128
. Each end of the strip of magnetoresistive material
124
is connected to a conductor (not shown). The conductors are in turn connected to a current source (not shown). Because the electrical resistance of the magnetoresistive material varies with the strength and direction of an applied magnetic field, magnetic flux transistions result in changes in the voltage drop across the magnetoresistive strip. These changes in the voltage drop are sensed and then converted into a digital signal for use by the host computer.
In order to sense the transistions between the small magnetic fields and thus retrieve data from the magnetic disk, the magnetoresistive read head
108
is held in close proximity to the track containing the desired information. The disk
28
is rotated under the head
44
, and flux transitions read by the head
44
are interpreted as a binary “one”, as described above. The magnetic shields on either side of the magnetoresistive material
124
limit the effect of magnetic flux transitions adjacent to or in the proximity of the precise area of the track from which information is to be retrieved. Often, one pole of the inductive write head also serves as part of the shield. This shared shield is typically about 1-3 &mgr;m thick.
In
FIG. 3
, a typical transducer head
100
having a write head
104
and a read head
108
is illustrated in plan view. As described above, the write head
104
generally includes a write pole
112
and a shared shield or pole
116
with a write gap
120
therebetween. The read head
108
generally includes the shared shield
116
, a magnetoresistive element
124
, and a read shield
128
. Such heads are typically manufactured using thin film layering techniques.
The strength of the magnetic field produced in the read head
108
from the data written to the storage disk
28
is small (from 10-50 oersteds). However, while writing the magnetic field that must be produced by the write head to encode the data by magnetizing the disk is relatively large (as much as several thousand oersteds). The strong magnetic field produced by the inductive write head during a write operation affects the operation of the magnetoresistive read head. The strength of the magnetic field produced in the read head
108
during a write operation can be as strong as several hundred oersteds. This strong magnetic field is believed to, at times, force an unstable magnetic domain state in the shield and/or permanent magnet structures of the read head, since conventional read heads are only designed to sense magnetic fields of about 50 oersteds. Accordingly, following a write operation, the magnetoresistive head may undergo write induced instabilities when the magnetic domain state of the shields and/or permanent magnet structures revert to their normal state. When the reversion occurs, the read head cannot reliably read information from the storage disk.
Because it is necessary to maintain the position of the transducer head over the disk with high accuracy, the transducer head must be able to read servo sector information embedded periodically about the disk both during, and following, write operations. Where the read transducer is unable to confirm the correct position of the transducer head relative to the storage disk
Himle Jenny
Liikanen Bruce
Schemmel Terry
Cao Allen
Maxtor Corporation
Sheridan & Ross P.C.
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