Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2000-05-17
2003-04-22
Letscher, George J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Core
C360S317000
Reexamination Certificate
active
06552874
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to magnetic write transducers, and more particularly to magnetic write transducers for achieving optimized erase band widths and methods of fabricating the same.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatus such as computers. In
FIGS. 1A and 1B
, a magnetic disk data storage system
10
of the prior art includes a sealed enclosure
12
, a disk drive motor
14
, a magnetic disk
16
supported for rotation by a drive spindle Si of motor
14
, an actuator
18
and an arm
20
attached to an actuator spindle S
2
of actuator
18
. A suspension
22
is coupled at one end to the arm
20
, and at its other end to a read/write head or transducer
24
. The transducer
24
(which will be described in greater detail with reference to
FIG. 2A
) typically includes an inductive write element with a sensor read element. As the motor
14
rotates the magnetic disk
16
, as indicated by the arrow R, an air bearing is formed under the transducer
24
causing it to lift slightly off of the surface of the magnetic disk
16
, or, as it is termed in the art, to “fly” above the magnetic disk
16
. Alternatively, some transducers, known as “contact heads”, ride on the disk surface. Various magnetic “tracks” of information can be written to and/or read from the magnetic disk
16
as the actuator
18
causes the transducer
24
to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 2A
depicts a magnetic read/write head
24
including a substrate
25
above which a read element
26
and a write element
28
are disposed. Edges of the read element
26
and write element
28
also define an air bearing surface (ABS), in a plane
29
, which can be aligned to face the surface of the magnetic disk
16
(see FIGS.
1
A and
1
B). The read element
26
includes a first shield
30
, an intermediate layer
32
which functions as a second shield, and a read sensor
34
that is located within a dielectric medium
35
between the first shield
30
and the second shield
32
. The most common type of read sensor
34
used in the read/write head
24
is the magnetoresistive (AMR or GMR) sensor, which is used to detect magnetic field signals from a magnetic medium through changing resistance in the read sensor.
The write element
28
is typically an inductive write element which includes the intermediate layer
32
, which functions as a first pole, and a second pole
38
disposed above the first pole
32
. The first pole
32
and the second pole
38
are attached to each other in a backgap region (not shown), with these three elements collectively forming a yoke generally designated
41
. The combination of a first pole tip portion
43
and a second pole tip portion
45
near the ABS are sometimes referred to as the yoke tip portion
46
. The write gap
36
is filled with a non-magnetic, electrically insulating material that forms a write gap material layer
37
. This non-magnetic material can be either integral with (as is shown here) or separate from a first insulation layer
47
that lies below the second pole
38
and extends from the yoke tip portion
46
to the backgap region.
Also included in write element
28
is a conductive coil generally designated
48
, formed of multiple windings
49
. The conductive coil
48
is positioned within a coil insulation layer
50
that lies above the first insulation layer
47
. The first insulation layer
47
thereby electrically insulates the windings
49
from each other and from the second pole
38
.
An inductive write head such as that shown in
FIG. 2A
operates by passing a writing current through the conductive coil layer
48
. Due to the magnetic properties of the yoke
41
, a magnetic flux is induced in the first and second poles
32
and
38
by write currents passed through the coil layer
48
. A magnetic field formed at the write gap
36
allows the magnetic flux to cross a magnetic recording medium that is placed near the ABS.
A critical parameter of a magnetic write element is the magnetic write width or trackwidth of the write element which defines track density. Generally, a narrower trackwidth results in a higher magnetic recording density. The trackwidth is defined by the geometries in the yoke tip portion
46
at the ABS. These geominetries can be better understood with reference to FIG.
10
. As can be seen from this view, the first pole
72
and the second pole tip portion
79
can have different widths W
1
and W
2
respectively in the yoke tip portion
46
(see FIG.
2
A). In the shown configuration, the trackwidth of the write element
28
is defined by the width of the second pole tip portion
79
at the ABS.
When a track of information is written on the magnetic medium, the magnetic write width is determined by the width of the magnetic flux generated at the gap
36
(the “write bubble”) which in turn is determined by the strength of the field between the poles of the write element. To achieve rotation of the transitions in the media, the field strength of the write bubble between the poles must correspond to the coercivity of the media. A field having such strength is schematically represented as a dashed flux line
56
in FIG.
3
. In fringe areas of the write bubble, such as those designated at
58
, a fringing field may be of insufficient strength to rotate the transitions, and partial rotation may be achieved resulting in re-magnetization of the medium close to the track edges. It has been found that at both sides of a data track, an erase band exists in a region where the magnetic field and field gradient are insufficient to write a well defined transition in the magnetic medium. As track pitch is reduced in order to increase track density, the erase bands become an increasingly significant portion of the track pitch and contribute to track edge noise which degrades the signal output.
The configuration shown in
FIG. 10
generates a significantly large fringing field during recording which is caused by flux leakage from the second pole tip portion
79
to the parts of the first pole
72
beyond the region defined by the width W
2
of the second pole tip portion
79
. The erase bands generated by this configuration have very wide widths and thereby limit the extent to which trackwidths can be narrowed.
A method for limiting erase band widths is shown schematically in
FIG. 2B
in which a pedestal
39
having the same width as the width W
2
of, the second pole tip portion
45
is formed on top of the first pole
32
. The shown configuration, called a self-aligned structure, limits the fringing field to the extent that the width of the pedestal
39
is substantially equal to the width W
2
of the second pole tip portion
45
and the pedestal
39
and second pole tip portion
45
are aligned. Misalignment can lead to erase bands of unequal widths or an erase band having too great a width.
Of additional importance in high density applications where tracks of information are written closely together is the off-track performance of the magnetic recording system. The off-track performance relates to the ability of the read element to accurately read the information stored in the write tracks and is measured by the offtrack capability (OTC). One approach employed in the prior art to improve the OTC of a magnetic recording system involves using a write element having a wide width and a read element having a comparatively narrow width. In this arrangement the demands placed upon the servo controlling the read element are relaxed as the read element can move from the center of the track before encountering the erase bands.
Another way to increase the OTC of a magnetic recording system is to increase the erase band width which has a practical limit beyond which the OTC fails. A very wide erase band can be a disadvantage when adjacent tracks are written close together as the magnetic write width is decreased. Wide erase bands degrade signal
Apparao Renuka
Chen Wenjie
Crue Bill
Carr & Ferrell LLP
Letscher George J.
Read-Rite Corporation
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