Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2002-06-13
2003-11-18
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Core
C360S317000
Reexamination Certificate
active
06650503
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to magnetic disk storage systems, and more particularly to write heads having low height, high moment pedestals.
BACKGROUND OF THE INVENTION
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
, one or more magnetic disks
16
, supported for rotation by a drive spindle
13
of motor
14
, and an actuator
18
including at least one arm
20
, the actuator being attached to an actuator spindle
21
. Suspensions
22
are coupled to the ends of the arms
20
, and each suspension supports at its distal end a read/write head or transducer
24
. The head
24
(which will be described in greater detail with reference to
FIGS. 2A and 2B
) 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 the surface of the magnetic disk
16
, or, as 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. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 2A
shows the distal end of the head
24
having a write element
26
. The write element
26
is shown enlarged and with portions exposed for clarity. The write element
26
includes a magnetic yoke
28
having an electrically conductive coil
30
passing therethrough.
The write element
26
can be better understood with reference to
FIG. 2B
, which shows the write element
26
and an integral read element
32
in cross section. The head
24
includes a substrate
34
above which the read element
32
and the write element
26
are disposed. An edge of the read element
32
and of the write element
26
also define an air bearing surface ABS, in a plane
36
, which can be aligned to face the surface of the magnetic disk
16
(see FIGS.
1
A and
1
B). The read element
32
includes a first shield
38
, a second shield
40
, and a read sensor
42
that is located within a dielectric medium
44
between the first shield
38
and the second shield
40
. The most common type of read sensor
42
used in the read/write head
24
is the magnetoresistive (AMR or GMR) sensor, which is used to detect magnetic field signal changes in a magnetic medium by means of changes in the resistance of the read sensor imparted from the changing magnitude and direction of the magnetic field being sensed.
The write element
26
is typically an inductive write element that includes the second shield
40
(which functions as a first pole for the write element) and a second pole
46
disposed above the first pole
40
. Since the present invention focuses on the write element
26
, the second shield/first pole
40
will hereafter be referred to as the “first pole”. The first pole
40
and the second pole
46
contact one another at a backgap portion
48
, with these three elements collectively forming the yoke
28
. The combination of a first pole tip portion and a second pole tip portion near the ABS are sometimes referred to as the yoke tip portion
50
. A write gap
52
is formed between the first and second poles
40
and
46
in the yoke tip portion
50
. The write gap
52
is filled with a non-magnetic, electrically insulating material that forms a write gap material layer
54
. This non-magnetic material can be either integral with (as is shown here) or separate from a first insulation layer
56
that lies upon the first pole
40
and extends from the yoke tip portion
46
to the backgap portion
40
. The conductive coil
30
, shown in cross section, passes through the yoke
28
, sitting upon the write gap material
54
. A second insulation layer
58
covers the coil and electrically insulates it from the second pole
46
.
An inductive write head such as that shown in
FIGS. 2A and 2B
operates by passing a writing current through the conductive coil
30
. Because of the magnetic properties of the yoke
28
, a magnetic flux is induced in the first and second poles
40
and
46
by write currents passed through the coil
30
. The write gap
52
allows the magnetic flux to fringe out from the yoke
28
(thus forming a fringing gap field) and to cross a magnetic recording medium that is placed near the ABS.
With reference to
FIG. 2C
, a critical parameter of a magnetic write element is the trackwidth of the write element, which defines track density. For example, a narrower trackwidth can result in a higher magnetic recording density. The trackwidth is defined by the geometries in the yoke tip portion at the ABS. In some newer designs a pedestal
60
is constructed of a high magnetic moment material (high B
sat
), having a width W
3
. The high B
sat
pedestal promotes concentration of magnetic flux in the yoke tip region
50
of the write element
26
. As can be seen from this view, the first and second poles
40
and
46
can have different widths W
2
and W
1
respectively in the yoke tip portion
50
. The pedestal has a width W
3
, which in some implementations can have the same width as that of the second pole W
1
, as when the pedestal is created by a self aligning process.
With reference to
FIG. 2B
, the fringing gap field of the write element can be further affected by the positioning of the zero throat level ZT. ZT is defined as the distance from the ABS to the first divergence between the first and second pole, and it can be defined by either the first or second pole
40
,
46
depending upon which has the shorter pole tip portion. If the first pole
40
includes a pedestal
60
, then ZT is usually defined by the pedestal depth. The pedestal provides a well defined ZT. In order to prevent flux leakage from the second pole
46
into the back portions of the first pole
40
, it is desirable to provide a zero throat level in a well defined plane which is parallel to the plane of the ABS. Thus, accurate definition of the trackwidth, and zero throat is critical during the fabrication of the write element.
The performance of the write element is further dependent upon the properties of the magnetic materials used in fabricating the poles of the write element. In order to achieve greater overwrite performance, magnetic materials having a high saturation magnetic flux density B
sat
are preferred. A common material employed in forming the poles is high Fe content (55 at % Fe) NiFe alloy having a B
sat
of about 16 kG. However, high Fe content NiFe alloy has a high magnetostriction constant &lgr;s (on the order of 10
−5
) which causes undesirable domain formation in the poles. It is known that the domain wall motion in the writer is directly related to the increase in popcorn noise in the read element, especially when the motion occurs in the first pole, which also serves as a shield for the read element.
A reduction in popcorn noise in the read element can be achieved through the use of soft magnetic materials, (i.e. materials having a low magnetostriction constant) in the fabrication of the first pole
40
. However, such materials generally have limited B
sat
. In order to promote concentration of magnetic flux density in the yoke tip region, a high B
sat
material is used to form the pedestal
60
.
The size and shape of the pedestal has a dramatic affect on the flow of magnetic flux in the yoke tip region
50
. For example, the abrupt angle between the pedestal
60
and the rest of the first pole
40
inhibits flux flow and can lead to choking or saturation of flux. In addition, a thick pedestal (i.e. in the direction from the first pole
40
to the write gap
52
) causes further choking of the flux and also leads to po
Barr Ron
Chen Yingjian
Shi Stone
Sin Kyusik
Tong Hua-Ching
Evans Jefferson
Read-Rite Corporation
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