Dynamic magnetic information storage or retrieval – Head – Gap spacer
Reexamination Certificate
2002-05-15
2004-12-21
Klimowicz, William (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Gap spacer
C360S125330, C360S121000
Reexamination Certificate
active
06833976
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to a thin film inductive write head for magnetic recording, and more particularly to a thin film write head having an improved write gap.
BACKGROUND OF THE INVENTION
In a magnetic recording disk drive, data is written by thin film magnetic transducers called “write heads” that are supported over the surface of the disk while the disk is rotated at high speed. Each write head is located on the trailing surface of a slider that is supported by a thin cushion of air (an “air bearing”) produced by the disk's high rotational speed.
A prior art thin film inductive write head is shown in the side sectional view of FIG.
1
and the partial end view, as seen from the disk, of FIG.
2
.
FIG. 1
also depicts the pole tips facing a magnetic recording disk that has a magnetic layer ML on the disk substrate SB and a protective overcoat OC on the ML. The distance D from the ends of the pole tips to the middle of the ML is referred to as the magnetic spacing. The write head includes a coil C located between bottom and top pole pieces P
1
and P
2
, respectively. The pole pieces are formed from thin films (“layers”) of magnetic material and have a pole tip height dimension commonly called the “throat height”. The throat height is measured between an air-bearing surface (“ABS”), formed by polishing the tips of the pole pieces, and a “zero throat level”, where the bottom pole piece P
1
and the top pole piece P
2
converge at the write gap G. A thin film inductive write head also includes a “pole tip region” which is located between the ABS and the zero throat level, and a “back region” which extends back from the zero throat level to and including a back gap BG. Each pole piece has a pole tip in the pole tip region and a back portion in the back region. The pole pieces are connected together at the back gap BG. The pole tips are extensions of the bottom and top pole pieces P
1
and P
2
of the write head. Each of the pole pieces P
1
and P
2
transitions to a pole tip (PT
2
and PT
1
a
, Pt
1
b
) in the pole tip region. The pole tips are separated by a gap G, which is a thin layer of nonmagnetic material, typically sputter deposited insulating alumina (Al
2
O
3
) or plated nickel-phosphorous (NiP). During the write process, write currents are sent to the coil C and a magnetic field is generated across the write gap G. The fringing field from the write gap G is used to reverse the magnetization in the magnetic layer ML, resulting in the recording of data on the disk. The width W of the pole tip PT
2
(
FIG. 2
) determines the width of the data track on the disk.
The write head shown in
FIGS. 1 and 2
is depicted as part of a prior art “merged” read/write head that employs a magnetoresistive (“MR”) read element and an inductive write element in combination. The MR read element is located between bottom shield S
1
and top shield S
2
. The bottom shield S
1
is formed on a substrate, typically the trailing surface of an air-bearing slider. The top shield S
2
also functions as the bottom pole P
1
of the write head. In the merged MR head the pole tip of pole P
1
is constructed as a narrow “pedestal” pole tip portion PT
1
b
on top of the second shield layer S
2
, as shown in
FIG. 2
, with the P
1
/S
2
layer then serving as a wider bottom pole tip portion PT
1
a
. Both of these pole tip portions PT
1
b
and PT
1
a
form the pole tip of the bottom pole P
1
, with the pole tip portion PT
1
b
forming a pedestal on the pole tip portion PT
1
a
. In the write head shown in
FIG. 1
, the throat height is less than the height of PT
1
b
because P
2
does not converge at precisely where PT
1
b
begins but at a point closer to the ABS.
The write field contour generated by the pole tips of a thin field inductive write head has a three-dimensional shape, referred to as the write “bubble”. The shape of the write bubble is defined by all points in space where the field is equal to the write threshold, which is the field strength sufficient to change the magnetization in the magnetic layer of the disk, i.e., the coercivity of the magnetic layer. For a given deep-gap field at the throat region of the write head, a larger write gap results in a wider write bubble along the in-track direction to yield better overwrite performance, i.e., the ability to overcome the influence of previously written data. However, a larger write gap also results in a wider write bubble in the off-track direction to yield a wider data track, thereby decreasing the track density that can be achieved on the disk.
To improve on this fundamental tradeoff between overwrite performance versus track density, what is needed is a thin film inductive write head that can create an improved write bubble geometry with a higher in-track to off-track aspect ratio. Such an improvement is especially desirable for very high data density applications, where overwrite performance is typically severely compromised by the need for small write gaps to maintain closely-spaced and narrow data tracks.
SUMMARY OF THE INVENTION
The invention is a thin film inductive write head with a write gap formed as a lamination of alternating layers of a nonmagnetic gap layer and a ferromagnetic spacer layer. There are N gap layers and N−1 spacer layers, with each pole tip of the write head being located adjacent to a gap layer. The spacer layers in the gap structure are formed of a ferromagnetic material with a high saturation moment density (Bs) that is close to the B
S
of the spacer material from which the pole tips are formed. Unlike the pole tips, the spacer layers are not part of a magnetic circuit and are magnetically isolated, i.e., completely surrounded by nonmagnetic gap material. The effect of the spacer layers is to effectively divide the gap into a plurality of smaller gaps. The write head with the laminated gap produces a write bubble that is narrower in the off-track direction and larger in the in-track direction with track edge writing similar to that of a small gap write head.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.
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Luo et al., “Write bubble and field rise time measurements”, J. Appl. Phys., vol. 85, No. 8, Apr. 15, 1999, pp. 5867-5869.
Steiner, “Write Bubble Measurement Under Realistic Recording Conditions”, IEEE Trans Mag, vol. 37 , No. 4, Jul. 4, 2001, pp. 1334-1336.
Hsu Yimin
Tsang Ching Hwa
Berthold Thomas R.
International Business Machine Corporation
Johnson Daniel E.
Klimowicz William
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