Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2001-09-14
2004-09-14
Letscher, George J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Core
Reexamination Certificate
active
06791793
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to data storage systems such as disk drives, and method of making the same. It particularly relates to a thin film read/write head for use in such data storage systems. More specifically, the present invention discloses an enhanced design of a thin film, inductive type write head for perpendicular magnetic recording. The write head employs a two-layer pole design with the main pole made of sputtered high moment magnetic material and the adjunct pole made of electroplated soft magnetic film and substantially recessed from the air bearing surface. This new design significantly enhances the magnetic write field, and substantially reduces sidewriting that could result in accidental erasure of data in adjacent tracks on the magnetic recording medium.
BACKGROUND OF THE INVENTION
In a conventional magnetic storage system, a thin film magnetic head includes an inductive read/write element mounted on a slider. The magnetic head is coupled to a rotary actuator magnet and a voice coil assembly by a suspension and an actuator arm positioned over a surface of a spinning magnetic disk. In operation, a lift force is generated by the aerodynamic interaction between the magnetic head and the spinning magnetic disk. The lift force is opposed by equal and opposite spring forces applied by the suspension such that a predetermined flying height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the spinning magnetic disk.
In the current magnetic storage technology, thin film, inductive write heads typically fall under two categories: longitudinal recording heads and perpendicular recording heads. Until recently, longitudinal recording heads have preceded perpendicular recording heads. As the continual push for very high density storage media has been the established trend in this field of technology, perpendicular recording heads have gained increasing acceptance owing to the ability of the perpendicular recording heads to provide more efficient recording methods for high-density storage applications than the longitudinal recording heads.
A perpendicular recording head is functionally distinguishable from a longitudinal recording head in the direction of the magnetic flux orientation with respect to the media such as a magnetic disk. During a write operation to a target track, the perpendicular recording head directs the magnetic flux substantially normal to the surface of the magnetic disk. This normal orientation is also the anisotropy direction of the media. In contrast, the magnetic flux developed by the longitudinal recording head is generally in the plane of the surface of the magnetic disk.
Further exemplary differences in the features of the two types of thin film, inductive write heads can be summarized as follows:
Longitudinal write heads typically employ a ring head configuration that is comprised of two magnetic poles separated by a narrow gap in between, to optimize the magnetic field in the longitudinal direction. Referring to
FIG. 3
(
FIGS. 3A
,
3
B), an exemplary longitudinal write head typically includes a thin film write head with a bottom pole (P
1
) and a top pole (P
2
).
The pole P
1
has a pole tip height dimension commonly referred to as “throat height”. In a finished write head, the throat height is measured between an air bearing surface (“ABS”), formed by lapping and polishing the pole tip, and a zero throat level where the pole tip of the write head transitions to a back region. The pole tip region is defined as the region between the ABS and the zero throat level. This region is also known as a pedestal, which is an extension of the pole P
1
.
Similarly, the pole P
2
has a pole tip height dimension commonly referred to as “nose length”. In a finished write head, the nose is defined as the region of the pole P
2
between the ABS and the “flare position” where the pole tip transitions to a back region.
Each of the poles P
1
and P
2
has a pole tip located in the pole tip region. The tip regions of the poles P
1
and P
2
are separated by a magnetic recording gap, which is a thin layer of insulation material. During a write operation, the magnetic field generated by the pole P
1
, channels the magnetic flux from the pole P
1
to the pole P
2
through an intermediary magnetic disk, thereby causing the digital data to be recorded onto the magnetic disk.
The magnetic flux immediately originated from the pole P
1
and directed towards the pole P
2
is substantially parallel with respect to the surface of the magnetic disk. This portion of the magnetic field is typically considered as a fringe field, which is responsible for the write operation of a longitudinal write head.
In the current magnetic storage technology, longitudinal magnetic recording is considered to have reached a thermal stability limit beyond which no significant increase in the areal density of magnetic media for use with longitudinal write heads could be achieved. This is due to the reduced thickness of the magnetic media in order to achieve reduced transition width as necessitated by the increase in the areal density. The transition width is the distance over which the magnetization of the stored bits changes.
In addition, since the signal-to-noise ratio is proportional to the number of grains in the bit volume, the grain size needs to be reduced as the bit volume becomes smaller. This poses a severe problem of thermal instability for the magnetization of the magnetic grain.
To address the aforementioned problems and the continual technological push for higher density magnetic storage devices, perpendicular write heads have become increasingly desirable. Specifically, the demagnetization field in a perpendicularly written bit tends to enhance the stability of neighboring bits. As a result, narrower transitions can be recorded in the perpendicular recording mode. The magnetic media used with perpendicular recording heads can be made thicker, and thus can have higher thermal stability than those used with longitudinal recording heads. The use of a soft underlayer can enhance the perpendicular or normal component of the magnetic field and field gradient generated by the perpendicular write head.
To accomplish this objective, the soft underlayer, which is deposited beneath a recording layer, is made of a high moment magnetic material. During a write operation, any magnetic flux approaching the soft underlayer from the write pole in effect creates a virtual image of the write pole, thereby enabling a much higher magnetic write field and sharper field gradient.
Practically, perpendicular write heads could be constructed by appropriate modification of conventional longitudinal write heads. Using this derivative technology, an exemplary perpendicular write head may still use a ring head configuration of a conventional longitudinal write head with two magnetic poles, similarly referred to as P
1
and P
2
.
Referring to
FIG. 4
, a significant feature of a perpendicular write head that substantially departs from a conventional longitudinal write head, is the large distance between poles P
1
and P
2
. A narrow gap between poles P
1
and P
2
is essential in longitudinal write heads but are not needed in perpendicular write heads. This is so because the most optimal configuration of a perpendicular write head usually is a single pole design.
Thus, in the exemplary perpendicular write head of
FIG. 4
, the pole P
2
would be considered as the write pole responsible for generating the magnetic flux in the perpendicular direction during a write operation. The magnetic flux permeates into the magnetic medium for use with perpendicular write heads to enable a recording of digital data onto the magnetic disk. The pole P
1
provides a return path for the magnetic flux.
The continual demand for a high areal density design of magnetic storage media has necessitated a reduction in the track width as a means to increase the track density without significantly altering the geometry of the storage medium. As the track wi
Chen Yingjian
Dang Xiaozhong
Jiang Hai
Liu Francis H.
Shi Xizeng
Letscher George J.
Western Digital (Fremont) Inc.
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