Dynamic magnetic information storage or retrieval – Record copying – Contact transfer
Reexamination Certificate
2003-05-12
2004-09-14
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Record copying
Contact transfer
C360S075000
Reexamination Certificate
active
06791774
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method of forming a servo pattern on a rigid perpendicular magnetic recording disk, and more particularly to contacting the recording disk with a pattern on a master disk and transferring the pattern to the recording disk.
BACKGROUND OF THE INVENTION
Conventional magnetic recording hard disk drives use horizontal or longitudinal recording, i.e., the magnetized regions that define the magnetically recorded data bits are oriented in the plane of the recording layer on the rigid or hard disk. Perpendicular magnetic recording has been suggested as a promising path toward ultra-high recording densities in magnetic recording rigid disk drives. The most common type of perpendicular recording system is one that uses a single write pole or “probe” recording head with a “dual-layer” media as the recording disk. The dual-layer media has a perpendicular magnetic data recording layer with perpendicular magnetic anisotropy formed on a “soft” or relatively low-coercivity magnetically permeable underlayer, the underlayer serving as a flux return path for the field from the write pole.
FIG. 1
is a schematic of such a system showing perpendicularly magnetized regions in the recording layer and a conventional magnetoresistive read element for reading the recorded data.
For both longitudinal and perpendicular magnetic recording hard disk drives, the most common method of generating the fixed, pre-recorded servo patterns that are used to position the recording head to the desired track and record location on the disk, is by “servo-writing” the patterns on a track by track basis, either with a special write head and servo-writer or with the production head in the drive. This is a time-consuming and therefore expensive process.
Contact magnetic duplication or transfer (CMT), sometimes referred to as magnetic printing, is a method of instantaneous recording of magnetic patterns onto magnetic media over large areas and has been proposed for transferring servo patterns to longitudinal magnetic recording disks in hard disk drives. The CMT method uses a “master” disk with a pattern of soft (low-coercivity) magnetic material corresponding to the servo pattern which is to be transferred to the magnetic recording disk (the “slave” disk). As shown in
FIGS. 2A-2B
, the slave disk is first exposed to a uniform magnetic field (i.e., “DC” magnetized) with a magnet
1
that applies an in-plane horizontal (longitudinal) magnetic field in a first direction
2
across a gap
3
between the magnet's poles, as shown in
FIG. 2A. A
rigid master disk supported on a carrier is then pressed into contact with the DC-magnetized slave disk, and a second horizontal DC magnetic field is applied by magnet
1
in the direction
4
opposite to the direction
2
of the first DC magnetization, as shown in FIG.
2
B. This produces a magnetization pattern on the slave disk because the first magnetization on the slave disk is shielded from the second DC field in the regions where the islands
5
of soft magnetic material of the master disk are present, and the first magnetization on the slave disk is reversed in the regions beneath the openings
6
in the pattern (the regions between the soft magnetic material on the master disk), as shown by arrows
7
in FIG.
2
B. The magnetic field applied to the slave disk beneath the openings
6
is enhanced by the dipole fields
8
in the soft magnetic regions adjacent the openings
6
, because in the presence of the field from the magnet these regions generate their own fields. CMT was first proposed for generating servo patterns in longitudinal magnetic recording media in U.S. Pat. No. 3,869,711. Co-pending application Ser. No. 10/055,638, filed Jan. 22, 2002, and assigned to the same assignee as this application, describes a CMT process for longitudinal rigid magnetic recording disks that uses a flexible master disk and differential air pressure to place the flexible master disk into contact with the rigid slave disk.
More recently, Ishida T. et al. “Magnetic Printing Technology-Application to HDD”, TMRC 2002, Paper A6, The 13
th
Magnetic Recording Conference, Aug. 26-28
th
, 2002, Santa Clara, Calif., has suggested that the same CMT process for longitudinal magnetic recording disks, wherein a longitudinal magnetic field is applied in the plane of the recording layer as shown in
FIGS. 2A-2B
, can also be applied to transfer servo patterns to perpendicular magnetic recording disks. However, a shortcoming of this approach is that it creates perpendicular field components only at the edges of features on the master disk. This limits the shape and size of magnetic patterns that can be transferred, and also has the potential to result in ill-defined boundaries in the transferred patterns.
What is needed is a CMT method for servo patterns on hard perpendicular magnetic recording disks that allows for the transfer of arbitrarily shaped magnetic patterns with sharp edge boundaries.
SUMMARY OF THE INVENTION
The invention is a contact magnetic transfer method for forming a pattern of magnetized servo regions in the magnetic recording layer of a rigid perpendicular magnetic recording disk. A master disk or template has a rigid or flexible base with a first film of soft magnetic material on the base and a pattern of islands of soft magnetic material on and extending above the first film and recesses between the islands. In one implementation, the slave disk to be servo patterned is first DC magnetized in a first direction perpendicular to the plane of the recording layer. The slave disk is then placed with its outer layer in proximity to the islands of the master template and a magnetic field is applied in a second direction opposite the DC magnetization direction. The magnetic field in the second perpendicular direction passes through the first film and islands on the master template and the regions of the recording layer beneath the islands, which causes a reversal of the magnetization in these regions. In the regions of the recording layer beneath the recesses of the template the magnetization is unchanged because the magnetic field is directed away from the spacings or air gaps in the recesses and toward the islands.
Alternatively, the slave disk to be servo patterned is first exposed to a magnetic field alternating in opposite directions (i.e., “AC erased”) with an electromagnet that applies a magnetic field in alternating opposite directions perpendicular to the plane of the recording layer. After being AC erased the recording layer of the slave disk has essentially no magnetization. The slave disk is then placed with its outer layer in proximity to the islands of the master template and a magnetic field is applied in a perpendicular direction. Just as in the DC magnetized implementation, the magnetic field in the perpendicular direction passes through the first film and islands on the master template and the regions of the recording layer beneath the islands, which causes a magnetization in these regions in the same perpendicular direction as the applied field. After the applied field is removed, the magnetization in the regions of the recording layer beneath the recesses of the template spontaneously reverses in the stable state due to the closure of the magnetic flux from the magnetized regions beneath the islands.
In one embodiment the master template is flexible template and a differential gas pressure is used to press the islands against the slave disk. The master disk base is a flexible plastic film that is sealed at the outer periphery of the opening of a pressure chamber with the islands located outside the chamber. The previously DC-magnetized slave disk is brought into gentle contact with the islands and gas pressure inside the chamber is increased to slightly above atmospheric. This controlled pressure presses the islands into contact with the slave disk, at which time a magnet magnetizes the regions of the recording layer that are located beneath the islands in the perpendicular direction opposite to the original DC-magnetized dir
Albrecht Thomas R.
Bandic Zvonimir Z.
Berthold Thomas R.
Figueroa Natalia
Hitachi Global Storage Technologies - Netherlands B.V.
Hudspeth David
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