HARD DISKS - Patterned Media.
The disk media in hard disks is undergoing a major transformation. Longitudinal
recording has been the standard for 20 years. The latest media use magnetic domains
perpendicular to the surface to increase density.

As the written area gets closer to the native domain size, the signal to noise ratio
declines. Discrete patterning of the written area is widely expected to take over from
perpendicular recording. For more details go to the Komag or Hitachi Global Storage
web sites. The first implementation will probably in with patterned tracks, and then
pillars.

The Chou group at Princeton reported  in a series of papers 3 - 45 GB squin longitudinal
and perpendicular storage devices (Kong 1998 and Wu 1998).

Komag have reported a cycle time Imprint of 20 sec for thermal imprint of 127 nm pitch
for a Discrete Track Recording substrate (Dorsey 2004). The magnetic material is
sputtered on top of a thick residual layer. The thick residual layer probably allows the
short cycle time. Komag claims that this can support 250 GB squ in. This implies that
the improved signal to noise ratio from discrete tracks allows a domain 125 nm x 20 nm.

The  insertion for patterned media appears to be somewhere from 250 GB to 1 TB per
squ in. For full patterned media consisting of an array of posts, a 50 nm repeating cell
(pitch) pattern gives 258 GB squ in density, a 25 nm cell gives a 1TB squ in. Substrates
are locally  very flat in order to support the flying of the read / write head.

Obducat showed 80-120 nm pitch post patterns made by thermal imprint (Heidari 2005).

Chou's team also fabricate spin valve memory cells (Kong 1999)

Magnetic microrings have been reported by (Chen 2001)

OPTICAL DISKS
Traditionally, CD's (650 MB) and DVD's  (4.7 GB) have been manufactured by injection
molding using Ni inserts as the patterned mold. The Ni inserts are made by electroless
Ni plating from a master.

The "Blue ray" disk is one of the competing standards for the next generation of disks.
The 100 nm features are 80 nm deep and must be placed on both sides of a 50 um
thick film. Ovionic reported on thermally imprinting into a thick polycarbonate film and
then cutting out disks and laminating to the disk. They were able to maintain the track
circularity specification, and imprinted in less than 10 secs (Ohta 2005).

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Storage Applications