Conceptually, patterned media is very simple. However,
mass producing disks at reasonable cost is an immense
challenge. To see why, consider how small the islands
have to be: At 100 Gbit/sq. inch (roughly equivalent
to today's shipping drives), the islands need to have
a center-to-center spacing of 86 nanometers. To move
to 1 Tbit/sq. inch (well beyond the capability of today's
longitudinal media), a spacing of 27 nm is needed. At
10 Tbit/sq. inch, this spacing is just 9 nm. These dimensions
are well beyond the capability of optical lithography
-- the technique used by the electronics industry to
make integrated circuits. To generate features for patterned
media, two challenging approaches are proposed: e-beam
lithography and nanoimprint replication.
Nanoimprint replication is a potentially low-cost method
of stamping a nm-scale resist pattern on disks for subsequent
etching steps. E-beam lithography is one of a very few
techniques that can be used to create the stamper whose
nm-scale patterns are replicated by the nanoimprint
process.
Here's how it is all envisioned to work:
A state-of-the-art e-beam exposure tool (similar to
what is used to make masks for optical lithography in
the electronics industry, but with significantly higher
resolution) creates the desired patterns in a resist
layer on the stamper substrate (Fig.
3a). After developing, this patterned resist
becomes a mask for etching a pattern of holes into the
surface of the stamper (Fig. 3b).
A thin layer of UV-curable liquid resist is coated
on the disk substrate, and the patterned stamper is
pressed into the resist layer. While the stamper is
in contact with the resist, UV light is projected through
the stamper onto the disk (Fig.
3c), which polymerizes the liquid, hardening
it into a solid which replicates the features on the
surface of the stamper. This patterned resist then becomes
a mask for etching pillars on the disk surface (Fig.
3d). The magnetic recording layer is deposited
over this array of pillars, resulting in elevated magnetic
islands (Fig. 3e). The residual magnetic layer at the
bottom of the pillars does not play a role in the recording
process, since only the magnetic material closest to
the head (flying over the surface of the disk) is sensitive
to the recording head's writing field. As with conventional
disks, a thin hard overcoat and lubricant layer is applied
over the magnetic layer to provide a mechanically robust
head-disk interface.
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