decoupled grains. Single switching volume magnetic islands are formed along
circular tracks with regular spacing. Magnetic transitions no longer meander
between random grains, but form perfectly distinct boundaries between pre-
cisely located islands. Since each island is a single magnetic domain, patterned
media is thermally stable, even at densities far higher than can be achieved
with conventional media. Though the concept of patterned media looks simple,
realization of this to achieve high recording density is immensely challenging.
For an areal density of 100 Gbits/square inch, the center to center spacing
between two islands need to be 86 nanometers. For 10 terrabits/square inch
density, this spacing is only 9 nm. Creating islands of such dimension is beyond
the capabilities of optical lithography. E-beam lithography and nano imprint
replication are considered to be two approaches that can be used to realize
patterned media commercially.
The HDD industry will soon embrace these and other technologies to manu-
facture commercially hard disk drives with extremely high areal density. This
makes the design of the head positioning servomechanism more challenging.
Shrinking bit size also means narrower track pitch. Many disturbances ignored
today will ask for special attention at such high track density. Ultra high areal
density will also require the head to fl y very low such that occasional contact
between head and disk will become inevitable. The servomechanism must be
robust enough to withstand these unpredictable disturbances.