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then the lithography is performed on the media, followed by lubrication and
other post-process techniques, and fi nally dc-erasing the patterned disk.
Land-and-groove patterns on the disk affect the fl ying of the head slider
on the spinning disk. Patterns must be identi fi ed so that they have minimum
effects on the fl yability. Improving the magnetic properties, increasing the
throughput, and manufacturability are some of the concerns associated with
the imprint technique of creating servo sectors [165].
One advantage of the nano-imprint method arises from the fact that the
magnetized segments of the disk are better isolated by the grooves. This
permits much higher signal overwrite and, as a result, higher signal output
can be achieved. However, making the nanostructure for each bit increases
considerably the number of fi ne structures in 100 nanometer scale de fi ned by
the NIL and hence increase the manufacturing cost. Discrete track recording
(DTR) medium that requires less dimensional control can be a bridge to the
fully patterned media. This makes the NIL pattern on HDD substrate with
sub-100 nm scale minimum features more cost effective [200].
Both DTR and patterned media results in higher SNR when data is read
from these media. Such technologies will push magnetic recording density
higher and will make the bits more square in shape. But such system requires
servo control with higher precision and novel servo pattern design and PES
generation scheme. The servowriting process, on the other hand, gives way to
the fabrication of the nanostructures.
5.6.2 Magnetic Printing
This approach uses a lithographically (such as NIL) patterned master disk and
copies the magnetization pattern from the master disk to slave disks. The
master disk is placed face to face with a slave disk and an external magnetic
fi eld is applied to the master disk. Due to the master disk's shielding effects,
the highly coercive medium of the slave disk can be written in with the servo
pattern in one shot. The master disk, made of more permeable soft magnetic
fi lm with higher magnetic moment than the recording media, provides a phys-
ical shape (and not the magnetic pattern) to guide the external fi eld. Hence,
the information on the master disk is not erased when a large external fi eld is
applied [97], [98].
Critical issues in this scheme include (i) the design of the master disk
pattern to have effective guidance of magnetic fl ux to switch on the magnetic
media, and (ii) close contact of the master disk and slave disk for effective
uniform printing. These issues must be resolved before successful magnetic
printing can be a reality. Signal obtained from patterns created by magnetic
printing has noise level higher than the signal obtained from patterns written
by inductive head.
Although these methods have not beed successfully realized for commer-
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