Hardware Reference
In-Depth Information
design. Although limited by the head width and the PZT actuator bandwidth,
this setup is capable of achieving a PES 3σ of 6.4 nm. Use of bettwe sensor
and actuator technologies can help to achieve better servo loop shaping and
help to achieve servo track writing at even narrower track width despite the
mechanical vibrations.
5.6 Printing the patterns
The processes discussed so far for creating servo tracks use either an HDA or
a more precise equipment which is also built on the same principle used in
HDD. However, since creating reference marks is the main objectives of servo
writing, it would serve the same if these marks can be created by some other
processes. Moreover, if these references are created by a batch process then the
bottleneck of the servo writing stage can be greately reduced. Several methods
have been explored to
fi
nd a suitable, batch processing alternative methods for
creating servo patterns. Two of these methods, nano-imprint and magnetic
print, are elaborated next.
5.6.1 Nano-Imprint
The
fi
rst of these nonconventional methods of creating servo reference is to
use pre-embossed disks. In this approach, the disks are embossed with the
servo patterns prior to applying the layer of magnetic coating on them. The
fi
rst such disk was produced by Sony; one may refer to [215] and the refer-
ences therein for more details. The required patterns of the servo sectors are
embossed on the disk creating land-and-groove patterns. When such a disk is
put in an HDD, the land-and-groove patterns cause head to disk separations
to change and hence the amplitude of readback signal varies according to the
embossed pattern. Such variations in signal amplitude can be used to encode
track numbers as well as the servo bursts. In recent years, the nanoimprint
lithography (NIL) technology makes it possible to stamp a rigid mold with
land-and-groove patterns as small as 10 nm into a soft polymeric layer [35].
There are different methods of developing nano patterns into recordable
bits. One of them has the following stages to be followed:
1. lithography of the substrate using the master designed for servo function,
2. sputter deposition and post process - magnetic layer is coated in this
stage,
3. dc-erase the disk surface so that the entire disk surface is magnetized in
the same polarization.
As an alternative, these steps can be performed in a slightly different order -
the disk is coated
fi
rst with magnetic
fi
lm by sputtering followed by overcoating,
