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Continuation of the rapid increase in the recording
density of magnetic disk drives necessitates the
reduction of magnetic spacing between the head
sensor and the magnetic medium. This can be partly
achieved by reducing the thickness of the protective
carbon overcoat on disks, which is mostly deposited
by sputter deposition today. There are two approaches
to making thinner and denser overcoat without
compromising the wear and corrosion resistance
of the disk. The first approach uses alternative
deposition techniques, such as ion beam deposition
(IBD), to produce denser a-C:H and a-CNx:H diamond-like
carbon (DLC) overcoats. In contrast to the conventional
sputtering process, the carbon atom in the IBD
process arrives at the substrate surface with
much higher energy (~100 eV), which results in
denser structure. DLC films produced by IBD are
very hard (25+ GPa) and scratch resistant. Another
approach is to replace the conventional sputtered
carbon with alternative materials, such as amorphous
silicon nitride (a-SiNx). Depending on the sputtering
conditions, a-SiNx overcoats can be very dense
(93% theoretical density of Si3N4) and contain
few pinholes, as illustrated in the following
figure.
[Surfaces of CoCrPt disks
coated with (a) 15 Å a-SiNx and (b) 45 Å
a-CNx after 3 min etch in Ce(NH4)2(NO3)6 solution.]
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