MS Thesis Presentation by Brian D. Horton
Tuesday, July 6, 2004
(Dr.Jeffrey Streator, Chair )
"Magnetic Head Flyability Over Patterned Media "
The superparamagnetic limit is the physical limit to magnetic storage density. In magnetic storage, superparamagnetism is the uncontrollable switching of stored bits during the lifespan of a hard disk. Theoretical analysis has predicted that densities of ~50 Gbit/in2 are not possible using traditional continuous media. One strategy to achieve high storage density, above the superparamagnetic limit, is patterned media. With patterned media the physical separation helps increase the stability of magnetic domains.
One of the major challenges of development of patterned media is achieving acceptable flyability of the read/write head. The goal of this thesis is to experimentally characterize the flyability of current generation read/write heads over media patterned to densities above the superparamagnetic limit.
A test stand is built to measure head liftoff speed, head to disk intermittent contact and head fly height. Tangential friction, an indicator of head liftoff is measured by a Wheatstone bridge strain circuit attached to a cantilever beam. Intermittent contact is quantified by the amount of noise emanating from the interface, which is measured by a high frequency acoustic emission sensor. Head fly height is measured indirectly with a capacitance circuit built around the head to disk interface.
Experimental samples of current generation read/write heads and media are obtained from industry. Current generation media is patterned using focused ion beam milling to a density approaching 50 Gbit/in2. Other, extremely dense samples, above 700 Gbit/in2, are created via thin film self assembly on silicon substrate.
Conclusions on slider head flyability over patterned media are based on comparison
with flyability over non-patterned media. It is demonstrated that loss of lubrication
is small for small pattern regions with high conserved surface area ratio. For
wafer scale patterned media with low conserved surface area ratio, head liftoff
cannot be achieved at designed normal load. However, 50% reduction of load allows
slider head liftoff.