Patterned media made from pre-etched wafers: a promising route toward ultrahigh-density magnetic recording

We have investigated a very efficient way to produce patterned media for ultrahigh density magnetic recording by first preparing patterned wafers made of silicon. Two ways of patterning the wafers were investigated: direct e-beam lithography with reactive ion etching and nanoimprinting. Features as small as 30 nm with a pitch of 60 nm were realized by nanoimprint. Subsequently, a magnetic material was deposited on these patterned wafers, covering the top of the dots, the bottom of the trenches between dots, and to a lesser extent, the sidewalls of the dots. The magnetic information is stored in the magnetic deposit located on top of the dots. In most of our studies, the deposited magnetic materials were (Co-Pt) multilayers with perpendicular magnetic anisotropy. The influence of the magnetic deposit in the trenches as well as on the sidewalls of the dots was investigated. Two techniques were developed to manipulate the information written on the dots. One is a thermomagnetic writing process which consists of locally heating a single dot by flowing a pulse of current from a conductive atomic force microscopy tip to the dot. The second writing technique consists of using standard write heads for hard disk to locally apply a magnetic field on each individual dot. This paper presents a review of our work on these arrays of dots made from prepatterned wafers.