Ricardo Ruiz of Hitachi GST gave a short lecture on the status of patterned media development, to the local section of the IEEE Magnetics Society yesterday. I summarize by pointing to four publications listed below. R Ruiz, et al. (Hitachi GST, U Wisc, Hitachi) gives a compact, readable overview of patterned media development circa 2008. Figure 2 is particularly noteworthy; in order to become commercially interesting, one needs a bit density above 1Tb/in^2. Since the read/write head design constrains one to a 2:1 or (better) 4:1 aspect ratio, the dot pitch has to be below 20 nm. [SST 51(9)(2008)]
For reliable operation, every bit on a hard disk should switch in the same way. Happily, electron-beam directed assembly yields tighter switching field distributions than either e-beam lithography or block copolymer self-assembly alone. [Appl. Phys. Lett. 96, 052511 (2010), doi:10.1063/1.3293301]
Recently, Hitachi GST has also reported on an integrated thermally-assisted recording head and its operation on patterned media. Going under the moniker of “BP-TAR”, the authors have achieved 1Tb/in^2 on a 24 nm track pitch. This represents a solid advance over writing on continuous media, even with thermal assist. [Nature Photonics 4, 484 - 488 (2010), doi:10.1038/nphoton.2010.90]
By means of orthogonal double patterning, Hitachi is able to show 27 nm full pitch dots of arbitrary aspect ratio. This is achieved by using e-beam directed self-assembly in the radial direction of the media, and then cutting the resulting long (radial) lines into tracks with EBL. Directed self-assembly can accomodate small (~5%) variations from the block-copolymer’s preferred lattice period, thereby making equi-angular spacing feasible. [ACS Nano, 2011, 5 (1), pp 79–84, doi:10.1021/nn101561p]
In summary, patterned media development appears to be on track. Like anything complex, a lot of engineering and learning remains to be done.