A study of switching field distribution in bit patterned media fabricated by ion beam lithography

Longitudinal magnetic recording is rapidly approaching the areal bit densities at which superparamagnetic instabilities lead to the deterioration of a recording system performance (∼200Gbit/in2). Recently introduced bit patterned media (BPM) offer a design which can extend magnetic recording to densities >10Tbit/in2. In BPM, each bit is a single magnetic domain island physically separated from other bits through lithographic patterning. To facilitate technology implementation, a feasible process for fabricating the media must be designed. Ion beam lithography (IBL) has the potential for printing the nanometer-size features required of BPM (<25nm for 1Tbit/in2) and offers high-throughput processing for economical manufacturing. Generating stencil masks with small openings for IBL represents a major hurdle for manufacturing BPM. A process is developed for producing silicon nitride (Si3N4) membranes patterned with high-aspect ratio openings upon which a scattering mask is applied and used to reduce the opening size to sub-25nm. The stencil masks are used to produce BPM samples from Co/Pd multilayers by patterning photoresist and transferring using Ar + milling. A novel technique is used to quickly produce samples with varying size distributions and the magnetic properties of these samples studied to understand switching field distribution (SFD) in BPM. After patterning, the magnetic field required to switch each nanodot in the array of nanodots varies. Ensuring accurate data writing if the SFD is large is difficult. A better understanding of the sources of SFD was developed and will help lead to finding solutions to this problem. Samples produced here with various size distributions decouple contributions to SFD due to extrinsic sources such as lithographic variation and intrinsic sources such as defects in the Co/Pd multilayers. The effects of these different sources have been studied and methods to reduce SFD suggested.