Performance of Bit-Patterned Media Recording According to Island Patterns

Abstract

To increase a density in hard disk drive, bit patterned media recording (BPMR) is regarded as a promising candidate for the next generation storage system. Reduction of spacing between bit islands is essential to increase the density in BPMR but causes inter-symbol interference (ISI) and inter-track interference (ITI). Islands can be arranged on a rectangular pattern (regular array) or packed in a staggered pattern (hexagonal lattice), depending upon the lithography approach adopted in BPMR. Since the staggered pattern can mitigate the effect of the ITI due to the presence of adjacent tracks, bit error rate (BER) performance of staggered pattern is better than that of rectangular pattern in previous study. In another work of channel modeling for staggered pattern, the staggered pattern with bit-aspect ratios (BAR $) =$ Track Pitch $(T_{z}) /$ Bit Length $(T_{x})$ of 2 performs better than the staggered pattern with BAR of 1. In this paper, we investigate the performance of BPMR island patterns according to the distances of track pitch and bit length, respectively. Fig. 1 presents BER performance of island arrangement according to areal densities of 2 Tb/in 2 and 3 Tb/in 2. When the areal density is 2 Tb/in 2, $(T_{x} \quad =15.5$ nm, $T_{z} \quad =21.0$ nm) provides best performance. Also, when the areal density is 3 Tb/in 2, $(T_{x} \quad =13.0$ nm, $T_{z} \quad =17.0$ nm) shows best performance. Fig. 2 illustrates BER performance in accordance with island arrangements. Case (1) represents the arrangement of islands that distributed over a rectangular array at $T_{x}$ of 18.0nm and $T_{z}$ of 18.0nm in 2 Tb/in 2 and $T_{x}$ of 14.5nm and $T_{z}$ of 14.5nm in 3 Tb/in 2. Case (2) represents the arrangement of islands that distributed over a staggered pattern at $T_{x}$ of 21.0nm and $T_{z}$ of 15.5nm in 2 Tb/in 2 and $T_{x}$ of 17.0nm and $T_{z}$ of 13.0nm in 3 Tb/in 2. Case (3) represents the arrangement of islands that distributed over a staggered pattern at $T_{x}$ of 18.0nm and $T_{z}$ of 18.0nm in 2 Tb/in 2 and $T_{x}$ of 14.5nm and $T_{z}$ of 14.5nm in 3 Tb/in 2. Case (4) represents the arrangement of islands that distributed over a staggered pattern at $T_{x}$ of 15.5nm and $T_{z}$ of 21.0nm in 2 Tb/in 2 and $T_{x}$ of 13.0nm and $T_{z}$ of 17.0nm in 3 Tb/in 2. Since the influence of adjacent tracks of Case (4) is less than that of Case (1), Case (2), and Case (3), i.e., the effect of ITI is reduced, Case (4) shows the best performance in both 2 Tb/in 2 and 3 Tb/in 2.