Channel Modeling and Multi-Island Recording Scheme on Bit-Patterned Media With Long-Range Island Orientation Fluctuations

Media noise is inevitable in bit-patterned media (BPM) due to fabrication imperfections, and degrades the bit error rate (BER) performance of channel. In this paper, a new channel model is proposed to characterize the media noise in BPM fabricated with cost-effective self-assembled technology, which exhibits long-range island orientation fluctuations in addition to the usual local island position and size fluctuations. To alleviate the effects of the significant media noise and write errors for such BPM at 4 Tera-islands/in
²
density, we have proposed a recording scheme that uses multiple islands (2 by 2 islands) for 1-bit information in contrast to the conventional recording scheme of recording 1 bit on one island. For both recording schemes using low-density parity check code at the same user areal density (0.9 Tb/in
²
), when the island orientation fluctuation is large (i.e.,
${\ge} 10$
°), the proposed 4 islands/bit scheme outperforms 1 island/bit scheme. This BER improvement is because the write error and media noise become increasingly dominant compared to the readback error caused by the inter-track interference and additive white Gaussian noise when the island orientation fluctuation is large. Although the proposed multiple islands recording scheme decreases the user density significantly, the proposed model can be helpful in developing more advanced signal processing and coding techniques that can alleviate the long-range island orientation fluctuations without such a sacrifice in user density.