Relaxing Media Requirements by Using Multi-Island Two-Dimensional Magnetic Recording on Bit-Patterned Media

Abstract

We introduce and investigate a new multi-island bit representation scheme with bit-patterned media (BPM) to increase the tolerance to the reader noise and the media noise compared with the standard BPM with a single island/bit and to granular media. The key idea is to use multiple islands in two dimensions to represent one bit. The redundancy in such a multi-island representation reduces the impact of the write in errors and decreases the effect of the media noise. We show that these multi-island representations offer improved bit error rate (BER), although only one readback sample per bit is used for equalization and detection. Here, a micromagnetic writing model and a read channel including media noise are used for the simulations, where optimized writer and reader architectures with one, two, and three read elements are investigated. Simulations at a 1 ${\rm Tb}/{\rm in}^{2}$ channel bit density, for the target BER of $10^{-2}$ and readback with two readers, indicate that the readback of BPM recording (BPMR) based on 1 ${\rm Tdot}/{\rm in}^{2}$ (1 dot/bit), 2 ${\rm Tdots}/{\rm in}^{2}$ (2 dots/bit), and 4 ${\rm Tdots}/{\rm in}^{2}$ (4 dots/bit) island density can tolerate 1, 3.1, and 3.3 dB more reader noise compared with the granular media. For readback with two readers, at $10^{-2}$ target BER, writing with 4 ${\rm Tdots}/{\rm in}^{2}$ and 2 ${\rm Tdots}/{\rm in}^{2}$ island density can tolerate the media noise (modeled by island position jitter and island size fluctuation) levels of 11% and 8.5% compared with the 1 ${\rm Tdot}/{\rm in}^{2}$ with the media noise level of 5%. When the channel bit density is increased to 1.5 ${\rm Tb}/{\rm in}^{2}$ , such a multi-island approach can still provide improved reader noise and media noise tolerances compared with the standard BPMR with one bit per island and to granular media at the same density.