Research on Development of Ultrahigh-Density Storage System Using Multi-Leve Perpendicular Magnetic Recording

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The multi-level perpendicular recording system for the storage system which can attain a ultrahigh- density more than 600Gb/in^2 and its signal processing are studied. At first, a micro track model considering correlation lengths in the directions of cross-track and down-track is studied. Then, three-level perpendicular magnetic recording using two tracks is proposed and the bit error rate of PR1ML-AR system which is the PRML system employing PR1 (partial response class I) and Viterbi decoder with an AR (autoregressive) channel model is obtained by computer simulation using the micro track model, where the noise at the reading point is given by the sum of the transition noise obtained by the micro track model and the white Gaussian noise.The readback waveform is shaped to a PR1 target waveform by the equalizer which consists of a low-pass filter with a cut-off frequency X_h normalized by a bit rate and a transversal filter with N_t taps. The Viterbi detector uses the correlation of the … More PR channel to recover the recorded sequence, where an AR channel model is used as a channel estimator in order to predict the current detector input noise from the noise sequence within the previous L bit interval. The bit error rate performance of three-level recording is compared with that of conventional two-level recording, where L=5,X_h=0.27 for three-level recording and X_h=0.4 for two-level recording. N_t is selected so as to minimize the bit error rate. It is assumed that the track width is 50nm for each track and the average cluster size is 6.5nm. The distribution of cluster size is also assumed to be a uniform one with a standard deviation of 0.3 times average cluster size.The results show that at a bit error rate of 10^<-4> the areal recording densities for the two-level recording and three-level recording are 552 Gb/in^2 and 679 Gb/in^2, respectively. Therefore, the improvement of the tree-level recording in the areal density over the two-level recording is about 127 Gb/in^2, which is a large improvement and indicates that our three-level perpendicular recording will be a strong candidate for ultrahigh-density storage system. Less