Dependence of Bit Error Rates on HAMR Transition Curvatures

Abstract

Transition curvature limits the performance of Heat-assisted Magnetic Recording (HAMR), especially when bit length is reduced below 10nm. The dependence of this transition curvature on bit length was obtained micromagnetically in our previous work [1]. In the current study, the dependence of signal-to-noise ratios (SNRs) and bit error rates (BERs) on HAMR transition curvatures is further investigated. More than 20,000 bits are written ideally (with an infinite thermal gradient) with various bit lengths and realistic transition curvatures. A pseudorandom binary sequence is used. The width of the read head is 20nm, shield to shield distance is 22nm, and element thickness is 4nm. Magnetic fly height is 6nm. A Viterbi algorithm is applied to decode the readback signals and calculate BERs. Fig. 1 and 2 show how SNRs and BERs change with transition curvatures (characterized by the coefficient to the quadratic term of the defining parabola) for a minimum bit length of 7.5nm. Clearly, larger transition curvatures result in lower SNRs and higher BERs, thus negatively affecting HAMR performance. Although the results in the figures represent very small bits compared to the readback resolution, our calculations for longer bits and/or narrower shield-shield spacing show similar results, albeit with improved SNR and BER, as will be shown in the presentation.  Fig. 1 Dependence of SNRs on HAMR transition curvatures with a bit length of 7.5nm.  Fig. 2 Dependence of BERs on HAMR transition curvatures with a bit length of 7.5nm.