<title>On-groove phase-change optical recording for a capacity of 25 GB</title>

Abstract

ABSTRACT The possibility of high-density groove-only recording was investigated by using a high-numerical-aperture lens unit and an InGaN semiconductor laser. Wobbled grooves of 20 nm in depth were formed through a deep-UV disk mastering process and replicated by injection molding onto a polycarbonate disk substrate. This shallow wobbled groove structure improves a signal-to-noise ratio (SNR) and also enables an address in pre-grooves. In the experiment, signals were recorded either in or on the grooves, and the achievable areal recording density was carefully examined in each case, comparing with a previous land-and-groove disk configuration. The authors’ results indicate that the signal recording on the grooves, which correspond to the structured area located closer to the objective lens, brings higher track density than that in the grooves. A bit size of 120×320 nm, an areal density of 16.8 Gbit/in 2 , was verified at the data transfer rate of !36 Mbps on a phase-change disk of SbTe-based eutectic composition. This bit density can realize a storage capacity of 23.3 GB on a ! 120 mm disk. Further investigation on higher areal density was also examined with an additional signal processing. Keywords : high-density recording, groove-only recording, high-numerical-aperture lens, InGaN, phase-change recording, DVR-blue, deep-UV mastering