HIGH-DENSITY PULSE-WIDTH MODULATION RECORDING AND REWRITABLE CAPABILITY IN GESBTE PHASE-CHANGE SYSTEM USING VISIBLE LASER-BEAM AT LOW LINEAR VELOCITY

Write and erase characteristics at low linear velocity in GeSbTe phase-change optical disks have been studied using 488 nm and 680 nm visible lasers. Good characteristics, which are carrier-to-noise ratio (CNR) of more than 50 Db and erasability of more than 25 Db, were obtained by optimizing the composition of GeSbTe and the layer structure. However, smaller erase power margin has been observed in comparison with the case of using a 780 nm laser. From transmission electron microscope (TEM) observation and numerical simulation, it is explained that these phenomena are mainly due to the difference in the temperature profile arising from the beam profile. For pulth width modulation (PWM) recording using a 680 nm laser, the resolution has been improved by 25% in comparison with the case of a 780 nm laser. Furthermore, a clear eye pattern of the eight-to-fourteen modulation (EFM) signal was observed at the 3 T mark length of 0.65 mum. Crosstalk of less than -26 Db was obtained even at 1.0 mum track pitch. In the overwrite cycle test using a 680 nm laser, no degradation of CNR up to 10000 cycles was observed.