We attempted to improve phase change media to achieve larger capacity for systems with blue lasers using numerical apertures (NA) of both 0.85 and 0.65. It was found that the Bi-added GeTe-rich pseudo-binary composition promised high erase ratio even when we did not use any interface layers on a recording layer. The use of an absorption control layer (ACL) was also attempted to suppress the cross erase (XE). It was found that the ACL was very effective in suppressing the XE. The advanced phase change media that used the above novel technologies showed good analog performance. The advanced media also showed bER of less than 1.0×10-4, promising 18 GB capacity for an NA of 0.65 and 30 GB capacity for an NA of 0.85.

In order to increase the recording density and decrease the track pitch of the digital versatile discs (DVD) media using the land-and-groove recording format, it is essential to suppress the magnitude of the cross-erasure of the recorded marks. A computational analysis to estimate the mark and erasure shapes was carried out, and comparisons with the experimental results have shown good agreement. The cross-erasure was reduced under the conditions given in this paper by increasing the duty ratio of land width to groove width (L/G) while keeping the groove pitch constant.

Advanced phase change medium of over 30GB data capacity has been proposed and the recording characteristics of the medium have been described. The medium has L-H polarity, Bi-substituted GeTe-rich pseudo-binary alloy film as the recording layer, and thin metal absorption control layer. The recording measurement was carried out by using a blue laser light source with the wavelength of 405nm and an objective lens with NA of 0.85. Both CNR and ER have been improved by the use of the Bi-substituted GeTe-rich composition. XE has been reduced by the use of the absorption control layer. The bER measurement demonstrated its capability for over 30GB data capacity.

We describe the recording characteristics of discs having Ge doped eutectic SbTe alloy recording films with various compositions. The recording characteristics are fairly sensitive on the film composition. For our recording condition, the Sb/Te ratio of around 4 and the Ge content of about 5 at.% were preferable to obtain good carrier to noise ratio (CNR). A disc with eutectic recording film of that composition is compared with one with a GeTe–Sb2Te3 pseudo-binary alloy recording film, varying the mark length and the track pitch. The eutectic disc showed better CNR for the shorter mark lengths than the pseudo-binary disc. The cross-erase ratio of the eutectic disc is substantially higher than that of the pseudo-binary disc. The result suggests that the eutectic disc is suitable for higher linear bit density and the pseudo-binary disc is suitable for higher track density.