High transmittance recording layer for rewritable dual-layer phase-change optical disk

摘要

We developed a phase-change recording medium which has a high transmittance and a large reflectivity contrast (that is defined as the equation of (R{sub}(cry)-R{sub}(amo))/(R{sub}(cry)+R{sub}(amo))). This medium is very suitable for the front-side recording layer of a dual-layer optical disk. The layer structure is characterized by a TiO{sub}2 top film with a large refractive index of 2.7 in addition to a conventional structure which has very thin films of GeTe-Sb{sub}2Te{sub}3 phase-change film (6nm) and Ag-alloy reflective film (1 Onm). A high transmittance (>50%) is realized by a new optical interference arising from a TiO{sub}2 top film. Moreover, we adopted so-called "high to low" optical designing (R{sub}(cry)>R{sub}(amo)) to achieve a large reflectivity contrast (>0.7). In the case of 50GB/side (25GB/layer) condition, the jitter value using a limit equalizer is 7.4%.