Phase-change optical disk having a nitride interface layer

A thin nitride layer formed at the interface of a Ge-Sb-Te recording layer and a ZnS-SiO2 protective layer successfully suppresses the phenomenon that reflectivity or signal amplitude becomes markedly small due to repented overwrites. Based on secondary ion mass spectrometry (SIMS) observations, the 5-nm-thick interface layer was found to restrain sulfur stems in the ZnS-SiO2 layer from diffusing into the Ge-Sb-Te layer and from changing the optical characteristics of the layer. Among several nitride materials, germanium nitride (Ge-N) sputtered film is found to have the most suitable properties as an interface layer: high barrier effect and good adhesiveness with Ge-Sb-Te and ZnS-SiO2 layers. The optical disk having the Ge-N interface layer achieves more than 5 x 10(5) cycles of overwrites with almost no changes in signal amplitude. reflectivity and jitter based on DVD-RAM specifications. The disk shows no degradation such as cracking, peeling, and corrosion after exposure to accelerated environmental conditions of 90 degrees C and 80% RH for 200 h.