| 摘要 |
PROBLEM TO BE SOLVED: To prevent the deterioration of a reproduced signal and to ensure high reliability and a long service life by imparting a two-layered structure to each of 1st and 2nd protective layers and making the coefft. of thermal expansion of layers on the recording layer side higher than that of the remaining layers. SOLUTION: The upper SiO2 layer 12a of a 1st protective layer is formed on a polycarbonate disk substrate 11 by RF sputtering and the lower ZnS layer 12b of the 1st protective layer having a higher coefft. of thermal, expansion than the layer 12a is formed on the layer 12a by RF sputtering. A recording layer 13 of Ge22 Sb23 Te55 is formed on the layer 12b by co-sputtering Ge50 Te50 and Sb40 Te60 . The upper ZnS layer 14a of a 2nd protective layer and the lower SiO2 layer 14b of the 2nd protective layer are successively formed on the layer 13. An Al-1.5wt.% Cr alloy film is then formed as a reflecting layer 15. Since each of the 1st and 2nd protective layers has a two-layered structure and the coefft. of thermal expansion of the layers on the recording layer side is higher, resistance to repeated overwriting is improved, a reproduced signal is not deteriorated and high reliability and a long service life are ensured. |
