Repeatability dependence of phase-change optical disks on morphology of protective layers

The surface or the Si3N4-sputtered protective layer of phase change optical recording media was observed with a scanning tunneling microscope. We found the morphology of the protective layer can be controlled by changing the sputtering gas conditions and that overwrite cycle repeatability strongly depends on it. As the Ar gas pressure in the sputtering chamber is decreased, the protective layers become denser and have a flatter surface, and the repeatability is improved from 3×103 to 5×105. The media sensitivity also depends on the morphology of the protective layers. The causes of media deterioration after a large number of overwrite cycles are discussed