Ge-Sb-Te high density overwritable phase-change optical disk

In the present work, some new Ge-Sb-Te system high density overwritable films using He-Ne laser as optical source were investigated. Static tests showed that, high write/erase cycles up to 10⁵ can be obtained in some Al/ZnS/Ge-Sb-Te/Zns/Glass substrate multilayer samples when both the writing and erasing pulse widthes are 100 ns and the writing and erasing powers are 22 mW and 11 mW, respectively. The contrast ratioes of reflectance of the written spots(amorphous state) and erased spots(crystalline state) of the samples are about 15–20%. To improve the write/erase cycling property of the above samples, the multilayer samples using ZnS+SiO₂ as protective films were also investigated. Dynamic tests of a 5.25 inches Al/ZnS/Ge-Sb-Te/ZnS/Glass substrate multilayer phase-change disk were also carried out. The multilayer disk can be overwritten at a rotating speed of 1800 rpm with a C/N ratio of 30 dB. Which means that, the multilayer overwritable disk may be a candidate of high density overwritable recording medium because of its good properties at short wave length. The chemical compositions of the Ge-Sb-Te system phase-change optical recording films using 830 nm laser as optical source are all stoichiometrical. On the contrary, those of the new kind of high density overwritable films are not stoichiometrical. Therefore, the traditional theory on the high erasing speed of erasable phase-change optical recording films is not applicable for these high density overwritable phase-change films. The mechanism of high speed erasing of these films is discussed according to the theory on critical cooling rate of crystallization.