Microstructural studies of direct-overwrite (DOW) Ag-In-Sb-Te phase-change optical recording media

An understanding of the processes involved in direct overwriting (DOW) of phase-change optical recording media is vital in the development of new, and the improvement of existing, products. The present work investigates the microstructural and crystalline phase changes during overwriting of Ag-In-Sb-Te disks. Samples were prepared for observation in a transmission electron microscope from initialised disks written 1, 2, 10, 100 and 1000 times. After initialisation, both bce and fee crystalline phases were observed, with a distinctive growth-dominated microstructure. After the first write (DOW (0)), a greater amount of the fcc phase was present within the groove, with an altered microstructure, again growth-dominated. A clear boundary between erased and as-initialised structures is observed. The second write (DOW(1)), produces a distorted mark shape, with a reduced amount of the fee phase in the groove. After DOW (1000), again the mark shape is distorted, but now only the bce remains within the groove. The phenomenon of jitter bump and the eventual failure of the disk are explained in terms of the differences in physical properties between these bce and fee crystalline phases.