Optimization of crystallization characteristics for phase-change optical disk with Ag-Ge-Sb-Te recording film

A Ag-Ge-Sb-Te recording film was developed, and its chemical composition was optimized to minumize overwrite jitter. The cause of the jitter was investigated by measuring the crystallization ratios and by transmission electron microscopy. It was found that the overwrite jitter increased with a shortage of Ge or Ag because the crystallization speed increased when these elements were added, while it increased with an excess of Ge or Ag because the crystallization speed decreased when these elements were added. A model based on the atomic bond distance and the strength of interatomic interactions in the crystal was devised. The model can be used to explain the mechanism by which a slight change in the chemical composition of recording films changes the crystallization speed. It was confirmed that the proposed disk with recording film having a small amount of Ag had the minimum overwrite jitter (under 10%).