Effect of Ag or Cu doping on erasable phase-change Sb-Te thin films

The crystallization process of the Ag or Cu doped Sb₂Te ₃ amorphous film was investigated by isothermal treatment for one hour at 100°C, 200°C and 300°C respectively. The crystallization temperatures of Ag_8.3Sb_34.9Te_56.8 and Cu_8.4Sb_35.1Te_56.5 films determined by DSC analysis were more than 125°C and 120°C respectively, while that of the undoped Sb₂Te₃ film was 97°C. It indicates that doping Ag or Cu can improve the room temperature stability of Sb₂Te₃ amorphous films. For pure and some Ag, Cu doped Sb₂Te₃ films, phase transformations from lower temperature metastable phases to higher temperature thermodynamic stable phases were found. This kind of phase transformation would cause the appearance of ambiguous exothermic peak in DSC curve. When the Ag content is increased to about 6.6 at%, the melting temperature of the film is enhanced from 415°C for undoped film to higher than 450°C. For the Cu doped film, same tendency can be achieved as Cu content is increased to 8.4 at%. The contrast ratios between as-deposited and 300°C annealed films of Ag_3.2Sb _35.8Te_61.0 and Cu₄₁Sb_37.4Te _58.5 films were more than 42% and 37% respectively