Enhancement of thermal stability by calcium doping in Sb2Te3 for ultrastable phase-change memory

Thermal stabilities, crystallization behaviors, amorphous/crystalline structures, and resistance drift, of Calcium (Ca) doped Sb ₂Te ₃ phase-change materials, have been investigated. It was found the thermal stability increases significantly by Ca doping, and the Ca _13.6(Sb ₂Te ₃) _86.4 exhibits the highest crystallization temperature (∼225 °C), largest activation energy for crystallization (2.31 eV), and best 10-years data retention ability. There is no Sb and/or Te atom bond with Ca, implying Ca atoms are in free state in Sb ₂Te ₃ matrix. Moreover, low resistance drift was found in amorphous Ca-doped Sb ₂Te ₃ film with high Ca concentration. Especially for the component of Ca _13.6(Sb ₂Te ₃) _86.4, an ultralow resistance drift coefficient of 0.004 and 0.005 was found in film and memory device, respectively. This is suggested that, the Ca _13.6(Sb ₂Te ₃) _86.4 film with moderate Ca doping, which has good thermal stability and ultralow resistance drift coefficient, can be a candidate as ultrastable phase-change material for using in the high security data storage applications.