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 Sb2Te3 phase-change materials, have been investigated. It was found the thermal stability increases significantly by Ca doping, and the Ca13.6(Sb2Te3)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 Sb2Te3 matrix. Moreover, low resistance drift was found in amorphous Ca-doped Sb2Te3 film with high Ca concentration. Especially for the component of Ca13.6(Sb2Te3)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 Ca13.6(Sb2Te3)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.