Electrical Properties of Ag-Doped Ge₂Sb₂Te₅ Films Used for Phase Change Random Access Memory

Ag-doped Ge₂Sb₂Te₅ films were deposited by rf magnetron sputtering on SiO₂/Si substrates. The content of Ag ranging from 4.5 to 11.3 at.% is determined by inductively coupled plasma atomic emission spectrometry. The crystallization temperature of Ag-doped Ge₂Sb₂Te₅ increases with the increasing Ag content and the stability of phase change film is improved greatly. Structures were measured by x-ray diffraction and the face-centered-cubic structure was more stable after Ag doping. Four-point probe was used to measure the sheet resistance of Ag-doped Ge₂Sb₂Te₅ films annealed at different temperatures and it is indicated that Ag atoms increase the sheet resistance of Ge₂Sb₂Te₅ thin film when the annealing temperature is higher than about 360°C, which is beneficial for reducing the reset current. Current-voltage curves were tested and it is demonstrated that 4.5 at.% Ag doping into the Ge₂Sb₂Te₅ film can reduce the threshold current from 1.46mA to 0.25mA and can only increase the threshold voltage slightly, which is very useful for low energy consumption.