Structure and phase change in Cu-Ge3Sb2Te5 films for use in phase change random access memory

The Cu-Ge3Sb2Te5 thin films with different Cu contents were prepared by magnetron sputtering method. The dependence of film resistance on temperature is measured in situ by using the four-point probe heating platform. The crystal structure, microstructure, optical gap, and bond states of the Cu-Ge3Sb2Te5 films are investigated by X-ray diffraction, transmission electron microscopy, transmission and Raman spectra, respectively. It is shown that the crystallization temperature and activation energy of crystallization increase with increasing Cu content, suggesting the improvement in thermal stability and data retention ability, while optical gap decreases with increasing Cu concentration. It is observed that the Raman peak shifts from 129 cm(-1) to 127 cm(-1), which may be ascribed to the vibration of polar Cu-Te bonds. The Cu-Ge3Sb2Te5 crystallizes into the embedded Cu-2 Te and Ge3Sb2Te5 phases with evenly grown grains.