Crystallization process and thermal stability of Ge1Cu2Te3 amorphous thin films for use as phase change materials

The crystallization kinetics of amorphous Ge1Cu2Te3 (GCT) films prepared by sputter deposition were investigated by differential scanning calorimetry under non-isothermal conditions. An exothermic peak due to crystallization was observed in the temperature range 230-270 °C. It was found that the local activation energy for crystallization is almost constant when the crystallization fraction is less than about 0.15 and then monotonically decreases with increasing crystallization fraction, which indicates that the crystallization of amorphous GCT films is a multi-step mechanism. The local Avrami exponent decreased from more than 5 to 1.7 with increasing crystallization fraction. It was demonstrated by the Ozawa method that GCT amorphous films show a higher thermal stability than Ge2Sb2Te5 amorphous films, with an estimated failure time of over 70 years at 125 °C, which is well beyond the data retention requirements of the International Technology Roadmap for Semiconductors. In addition, the thickness change in GCT amorphous films accompanying crystallization was measured by atomic force microscopy. The GCT amorphous film was found to show a thickness increase of only 2.0% on crystallization, which is desirable to enhance the endurance of phase change random access memory devices.