In situ TEM study of crystallization and chemical changes in an oxidized uncapped Ge2Sb2Te5 film

Ge2Sb2Te5 (GST-225) has been the most used active material in nonvolatile phase-change memory devices. Understanding the kinetics and dynamics involved in crystallization is critical for the optimization of materials and devices. A GST-225 thin film of 20nm thickness was prepared by sputtering directly onto a Protochip and left uncapped and exposed to atmosphere for approximately 1 year. Early stages of crystallization and growth of the film have been studied inside the TEM from room temperature to 140 degrees C. The morphological and structural transformations have been studied by a C-s-corrected environmental TEM, and images have been recorded using a high-speed low electron dose camera (Gatan K3 IS). The amorphous to crystalline transformation has been observed at similar to 35 degrees C. From the large field, high-resolution images obtained using the Gatan K3 IS camera early crystallization can be detected and nucleation rates and growth velocities can be obtained.