Phase-change characteristics of chalcogenide Ge1Se1Te2 thin films for use in nonvolatile memories

Abstract

In the present work, the authors show that Ge1Se1Te2 thin films provide a promising alternative for phase-change random access memory (PRAM) applications to overcome the problems of conventional Ge2Sb2Te5 PRAM devices. 100‐nm-thick chalcogenide Ge1Se1Te2 thin films were prepared by evaporating a stoichiometric bulk target, and Ge1Se1Te2 thin-film PRAM devices with a 20‐μm-sized memory cell have been fabricated. The devices exhibited a successful switching between an amorphous and a crystalline phase by applying a 50ns, 7.3V set pulse and a 30ns, 7.4V reset pulse with a switching dynamic range (the ratio of Rhigh to Rlow) as high as 103. For a static-mode switching operation, two different resistance states in Ge1Se1Te2 thin films have been observed at low voltages, depending on the two different crystalline states of the film. The first phase-transition temperature of Ge1Se1Te2 thin film is found to be 110°C, which is clearly lower than that of Ge2Sb2Te5 films from the temperature-dependent conductivity measurements. From field emission scanning electron microscope and x-ray diffraction analyses, the authors confirmed that phase-change properties of Ge1Se1Te2 materials are closely related to the structure of the amorphous state and crystalline state.