Phase-change characteristics of chalcogenide Ge 1 Se 1 Te 2 thin films for use in nonvolatile memories

In the present work, the authors show that Ge 1 Se 1 Te 2 thin films provide a promising alternative for phase-change random access memory (PRAM) applications to overcome the problems of conventional Ge 2 Sb 2 Te 5 PRAM devices. 100 ‐ nm -thick chalcogenide Ge 1 Se 1 Te 2 thin films were prepared by evaporating a stoichiometric bulk target, and Ge 1 Se 1 Te 2 thin-film PRAM devices with a 20 ‐ μ m -sized memory cell have been fabricated. The devices exhibited a successful switching between an amorphous and a crystalline phase by applying a 50 ns , 7.3 V set pulse and a 30 ns , 7.4 V reset pulse with a switching dynamic range (the ratio of R high to R low ) as high as 10 3 . For a static-mode switching operation, two different resistance states in Ge 1 Se 1 Te 2 thin films have been observed at low voltages, depending on the two different crystalline states of the film. The first phase-transition temperature of Ge 1 Se 1 Te 2 thin film is found to be 110 ° C , which is clearly lower than that of Ge 2 Sb 2 Te 5 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 Ge 1 Se 1 Te 2 materials are closely related to the structure of the amorphous state and crystalline state.