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

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.