Crystallization behavior of non-stoichiometric Ge–Bi–Te ternary phase change materials for PRAM application

We investigated the properties of a Ge–Bi–Te ternary chalcogenide thin film which was deposited on a SiO 2 /Si substrate by varying RF-sputtering power on the GeTe and Bi target. The aim was to search for an appropriate candidate for a new phase change memory. Various analyses are conducted in order to investigate the composition, phase separation, and crystallization behavior of the Ge–Bi–Te alloy. The XRD results of each annealed sample showed that the Ge–Bi–Te alloy crystallized into Ge 2 Bi 2 Te 5 , GeBi 2 Te 4 , GeBi 4 Te 7 phase at around 300 °C according to Ge content and expelled amorphous Ge crystallized as a single phase over 400 °C. Combining these with the differential scanning calorimetry (DSC) results, we demonstrated that T c and T m of the Ge–Bi–Te alloy are respectively higher and lower than those of conventional Ge–Sb–Te (GST) films. All the phases, including not only various Ge–Bi–Te ternary phases but also the Ge phase crystal structure, were also confirmed with high-resolution transmission electron microscopy (HR-TEM) images and diffraction patterns. It is noted that some of the Ge 2 Bi 2 Te 5 grains show specific facetted planes such as {0113}, {0112}, and {0001}. Through successive analyses, we revealed the structural evolution of the Ge–Bi–Te alloy according to Ge contents and confirmed the potential of the Ge–Bi–Te alloy for phase-change random access memory (PRAM) applications.