Structural Stability and Phase-Change Characteristics of Ge_2Sb_2Te_5/SiO_2 Nano-Multilayered Films

摘要

The phase-change characteristics of Ge_2Sb_2Te_5/SiO_2 multilayered films with various bilayer thicknesses were investigated using high-resolution transmission electron microscopy. The change in the electrical sheet resistance of the films shows that the metastable face-centered cubic (fcc) structure formation was significantly affected by the bilayer thickness of the multilayer film. That is, compared with the single-layered Ge_2Sb_2Te_5 film, the multilayered films transformed to hexagonal at lower temperatures. In particular, the transition temperature region of the fcc structure with semiconductor properties was significantly reduced. We observed that as the bilayer thickness decreased and annealing temperature increased, the structure of the multilayer film was transformed into Ge-deficient and hexagonal phases such as GeSb_2Te_4 and Sb_2Te_3. This behavior was induced by the out-diffusion of Ge atoms from the outer surface layer, which can be caused by a difference in thermal strain at the interface between the Ge_2Sb_2Te_5 and SiO_2 films.