Self-aligned formation of nanoscale phase change materials for nonvolatile memory application

We present a novel concept for the formation of active phase change regions in nonvolatile memory. Nanoscale phase change materials were prepared in a self-aligned manner by intermixing of two different components chosen from Ge, SiGe, Sb, and SbTe. The interdiffusion of Ge and Sb atoms increased gradually with increasing annealing temperature to 500 °C, whereas Ge, Sb, and Te atoms were completely mixed at 300 °C or higher. In addition, we found that Ge and Sb elements disappeared at 600 °C, exceeding the eutectic point (592 °C) of GeSb. Transmission electron microscopy revealed that a GeSb layer about 20 nm thick formed at the interface between the Ge and Sb layers. The memory devices fabricated based on the concept exhibited reduced programming currents, which is attributed to the small-sized phase change material made using the self-aligned formation.