In-Plane Thermal Conduction and Conductivity Anisotropy in Ge2Sb2Te5 Films for Phase Change Memory

Abstract

Thermal conduction governs the program/erase speed and power consumption of phase change memory (PCM) devices. This work presents the in-plane thermal conductivity measurement of Ge2Sb2Te5 (GST) films suspended in a microfabricated structure for the amorphous (a-GST), face-centered cubic (f-GST) and hexagonal close packed (h-GST) phases. The unique design of free-standing GST films eliminates the out-of-plane heat loss to the substrate and achieves high sensitivity to lateral heat conduction. The measured in-plane thermal conductivities of GST thin films are 0.18 ± 0.02 Wm−1K−1 for a-GST, 0.49 ± 0.04 Wm−1K−1 for f-GST and 1.03 ± 0.06 Wm−1K−1 for h-GST. The out-of-plane thermal conductivities are measured by using the 3ω technique. We report the in-plane thermal conductivity is 81% of the out-of-plane thermal conductivity for the crystalline phases while no anisotropy is observed for the amorphous phase. The microstructure of the GST thin film is responsible for the direction-dependent thermal conductivities.