Stress-Induced Crystallization of Ge-Doped Sb Phase-Change Thin Films

The large effects of moderate stresses on the crystal growth rate in Ge-doped Sb phase-change thin films are demonstrated using direct optical imaging. For Ge6Sb94 and Ge7Sb93 phase-change films, a large increase in crystallization temperature is found when using a polycarbonate substrate instead of a glass substrate. This increase is attributed to the tensile thermal stress induced in the phase-change film due to a difference in thermal expansion coefficient between the film and the polycarbonate substrate. By applying a uniaxial compressive stress to a phase-change film, we show and explain that isotropic crystal growth becomes unidirectional (perpendicular to the uniaxial stress) with a strongly enhanced growth rate. This is a direct proof that modest stresses can have large consequences for the amorphous phase stability and for the crystal growth rates, and these stresses are thus highly relevant for memories based on phase-change materials.