Viscosity and elastic constants of thin films of amorphous Te alloys used for optical data storage

The biaxial modulus and the linear coefficient of thermal expansion of sputtered amorphous Ge4Sb1Te5, Ge2Sb2Te5, and Ag0.055In0.065Sb0.59Te0.29 thin films were determined from stress versus temperature measurements on two different substrates. Viscous flow was measured by stress relaxation at constant temperature using wafer curvature measurements. The shear viscosity increased linearly with time, which can be attributed to bimolecular structural relaxation kinetics. The isoconfigurational activation energy was 1.94±0.09 eV for Ge4Sb1Te5, 1.76±0.05 eV for Ge2Sb2Te5, and 1.33±0.09 eV for AgInSbTe. These values scale with the absolute melting temperatures of the material.