Thermomechanical properties and mechanical stresses of Ge2Sb2Te5 films in phase-change random access memory

The biaxial modulus and the coefficient of thermal expansion (CTE) of Ge2Sb2Te5 (GST) films with the thickness of 300 nm were characterized using the substrate curvature method on two different substrates. The elastic modulus of the GST films was also separately determined using nanoindentation. Measured biaxial modulus and CTE from substrate curvature method were 29.5 +/- 1.87 GPa and (13.3 +/- 1.39) x 10(-6) K-1 for the amorphous state and 36.8 +/- 1.54 GPa and (17.4 +/- 1.21) x 10(-6) K-1 for the crystalline state. The elastic moduli determined using nanoinclentation for the amorphous and crystalline states were 33.9 +/- 0.67 GPa and 58.7 +/- 0.48 GPa, respectively. Based on the results of the thermomechanical properties, the stresses in the phase-change random access memory (PRAM) structures were calculated using finite element analysis (FEA) considering the thermal and the phase-change stress. The FEA simulations showed that the thermal stress is higher in magnitude than the phase-change stress in a PRAM structure, but the gradient of the phase-change stress is higher than the gradient of the thermal stress. (C) 2008 Elsevier B.V. All rights reserved.