Coupled mechano-electro-thermal model to predict phase transition in phase change materials

An advanced coupled Mechano-Electro-Thermal Phase Field model is presented to capture the crystallization/ amorphization of phase change nanofilm under external voltage. It consisted of the Allen-Cahn equation for phase transition (PT), elasticity equations to resolve stresses, heat conduction, and the Poisson equation to consider thermoelectricity. The proposed model depicts the intricate interplay between temperature, stress, preexisting defects (surface void), and PT in model phase change material, i.e., Germanium-antimony-tellurium (GeSbTe or GST). The predicted stress generation, thermal and PT-induced, agrees with existing experimental data. Additionally, surface voids can cause remarkable temperature and PT kinetics changes, decreasing the transformation rate. Also, due to a highly heterogeneous temperature, the thermal strain shows a crucial effect on crystallization kinetics. Finally, the critical stepwise voltage (V-cr) is calculated, representing an inverse power relation with the pulse time, i.e., the maximum voltage results in complete crystallization below the melting temperature. An initial increase in the average temperature occurs at the critical voltage, followed by a constant temperature regime as crystalization evolves and a jump to higher temperatures until complete crystallization. However, the temperature rapidly jumps above the melting temperature for larger voltages (V > V-cr), leading to the reverse transformation, i.e., amorphization.