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Creep and stress relaxation in bilayer Au/Si microcantilevers

We examine creep of thin film Au on curved bimaterial Au/Si microcantilevers. Time-dependent inelastic strains in the Au film lead to gradual changes in the microcantilever curvature over time. Curvature-temperature-time experiments are used to examine the effects of hold temperature and maximum annealing temperature on the inelastic response of the Au films. Experiments reveal inelastic strains in the Au films due to creep, recovery, and microstructural coarsening. At moderate hold temperatures, 30 °C < T < 175 °C, inelasticity in the Au films is observed to be a competition between creep and recovery. Creep strains are driven by tensile stresses in the film and serve to decrease the microcantilever curvature towards the equilibrium curvature of the underlying Si beam. Strains due to recovery of the metastable Au cause contraction of the film and the development of intrinsic tensile film stresses. The recovery leads to "anomalous’ changes in microcantilever curvature since the curvature gradually increases or decreases away from the equilibrium curvature of the underlying Si. The inelastic behavior of the Au film is shown to depend on annealing temperature through changes in initial film stress after thermo-elastic cooling and degree of recovery.