On the evolution of surface morphology of polysilicon MEMS structures during fatigue

This paper presents the results of an atomic force microscopy (AFM) study of the evolution of surface topology in notched polysilicon MEMS structures deformed under cyclic loading at room temperature. The in-situ and ex-situ AFM studies reveal changes in surface topology after cyclic actuation at a relative humidity of ∼70%. These lead ultimately to large wavelength modulations close to the bottom of the notch, in the areas where the tensile stresses are maximum. This is in contrast with the wavelength of the surface modulations away from the notch, which remain relatively unchanged. The results are discussed in terms of possible chemical/surface processes that can occur in the presence of water vapor.