Predictions of strength in MEMS components with defects--a novel experimental-theoretical approach

This paper presents a novel experimental-theoretical method to investigate the strength of structures having complex geometries, which are commonly used in microelectromechanical systems (MEMS). It involves the stretching to failure of freestanding thin-film membranes, in a fixed-fixed configuration, containing micro-fabricated sharp cracks, blunt notches and re-entrant corners. The defects, made by nanoindentation and focused ion beam milling, are characterized by scanning electron microscopy (SEM). MEMS structures made of ultra-nano-crystalline-diamond (UNCD), a material developed at Argonne National Laboratory, were investigated using this methodology. A theory to predict the strength of microstructures with defects is proposed and compared with experimental results. It is shown that fracture mechanics general concepts can be applied with confidence in the design of MEMS. An experimental methodology and formulas to predict strength of MEMS structures possessing defects of various geometries are provided.