Fatigue lifetime prediction of arbitrarily-shaped MEMS structures made of polysilicon thin films

This paper reports the results of fatigue lifetime prediction of polycrystalline silicon thin film structures on the basis of their static strength. The fatigue lifetime is formulated using Paris’ law as a crack extension process starting from initial cracks which represent the etching damage and thus determine the strength distribution described by Weibull distribution. The predictions were performed on three groups of specimens fabricated under different etching conditions. Specimens in each group were patterned with different types of shapes to have different stress distributions. The results showed that their fatigue lifetimes were predicted well despite the difference of stress distribution and the initial damage induced by etching process. This means that the damage accumulation under fatigue loading was independent of the fabrication conditions, the shapes and thus of the stress distributions of structures.