Seamless interpretation of the strength and fatigue lifetime of polycrystalline silicon thin films

Abstract

Thin film polycrystalline silicon was subjected to strength and fatigue tests. A model is proposed which correlates the strength of this material under monotonic loading and its fatigue lifetime under cyclic loading in a seamless manner on a three-dimensional surface. This surface describes the cumulative failure probability as a function of both applied stress and fatigue cycles. In the first step, the statistical distribution of equivalent initial crack lengths corresponding to the defects introduced into the specimens in the etching process is deduced from the strength distribution of the specimens fabricated on a silicon wafer. From this distribution, the fatigue lifetime under different stress levels is estimated by applying the well-known Paris law of fatigue crack extension. The Paris law exponent determining the crack extension behavior as a function of the applied stress intensity factor was obtained by solving an inverse problem by fitting the estimated lifetime to the experimental results.