Stochastic reliability of brittle microsystems

A high-throughput sequential tensile test method has been developed to characterize the fracture strength distribution of microfabricated polycrystalline silicon, which is the primary structural material used in microelectromechanical systems (MEMS). The resulting dataset of over 1000 microtensile tests reveals subtle extreme-value behavior in the tails of the distribution, demonstrating that the common two-parameter Weibull distribution is inferior to a three-parameter Weibull model. The results suggest the existence of a cut-off or threshold stress (1.446 GPa for this particular material) below which tensile failure will not occur. The existence of a cut-off stress suggests that the material's flaw size distribution and toughness distribution are both also bounded. From an application perspective, the cut-off stress provides a statistically-sound basis for reliable design. While the sequential method is demonstrated here for polycrystalline silicon MEMS, the technique could be extended to a wide range of both microsystem and conventional materials. ©2009 Society for Experimental Mechanics Inc.