Failure Analysis of Micron Scaled Silicon Under High Rate Tensile Loading

Abstract

Structures have been built at micro scales with unique failure mechanism not yet well understood, in particular, under high-rate loading conditions. Consequently, MEMS devices suffer from inconsistent performance and insufficient reliability. This research aims to understanding the failure mechanisms in micro-scaled specimens deforming at high rates. Single crystal silicon micro beams that are 4 μm thick are subjected to tensile loading at average strain rates of 100 s⁻¹ using a miniature modified Kolsky tension bar. A capacitance displacement system and piezoelectric load cell are incorporated to measure the strain and stress of the silicon micro beams directly to ensure precision. Extreme fragmentation of the beams occurs during failure and this phenomenon is observed using a high speed camera. A debris retention system is used to capture the silicon fragments for direct inspection using a Scanning Electron Microscope. The failure mechanism of the micro beams is attributed the presence of sub micron scaled surface defects rather than any one large critical flaw.