The failure mechanisms of micro-scale cantilevers under shock and vibration stimuli

Recent advances in micro-electro-mechanical system (MEMS) fabrication technology have resulted in proliferation of micro-scale mechanical devices, some of which are applied in environments with severe levels of shock. The objective of this paper was to investigate the use of experimental and numerical methods in quantifying the behaviour of representative MEMS devices subject to high- g impact stimuli. Micro-cantilevers were analysed under vibration and shock on a modified Hopkinson pressure bar and vibration table to determine the mechanical properties of single crystal silicon (SCS). The characteristic dimensions of the beams were of 100 μm in height/width with beam lengths ranging from 5 to 7 mm. The experimental approach allowed non-invasive in situ monitoring of the micro-cantilevers upon impact through accelerometry and high-speed imaging. An investigation of the shock response of micro-cantilever beams indicates that orientation plays a significant role in their sensitivity to shock because of the planarity of the fabrication technique. Scanning electron microscopy identified octahedral cleavage of SCS as the dominant failure mechanism of the micro-cantilevers. Finite element analysis in conjunction with in situ high-speed imaging proved to be a viable non-invasive inverse technique to determine the loci and amplitude of tensile stress within generic micro-scale devices.