The design, modeling, and experimental tests results of both a single-crystal silicon and a polycrystalline nickel micromechanical device developed to evaluate fracture and fatigue of very small fractures are described. The devices are cantilever beams, approximately 300- mu m long. Electrodes excite the devices at resonance. Fatigue crack propagation or time dependent structural change is measured by detecting the shift in resonant frequency. In the silicon device, the frequency change is caused by the extension of a preexisting crack introduced near the fixed end of the cantilever. Experimental data are presented demonstrating time-dependent crack growth in silicon. This study indicates the possibility of crack growth in silicon structures, given the correct environment. Given the greater dislocation mobilities in metals and additional failure modes available in polysilicon, long-term crack growth should be included as a design consideration in the design of micromechanical structures.
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