Low cycle fatigue of Si3N4/SiO2/Si micro-cantilever beams

Fatigue behavior is very important to reliability of micromechanical components. Therefore, there are some emerging research efforts that focus on fatigue of silicon. However, few have looked across the interacting spectrum of several material systems, which is more crucial in MEMS components. This paper presents investigation of fatigue of Si3N4/SiO2 coated single crystal silicon (CSCS) cantilever microbeams. The composite microbeams were tested using a bending mode under cyclic strain. A micro-force testing machine with a micro-probe was used to load the beams. In the fatigue testing, various percentages of failure strain obtained from static testing were adopted as the maximum cyclic strain, and their strain ratios were set as zero. The fatigue strain-life curves were achieved. Furthermore, the enhancement of fatigue performance by coatings was investigated by scratch tests and microscopic examination of the scratch surface. In order to determine the fatigue failure modes, SEM was employed to carefully observe the failed CSCS beams. Interface bonding, surface roughness, residual stress, and mechanical properties that influence the contribution of the coating were discussed. The results demonstrate that very thin ceramic coating can significantly improve the fatigue performance of silicon.