MEMS are increasingly being considered for applications that involve immersion in liquids. However, there
are very little reliability data for MEMS structures in liquids environments. In this study, an apparatus was developed
which enables the investigation of fatigue failure of MEMS in liquids. MEMS cantilever beams were mounted on a PZT
piezoelectric actuator and immersed in a liquid. A laser is reflected off the tip of the vibrating cantilever and onto a
position-sensing photo-diode device (PSD) to obtain position data. From this data resonance frequency can be extracted
for long-term monitoring. Cantilevers are resonated for at least 108
cycles. This apparatus allows for the testing of many
combinations of materials and environments. For this study, the fatigue performance in liquid of silicon nitride
cantilever beams was evaluated and compared to single crystal silicon cantilever beams. Tests were conducted in
deionized water and a saline solution. Silicon nitride exhibited no long-term degradation of resonance frequency within
measurement limits in air, DI water, and saline environments. Silicon exhibited a steady decrease in resonance. Results
showed that this method could be extended to conduct reliability studies on other MEMS materials.
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