Reliability of a MEMS Actuator Improved by Spring Corner Designs and Reshaped Driving Waveforms

In this paper, we report spring corner designs and driving waveforms to improve the reliability for a MEMS (Micro-Electro-Mechanical System) actuator. In order to prevent the stiction problems, no stopper or damping absorber is adopted. Therefore, an actuator could travel long distance by electromagnetic force without any object in moving path to absorb excess momentum. Due to long displacement and large mass, springs of MEMS actuators tend to crack from weak points with high stress concentration and this situation degrades reliability performance. Stress distribution over different spring designs were simulated and a serpentine spring with circular and wide corner design was chosen due to its low stress concentration. This design has smaller stress concentration versus displacement. Furthermore, the resonant frequencies are removed from the driving waveform based on the analysis of discrete Fourier transfer function. The reshaped waveform not only shortens actuator switching time, but also ensures that the spring is in a small displacement region without overshooting so that the maximum stress is kept below 200 MPa. The experimental results show that the MEMS device designed by theses principles can survive 500 g (gravity acceleration) shock test and pass 150 million switching cycles without failure.