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Abstract
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.
Highlights
During past few years, MEMS technology has enabled many types of sensors, actuators and systems to be reduced in size by orders of magnitude, while often even improving its performance, such as accelerometers, optical switches, biochemical analysis systems [1]
The flap and serpentine springs were patterned by deep reactive ion etching (DRIE) on the device layer to release the microactuators [8]
A highly reliable MEMS device is achieved by the proper design of the spring beam structure and reshaped driving waveform
Summary
MEMS technology has enabled many types of sensors, actuators and systems to be reduced in size by orders of magnitude, while often even improving its performance, such as accelerometers, optical switches, biochemical analysis systems [1]. The function of signal switching on most MEMS devices is implemented by a micromirror which has a reflecting metal coating. Springs made of silicon still need to be carefully designed to prevent fracture. It must be reliable especially in some critical environments, such as devices in a deep ocean. In order to prevent the stiction problem, we removed stoppers which are usually seen in MEMS devices with large displacement [4]. By the aid of proper spring design and edited driving waveform, springs are limited to operate in a low stress region. The experimental results of the device that passed rigorous requirement are shown
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