Deformation and Fatigue Analysis of Micro Thermal-Electrostatic Actuator Devices

Micro thermal-electrostatic actuator devices are widely used in MEMS. However, the effect of structure sizes on deformation and fatigue is seldom discussed. In this work, the effect of structure sizes on deformation and fatigue is investigated. In this device, two beams called hot and cold arms with different width under applied voltage will have different elongation for there different width and the structure will cause the structure laterally bent. Theoretical solutions of deformation and stresses are derived. And numerical methods of finite element are used to analyze for details. The stresses obtained from the finite element are used in fatigue analysis. In the fatigue analysis, high-cycle fatigue model is used as the load in the elastic regime. Considering the accumulation of damage by fatigue being linear, Miner theory is used to estimate the life of the thermal-electrostatic devices under high-cycle fatigue. The result shows with the same length and flexible beam length connecting the hot and cold arms, the large width will cause larger displacement and stresses. However, the difference is not significant. It is also found that as the applied voltage increasing, the displacement and stresses will increase nonlinearly. With the same width and flexible beam length, the larger length will cause larger stresses and small displacement. For fatigue analysis, as the gap increasing and the length and width decreasing, the fatigue cycle increases. It shows when the length and gap are 220 and 5 μm, the fatigue cycle of 50 μm width is more than ten times of 90 μm width. When the width and gap are 50 and 5 μm, the fatigue cycle of 220 μm length is more than ten times of 260 μm length. When the length and width are 220 and 50 fatigue cycles of 50 μm width are more than ten times of 90 μm width, the difference of fatigue cycle between gap 9 and 5 μm is more than 10 times. However, the most significant effect on fatigue is the applied voltage. It shows the fatigue cycle decays very fast as the applied voltage increasing. When the applied voltages are 2 and 8 volts, the fatigue cycles will decrease from 1018 to less than 108. As the applied voltage being 25 volt, the fatigue cycle near zero. Therefore, the limit applied voltage is about 25 volt.