Joule heating simulation of poly-silicon thermal micro-actuators

Previous studies of surface micro-machined polycrystalline silicon MEMS thermal micro-actuators have shown that these simple devices can provide deflections on the order of 10 micrometers at CMOS compatible drive voltages. These thermo-mechanical devices operate by differential thermal expansion caused by ohmic heating in higher resistance regions of the double beam device. Because of thermal conductivity and temperature dependent resistivity in polycrystalline silicon, the temperature profile along the "pusher" section of the beam is not uniform, and motion simulation can be complex. Using a new Joule-heating finite element simulation module, reasonable agreement between simulation and near-IR microscopy on MEMS thermal actuators has been established. This work demonstrates the need to develop optimized design criteria in this class of devices to mitigate the thermal conduction and temperature variation effects in the pusher beam, which degrade displacement performance.