Design and modeling of a MEMS bidirectional vertical thermal actuator

In this paper, a new micro electro-thermal actuator with bidirectional vertical motion is introduced, analyzed and tested. In traditional vertical electro-thermal actuators, the arms of actuators are fabricated with different widths to provide high and low electrical resistance for the hot and cold arms. Applying electrical current to the arms results in different thermal expansions between the hot and cold arms, which force the tip of the device to bend. The new bidirectional vertical thermal actuator (BVTA) eliminates the parasitic electrical resistance of the cold arm through the use of a 'U' shape structure. This U-shape structure provides a larger deflection with improved electrical efficiency due to the use of an active return current pass. The U-shape actuator is more beneficial in applications such as variable capacitors where a larger deflection is needed to increase the tuning range. For analysis and design purposes, an effective method to transfer the continuous system to a lumped model is presented. Simulation and test results are provided to show the deflection and effects of the design parameters on the actuator performance.