Out-of-plane electrothermally actuated bistable buckled microbridge actuator

In this paper, we report the design, simulation, and fabrication of a novel electro-thermally actuated buckled micro-bridge for out of plane-actuation. The new structure consists of a beam supported by four springs and four ´legs´ at the supporting ends. The springs mainly control the torsional stiffness of the supporting ends while the ´legs´ provide large axial stiffness to cause initial buckling. Both the beam and the spring consist of a bi-layer of 3.5mum thick PECVD oxide, and 2mum thick phosphorus doped silicon while the ´legs´ are made of single layer of 2mum thick silicon. Buckled shape model is used to design the micro-bridge to exhibit bi-stability. The micro-bridge is simulated in FE ANSYS to verify the bi-stability, and the actuation steps. The structure is actuated by applying 11mA for 1ms to the ´legs´ followed by 15mA for 3ms to the beam in one direction, and 21mA for 1ms to the legs in the other direction. Out of plane movement of about 30mum m is achieved. Within limits, larger movement can be obtained by employing a longer micro-bridge and increasing the compressive stress in the oxide layer of the bridge