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 3.5 mu m thick PECVD oxide, and 2 mu m thick phosphorus doped silicon while the 'legs' are made of single layer of 2 mu m thick silicon. Buckled shape model is used to design the micro-bridge to exhibit hi-stability. The micro-bridge is simulated in FE ANSYS to verify the bistability, 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 30 mu 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.