A 3-DOF MEMS Electrostatic Piston-Tube Actuator

A three-degrees-of-freedom microelectromechanical systems (MEMS) electrostatic actuator was developed, fabricated, and tested. The actuator utilizes a piston-tube configuration that enables the use of electrodes with a wide area. Therefore, a large output force can be generated. The actuator also utilizes a flexure mechanism in which the in-plane (x-y) stiffness is high compared with the out-of-plane (z-axis) stiffness. This flexure mechanism enables a large translation stroke along the z-axis before experiencing lateral pull-in instability. A prototype of the actuator was able to achieve a pure translation (piston-style motion) of 28 μm at 80 V and an angle of rotation of 0.78° at 70 V. A mass of 1 mg was translated 24 μm at 80 V, indicating the ability of the actuator to provide high output force. The actuator was fabricated using the Micralyne MicraGEM-Si MEMS fabrication process, in which the pistons and tubes are fabricated in the device layers of two bonded Silicon on insulator (SOI) wafers. The misalignment between the pistons and the tubes using this process was ~0.005 of the gap between adjacent pistons and tubes. This amount of misalignment leads to a negligible lateral instability effect.