Surface Micromachined Out-of-plane Electrostatic MEMS Actuator Integrated with Displacement Sensor

We propose an out-of-plane electrostatic MEMS actuator capable of sensing its displacement. A repulsive force electrostatic arm is designed to form an actuator that push a suspended plate away from the substrate. A single capacitance sensing electrode is located beneath the moveable plate to measure the actuator vertical displacement. We demonstrate that the actuator, which was fabricated using a standard surface micromachining process, can provide a vertical displacement of 1.8 mu m when excited with a 50 V DC voltage. This movement results in a reduction of the sensing electrode capacitance. Hence, the displacement of the actuator can be monitored as a function of the change in capacitance at the sensing electrode. This self-sensing feature allows the actuator to be utilized in closed-loop control systems as well as self-aligned optical platforms.