Modeling And Feedback Control Of MEMS Devices

As MEMS actuators reach maturity and emerge from the research lab into commercial applications, their increased reliability, speed, and performance accuracy is needed. MEMS are typically driven directly in an open-loop fashion by applying simple actuating signals. The requirements for better dynamical behavior, however, have resulted in the gradual introduction of improved actuation approaches, such as pre-shaped open-loop driving and closed-loop control. Unlike macro mechanical systems where the implementation of the feedback is relatively simple, it is quite problematic in the MEMS case. The presence of fast system dynamics, and physical area efficiency requirements have introduced additional challenges for feedback control design. The main purpose of this work is to explore possibilities and envision applications where closed-loop strategies can be successfully used. Naturally, the design of reliable actuating techniques requires simple but accurate dynamic models of the device, either in input/output or in the state variable form. Accurate models lead towards optimal design, better performance, better understanding of the device, short development time, and consequently, lower cost of the device. The modeling of thermal and electrostatic actuators, based on synergy between finite element analysis (FEA) and analytical approaches is, therefore, another subject that this dissertation deals with. The dissertation focuses mainly on the two most common types of MEMS actuators- thermal and electrostatic. It encloses several chapters addressing development of the modeling methods and advanced actuating techniques, including closed-loop control. The dissertation contains a novel, finite element analysis (FEA)-based modeling method for thermal actuators, position and light intensity control techniques for an optical MEMS device actuated by an electrostatic comb drive, a control system for preventing lateral instability for the comb electrostatic actuator and, finally, a discussion on the sensing structure and force contribution model for the lateral motion control.