Modeling and Simulation of Electrostatically Actuated Micromechanical Devices E. K. Chan Sensors, actuators, transducers, microsystems and MEMS (MicroElectroMechanical Systems) are some of the terms describing technologies that interface information processing systems with the physical world. Electrostatically-actuated micromechanical devices are important building blocks in many of these technologies. Arrays of these devices are used in video projection displays, fluid pumping systems, optical communications systems, tunable lasers and microwave circuits. Well-calibrated simulation tools are essential for propelling ideas from the drawing board into production. This work characterizes a fabrication process -- the widely-used polysilicon MUMPs process -- to facilitate the design of electrostatically actuated micromechanical devices. The operating principles of a representative device -- a capacitive microwave switch -- are characterized using a wide range of electrical and optical measurements of test structures along with detailed electromechanical simulations. Young's modulus and residual stress are extracted consistently from measurements of both pull-in voltage and buckling amplitude. Gold is identified as an area-dependent source of nonuniformity in polysilicon thicknesses and stress. Using well-characterized beams as in-situ surface probes, capacitance-voltage measurements reveal that surface residue adds to the effective gap when the movable electrode contacts an underlying silicon nitride layer. A compressible contact surface model used in simulations improves the fit to measurements. In addition, the electric field across the nitride causes charge to build up in the nitride, increasing the measured capacitance over time. The rate of charging corresponds to charge injection through direct tunneling. A novel actuator that can travel stably beyond one-third of the initial gap (a trademark limitation of conventional actuators) is demonstrated. A "folded capacitor" design, requiring only minimal modifications to the layout of conventional devices, reduces the parasitic capacitances and modes of deformation that limit performance. This device, useful for optical applications, can travel twice the conventional range before succumbing to a tilting instability.