Positioning, control, and dynamics of electrostatic actuators for use in optical and RF systems

Abstract

This thesis describes work on incorporating electrostatically-actuated microstructures for analog tuning and positioning applications within optical and RF systems. The work focuses on the design, simulation, and optimization of actuators which undergo large-amplitude motion, including ways to overcome the so-called pull-in instabil­ity which typically limits the stable travel distance of electrostatic actuators. These techniques are applied to the design and fabrication of: (1) the polychromator, a micromcchanical diffraction grating with a thonsand analog-positioned mirrors for use in a correlation spectroscopy system, and (2) a tunable capacitance device with a lithographically-programmable capacitance-voltage (C-V) characteristic for use in tunable RF oscillators. With the polychromator, 1 cm long electrostatic mirror actua­tors have achieved over 1. 75µm of displacement out of a 2[mu]m gap. Prototype tunable capacitors fabricated in a non-optimized process exhibit a 25% capacitance tuning range with a linear C-V characteristic and 35V actuation voltage. With an optimized process, simulations show that a 150% capacitive tuning range can ht: achieved with 3.3V actuation voltage. The integration of micromechanical devices into complex, mixed technology sys­tems also requires methods for efficiently simulating the dynamics of micromcchani­cal devices. We present work on generating efficient reduced-order macromodels for simulating the dynamics of micromechanical devices by extracting global basis func­tions using information from a few runs of a computationally expensive finite element. model. Using a squeeze-film air-damped, electrostatically-actuated beam as an ex-­ample, a macromodel with 2 pressure and 2 displacement basis functions achieves less than 2% error and a factor of 37 increase in efficiency compared to meshed simulation techniques along with good correspondence to experimental data.