Design and fabrication of SOI-based micromirrors for optical applications

In this dissertation, we present the design and fabrication process of two types of Silicon-On-Insulator (SOI)-based micromirrors for optical applications: Single-axis and two-axis scanning mirrors actuated by staggered self-aligned electrostatic vertical combdrives in two SOI layers, and MEMS-actuated optical-quality vertical mirrors for silicon optical bench (SOB) technology.; We present a complete pull-in analysis of a single-axis scanner actuated by the vertical combdrives with a general comb gap arrangement and comb cross-section. We derive a precise expression of the maximum stable deflection for symmetric capacitance and a good approximation of the maximum stable deflection for asymmetric capacitance with misaligned combs. Perfect alignment of combs is critical because it maximizes the stable deflection angle. The analysis shows that the mirror design can be optimized by combining the maximum stable deflection angle, the capacitance maximum angle, and the balanced torque equation.; We present a three mask fabrication process enabling precise gap control between three structural layers consisting of upper, lower, and double-stacked layers defined in two SOI layers. We demonstrated single-axis scanners and two-axis gimbaled scanners actuated by self-aligned vertical combdrives with capabilities of bi-directional rotations and downward piston on each axis. The generalization of the self-alignment process to multi-SOI layers with optimum process design is established. A pure torque actuator with aligned combs can be implemented in three SOI layers.; We present our novel methodology of fabricating optical quality vertical mirrors by combining Potassium hydroxide (KOH) and Deep Reactive Ion Etching (DRIE) etching of (110) SOI wafers. The process starts with fabricating vertical optical surfaces by KOH etching followed by protecting them with oxidation. Then the patterned wafer is etched by DRIE to define actuators. The process development was focused on combining KOH and DRIE etching such that each process is independently optimized without compromising either, while at the same time meeting the challenge of lithographic pattern definition on high-aspect-ratio structures. Three enabling fabrication processes using double masking layers and silicon masking layer were developed. We demonstrated in-plane scanners, fast translational vertical mirrors, and miniaturized Fourier transform spectrometers.