Integrated passives and resonant inductive coupling as a displacement sensing mechanism for large piston/rotation micromirrors.

摘要

Precise position control of large displacement/rotation micro-electro-mechanical systems (MEMS) micromirrors is a highly desired albeit difficult task. To implement closed loop control, integrating position sensors with MEMS micromirrors is ultimately required, which must provide a large sensing dynamic range with good sensitivity and linearity, have high bandwidth, and be cost effective. This work aims to demonstrate resonant inductive coupling (RIC) as a promising position sensing mechanism for large vertical displacement/rotation micromirrors. The oscillation generated by two closelymatched LC cells is a function of the coupling between the two microfabricated coil inductors, which is in turn dependent on the mirror plate to coil distance. Analytical modeling, design optimization, and macro/micro-scale experiments were conducted. The microfabricated sensor prototype was tested with an electrothermally actuated large vertical displacement micromirror to demonstrate the sensing mechanism feasibility. It was confirmed that the RIC position sensor can achieve a sensitivity of 0.012 mV/mum over a 1.05 mm range, and/or 0.185 mV/mum over a 130 mum range, with a minimum resolution of 306 nm and 19.9 nm in the respective ranges. Another frequency shift based sensing method was also devised to monitor the tilt angle of the mirror plate throughout a 500 mum piston displacement.;This dissertation also presents the fabrication and characterization of a novel high density stacked metal-insulator-metal capacitor based on fine polishing and selective metal etching. With an oxide-nitride-oxide dielectric, a capacitance density of 3.8 fF/mum2 was achieved with a maximum capacitance of 2.47 nF, and the linear and quadratic voltage coefficients of capacitance were below 21.2 ppm/V and 2.31 ppm/V2. A broadband analytical model for the impedance was constructed and matched well with measurement results. This capacitor fabrication technology can aid the miniaturization of the aforementioned RIC position sensor.;Also presented is the work on a permalloy based electromagnetically actuated micromirror with precise +/- 2.3° tilt angle control achieved through overlapping stopper structures, which is intended for optical switching in harsh environments. A pulsed voltage driving circuit was constructed to increase the switching speed. The aforementioned RIC position sensor can be also applied to measure the tilt angle of this device as well.