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Abstract
This thesis presents the design, fabrication, development, and test of the first microfabricated motor-driven compression system that integrates high speed rotating components for electrical-to-fluidic power conversion. This power MEMS device consists of a centrifugal compressor supported on gas-lubricated bearings and driven by an electrostatic induction micromotor, integrated on a 1.5 cm silicon chip through thin film processing, deep reactive ion etching, and wafer fusion bonding.
The development approach consisted of first building all-silicon devices to experimentally study the gas-lubricated bearings, and then integrating the thin film electrical components in the silicon structure to develop the micromotor and demonstrate the integrated system. The all-silicon devices consisted of a 4.2 mm diameter single crystal silicon microturbine rotor enclosed in a bonded stack of five deep reactive ion etched wafers. They were used to define a stable operating protocol for the low aspect ratio hydrostatic journal bearing, which is new to this type of device. The protocol allowed the rotation of a turbine-driven microrotor up to 1.4 million revolutions per minute (300 m/s peripheral speed).
The motor-driven devices were then built and tested to assess the micromotor and system operation. The electrical components were fabricated using thin and thick (10 μm) film processing, and integrated with the micromachined structures in a bonded five wafer stack. Testing of these devices demonstrated typical operation of the electrostatic induction motor, with a peak torque at a given frequency (5 MHz) and a quadratic dependence on applied voltage. The maximum speed achieved was 15,000 revolutions per minute (3 m/s peripheral speed), corresponding to a motor torque of 0.3 μNm and a shaft power of 0.5 mW. Operation was limited to 100V amplitude, beyond which breakdown occurred in the motor. The viscous drag on a bladeless rotor was measured using a transient spindown technique, inferring a peak electrostatic induction torque level of 65 μNm/kV 2, which is one third the predicted value for the fabricated device. The cause for this discrepancy has not yet been determined.
This work opens the road for a new type of compact, potentially low-cost, high power density compression system, for applications such as air circulation through portable analytical instruments, pressurization of portable power generation devices, and cooling of electronics, sensors, or people. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)
