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Type of Document	Dissertation
Author	Yao, Tze-Jung
URN	etd-07202004-135306
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-07202004-135306
Title	Parylene for MEMS applications
Degree	PhD
Option	Electrical Engineering
Advisory Committee	Advisor Name Title Yu-Chong Tai Committee Member
Keywords	none
Date of Defense	2002-01-09
Availability	restricted
Abstract The goal of this thesis is to utilize Parylene, a room-temperature chemical-vapor-deposited (CVD) polymer, for MicroElectroMechanical Systems (MEMS) applications. The identified unique properties of Parylene are used to fabricate various micromachining devices such as thermopneumatic microvalve, in-channel microflow restrictor, and electret microphones. First, the properties of Parylene as a MEMS material are reviewed. The electrical, thermal, surface, and mechanical properties are first compared with that of other materials and further studied specifically for MEMS applications. The high dielectric strength (determined as 250V/pm) of Parylene makes it suitable for use as an electrical insulation material. However, its high resistivity causes un-desired charging effects first described in polymer-based electrostatic devices. The undesired high pull-in voltage, "bounce-back," and "snap-down" effects caused by dielectric charging are studied. Second, to make Parylene as a surface-micromachined material, a process that overcomes the stiction problem has to be developed. Thus, a new technique that combines wet-acetone dissolution and dry BrF3 dry etching has developed to overcome the stiction problem, which prevents Parylene microstructures from freestanding. The devices of mm*mm size with high yield are demonstrated using this technology. A thermopneumatic microvalve with a corrugated silicone/Parylene composite membrane is designed, fabricated, and tested for gas flows of several slpm and inlet pressures of tens of psi. The lowest power consumption to turn off the gas flow is determined to be 73mW. A silicone-based microfluidic coupler, initially designed for microvalve packaging, is also demonstrated for its ability to connect the external macrofluidic world to microfluidic devices. The demonstrated "quick-connect" microfluidic coupler has low leakage, is reusable, and can maintain good seal up to 60 psi. An in-channel microflow restrictor is also demonstrated with freestanding Parylene integration technology. The demonstrated restrictor can modulate flow at several tens of nl/min range with inlet pressures of several psi. The restrictor, although AC-actuated, can modulate the flow up to 50%. Finally, an electret microphone with thin-film Teflon AF is demonstrated. Parylene is shown to enhance the rigidity and yield of the microphone back plate. The demonstrated electret microphone has an open sensitivity of up to 45mV/Pa with a bandwidth of up to 10KHz.
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