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Parylene for MEMS Applications


Yao, Tze-Jung (2002) Parylene for MEMS Applications. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/caxb-sr18.


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.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:(Electrical Engineering and Biology)
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Electrical Engineering
Minor Option:Biology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Tai, Yu-Chong
Thesis Committee:
  • Tai, Yu-Chong (chair)
  • Bridges, William B.
  • Pine, Jerome
  • Shumate, M.
  • Wu, Theodore Yao-tsu
Defense Date:9 January 2002
Record Number:CaltechETD:etd-07202004-135306
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2944
Deposited By: Imported from ETD-db
Deposited On:26 Jul 2004
Last Modified:03 Dec 2022 00:38

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