| A MEMS-based solid state corrosion sensor based on the metal particle polymer composite materials has recently been proposed by the Engineered Micro/Nano-Systems Laboratory at the University of Arkansas. The sensor consists of micro/nano-scale metal particles embedded in a polymer (elastomer) matrix. The variability in the chemical and dimensional properties of the sensor element will provide the tailorability in sensor sensitivity, selectivity, time response, and operating life-span. This thesis focuses on the electrical resistivity property of the sensor element and the MEMS-based patterning technique for the fabrication of the sensor element. The investigation of the electrical resistivity as a function of particle mass or volume percentage provides the understanding of the role size plays in the selection of the metal particles. Three types of particles, carbon, silver-coated aluminum, and nickel, have been studied with the mass percentage ranges of 13-15%, 63-65%, and 64-68%, respectively. Due to the natural oxidation of the metal particle surfaces, a wet etch approach is used to demonstrate the feasibility of oxide removal for particles prior to embedding in the polymer (using HCl on Nickel particles). After etching, these particles are then rinsed by IPA (Isopropyl alcohol), and mixed with polymer material in nitrogen gas environment to prevent further oxidization. The mixed metal particle polymer composite material can then be used to pattern the sensor element. The basic Direct Polymer Patterning On Substrate Technique (DPPOST) is used to microfabricate the sensor element. DPPOST has the ability to form a wide range of structural features found in MEMS, from tens of millimeter structures to micrometer level resolutions. A modified process has been researched to provide higher robustness in the fabrication process, with the goal of achieving near 100% patterning yields. The modified-DPPOST process uses conformal coating of Omnicoat(TM) nano-films to provide a barrier between the SU-8 RTM and the patterned polymer, hence reducing stiction during the release process. Research performed in this thesis provides a stepping stone to the further development of a MEMS-based corrosion sensor. |
