Design, fabrication, and characterization of microfabricated preconcentrator -focuser for micro gas chromatography.

Abstract

The design, fabrication, and characterization of a microfabricated preconcentrator-focuser (muPCF) for micro gas chromatography (muGC) are presented in this thesis. Micromachining technologies were developed to decrease size, lower power consumption, reduce cost, and increase the performance of the muPCFs. Advanced dry etching technologies were first developed to fabricate micromachined devices with high aspect ratio microstructures. Techniques to etch through the wafer and pattern submicrometer trenches were studied to meet the design requirements of microelectromechanical systems (MEMS). With the optimized dry etching technologies, rf mechanical resonators with submicrometer gaps (&sim;100 nm) and high aspect ratio microheaters (>80:1) for muPCFs were demonstrated. Over 500 mum thick, thermally isolated microheaters in Si were fabricated using advanced dry etching technology were fabricated. Such three-dimensional (3D) thick microheaters with large surface area provide the large adsorbent capacity needed for high capacity muPCFs. Power efficiency for the microheaters has been improved by either applying air gaps around the microheater, operating the microheater in a 1.2 Torr ambient, or supporting the microheater on a thin polymer membrane. After developing the thick and thermally isolated microheaters, adsorbents were placed into the heater to complete the muPCF. These muPCFs have small dead volume and large adsorption capacity and make it possible for the muGC to detect low concentration compound at 25 ppb-<italic>l</italic>. For a single-stage muPCF with a sample volume of 250 mu<italic>l</italic>, a high preconcentration factor of 5600 and a small peak width at half height (PWHH) of 0.8 s were obtained for benzene, which represented a significant improvement in performance over the capillary-tube preconcentrator. To analyze organic compounds with a wide range of volatility (0.01 to 231 Torr), three different adsorbents in a three-stage muPCF were designed and fabricated. Using this three-stage muPCF in a commercial GC, 30 different common organic compounds were successfully separated and the PWHHs of all compounds were very small (0.4 to 2.1 s). A partially integrated muGC, consisting of a three-stage muPCF, a 3 m long non-polar column, and micro chemiresistor sensors, was characterized. This was the first demonstration of separating 11 compounds using the partially integrated muGC.