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

摘要

The design, fabrication, and characterization of a microfabricated preconcentrator-focuser (μPCF) for micro gas chromatography (μGC) are presented in this thesis. Micromachining technologies were developed to decrease size, lower power consumption, reduce cost, and increase the performance of the μPCFs.; 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 (∼100 nm) and high aspect ratio microheaters (>80:1) for μPCFs were demonstrated.; Over 500 μm 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 μPCFs. 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 μPCF. These μPCFs have small dead volume and large adsorption capacity and make it possible for the μGC to detect low concentration compound at 25 ppb-l. For a single-stage μPCF with a sample volume of 250 μl, 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 μPCF were designed and fabricated. Using this three-stage μPCF 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 μGC, consisting of a three-stage μPCF, 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 μGC.