Low-power temperature -programmed micro gas chromatography columns.

Abstract

This thesis focuses on the development of separation columns for a micro gas chromatography (muGC) system. Using MEMS technology, muGC columns have been developed with the on-chip heaters and sensors necessary for temperature programming, pressure tuning, and flow control. These 3m-long, 150mum-wide and 250mum-deep columns, integrated on a 3.3cm square die, were fabricated using a silicon-on-glass dissolved wafer process. Demonstrating the contributions to heat dissipation from conduction, convection, and radiation with and without packaging, it has been shown that using a 7.5mm-high atmospheric package reduces power consumption to about 650mW at 100°C, while vacuum packaging reduces power requirements in steady-state to less than 100mW. Under vacuum conditions, 600mW is needed for a temperature-programming rate of 40°C/min. The 2300ppm/°C TCR of the temperature sensors and the 50fF/kPa sensitivity of the pressure sensors satisfy the requirements needed to achieve reproducible separations in a muGC system. These column have yielded high-performance separations of 20-component gas mixtures in less than 10min. Silicon-glass columns 25cm-long have produced high-speed separations of multi-component gaseous mixtures, including chemical warfare agent simulants, in less than 10s with temperature ramps up to 600°C/min. A new buried channel technology, that utilizes silicon oxynitride deposited by plasma enhanced chemical vapor deposition (PECVD), has been developed to form ultra-low-mass 25cm-long columns with two orders of magnitude lower thermal capacitance compared to their silicon-glass counterparts. The development of these PECVD columns has been an important step to realize low-power high-speed muGCs. These columns have yielded separations of n-alkanes comparable to those from conventional fused-silica capillary columns. The comprehensive thermal analysis of PECVD columns has shown that they have the ability to operate with less than 10mW at 130°C when sealed in vacuum. These columns can achieve cool-down times less than 10s when coupled to a substrate, acting as a heat sink, by bridge microactuators.