Design and Fabrication of the Fundamental Components Integrated to Realize a Functional Silicon Micromachined Gas Chromatography System

Abstract

A miniature gas chromatography (GC) system has been designed, fabricated and developed using modem silicon micromachining and VLSI circuit processing techniques. The GC system is composed of a miniature sample injector that incorporates a 10 μ1 sample loop; a 0.9 m long, rectangular-shaped (300 μm width and 10 μm height) capillary column coated with a 0.2 μm thick copper phthalocyanine (CuPc) stationary phase; and a dual-detector scheme based upon a CuPc-coated chemiresistor and a commercially available, 125-μm diameter thermal conductivity detector (TCD) bead. Silicon micromachining was employed to fabricate the interface between the sample injector and the GC system’s column, the GC system’s column itself, and the dual-detector cavity. A novel integrated circuit thin film processing technique was developed to sublime the CuPc stationary phase coating on the GC system’s column walls micromachined in the host silicon wafer substrate and the Pyrex® cover plate which are subsequently electrostatically bonded together. The CuPc-coated chemiresistor was designed and fabricated using conventional VLSI circuit processing techniques. The miniature GC system has demonstrated the capability to directly and completely separate parts-per-million (ppm) ammonia and nitrogen dioxide concentrations when isothermally operated (55–80°C). With a helium carrier gas and nitrogen diluent, a 10 μl sample volume containing ammonia and nitrogen dioxide injected at 40 psi can be separated in less than 30 minutes.