Fabrication and Characterization of a Suspended TCD Integrated With a Gas Separation Column

Abstract

This paper reports the design, fabrication, and performance evaluation of a unique high aspect ratio resistor on glass employed in a micro thermal conductivity detector (μTCD). Finite-element simulations demonstrate significant improvements in power dissipation and warm-up time by suspending the resistors in the microchannels. Microfabrication techniques employed here enable dry release of 170 μm-diameter coil-shaped resistors on Borofloat in a two-mask process. The microfluidic channels on silicon wafers are independently processed using deep reactive ion etching and subsequently anodic bonded to the glass substrate harboring the TCD resistors. Experiments reveal that the suspended resistors need only 13 mW to reach 100 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C in less than 6 ms and could yield 200 ppm minimum detection limit. The completed chip containing a 1-m-long, 100- μm-wide column with embedded TCD resistors occupies an area of 2.5 × 2 cm. The column coated with an OV-1 stationary phase using the static coating method successfully separated a mixture of hydrocarbons, while the TCD resistors connected in a Wheatstone configuration were able to generate the chromatogram verified by that produced by a commercial flame ionization detector.