Micro thermal conductivity detector based on SOI substrate with low detection limit

Abstract

In this paper, a micro thermal conductivity detector (TCD) with suspended thermistors based on a Silicon-On-Insulator (SOI) substrate was successfully fabricated by using a MEMS technique. The top layer of silicon of the SOI substrate was utilized as the supporting layer of the thermistor, which possessed excellent mechanical strength. The buried SiO2 was utilized as the etch stop layer of deep reactive ion etching in the thermistor release process, which precisely defined the channels with a high depth-to-width ratio and acquired an ultra-small dead volume (∼200 nL). The micro TCD showed sensitive detection at levels as low as 5 ppm of n-alkanes C14-C16 mixtures. Besides, the micro TCD demonstrated excellent universal detection to gas mixtures, which detected all thirteen analytes in the standard sample of n-alkanes C8-C20 mixtures and all eight analytes in the standard sample of VOCs (volatile organic compounds).