Development of a high performance integrated sensor chip with a multi-walled carbon nanotube assisted sensing array

For room temperature toxic gas sensing, a system chip with a MWCNT (multi-walled carbon nanotube)-assisted array of 30 sensors (two sensors for each of 15 sensor types) was developed. Gases tested include four simulants of chemical warfare agents: dichloromethane, acetonitrile, 2-chloroethyl ethyl sulfide, and dimethyl-methyl phosphonate (DMMP). By selecting 15 different functional polymer materials, each composite sensor composed of 15 sensing stacks (polymer/MWCNTs/Si(001), wafer) was fabricated by a solution droplet casting method to simplify the process. The principle of gas sensing is basically to measure the resistivity change of the composite sensor device upon contact with a target gas. One of the advantages of the sensing stack having a polymer overlayer above the MWCNT layer is being able to protect the MWCNT from direct interaction with the gas to improve sensor life and sensitivity. The results indicate that a fingerprint pattern of the sensor radar plot can be determined for each testing run, and that specificity can be achieved through a 3-D principal component analysis of the radar plots. The results also show that a linear relationship between the resistance response and concentration is clearly evident for these four toxic gases. By extrapolation and careful process monitoring, a sensitivity much lower than 43 ppm for DMMP vapor is likely. The gas sensing mechanisms are discussed in the text. (C) 2012 Elsevier B.V. All rights reserved.