Investigation of the sensitivity, selectivity, and reversibility of the chemically-sensitive field-effect transistor (CHEMFET) to detect NO/sub 2/, C/sub 3/H/sub 9/PO/sub 3/, and BF/sub 3/

Abstract

The sensitivity, selectivity, and reversibility of a CHEMFET gas microsensor were investigated as a function of several physical operating parameters. The CHEMFET's responses were expressed based upon the changes generated by modulating the electrical conductivity of the microsensor's thin-film, metal-doped, phthalocyanine-coated interdigitated gate electrode when exposed to a family of challenge gases. Copper phthalocyanine (CuPc) and lead phthalocyanine (PbPc) were used as the chemically-sensitive thin-films which ranged in thicknesses from 250 /spl Aring/ to 1100 /spl Aring/. The challenge gases included: nitrogen dioxide (NO/sub 2/), dimethyl methylphosphonate (C/sub 3/H/sub 9/PO/sub 3/), boron trifluoride (BF/sub 3/), methanol (CH/sub 3/OH), carbon monoxide (CO), vinyl chloride (CH/sub 2/CHCl), and trichloroethylene (C/sub 2/HCl/sub 3/). The concentrations of the gases ranged from 10 parts-per-billion (ppb) to 50 parts-per-million (ppm). Tests performed at at 22/spl deg/C and 110/spl deg/C (70/spl deg/C for the latter four gases) revealed that CuPc was more sensitive to C/sub 3/H/sub 9/PO/sub 3/ and BF/sub 3/, whereas PbPc was more sensitive to NO/sub 2/, CH/sub 3/OH, CO, CH/sub 2/CHCl, and C/sub 2/HCl/sub 3/. The CHEMFET was also moderately selective when challenged with several binary challenge gas mixtures. The metal-doped phthalocyanine thin films were most selective to NO/sub 2/, followed by C/sub 3/H/sub 9/PO/sub 3/. The CHEMFET was not as selective for BF/sub 3/ when combined with several other challenge gases. The CHEMFET was totally reversible for both thin-film candidates and all challenge gases. >