Investigation of the sensitivity, selectivity, and reversibility of the chemically-sensitive field-effect transistor (CHEMFET) to detect NO 2, C3H9PO3, and BF3

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 Å to 1100 Å. The challenge gases included: nitrogen dioxide (NO₂), dimethyl methylphosphonate (C₃H₉PO₃), boron trifluoride (BF₃ ), methanol (CH₃OH), carbon monoxide (CO), vinyl chloride (CH₂CHCl), and trichloroethylene (C₂HCl ₃). The concentrations of the gases ranged from 10 parts-per-billion (ppb) to 50 parts-per-million (ppm). Tests performed at at 22°C and 110°C (70°C for the latter four gases) revealed that CuPc was more sensitive to C₃H₉PO ₃ and BF₃, whereas PbPc was more sensitive to NO ₂, CH₃OH, CO, CH₂CHCl, and C₂HCl₃. The CHEMFET was also moderately selective when challenged with several binary challenge gas mixtures. The metal-doped phthalocyanine thin films were most selective to NO₂ , followed by C₃H₉PO₃. The CHEMFET was not as selective for BF₃ when combined with several other challenge gases. The CHEMFET was totally reversible for both thin-film candidates and all challenge gases