NO2 sensitive Au gate metal-oxide-semiconductor capacitors

Au gate metal-oxide-semiconductor capacitors are sensitive to NO2 in air up to 200 ppm, depending on operating temperature (100 degreesC to 200 degree sC), gate thickness (50 to 900 nm), and morphology. In the absence of catal ytic properties or lattice diffusivity, a model invoking molecular surface adsorption and grain boundary diffusion is proposed, which quantitatively d escribes the transient and steady state response of the devices. Sensitivit y is given by the arrival of the diffusing species to the gate-dielectric i nterface, where capacitive coupling of the adsorbed molecules induces work function changes, which shift the flat band voltage positively, opposite th at observed for H-2 with Pd gates, consistently with an oxidizing, rather t han reducing, character. (C) 2001 American Institute of Physics.