Mechanism of formation of the response of a hydrogen gas sensor based on a silicon MOS diode

Experimental data on the dependence of the flat-band voltage and relaxation time for the capacitance of the space-charge region in an MOS diode (Pd-SiO2-n-Si) on the hydrogen concentration in a hydrogen/air gaseous mixture are discussed. It is assumed that variation in the flat-band voltage Ufb in an MOS structure with the thickness d = 369 nm subjected to a hydrogen/air gaseous mixture can be accounted for by the formation of dipoles in the Pd-SiO2 gap due to polarization of hydrogen atoms (Ha). An analytical expression describing the dependence of variation in the flat-band voltage ΔUfb on the hydrogen concentration \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ n_{H_2 } $$\end{document} was derived. In MOS structures with d ≤ 4 nm (or MOS diodes), the value of ΔUfb is mainly controlled by passivation of the centers responsible for the presence of the surface acceptor-type centers at the SiO2-n-Si interface by hydrogen atoms. Analytical expressions describing the dependences of ΔUfb and the capacitance relaxation time in the space-charge region on \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ n_{H_2 } $$\end{document} are derived. The values of the density of adsorption centers and the adsorption heat for hydrogen atoms at the Pd-SiO2 and SiO2-n-Si interfaces are found.