Constitutive equation of the dipole layer in hydrogen-sensing metal-oxide-semiconductor structures

Essential part of MOS-based hydrogen sensors is constituted by a dipole layer of polarized H atoms at the metal-oxide interface. This layer decreases barrier height of the Schottky diodes or causes a shift in the threshold voltage of the FET devices. Constitutive P - E (dielectric polarization versus external electric field intensity) equation of the dipole ensemble is derived supposing Langmuir-type hydrogen absorption and a two-valley model of the elementary dipole potential energy. Depending on the energy difference of the minima, the P - E isotherms suggest a rather sudden flip of the dipole orientation from antiparallel to parallel with respect to the E vector. Rabi resonance experiments could be based on this phenomenon, providing information about the adsorbed hydrogen atoms. Dependences of polarization on parameters of the potential profile and on temperature at selected E values are also presented.