Dielectric permittivity of SiO2 thin films in dependence on the ambient hydrogen pressure

Abstract

Metal–silicondioxide–silicon structures with palladium electrodes, instead of standard gold or aluminum electrodes, show an increasing dielectric permittivity of the SiO2 films with increasing ambient hydrogen pressure. Measurements of the complex dielectric permittivity ε_SiO2(f ) in dependence on the hydrogen pressure are carried out at room temperature. The broad relaxational response spectra of the thin films result from a volume polarization effect. Correspondingly, the contribution of absorbed hydrogen to the dielectric permittivity is modeled by proton fluctuations in coulombic double-well potentials between pairs of oxygen ions. The broad distribution of relaxation times can be attributed to the distribution of interatomic distances between the oxygens within the amorphous SiO2. From the experimental dielectric response spectra, a pair distribution function (PDF) of oxygens is derived. This PDF is similar to PDFs from literature, which originate from theoretical lattice simulations of amorphous SiO2. As a quantitative result, we estimate the number of relaxation centers, i.e., oxygen pairs occupied by a proton, which contribute to the dielectric permittivity of the SiO2 thin films in dependence on the hydrogen pressure.