Increased dielectric permittivity of SiO2 thin films

The dielectric permittivity of amorphous SiO2 thin films could be increased by the evaporation of palladium electrodes. The evaporation of gold electrodes does not show a comparable effect. Gold electrodes reproduce the literature value for the dielectric permittivity of SiO2. Because the preparation processes of both types of electrodes have been carried out in the same manner, the detected increase of the dielectric permittivity must be caused by the physical properties of the used evaporated material. A significant difference between gold and palladium is the ability of palladium to absorb large amounts of hydrogen. Therefore we assume in the case of evaporated Pd electrodes a diffusion process of hydrogen atoms into the insulator, which cause additional relaxation centers. The contribution of these relaxation centers to the polarization is measured as an enhanced dielectric permittivity of the SiO2 thin film. Measurements of the small signal response have been carried out in the frequency domain, the time domain, where a Kohlrausch law is found, and in dependence of the temperature. The large signal response was studied using isochronal time domain measurements. A double well potential model is discussed to interpret the experimental results quantitatively. It is shown that a distribution of relaxation times is caused by a distribution of distances between neighbored atoms in the amorphous state. Copyright 2001 American Institute of Physics