Hydrogen induced relaxations in disordered dielectrics

Abstract

In many non-crystalline or amorphous dielectrics, for example in aluminumoxide, siliconnitride, siliconoxide, or polyimide, the Kohlrausch behaviour of the time dependent polarization current j≈t−α is observed. This empirical law can be detected from the sub-microsecond range up to several thousand seconds indicating a broad distribution of relaxation times. The effect is caused by protons fluctuating in double well potentials between neighboured electronegative atoms, i. e. oxygens or nitrogens. The wells are located at the atomic shells. The transition probability or its inverse, the relaxation time, depends exponentially on the barrier height and for a tunneling transition it depends also on the distance between the wells. The barrier height increases with increasing distance. Therefore the distribution of interatomic nearest neighbour distances in the amorphous state causes the distribution of dielectric relaxation times. The model is confirmed by experiments using palladium instead of gold electrodes. The palladium absorbs hydrogen from the atmosphere and enhances the density of protons in the dielectric resulting in an increase of the polarization strength. This is shown here for thermally grown siliconoxide and electron beam evaporated aluminumoxide.