Interface-related decrease of the permittivity in PbZrxTi1−xO3 thin films

In ferroelectric thin films, a decrease of the permittivity is observed obeying a logarithmic time dependence. In the literature, a similar effect has been reported for ferroelectric single crystals and ceramics, which is referred to as ferroelectric aging, and different models have been proposed to explain this phenomenon. In this letter, ferroelectric aging of PbZrxTi1−xO3 thin films is studied as a function of dopant types and concentrations as well as the temperature. The results clearly show that the traditional models for the aging mechanism of ferroelectric single crystals and ceramics are not applicable. Based on these results, a mechanism is proposed which explains the decrease of the dielectric constant in ferroelectric thin films by the growth of a thin surface layer with suppressed ferroelectric properties in the course of aging.