Comprehensive imprint measurements on PbZrxTi1−xO3 (PZT) thin films were carried out. Different models, which were proposed in literature to explain imprint in ferroelectric thin films or a similar aging effect (internal bias) in ferroelectric bulk material, are reviewed. Discrepancies between the experimental results obtained on the PZT films in this work and the prediction of the literature models indicate that these models do not describe the dominant imprint mechanism in PZT thin films. Hence, in this work a model is proposed which suggests imprint to be caused by a strong electric field within a thin surface layer in which the ferroelectric polarization is smaller or even absent compared to the bulk of the film. With the proposed imprint model the influence of important experimental parameters like dopant, illumination, and bias dependence can be qualitatively explained.

The polarization reversal process of tetragonal Pb(Zr,Ti)O 3 thin films has been intensively studied using conventional hysteresis and rectangle pulse measurements. Decreasing the voltage level of the pulses significantly slows down the polarization switching to the range of milliseconds. The switching current response shows a Curie-von Schweidler behavior over a broad time range. The transient current and the frequency dependence of the P -V loops of these films compared to the properties of ferroelectric single crystals show some similarities but also significant differences. The theoretical models of the classical ferroelectric phase transition and especially the conditions of the pulse measurements in single crystals and thin films are discussed. It leads to the conclusion that it is not the domain wall structure and domain wall motion that determine the polarization reversal but dissipative polarization processes which can take place in both ferroelectric and nonferroelectric high-k dielectric thin films.

In this article, the interface screening model is theoretically discussed which explains imprint in ferroelectric thin films caused by a large electric field within a surface layer with deteriorated ferroelectric properties. During aging this field is gradually screened by electronic charges. Different screening mechanisms such as charge injection from the electrodes into the film as well as charge separation within the surface layer are considered by implementing a numerical simulation based on the different screening mechanisms. A comparison between experimental and simulation results is presented. The best agreement between experiment and simulation is obtained for a Frenkel–Poole type charge separation mechanism within the surface layer. The simulation results indicate relatively shallow trap states (0.35 eV) and a surface layer extension of approximately 5 nm.

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.

In this letter, the reversible and irreversible polarization contributions in donor-doped Pb(Zr,Ti)O3 are investigated using conventional capacitance–voltage (C–V) and hysteresis measurements. The dependence of the Rayleigh coefficient in the subcoercive regime on the doping concentration is investigated and shown to be consistent with the assumption of an interaction of the domain walls with randomly distributed defects.