Formulization of long-time domain switching around the coercive field from imprint measurements on ferroelectric thin films

Abstract

The time interval for the completion of slow polarization reversal in ferroelectric thin films measured in the order of magnitude of 10−9–100s is broadened by more than two decades as the applied field approaches the coercive field of domain switching. The domain-switching kinetics is conjectured to change from the classical Kolmogorov–Avrami–Ishibashi (KAI) model at high fields to nucleation-limited-switching (NLS) model at low fields. However, the true voltage drop across the film from the real-time measurement of the oscilloscope remains constant at a coercive voltage Vc during polarization reversal irrespective of the applied voltage. Therefore, the above high-field assumption for KAI does not exist. From our measurements, a long-time effect of imprint can occur for any slow processes of physical phenomena, even if the imprint field is very weak. The imprinted Vc can be estimated either from the voltage shift in the curve of switched polarization versus the applied voltage or directly from the height variation in domain-switching current plateau after an imprint voltage Vimp for time timp (1μs<timp<10ms). Vc reduces continually with timp under Vimp>0 to exhibit a linear time dependence in a logarithmic scale above an initial time on the order of 1.0μs, even if under Vimp<Vc, which foretells the possibility of the initial unswitched domains with negative polarizations to switch into positive states with the prolonged imprint time under a positive voltage of Vimp. After formulation of the Vc-timp dependence under Vimp according to imprint principles, we derive the time evolution of slow polarization reversal without evoking KAI and NLS approaches once the Vc distribution is obtained for a genuine thin film. The spectrum derivation is completely comparable to experimental measurements, which suggests the common physics between imprint and long-time domain switching of ferroelectric thin films.