Switching dynamics in ferroelectric P(VDF-TrFE) thin films

Switching, i.e., polarization reversal, of ferroelectric P(VDF-TrFE) thin films has been investigated in a wide range of applied electric field and temperature. The measured polarization transients can be quantitatively described by a compressed exponential function as originally formulated by Kolmogorov, Avrami, and Ishibashi (the KAI model). The phenomenological parameters switching time and Avrami index are related to the velocity and morphology of the domain walls, respectively. We show that the switching time depends exponentially on the electric field as described by the Merz law. The experimentally obtained Avrami index is independent of temperature but decreases with applied electric field from 1.55 at low field to 1.0 at 300 MV/m, indicative of an out-of-equilibrium dynamics of the growing domains. Using a random walk model we demonstrate that the observed switching dynamics is in agreement with a domain growth mechanism where domains are circular at low electric field with few nucleation sites, whereas at high field irregular entangled domains are formed. The density of nucleation sites is extracted as 1.5% of the monomeric units in this work. Switching transients on capacitors where the nuclei density has been artificially increased exhibit one-dimensional-like growth, as predicted by our model.