Thickness-Dependence of the Coercive Field in Ferroelectrics

TL;DR

This paper extends the understanding of the thickness dependence of coercive fields in ferroelectrics by applying a generalized nucleation and growth model, incorporating screening effects, and successfully matching experimental data across various materials and thicknesses.

Contribution

It introduces a more general Kolmogorov-Avrami model with screening corrections to accurately describe coercive fields in ferroelectrics over a wide thickness range.

Findings

Quantitative agreement with experimental data for PZT, potassium nitrate, and PVDF.

Switching kinetics in PVDF are domain-wall limited down to 1 nanometer.

The model explains the thickness dependence without invoking new effects.

Abstract

For forty years researchers on ferroelectric switching have used the Kay-Dunn theory to model the thickness-dependence of the coercive field; it works surprisingly well, despite the fact that it is based upon homogeneous nucleation and a small-field expansion, neither of which is realized in thin films. Here we demonstrate that this result can be obtained from a more general Kolmogorov-Avrami model of (inhomogeneous) nucleation and growth. By including a correction to the switching field across the dielectric that includes Thomas-Fermi screening in the metal electrode, we show that our theory quantitatively describes the coercive fields versus thickness in several different families of ferroelectric (lead zirconate-titanate [PZT], potassium nitrate, and polyvinylidenefluoride [PVDF]) over a wide range of thickness (5 decades). This agreement is particularly satisfying in the case of PVDF, as it indicates that the switching kinetics are domain-wall limited down to 1 nanometer and thus require no new effects.