Ab Initio Study on 3D Anisotropic Ferroelectric Switching Mechanism and Coercive Field in HfO2 and ZrO2

Abstract

This study proposes a new ferroelectric switching mechanism in HfO2-based ferroelectric films by using density functional theory calculations. It predicts a theoretical coercive field (E-c) consistent with the experimental value (approximate to 1 MV cm(-1)). To this end, this work considers the anisotropic nucleation and growth of reversed polarization along the three principal axes of the orthorhombic phase of HfO2 and ZrO2. This approach differs from the earlier theoretical study that assumed homogeneous switching and predicted too high E-c (approximate to 10 MV cm(-1)), and from the recent theoretical prediction that assumed domain switching but still predicted unrealistically high E-c. Along the b-direction involving the non-polar spacer sub-unit cell layer, the switching barriers (E(s)s) for nucleation and growth of a reversed domain are similar. In contrast, along the a-direction, which lacks a non-polar layer and is previously overlooked, nucleation affects neighboring polar layers, significantly reducing the E-s for growth. Switching types along the c-direction (homogeneous or stepwise) has little effect on the overall E-s. These distinct E-s characteristics along three directions predict an E-c of 1-2 MV cm(-1) for a 10-nm-thick (Hf,Zr)O-2 film, consistent with experimental results.