Origin of Interstitial Doping Induced Coercive Field Reduction in Ferroelectric Hafnia

TL;DR

This study uncovers how interstitial Hf dopants in hafnia ferroelectrics reduce coercive fields by promoting domain wall mobility, supported by theoretical and simulation insights, paving the way for faster, lower-power ferroelectric devices.

Contribution

It identifies the $Pca2_1$ phase as key to coercive field reduction and demonstrates the role of interstitial defects in domain wall dynamics through combined computational methods.

Findings

Interstitial Hf dopants facilitate polarization reversal.

Pre-poling reduces switching field below 1 MV/cm.

Certain dopants are promising for coercive field reduction.

Abstract

Hafnia-based ferroelectrics hold promise for nonvolatile ferroelectric memory devices. However, the high coercive field required for polarization switching remains a prime obstacle to their practical applications. A notable reduction in coercive field has been achieved in ferroelectric Hf(Zr)$_{1+x}$O$_2$ films with interstitial Hf(Zr) dopants [Science 381, 558 (2023)], suggesting a less-explored strategy for coercive field optimization. Supported by density functional theory calculations, we demonstrate the $Pca2_1$ phase, with a moderate concentration of interstitial Hf dopants, serves as a minimal model to explain the experimental observations, rather than the originally assumed rhombohedral phase. Large-scale deep potential molecular dynamics simulations suggest that interstitial defects promote the polarization reversal by facilitating $Pbcn$-like mobile 180$^\circ$ domain walls. A simple pre-poling treatment could reduce the switching field to less than 1 MV/cm and enable switching on a subnanosecond timescale. High-throughput calculations reveal a negative correlation between the switching barrier and dopant size and identify a few promising interstitial dopants for coercive field reduction.