Ferroelectric domain nucleation and switching pathways in hafnium oxide

TL;DR

This study investigates the atomic-scale polarization switching pathways in hafnium oxide thin films, revealing a transient tetragonal-like structure during ferroelectric switching using advanced electron microscopy techniques.

Contribution

It provides the first real-time atomic-scale observation of ferroelectric switching pathways in hafnium oxide, highlighting the role of transient structures in the process.

Findings

Switching involves a transient tetragonal-like structure.

Oxygen ions shift within hafnium polyhedra during switching.

Real-time atomic imaging elucidates the switching mechanism.

Abstract

Nanoscale ferroelectrics that can be integrated into microelectronic fabrication processes are highly desirable for low-power computing and non-volatile memory devices. However, scalable novel ferroelectric materials, such as hafnium oxide (HfO2), remain in a state of development, and a clear understanding of the effects of relevant compositional and processing parameters to control their ferroelectric properties and the actual polarization switching mechanisms are still under investigation. One key fundamental knowledge gap is the polarization switching pathway in ferroelectric hafnia. To further our fundamental understanding of domain nucleation and switching, we have studied polarization switching pathways in HfO2-x thin films in real-time at the atomic scale using transmission electron microscopy. We employed differential phase contrast imaging that allows for the acquisition of both hafnium and oxygen atomic column signals and facilitates the observation of relative movement of atomic columns between both sublattices. Our results demonstrate that the switching pathway involves a transient tetragonal-like local structure, as oxygen ions shift in locations and remain within their parent hafnium polyhedra.