  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.
