Engineering ferroelectricity in monoclinic hafnia

TL;DR

This paper proposes a theoretical design of defect-free, epitaxial superlattices of HfO$_2$ and CeO$_2$ that stabilize the monoclinic phase of HfO$_2$, enabling robust ferroelectricity suitable for high-performance devices.

Contribution

It introduces a novel epitaxial superlattice approach to achieve stable ferroelectricity in HfO$_2$ without defects, based on the monoclinic phase.

Findings

Achieves electric polarization >25 μC/cm²

Ultralow polarization-switching energy barrier (~2.5 meV/atom)

Defect-free, thermodynamically stable ferroelectric superlattices

Abstract

Ferroelectricity in the complementary metal-oxide semiconductor (CMOS)-compatible hafnia (HfO$_2$) is crucial for the fabrication of high-integration nonvolatile memory devices. However, the capture of ferroelectricity in HfO$_2$ requires the stabilization of thermodynamically-metastable orthorhombic or rhombohedral phases, which entails the introduction of defects (e.g., dopants and vacancies) and pays the price of crystal imperfections, causing unpleasant wake-up and fatigue effects. Here, we report a theoretical strategy on the realization of robust ferroelectricity in HfO$_2$-based ferroelectrics by designing a series of epitaxial (HfO$_2$)$_1$/(CeO$_2$)$_1$ superlattices. The advantages of the designated ferroelectric superlattices are defects free, and most importantly, on the base of the thermodynamically stable monoclinic phase of HfO$_2$. Consequently, this allows the creation of superior ferroelectric properties with an electric polarization $>$25 $\mu$C/cm$^2$ and an ultralow polarization-switching energy barrier at $\sim$2.5 meV/atom. Our work may open an entirely new route towards the fabrication of high-performance HfO$_2$ based ferroelectric devices.