Antiferroelectric Hafnia Down to the 2D Limit

TL;DR

This paper demonstrates that lead-free hafnia exhibits antiferroelectricity under strain, with stable double-hysteresis and high ordering temperature down to the 2D limit, opening new avenues for energy storage and memory devices.

Contribution

It reveals that hafnia can be antiferroelectric under strain, with stable properties in ultra-thin films, expanding the material's application potential.

Findings

Antiferroelectricity observed in strained hafnia films.

Stable double-hysteresis in single-crystalline hafnia.

Achieved 850°C ordering temperature in 2D limit.

Abstract

Antiferroelectricity is a material property characterized by alternating electric dipoles spontaneously ordered in antiparallel directions. Antiferroelectrics are promising for energy storage, solid-state cooling, and memory technologies; however, these materials are scarce, and their scalability remains largely unexplored. In this work, we demonstrate that single-crystalline hafnia, a lead-free CMOS-compatible material, exhibits antiferroelectricity under compressive-strain conditions. We observe antiparallel sublattice polarization and stable double-hysteresis in single-crystalline (111)-oriented epitaxial La-doped hafnia films grown on yttrium-stabilized zirconia and show that the antipolar orthorhombic phase of hafnia adheres to the Kittel model of antiferroelectricity. Notably, compressive strain strengthens the antiferroelectric order in thinner La-doped hafnia films, achieving an unprecedented 850 C ordering temperature in the two-dimensional limit, highlighting hafnia's potential for advanced antiferroelectric devices.