Epitaxial ferroelectric hafnia stabilized by symmetry constraints

Abstract

Ferroelectric memories experienced a revival in the last decade due to the discovery of ferroelectricity in HfO${}_2$-based nanometer-thick thin films. These films exhibit exceptional silicon compatibility, overcoming the scaling and integration obstacles that impeded perovskite ferroelectrics' use in high-density integrated circuits. The exact phase responsible for ferroelectricity in hafnia films remains debated with no single factor identified that could stabilize the ferroelectric phase thermodynamically. Here, supported by density functional theory (DFT) high-throughput (HT) calculations that screen a broad range of epitaxial conditions, we demonstrate conclusively that specific epitaxial conditions achievable with common substrates such as yttria-stabilized zirconia (YSZ) and SrTiO${}_3$ can favor the polar Pca2${}_1$ phase thermodynamically over other polar phases such as R3m and Pmn2${}_1$ and nonpolar P2${}_1$/c phase. The substrate's symmetry constraint-induced shear strain is crucial for the preference of Pca2${}_1$. The strain-stability phase diagrams resolve experiment-theory discrepancies and can guide the improvement of ferroelectric properties of epitaxial hafnia thin films.

References in corpus (13)

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• Super-R BiFeO${}_3$: Epitaxial stabilization of a low-symmetry phase with giant electromechanical response
• Stabilization of phase-pure rhombohedral HfZrO4 in Pulsed Laser Deposited thin films

Cited by in corpus (4)

• Progress in Computational Understanding of Ferroelectric Mechanisms in HfO${}_2$
• Disentangling stress and strain effects in ferroelectric HfO2
• Origin of Interstitial Doping Induced Coercive Field Reduction in Ferroelectric Hafnia
• Engineering ferroelectricity in monoclinic hafnia