Revealing the Ferroelectric Fatigue Pathways in HfO₂ Film

Hafnium oxide (HfO₂) has emerged as a transformative material for next-generation non-volatile memory technologies due to its unique ability to exhibit ferroelectricity in ultrathin films. Its practical application is critically hindered by polarization fatigue and depolarization phenomena, while the inherent complexity of these transitions between ferroelectric and paraelectric state in HfO₂ has posed significant challenges. Here, symmetry analysis and with first-principles calculations is leveraged to systematically explore all potential transition pathways from the ferroelectric oIII/oIV phases to the paraelectric mI/mII phases. The results demonstrate that multiple-pathways involving intermediate phases, such as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>F</mml:mi> <mml:mi>m</mml:mi> <mml:mover><mml:mn>3</mml:mn> <mml:mo>¯</mml:mo></mml:mover> <mml:mi>m</mml:mi></mml:mrow> <mml:annotation>$Fm\bar 3m$</mml:annotation></mml:semantics> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>P</mml:mi> <mml:msub><mml:mn>4</mml:mn> <mml:mn>2</mml:mn></mml:msub> <mml:mo>/</mml:mo> <mml:mi>nmc</mml:mi></mml:mrow> <mml:annotation>$P{4}_{2}/\textit{nmc}$</mml:annotation></mml:semantics> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>P</mml:mi> <mml:msub><mml:mn>4</mml:mn> <mml:mn>2</mml:mn></mml:msub> <mml:mo>/</mml:mo> <mml:mi>nmc</mml:mi></mml:mrow> <mml:annotation>$P{4}_{2}/\textit{nmc}$</mml:annotation></mml:semantics> </mml:math> , require relatively high energy barriers ranging from 0.33 to 0.71 eV per unit cell. In contrast, a direct transition from oIII to mI requires overcoming an energy barrier of only 0.11 eV per unit cell, suggesting that ferroelectric fatigue can occur along the direct pathway rather than multiple ones. This direct transition induces an in-plane expansion of ≈4%, thus applying in-plane confinement or compressive strain can be effective in suppressing fatigue. These findings provide a comprehensive framework for elucidating the phase transition dynamics and mechanisms underlying ferroelectric fatigue in HfO₂, offering critical insights for optimizing its integration into advanced memory technologies.