A General Physics Model of Oxygen Vacancy Dynamics for Ferroelectricity Enhancement and Degradation in Hafnia-Based Thin Films

Oxygen vacancy (V<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text {O}}\text {)}$ </tex-math></inline-formula> defects have been proven to significantly influence polarization switching, particularly in hafnia-based ferroelectric (FE) thin films. In this study, we developed a physical model to delve into a fundamentally deeper understanding of various VO dynamics and their impacts on FE responses in Hf<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{1}-{x}}$ </tex-math></inline-formula>ZrxO2 (HZO) thin films. Specifically, the dynamic generation, drift, and diffusion of VOs during electric field cycles alter the P-E loop. Hence, the underlying mechanism of the ferroelectricity enhancement during wake-up and subsequent degradation during fatigue can be clarified. During the wake-up, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2{P}_{\text {r}}$ </tex-math></inline-formula> enhancement by VO generation and pinch opening by VO migration occur simultaneously. The aggregation of high-concentration VOs stops contributing to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2{P}_{\text {r}}$ </tex-math></inline-formula> and degrades the FE properties. The competing effects lead to the transition from a ferroelectrically stable stage to fatigue.