Robust ferroelectric and low coercive field in ZrO2 thin film through wide chemical-processing window

Abstract

Fluorite-based ferroelectric thin films offer significant potential as candidates for next-generation non-volatile memory logic devices due to their excellent compatibility with existing silicon-based semiconductor technology. However, the challenge lies in the complex preparation of stable fluorite based ferroelectric thin films, as several metastable phases typically exist under narrow and unpredictable experimental conditions, such as harsh temperature, specific thickness, unique strain conditions et al. Here, stable and cost-effective ZrO₂ ferroelectric thin film with tetragonal-orthorhombic-monoclinic phase transition can be fabricated in a wide chemical-processing window. Notably, within a considerable temperature range (∼200 °C) and thickness range (∼250 nm), the ZrO₂ films show robust ferroelectric polarization with a peak value of around 15 μC/cm², comparable to previous reports. The stable ferroelectric phase range can be controlled by adjusting oxygen content and implementing strain engineering. Intriguingly, we further achieve the highest remanent polarization of 20.15 μC/cm² and the lowest coercive field of 1.18 MV/cm by a combination of annealing times and strain engineering. Synchrotron-based X-ray absorption spectroscopy has revealed oxygen tetrahedral distortions, indicating the transition of from the tetragonal to orthorhombic phases. Furthermore, the migration of oxygen ions between the ferroelectric and antiferroelectric phase under electric field activation has been directly detected through integrated differential phase-contrast scanning transmission electron microscopy. This study significantly contributes to the further development of the fabrication procedure and enhances the understanding of the ferroelectric origin for ZrO₂-based fluorite ferroelectric thin films.