Orientation-Confinement-Engineered Stabilization of Ferroelectricity in HfO₂ toward Maximum Polarization.

Ferroelectric HfO₂-based materials are promising candidates for memory applications because of their compatibility with complementary metal-oxide-semiconductor (CMOS) technology. However, the ferroelectric phase of HfO₂ is not the ground state, and collective displacements of oxygen atoms could generate multiple polarization switching paths, causing variations in measured polar magnitude across different experiments. To date, the mechanisms underpinning ferroelectric phase stabilization and the observed variations in polarization remain poorly understood. Here, by combining density functional theory (DFT) simulations and experimental measurements, we propose that (111) crystallography orientation confinement in Hf0.5Zr0.5O₂ film can effectively stabilize the ferroelectric phase. Moreover, to account for different polarization magnitudes observed experimentally, we calculate the electric polarizations along different crystal orientations, incorporating both crossing and non-crossing switching paths. These results show that all the crossing switching paths always yield high polarizations. However, relatively high switching barriers in crossing paths make them less likely to occur in measurements. Finally, to achieve high polarization together with low switching barriers, specific oxygen vacancies and cation dopants that facilitate crossing pathways and yield the highest polarization (∼70 µC/cm²) are determined. These insights clarify the preferred (111) orientation and polarization behavior of HfO₂-based films and advance the design of high-performance ferroelectric devices.