Rhombohedral R3 Phase of Mn-Doped Hf_0.5Zr_0.5O₂ Epitaxial Films with Robust Ferroelectricity

HfO₂-based ferroelectric materials are emerging as key components for next-generation nanoscale devices, owing to their exceptional nanoscale properties and compatibility with established silicon-based electronics infrastructure. Despite the considerable attention garnered by the ferroelectric orthorhombic phase, the polar rhombohedral phase has remained relatively unexplored due to the inherent challenges in its stabilization. In this study, the successful synthesis of a distinct ferroelectric rhombohedral phase is reported, i.e., the R3 phase, in Mn-doped Hf_0.5Zr_0.5O₂ (HZM) epitaxial thin films, which stands different from the conventional Pca2₁ and R3m polar phases. These findings reveal that this R3 phase HZM film exhibits a remnant polarization of up to 47 µC cm^{- 2} at room temperature, along with an exceptional retention capability projected to exceed a decade and an endurance surpassing 10⁹ cycles. Moreover, it is demonstrated that by modulating the concentration of Mn dopant and the film's thickness, it is possible to selectively control the phase transition between the R3, R3m, and Pca2₁ polar phases. This research not only sheds new light on the ferroelectricity of the HfO₂ system but also paves the way for innovative strategies to manipulate ferroelectric properties for enhanced device performance.