Oxygen migration impact on ferroelectric evolution in Hf0.5Zr0.5O2 devices

Abstract

Ionic migration in Hf0.5Zr0.5O2 (HZO) films play a crucial role in shaping the ferroelectric (FE) properties of HZO, although the underlying mechanisms remain poorly understood. We employed in situ extended x-ray absorption fine structure (EXAFS), a highly challenging technique due to its sensitivity to subtle changes in atomic coordination, to track real-time variations in the local atomic environment of HZO under applied voltage. Despite the inherent complexity of in situ EXAFS, we observed that the migration of oxygen vacancies (Ov) was a key factor in regulating the FE wake-up effects and phase development during device operation. Complementary hard x-ray photoelectron spectroscopy revealed that non-lattice oxygen states are particularly concentrated at the film interfaces. The differential distribution of these oxygen-related states, whether at the interface or within the bulk, showed distinct influences on the formation of the FE orthorhombic (O)- phase (Pca21), as well as the non-FE monoclinic (M)-phase (P21/c) and tetragonal (T)-phase (P42/mnc), as determined by the x-ray phase mapping technique. The combination of these techniques is crucial in uncovering the intricate interplays between structural, electronic, and phase transitions linked to HZO's FE properties during device operation. Based on these findings, we propose strategically adjusting oxygen levels to enhance FE performance while mitigating the wake-up effect.