Origin of La Doping-Induced Endurance Improvement and Wake-up Effect Reduction in Ferroelectric Hf O2 Thin Films

Ferroelectric HfO2 is a promising material for ferroelectric memory applications due to its compatibility with the complementary metal-oxide-semiconductor technology. However, its practical application is hindered by the reliability issues associated with oxygen vacancies (VO), such as endurance failure and wake-up effect. La doping is a highly effective approach to improving the endurance and reducing the wake-up effect. In this study, we investigate the origin of these performance improvements in ferroelectric HfO2 through density functional theory calculations. Our results reveal that the undoped ferroelectric HfO2 requires a certain amount of VO to stabilize its phase, which can only be achieved under a relatively oxygen-poor condition. However, the neutral charge state of VO, stabilized by the Fermi level above the (0/2+) transition level, may cause a dielectric breakdown. La doping at the Hf sites significantly reduces the formation enthalpy of VO by pushing down the Fermi level, leading to a moderate concentration of the doubly positive VO (VO2+) in most of the chemical potential regions. This prevents the dielectric breakdown and improves the device endurance. Furthermore, the presence of La dopants in ferroelectric HfO2 significantly increases the diffusion barrier of VO2+, reducing the wake-up effect. Our findings provide insights into the design and optimization of ferroelectric films for practical applications. © 2023 American Physical Society.