Origin of La Doping-Induced Endurance Improvement and Wake-up Effect Reduction in Ferroelectric HfO2 Thin Films

Ferroelectric ${\mathrm{Hf}\mathrm{O}}_{2}$ 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 (${V}_{\mathrm{O}}$), such as endurance failure and wake-up effect. $\mathrm{La}$ 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 ${\mathrm{Hf}\mathrm{O}}_{2}$ through density functional theory calculations. Our results reveal that the undoped ferroelectric ${\mathrm{Hf}\mathrm{O}}_{2}$ requires a certain amount of ${V}_{\mathrm{O}}$ to stabilize its phase, which can only be achieved under a relatively oxygen-poor condition. However, the neutral charge state of ${V}_{\mathrm{O}}$, stabilized by the Fermi level above the (0/2+) transition level, may cause a dielectric breakdown. $\mathrm{La}$ doping at the $\mathrm{Hf}$ sites significantly reduces the formation enthalpy of ${V}_{\mathrm{O}}$ by pushing down the Fermi level, leading to a moderate concentration of the doubly positive ${V}_{\mathrm{O}}$ $({V}_{\mathrm{O}}^{2+})$ in most of the chemical potential regions. This prevents the dielectric breakdown and improves the device endurance. Furthermore, the presence of $\mathrm{La}$ dopants in ferroelectric ${\mathrm{Hf}\mathrm{O}}_{2}$ significantly increases the diffusion barrier of ${V}_{\mathrm{O}}^{2+}$, reducing the wake-up effect. Our findings provide insights into the design and optimization of ferroelectric films for practical applications.