Highly Reliable Hf_1‐XZr_XO₂ with Ultra‐Low Operation Voltage (< 1 V) Enabled by Stoichiometric Control of Tungsten Oxide Interfacial Layer

Abstract The reliability of hafnia‐based ferroelectrics at operating voltages below 1 V, the required voltage range for compatibility with advanced nodes, remains unexplored. Additionally, the impact of the position and conductivity of the interfacial layer (IL) on capacitor characteristics is not well understood. In this study, an Hf_1‐XZr_XO₂ capacitor capable of ultra‐low operation voltage (<1 V) is developed with excellent endurance (>10¹¹ cycles) and retention (>10 years at 85 °C). This performance is achieved by modulating the oxygen stoichiometry of the interfacial oxide. By investigating the oxygen content of the tungsten oxide IL and its effects on conductance and oxygen supply, it is demonstrated that an oxygen‐deficient WO_3‐X layer is the optimal IL for enhancing fatigue and switching kinetics. Moreover, placing WO_3‐X at the top interface significantly enhances crystallization, resulting in wake‐up‐free operation, which enables efficient thickness scaling. Finally, by integrating a precisely engineered WO_3‐X layer with optimized atomic layer deposition in a 5.6 nm capacitor, reliable operation is demonstrated at voltages as low as 0.7–0.8 V. These findings are supported by density functional theory calculations and comprehensive physical and electrical analyses. This study represents a critical advancement in addressing the persistent challenge of reliable low‐voltage operation in ferroelectric memories.