Oxygen Vacancy Energetics and Kinetics at Hf _0.5 Zr _0.5 O ₂ –WO ₃ Interfaces: Impact on Ferroelectric Behavior and Device Functionality

Tungsten is a common electrode material for Hf 0.5 Zr 0.5 O 2 (hafnium zirconium oxide) ferroelectric devices, and WO 3 can form at the interfaces. Here, the role of WO 3 interfacial layers in controlling the oxygen vacancy behavior in Hf 0.5 Zr 0.5 O 2 –WO 3 (HZO/WO 3 ) heterostructures is investigated using density functional theory (DFT). Charge transition level (CTL) analysis shows that the (+2/0) level lies above the conduction band minimum of WO 3, suggesting that oxygen vacancies are thermodynamically stable in the doubly charged state (V O 2+ ) throughout the entire accessible Fermi-level range of the heterostructure. Corresponding formation energy calculations reveal that, at the Fermi level determined by the charge neutrality level calculations, these charged vacancies exhibit the lowest formation energies in the WO 3 region (−0.44 eV) and progressively higher energies toward HZO (up to ∼1.26 eV), demonstrating a strong thermodynamic driving force for vacancy localization in WO 3 . Migration barrier calculations further reveal that V O 2+ defects can diffuse readily from HZO to WO 3, with interfacial barriers as low as 0.45–0.68 eV. These results demonstrate that WO 3 serves as both a thermodynamic sink and a kinetic trap for charged oxygen vacancies, offering a promising pathway to suppress defect-induced degradation and improve endurance in HZO-based ferroelectric devices: instead of striving for an abrupt HZO/W interface, an engineered interlayer of WO 3 would be advantageous.