Fabrication of vacancy-independent and intrinsically stable ferroelectric HfO2 through valence-complementary codoping

Ferroelectric HfO ₂ is attractive for next-generation devices because it retains ferroelectricity in nanometer-scale films and is compatible with semiconductor processing. Most reports ascribe ferroelectricity to a metastable orthorhombic ( Pca 2 ₁ ) phase stabilized by oxygen vacancies, and vacancy migration under electric field is regarded as the origin of remanent-polarization instability (wake-up, fatigue). This study introduces a design strategy for vacancy-independent ferroelectricity: valence-complementary codoping. Substituting Hf ⁴⁺ with equimolar Y ³⁺ and Nb ⁵⁺ (6% each) maintains the average cation valence at 4+ while intentionally creating local charge inhomogeneity that induces internal fields and lattice strain to stabilize a ferroelectric phase. The resulting Y _0.06 Nb _0.06 Hf _0.88 O ₂ (YNHO) is identified as noncentrosymmetric tetragonal P 4 mm by transmission electron microscope, electron diffraction, and grazing-incidence X-ray diffraction. The tetragonal phase persists after annealing in air at 600 °C for 100 h, indicating near-thermodynamic stability. TaN/YNHO/TaN capacitors endure 10 ¹⁰ polarization-switching cycles at 3.3 MV cm ⁻¹ without detectable wake-up or fatigue, indicating that polarization stability does not rely on vacancy migration. Unlike Pca 2 ₁ ferroelectric HfO ₂ , P 4 mm YNHO contains no non-polar sublayers (spacers), suggesting a distinct ferroelectric HfO ₂ . These findings suggest valence-complementary codoping as a practical strategy for realizing intrinsically reliable ferroelectric HfO ₂ and outline a pathway to next-generation logic and memories.