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

Ferroelectric HfO ₂ is a promising material platform for next-generation devices because it retains ferroelectricity at the nanometer scale and remains compatible with semiconductor processing. In most cases, its ferroelectricity is attributed to a metastable orthorhombic Pca 2 ₁ phase stabilized by oxygen vacancies. However, the high mobility of oxygen vacancies under an electric field destabilizes this phase and causes remanent-polarization instabilities such as wake-up and fatigue, which limits practical application. Here, a valence-complementary codoping strategy is introduced to stabilize ferroelectricity through cation-induced local electric fields rather than oxygen vacancies. Specifically, Hf4+ is replaced by equimolar Y ³⁺ and Nb ⁵⁺ (6% each), preserving the average cation valence while intentionally creating local charge inhomogeneity and lattice strain. The resulting Y _0.06 Nb _0.06 Hf _0.88 O ₂ exhibits a noncentrosymmetric tetragonal P 4 mm structure and remains stable even after annealing in air at 600 °C for 100 h. TaN/YNHO/TaN capacitors endure 10 ¹⁰ polarization-switching cycles at 3.3 MV cm ^-1 without wake-up or fatigue, and the frequency dependence of remanent polarization confirms the ferroelectric nature of YNHO. These results demonstrate intrinsically stable, vacancy-independent ferroelectricity and establish valence-complementary codoping as an effective route toward reliable ferroelectric HfO ₂ devices.