Abstract Ferroelectric HfO2 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 (Pca21) 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 Hf4+ with equimolar Y3+ and Nb5+ (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 Y0.06Nb0.06Hf0.88O2 (YNHO) is identified as noncentrosymmetric tetragonal P4mm 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 1010 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 Pca21 ferroelectric HfO2, P4mm YNHO contains no non-polar sublayers (spacers), suggesting a distinct ferroelectric HfO2. These findings suggest valence-complementary codoping as a practical strategy for realizing intrinsically reliable ferroelectric HfO2 and outline a pathway to next-generation logic and memories.
Asanuma et al. (Thu,) studied this question.