High‐κ Perovskite‐Like Ternary Niobium Oxide Dielectrics for 2D Electronics

High-κ dielectrics with exceptional interface quality are essential for the field-effect control of nanoscale transistors. However, their design remains challenging due to competing atomic-scale polarization requirements. Here, we demonstrate nonlayered perovskite-like ternary niobium oxides (CaNb₂O₆, KNb₃O₈, and Na₂Nb₄O₁₁) as promising candidates, where strong Nb 4d-O 2p covalent hybridization enables pronounced Nb⁵⁺ ionic displacements and enhanced polarization, while ionic bonding from intercalated Ca/K/Na suppresses electronic transitions, widening the bandgap and enhancing stability via configurational entropy. We successfully synthesize these high-quality nanoflakes through a scalable molten-salt method. Crucially, these oxides demonstrate a combination of high dielectric constants (∼16, 9, and 68 for CaNb₂O₆, KNb₃O₈, and Na₂Nb₄O₁₁, respectively), wide bandgaps (∼4 eV), large breakdown field strengths (> 4.9 MV cm^-1), and excellent air stability. Furthermore, due to the low-contamination transfer via a fully dry process, MoS₂ field-effect transistors with these gate dielectrics achieve low subthreshold swings (∼60 mV dec^-1), ON/OFF ratios > 10⁷, gate leakage currents below 10^-6 A cm^-2, and ultralow trap densities. We show high-performance NOT and NAND gates using a CaNb₂O₆ dielectric layer, with the inverter achieving a static power consumption of < 0.02 µW and a gain of ∼20. This work provides new opportunities for the development of next-generation 2D electronics devices.