Single-crystalline metal-oxide dielectrics for top-gate 2D transistors

Two-dimensional (2D) structures composed of atomically thin materials with high carrier mobility have been studied as candidates for future transistors^1-4. However, owing to the unavailability of suitable high-quality dielectrics, 2D field-effect transistors (FETs) cannot attain the full theoretical potential and advantages despite their superior physical and electrical properties^3,5,6. Here we demonstrate the fabrication of atomically thin single-crystalline Al₂O₃ (c-Al₂O₃) as a high-quality top-gate dielectric in 2D FETs. By using intercalative oxidation techniques, a stable, stoichiometric and atomically thin c-Al₂O₃ layer with a thickness of 1.25 nm is formed on the single-crystalline Al surface at room temperature. Owing to the favourable crystalline structure and well-defined interfaces, the gate leakage current, interface state density and dielectric strength of c-Al₂O₃ meet the International Roadmap for Devices and Systems requirements^3,5,7. Through a one-step transfer process consisting of the source, drain, dielectric materials and gate, we achieve top-gate MoS₂ FETs characterized by a steep subthreshold swing of 61 mV dec^-1, high on/off current ratio of 10⁸ and very small hysteresis of 10 mV. This technique and material demonstrate the possibility of producing high-quality single-crystalline oxides suitable for integration into fully scalable advanced 2D FETs, including negative capacitance transistors and spin transistors.