Magnesium niobate as a high-κ gate dielectric for two-dimensional electronics

Integrated circuits based on two-dimensional semiconductors require ultrathin gate insulators that can provide high interface quality and dielectric reliability, minimized electrically active traps and efficient gate controllability. However, existing two-dimensional insulators do not provide a good trade-off in terms of bandgap, breakdown strength, dielectric constant, leakage current and bias temperature stability. Here, we show that single crystals of magnesium niobate (MgNb₂O₆) can be obtained through a buffer-controlled epitaxial growth process on a mica substrate. The atomically thin MgNb₂O₆ crystals have a wide bandgap (around 5.0 eV), high dielectric constant (around 20), large breakdown voltage (around 16 MV cm⁻¹) and good thermal reliability. The MgNb₂O₆ can form a van der Waals interface with monolayer molybdenum disulfide (MoS₂) with an extremely low density of trap states. MoS₂ field-effect transistors with MgNb₂O₆ gate dielectrics exhibit a hysteresis under 0.9 mV (MV cm⁻¹)⁻¹, a subthreshold swing of 62 mV dec⁻¹, an on/off current ratio of up to 4 × 10⁷ and high electrical reliability at 500 K. The excellent electrostatic controllability of MgNb₂O₆ allowed us to create graphene-contacted transistors and inverter circuits with a channel length of 50 nm.