Ultrathin calcium fluoride insulators for two-dimensional field-effect transistors

摘要

Two-dimensional semiconductors could be used to fabricate ultimately scaled field-effect transistors and more-than-Moorenanoelectronic devices. However, these targets cannot be reached without appropriate gate insulators that are scalable to thenanometre range. Typically used oxides such as SiO_2, Al_2O_3 and HfO_2 are, however, amorphous when scaled, and 2D hexagonalboron nitride exhibits excessive gate leakage currents. Here, we show that epitaxial calcium fluoride (CaF_2), which can forma quasi van der Waals interface with 2D semiconductors, can serve as an ultrathin gate insulator for 2D devices. We fabricatescalable bilayer MoS_2 field-effect transistors with a crystalline CaF_2 insulator of ~2 nm thickness, which corresponds toan equivalent oxide thickness of less than 1 nm. Our devices exhibit low leakage currents and competitive device performancecharacteristics, including subthreshold swings down to 90 mV dec~（−1), on/off current ratios up to 107 and a small hysteresis.