Few-Layered MnAl₂S₄ Dielectrics for High-Performance van der Waals Stacked Transistors

The gate dielectric layer is an important component in building a field-effect transistor. Here, we report the synthesis of a layered rhombohedral-structured MnAl₂S₄ crystal, which can be mechanically exfoliated down to the monolayer limit. The dielectric properties of few-layered MnAl₂S₄ flakes are systematically investigated, whereby they exhibit a relative dielectric constant of over 6 and an electric breakdown field of around 3.9 MV/cm. The atomically smooth thin MnAl₂S₄ flakes are then applied as a dielectric top gate layer to realize a two-dimensional van der Waals stacked field-effect transistor, which uses MoS₂ as a channel material. The fabricated transistor can be operated at a small drain-source voltage of 0.1 V and gate voltages within ranges of ±2 V, which exhibit a large on-off ratio over 10⁷ at 0.5 V and a low subthreshold swing value of 80 mV/dec. Our work demonstrates that the few-layered MnAl₂S₄ can work as a dielectric layer to realize high-performance two-dimensional transistors, and thus broadens the research on high-κ 2D materials and may provide new opportunities in developing low-dimensional electronic devices with a low power consumption in the future.