Top gate engineering of field-effect transistors based on wafer-scale two-dimensional semiconductors

Abstract

l The threshold voltage of the MoS 2 field-effect transistor was controlled by the work function of top gate metal (Au, Cu, Ag, and Al). l The oxidation of the Al gate produced surplus oxygen vacancy (positive charge) and the dipole effect in the HfO 2 dielectric layer. l Transmission electron microscope was employed to explore the thin Al 2 O 3 interlayer in the Al/HfO 2 interface. l The proposed MoS 2 inverter has an optimized inverter switching threshold voltage and DC voltage gain, which possesses significant potential for integrated multistage logic circuits. The investigation of two-dimensional (2D) materials has advanced into practical device applications, such as cascaded logic stages. However, incompatible electrical properties and inappropriate logic levels remain enormous challenges. In this work, a doping-free strategy is investigated by top gated (TG) MoS 2 field-effect transistors (FETs) using various metal gates (Au, Cu, Ag, and Al). These metals with different work functions provide a convenient tuning knob for controlling threshold voltage ( V th ) for MoS 2 FETs. For instance, the Al electrode can create an extra electron doping (n-doping) behavior in the MoS 2 TG-FETs due to a dipole effect at the gate-dielectric interface. In this work, by achieving matched electrical properties for the load transistor and the driver transistor in an inverter circuit, we successfully demonstrate wafer-scale MoS 2 inverter arrays with an optimized inverter switching threshold voltage ( V M ) of 1.5 V and a DC voltage gain of 27 at a supply voltage ( V DD ) of 3 V. This work offers a novel scheme for the fabrication of fully integrated multistage logic circuits based on wafer-scale MoS 2 film.