Nano Lett. 12, 4674–4680 (2012)

Graphene is known for its exceptional purity and its high charge carrier mobilities. But the absence of a bandgap in monolayer graphene renders the material unsuitable for applications in electronics where low off-currents are required. Molybdenum disulphide (MoS2), in contrast, is a two-dimensional semiconductor that could in principle allow for large on/off ratios in field-effect transistors (FETs). Large-scale growth routes and techniques for the fabrication of MoS2-based devices are, however, only just emerging. More complex circuits require the cascading of individual logic elements with compatible input and output signal ranges. Tomas Palacios and colleagues now report the successful fabrication of integrated inverters, NAND logic gates, flip-flop gates and ring oscillators on exfoliated flakes of bilayer MoS2. The key to their integration scheme is the use of FETs with Al and Pd gates in the inverters. The different gate metals have different work functions, leading to opposite shifts in the transistor threshold voltages and inverter operation at signal levels from 0 to 2 V that enable the direct coupling of the devices.