  Two-dimensional (2D) materials, such as molybdenum disulfide (MoS2), have
been shown to exhibit excellent electrical and optical properties. The
semiconducting nature of MoS2 allows it to overcome the shortcomings of
zero-bandgap graphene, while still sharing many of graphene's advantages for
electronic and optoelectronic applications. Discrete electronic and
optoelectronic components, such as field-effect transistors, sensors and
photodetectors made from few-layer MoS2 show promising performance as potential
substitute of Si in conventional electronics and of organic and amorphous Si
semiconductors in ubiquitous systems and display applications. An important
next step is the fabrication of fully integrated multi-stage circuits and logic
building blocks on MoS2 to demonstrate its capability for complex digital logic
and high-frequency ac applications. This paper demonstrates an inverter, a NAND
gate, a static random access memory, and a five-stage ring oscillator based on
a direct-coupled transistor logic technology. The circuits comprise between two
to twelve transistors seamlessly integrated side-by-side on a single sheet of
bilayer MoS2. Both enhancement-mode and depletion-mode transistors were
fabricated thanks to the use of gate metals with different work functions.
