Goodbye graphene, hello MoS2
Graphene, a one-atom-thick sheet of carbon atoms, is seen as a potential replacement for silicon in future transistors thanks to its exceptional set of properties (high current density, mobility, and saturation velocity). However, transistors made of graphene cannot be turned off because graphene has almost no bandgap. So investigations have begun for a new 2D material, molybdenum sulfide (MoS), which has similar characteristics but offers something graphene doesn’t: a wide energy bandgap, enabling transistors and circuits to be built from it directly. At IEDM, an MIT-led team will describe the use of CVD processing to grow uniform, flexible, single-molecular layers of MoS, comprising a layer of Mo atoms sandwiched between two layers of S atoms. They exploited the material’s 1.8 eV bandgap to build MoS transistors and simple digital and analog circuits (a NAND logic gate and a 1-bit ADC converter). The transistors demonstrated record MoS mobility (>190 cm2/Vs), an ultra-high on/off current ratio of 108, record current density (~20μA/μm) and saturation, and the first GHz RF performance from MoS. The results show MoS may be suitable for mixed-signal applications and for those which require high performance and mechanical flexibility. (#4.6: "Large-Scale 2D Electronics Based on Single-layer MoS2 Grown by Chemical Vapor Deposition")
A schematic of the CVD process for growing single-layer MoS.