Inkjet-Printed MoS₂ Transistors with Predominantly Intraflake Transport

2D semiconductors, such as transition metal dichalcogenides (TMDs) show a rare combination of physical properties that include a large-enough bandgap to ensure sufficient current modulation in transistors, matching electron and hole mobility for complimentary logic operation, and sufficient mechanical flexibility of the nanosheets. Moreover, the solvent-exfoliated TMD-nanosheets may also be processed at low temperatures and onto a wide variety of substrates. However, the poor inter-flake transport in solution-cast 2D-TMD network transistors hinders the realization of high device mobility and current modulations that the intraflake transistors can regularly demonstrate. In this regard, fully printed and electrolyte-gated, narrow-channel MoS₂ field-effect transistors (FETs) with simultaneous high current saturation (>310 µA µm^-1 ) and on-off ratio (>10⁶ ) are proposed here. The transport limitation is overcome by printing an additional metal layer onto the 2D-TMD nanosheet channel, which substantially shortens the effective channel lengths and results in predominant intraflake transport. In addition, a channel-capacitance-modulation induced subthermionic transport is recorded, which leads to a subthreshold slope value as low as 7.5 mV dec^-1 . On the other hand, thermionic MOSFETs and fully printed depletion-mode NMOS inverters are also presented. The demonstrated generic approach involving chemically exfoliated nanosheet inks and the absolute device yield indicates the feasibility of fully printed 2D-TMD electronics.