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.

Effect of semiconductor surface homogeneity and interface quality on electrical performance of inkjet-printed oxide field-effect transistors.

In semiconductor technology, the crystallite size of semiconductors is often directly correlated with their superior intrinsic and device mobility. However, when solution-processed, large crystals may bring in higher surface roughness and layer inhomogeneity, which can deteriorate the interface quality and device performance. Along this line, a thorough study on printed oxide field-effect transistors (FETs) has been performed, where the relative significance of crystallite size, surface roughness and spatial homogeneity are evaluated. The comprehensive investigations suggest the spatial homogeneity to be more important than crystallite size in solution processed/printed devices. It is demonstrated that the addition of a small amount of high boiling point polyol in the precursor ink can create large nucleation sites, resulting in reduced average crystallite size, superior inter-particle neck formation, and high spatial homogeneity. Interestingly, carefully estimated device mobility of these polyol-derived In2O3 FETs (∼50-55 cm2 V-1 s-1) is found to be larger than the FETs prepared without polyols, although the crystallite size of the former is an order of magnitude smaller. The high spatial homogeneity and the large mobility values of the polyol-derived In2O3 transistors, as compared to the amorphous oxide FETs, lowers the importance of the latter, at least within the solution-processed/printed electronics domain.