Self‐Assembled Monolayer Dielectrics for Low‐Voltage Carbon Nanotube Transistors with Controlled Network Density

Control of the density and uniformity of semiconducting single‐walled carbon nanotube (SWNT) networks is crucial for their application in field‐effect transistors (FETs) and critically depends on the surface of the substrate. Here, the concept of self‐assembled monolayer (SAM) dielectrics on aluminum/aluminum oxide bottom‐gate electrodes is used to create low‐voltage (<2 V) FETs with SWNT networks. The influence of different phosphonic acid SAMs is investigated on the final network density and charge transport properties of solution‐deposited, polyfluorene‐sorted large‐diameter semiconducting SWNT. Positively charged, imidazolium‐terminated SAMs and those with high dipole moments result in the highest network densities for both spin‐coating and dip‐coating. However, FETs with moderate SWNT coverage on SAMs with long alkyl chains and amine or hydroxyl end‐groups yield the best combination of high on‐conductances and high hole mobilities (up to 20 cm² V⁻¹ s⁻¹) with low trap densities and short critical channel lengths (<2 μm). These parameters are suitable for future short channel, flexible, and high‐frequency FETs.