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.