Solution-based fabrication of carbon nanotube thin-film logic gate

Carbon nanotubes (CNTs) have attracted significant attention for numerous research fields due to their exceptional electrical properties. The prospect of creating sophisticated CNT devices offers enormous potential for electronic circuits and systems. A critical step in the development of practical electronics is the creation of complementary logic circuits. Such circuits require both p-channel and n-channel semiconductors. However, the CNT field-effect transistors (FETs) usually exhibit p-channel characteristics under ambient conditions with holes as the majority carriers. Previous approaches such as potassium doping and high-temperature annealing to convert p-channel CNT FETs into n-channel devices rely on expensive systems and are timeconsuming. In this chapter, we report the fabrication of low-cost p-channel and n-channel thin-film transistors (TFTs) using single-walled CNT (SWCNT) thin films. The p-type TFTs are fabricated with two solution-based approaches: one device uses aligned SWCNTs prepared by dielectrophoresis, whereas the other contains random-network SWCNTs prepared by layer-by-layer self-assembly. A comparative analysis of these two TFTs is conducted. Their electrical characteristics are analyzed and compared with a focus on the on/off ratios. After the verification of the p-type characteristics, the devices are converted to n-type with surface coating of an electron-donating polymer polyethylenimine (PEI). The p-type and n-type TFTs are combined to form a logic gate device: a voltage inverter. The results demonstrate low-cost, solution-based methods for fabricating SWCNT-based electronic devices. We believe that the combination of the simple fabrication methods, easy conversion of the transistors, and satisfactory logic gate switching performance can influence fundamental research in nanomaterials and practical applications of nanoelectronics.