Solution-based fabrication of nanoelectronics using carbon nanotube thin films

Yan Duan

Single-walled carbon nanotubes (SWNTs) have attracted significant attention for many research fields due to their exceptional electronic properties. The prospect of realizing more complicated SWNT-based devices offers enormous potential both as an alternative to silicon technology and as a way to implement high-speed devices and circuits. A critical step in the development of practical electronic devices is the creation of complementary logic gate circuits. Such circuits require both p-channel and n-channel semiconductors. Unfortunately, the SWNT field-effect transistors (FETs) usually exhibit p-channel characteristics under ambient conditions with holes as the majority carriers. Previously, researchers from different groups have developed various methods such as potassium doping in vacuum, annealing in vacuum and annealing in hydrogen to convert p-channel SWNT FETs into n-channel devices. However, these methods rely on expensive annealing systems to remove the air and create an inert environment for the devices. The idea of using simple instruments and easy-to-control procedures to obtain air-stable nchannel SWNT FETs was previously explored. However, the fabrication processes of individual SWNT-based FETs are usually expensive and time-consuming, further reduction in cost and time is therefore needed. In this thesis, we report the fabrication of low-cost p-channel and n-channel FETs using SWNT thin films. The p-channel FETs are fabricated with two solution-based approaches: one device uses random-network SWNTs while the other contains aligned SWNTs using dielectrophoresis. A comparative analysis of thin-film transistors using aligned and random-network carbon nanotubes is investigated. Their electrical characteristics are analyzed and compared with a focus on the on/off ratios and film conductivity. After the verification of the p-channel characteristics, the devices are converted to n-channel with polyethylenimine (PEI) surface coating. This thesis also investigates design and fabrication of our SWNT-based logic gate device: a voltage inverter. Both p-type and n-type FETs produce typical field effects and the voltage inverter exhibits satisfactory switching characteristics. Our results demonstrate a low-cost solution-based method for fabricating SWNT-based electronic devices.

Solution-based fabrication of nanoelectronics using carbon nanotube thin films

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