Achieving low-voltage thin-film transistors using carbon nanotubes

The potential to perform at low voltages is a unique feature of carbon nanotube thin-film transistors (CNT-TFTs) when compared to more common TFT material options, such as amorphous Si or organic films. In this work, CNT-TFTs are fabricated using high-purity CNTs (verified electrically to be ∼99% semiconducting) on an embedded gate device structure, which allows for scaling of the dielectric (equivalent oxide thickness ∼ 3 nm) and yields a high gate capacitance. The high gate capacitance, coupled with the high semiconducting purity, leads to devices with excellent low-voltage performance having an average subthreshold swing of ∼200 mV/decade (low of ∼90 mV/decade) and on/off current ratios of 10⁵. Testing hundreds of the CNT-TFTs on a chip at various channel lengths and widths provided a first look at the distribution of key performance metrics across a substrate. Favorable trade-offs between on-current and on/off current ratio were observed along with high field-effect mobility and narrow distributions in both the threshold voltage and subthreshold swing. The methods and results demonstrated here show that the low-voltage performance of CNT-TFTs is accessible for macroelectronic applications.