Large-Area Flexible Printed Thin-Film Transistors with Semiconducting Single-Walled Carbon Nanotubes for NO₂ Sensors

Development of large-area, low-cost, low-voltage, low-power consumption, flexible high-performance printed carbon nanotube thin-film transistors (TFTs) is helpful to promote their future applications in sensors and biosensors, wearable electronics, and the Internet of things. In this work, low-voltage, flexible printed carbon nanotube TFTs with a large-area and low-cost fabrication process were successfully constructed using ultrathin (∼3.6 nm) AlOx thin films formed by plasma oxidation of aluminum as dielectrics and screen-printed silver electrodes as contact electrodes. The as-prepared bottom-gate/bottom-contact carbon nanotube TFTs exhibit a low leakage current (∼10–10 A), a high charge carrier mobility (up to 9.9 cm2 V–1 s–1), high on/off ratios (higher than 105), and small subthreshold swings (80–120 mV/dec) at low operation voltages (from −1.5 to 1 V). At the same time, printed carbon nanotube TFTs showed a high response (ΔR/R = 99.6%) to NO2 gas even at 16 ppm with a faster response and recovery speed (∼8 s, exposure to 0.5 ppm NO2), a lower detection limit (0.069 ppm NO2), and a low power consumption (0.86 μW, exposure to 16 ppm NO2) at a gate voltage of 0.2 V at room temperature. Moreover, the printed carbon nanotube devices exhibited excellent mechanical flexibility and bias stress stability after 12,000 bending cycles at a radius of 5 mm and a bias stress test for 7200 s at a gate voltage of ±1 V, which originated from the ultrathin and compact AlOx dielectric and the super adhesion force between screen-printed silver electrodes and polyethylene terephthalate substrates.