Field effect characteristics and gas sensing properties of vertically grown PANI nanofibers

Field effect transistor (FET) type gas sensors are suitable for various wearable and portable applications due to tuneable sensitivity, miniaturized structure, ease of integration, and low power consumption. However, semiconductors such as Si and IGZO did not show good sensing characteristics due to the chemical inertness of the analyte gases. PANI-based conductometric gas sensors have shown good gas sensing characteristics, yet the transfer characteristics for pristine PANI have not been reported due to their inherent conductivity. In this work, transfer characteristics of a PANI based p-FET gas sensor and modulation of gate voltage for tuning of the NH3 sensing characteristics are reported for the first time. Vertical nanofibers of PANI semiconductor grown on SiO2 substrate showed depletion mode transfer characteristics with Ion/Ioff ratio of 184, mobility of 0.051 cm2/V.s, threshold voltage of 39.3 V, and subthreshold swing of −1.46 V/dec. The threshold voltage of FET decreased upon exposure to NH3 gas, which confirmed deprotonation of the PANI nanofibers. Further, the NH3 sensitivity and detection limit were optimized by tuning the gate voltage at 20 V. The drain current of the FET type sensor was decreased by 41% upon exposure to 50 ppm NH3, and the sensor can detect NH3 concentrations as low as 2 ppm at a gate bias of 20 V. Response of the FET type sensor was found to be ∼20 times higher than the spin-coated conductometric gas sensor.