Tailoring of the Gas Sensing Performance of TiO2 Nanotubes by 1-D Vertical Electron Transport Technique

Aligned TiO₂ nanotubes (NTs), having diameter of 75 ± 10 nm and length of 280 ± 20 nm were synthesized by electrochemical anodization technique. Two types of device configurations, viz., planar/lateral and metal-insulator-metal (MIM)/vertical sensor structures were fabricated with TiO₂ NTs as the sensing layer. Vertical 1-D electron transport technique of MIM configurations was found to be very effective over the random (across the connected tubes) electron transport kinetics of planar devices, in determining the vapor (ethanol) sensor characteristics like response time and operating temperature. The optimum operating temperature of ethanol sensing was found to be much lower (75 °C) in case of MIM compared with its planar counterpart (150 °C). In addition, MIM configuration offered four and six times faster response and recovery times, respectively, compared with the planar ones toward 100-ppm ethanol at 75 °C. Sensing performance of the device configuration was correlated with the corresponding grain boundary model and carrier transport time with the help of 1-D electron transport path constituted of TiO₂ NT array.