Room-Temperature Au/TiO₂Nanorods/Ti TFT Butanone Sensor: Role of Surface States

A one-dimensional TiO₂ nanorod-based thin film transistor (TFT) for butanone sensing is presented here. A low-cost hydrothermal process was used to deposit TiO₂ nanorods on a Si/SiO₂ substrate. X-ray diffraction, field-emission scanning electron microscopy (FESEM), photoluminescence spectroscopy, and Raman spectroscopy were used to examine the structural, morphological, and optical features of the nanostructure. Formation of aligned nanorods as the carrier transport channels in FET structure were confirmed through FESEM. Electrical characterization revealed the threshold voltage (V_T), mobility (µ), transconductance (g_m), I_on/I_off ratio, and sub-threshold swing (SS) as 0.77 V, 12.2 cm²/V-s, 5.37 mS, 0.6 × 10⁴, and 64.63 mV/dec, respectively. Sensor study exhibited an increase in the drain current (I_d) and shifts in the threshold voltage (V_T) upon exposure to different concentrations of butanone with respect to those in air. These two effects were correlated with the de-trapping of charge carriers at surface sites in association with resistance variation in the sensing layer. However, the room- temperature response towards butanone (82%) at V_gs of 3 V were found to be 16 times greater than the response under a no biasing (5%) condition. The repeatability of the as-fabricated and aged TFT indicates the potentiality of the device over conventional device structures even in harsh environments.