A highly stable room temperature titania nanostructure-based thin film transistor (TFT) alcohol sensor

Abstract

The present study is concerned with the room temperature field-induced alcohol sensitivity of nanostructured TiO₂ thin films in field-effect transistor (TFT) configurations. The structural, morphological and optical characterizations of the TiO₂ thin film (grown via a low-cost solution process) revealed that the thickness of the film was ∼220 nm with numerous pores on the surface. The average particle size was found to be 22 nm from XRD characterization. The surface roughness of the film was 215 nm. Photoluminescence studies showed that the TiO₂ band was 3.12 eV. The presence of oxygen vacancies and defect states was confirmed through PL spectroscopy and XPS studies. Electrical characteristics revealed a device mobility of ∼13 cm² V⁻¹ s⁻¹, I_ON/I_OFF ratio of ∼2.16 × 10⁴, subthreshold swing of ∼31.4 mV dec⁻¹ and threshold voltage of 0.65 V. The tuning of carrier concentrations at the sensing channel was achieved through gate biasing in the presence of vapor concentrations. At room temperature, exposure to ethanol, methanol and 2-propanol revealed a drastic drain current variation with shifts in the threshold voltage (V_th) for fixed V_gs and V_ds. The maximum alcohol response of the sensor in terms of drain current variation upon exposure to 100 ppm methanol, ethanol and 2-propanol were 71%, 60% and 51% at room temperature. Such drain current modulation and shifts in threshold voltage were correlated with carrier accumulation at the sensing channel, effects of near-surface bonds and polarization of gas molecules. The long-term stability and excellent alcohol sensing capability at room temperature will possibly pave way for the utilization of the sensor in low-temperature applications such as food storage and space application.