Highly Repeatable Low-ppm Ethanol Sensing Characteristics of p-TiO2-Based Resistive Devices

In this paper, we report on the development of a highly sensitive, relatively low-temperature ethanol sensor based on sol-gel derived p-TiO2 thin film. The p-type anatase TiO2 thin film was deposited by sol-gel technique on a thermally oxidized <;100> p-Si (resistivity 5 Ω cm) substrate. Anatase TiO2 phase with <;101> nanocrystallinity was confirmed with an average particle size of ~11 nm from X-ray diffraction and field emission scanning electron microscopic study. Ethanol sensor study, in the resistive mode, was carried out at a relatively low operating temperature range (75 °C-175 °C) for sensing low concentrations of ethanol in air (5-100 ppm). Response magnitude of ~146% was observed at 150 °C toward 100-ppm ethanol (in air) with corresponding response time and recovery time of 39 and 15 s, respectively. The sensor showed appreciably high-response magnitude (129%) even at low ethanol concentration (5 ppm) with acceptable response and recovery time (54 and 22 s, respectively) at the same operating temperature (150 °C). At a particular temperature, for all the ethanol concentrations, sensor showed minimal base line resistance drift, thereby offering highly repeatable and stable sensing performance. Ethanol selectivity study against other volatile organic compounds, such as methanol, acetone, and 2-butanone, was also investigated and was found to be quite promising. Ethanol sensing mechanism for such p-type TiO2 has also been discussed in the light of corresponding oxygen vacancy model.