Low temperature acetone detection by p-type nano-titania thin film: Equivalent circuit model and sensing mechanism

Undoped nanocrystalline anatase p-type TiO2 thin film was deposited by sol-gel method on thermally oxidized p-Si (2-5 Omega cm, < 100 >) substrates. The thin film was characterized by X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) to confirm the formation of nanocrystalline anatase titania and to determine the crystallite size (similar to 7 nm). The resistive sensor structure was fabricated employing two lateral Pd electrodes on top of the TiO2 sensing layer. The developed sensor was tested in the temperature range of 50-200 degrees C for the detection of low ppm acetone (0.5-50 ppm). The maximum response of similar to 115% was obtained at 150 degrees C with response/recovery time of 14 s/22 s at 50 ppm acetone (in air). Moreover, the sensors were capable of detecting acetone as low as 0.5 ppm with acceptable response magnitude. As titania acetone sensors are mostly n-TiO2 based, the acetone sensing mechanism for p-TiO2 is yet to be established authentically. To address the issue, an equivalent circuit model, based on the corresponding band diagram of nanocrystalline p-TiO2 with Pd electrode, was developed to describe the electron transfer mechanism through grain, grain boundary and Pd electrode under the influence of acetone vapor. (C) 2014 Elsevier Ltd. All rights reserved.