Sensitivity of thermally deposited titanium Dioxide thin film for Liquefied petroleum gas sensing application

Abstract

Titanium dioxide thin films have a wide scope of application including gas sensing. Other studies have been carried on the sensing ability ofTi02 to natural gases (02, CO2 and H2) and hydrocarbons (ethanol and butane). This study investigated if thermally deposited Ti02 thin film is sensitive to LPG by identifying thermal deposition conditions, assessing the variation in sheet resistivity of Ti02 when exposed to LPG and correlating the sensitivity to the optical properties of the Ti02 films. Ti02 films were thermally deposited on microscope glass slides in a square pattern to allow for a four point probe using Van der Pauw setup to measure the sheet resistivity of the films using Keithley 2400 sourcemeter. The resistivity was mea sured in three phases; before, during and after exposure to LPG at room temperature. In all the samples tested, there was a decline in resistance between 0.009 kn and 0.04 kn when the film' was exposed to LPG and about 90% recovery when withdrawn from the LPG rich environment. The change in sheet resistivity was used to deduce film sensitivity to LPG. The film's refractive index was obtained in the range of 1.67 to 1.88 at 550 nm wavelength from the transmittance spectra and used to calculate film porosity. The film thickness was measured using Alpha-step IQ (surface profilometer). The sensitivity of the film was observed to increase with increase in refractive index and decrease in film thickness and film porosity. The improved response of the thinner films over thicker films shows that conduction mainly occurs at the pore phase rather than at the solid phase. This study reveals that Ti02 thin film is sensitive to LPG at room temperature and hence the material is viable for use in fabricating LPG sensors.