Influence of Heat Treatment on the Characteristic of SnO2 Thin Films for Gas Sensor Application

Nano-crystalline SnO₂ films were deposited on glass substrates using dip coating by sol–gel technique for gas sensor applications. These films have been annealed in air at 300, 350 400, and 450 °C for 60 min, and at 400 °C for 15, 30 min. The films have been analyzed through x-ray diffraction and optical absorption spectroscopy. The deposited films have shown tetragonal rutile structures. The average crystallite size increased as annealing temperature increased. The crystallite sizes of the annealed films were 8 nm at 300 °C, 10 nm at 350 °C, 14 nm at 400 °C, and 22 nm at 450 °C for 60 min. Whereas the crystallite sizes showed 16 and 15 nm at annealing temperature of 400 °C for 15 and 30 min, respectively. The energetic values of optical band gaps of the films showed increment with the elevation in annealing temperatures. The optical band gap energies were 2.86, 2.86, 3.14 and 3.35 eV at annealing temperatures of 300, 350, 400, and 450 °C, for 60 min, respectively, and 3.43 and 3.35 eV at annealing temperature of 400 °C for 15 and 30 min, respectively. Electrical D.C. conductivity were measured at temperatures ranging from 30 °C to 170 °C, and these measurements showed an exponential increment as the temperature and time increased. The films were studied in the matter of sensing capabilities for CO gas through evaluation at various times and temperatures. The optimum sensitivity was found at annealing temperature 400 °C. The outcomes revealed a high sensitivity of the deposited films for carbon monoxide at operation temperature of 200 °C. (paper)