WO3 Hydrogen resistive gas sensor and its wide-range current-mode electronic read-out circuit

"Tungsten oxide (WO3) thin films are prepared via sol-gel route by spinning (WCl6 in ethanol, 0.2 M) on Pt interdigitated Si\/Si3N4 substrates and annealed at 300 degrees C for 12, 24, 96, and 200 hours. Films morphology and crystalline phase are characterized through scanning electron microscopy, atomic force microscopy, and glancing angle X-ray diffraction. The increasing of the annealing time shows a positive effect on the degree of crystallization but with no substantial influence on the crystallite size, surface area, and mean roughness of the films. Electrical tests are carried out using a current-mode dedicated read-out circuit to perform gas-sensing measurements of the poly-crystalline WO3 films to H-2 gas (0-250 ppm) in dry air and operating temperatures ranging from 25 to 250 degrees C. Electrical tests confirmed an n-type response of the films. Although improved sensitivity (S = R-A\/R-SENS) is achieved when decreasing the annealing time, best performances in terms of reproducibility and long-term stability of the response are obtained by annealing the film for 200 hours at 300 degrees C temperature."