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 (WCl6in ethanol, 0.2 M) on Pt interdigitated Si/Si3N4substrates and annealed at 300°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 polycrystalline WO3films to H2gas (0-250 ppm) in dry air and operating temperatures ranging from 25 to 250°C. Electrical tests confirmed ann-type response of the films. Although improved sensitivity (S=RA/RSENS) 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°C temperature.