Ultrahigh-sensitive tin-oxide microsensors for H2S detection

Ultrahigh-sensitivity SnO2-CuO sensors were fabricated on Si(100) substrates for detection of low concentrations of hydrogen sulfide. The sensing material was spin coated over platinum electrodes with a thickness of 300 nm applying a sol-gel process. The SnO2-based sensors doped with copper oxide were prepared by adding various amounts of Cu(NO3)(2).3H(2)O to a sol suspension. Conductivity measurements of the sensors annealed at different temperatures have been carried out in dry air and in the presence of 100 ppb to 10-ppm H2S. The nanocrystalline SnO2-CuO thin films showed excellent sensing characteristics upon exposure to low concentrations of H2S below 1 ppm. The 5% CuO-doped sensor having an average grain size of 20 nm exhibits a high sensitivity of 2.15 x 10(6) (R-a/R-g) for 10-ppm H2S at a temperature of 85 degreesC. By raising the operating temperature to 170 degreesC, a high sensitivity of similar to 10(5) is measured and response and recovery times drop to less than 2 min and 15 s, respectively. Selectivity of the sensing material was studied toward various concentrations of CO, CH4, H-2, and ethanol. SEM, XRD, and TEM analyses were used to investigate surface morphology and crystallinity of SnO2 films.