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)₂.3H₂O 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 2.15×10⁶ (R_a/R_g) for 10-ppm H₂S at a temperature of 85°C. By raising the operating temperature to 170°C, a high sensitivity of ∼10⁵ 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, H₂, and ethanol. SEM, XRD, and TEM analyses were used to investigate surface morphology and crystallinity of SnO₂ films.