H2S sensors based on SnO2 films: RGTO verses RF sputtering

• H2S sensing properties of RF sputtered and RGTO grown films is compared.
• RF sputtered films exhibited better response kinetics as compared to RGTO films.
• For sputtered film, response curves are highly reversible and repeatable for H2S concentrations from 0.5 to 500 ppm.
• Enhanced response in sputtered films is attributed to bridging type oxygen vacancies.

Gas sensing characteristics of SnO2 thin films prepared by RF sputtering have been investigated and compared to that of RGTO (Rheotaxially Grown and Thermally Oxidized) films. Both the sensor films exhibited a highly selective response towards H2S with RF sputtered film showing better response characteristics. RF sputtered and RGTO films exhibited a maximum response of 54 and 15 towards 10 ppm of H2S at an optimum operating temperature of 150 and 250 °C, respectively. Sputtered films exhibited a linear response in the wide concentration range from 500 ppb to 500 ppm while RGTO films were found to saturate for concentrations above 100 ppm. XPS investigations revealed that the RGTO films are more sub–stoichiometric or oxygen deficient than the sputtered films. Raman studies further indicates that the surface of sputtered and RGTO films are characterized by the presence of oxygen deficiency attributed to the “bridging-type” and deeper “in-plane/sub-bridging” oxygen vacancies, respectively. The improved response kinetics of the RF sputtered films is attributed to the presence of bridging type oxygen vacancies that facilitates the charge transfer between the sensor surface and H2S molecules.