Sensitive, selective and stable tin dioxide thin-films for carbon monoxide and hydrogen sensing in integrated gas sensor array applications

This paper reports on the preparation, electrical and surface characterization of Cu doped tin dioxide thin-films for highly selective integrated gas sensor devices. The 3000 Å thin-film of 0.16 wt.% copper doped tin dioxide was deposited by reactive R.F. sputtering at room temperature and followed by 10 Å Pt on top of Cu doped tin dioxide thin-film (SnO2–Cu/Pt). In another batch, the 100 Å SiO2 thin-film was deposited on top of the SnO2–Cu/Pt thin-film structure (SnO2–Cu/Pt/SiO2). The electrical response of these thin-films was investigated for CO and H2 gases at different temperatures and gas concentrations. The device with the SnO2–Cu/Pt thin-film, showed excellent electrical response towards CO gas and device with SnO2–Cu/Pt/SiO2 thin-film showed response towards hydrogen only. The SiO2 thin-film prevents the diffusion of CO gas and only hydrogen gas diffuse through silicon dioxide layer. Using thin-films structure SnO2–Cu/Pt and SnO2–Cu/Pt/SiO2, a highly selective sensor device for CO and H2 gas was fabricated. The surface characterization of these thin-films was performed using scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS) techniques. The SEM picture showed that surface structure of the SnO2 thin-film improved by copper doping.