Sensing characteristics of epitaxially-grown tin oxide gas sensor on sapphire substrate

Epitaxial SnO₂ film was grown on a sapphire substrate using a reactive rf magnetron sputter. The microstructure of the thin film was investigated using the 3C₂ beam line from a Pohang Light Source (PLS) consisting of a 2 GeV electron accelerator, four circle X-ray diffractometer, atomic force microscopy (AFM), and transmission electron microscopy (TEM) comparing with the SnO₂ film on the polished alumina. It was confirmed that the thin film grew epitaxially on the sapphire substrate with a variant crystal structure [Development of microstructure controlled and ultrathin SnO₂ gas sensing film, in: Proceedings of the 5th International Meeting on Chemical Sensors, Rome, Italy, 1994]. No grain boundary was exhibited on the surface of the epitaxial thin film. A large portion of the sorption sites in SnO₂ films appears to react easily with the gas. An epitaxial SnO₂ gas sensor, with a Pt heater and electrodes, exhibited a high sensitivity to combustible gases and a particular sensitivity of 95% to alcohol at 2000 ppm and 350°C. The sensor also showed a good stability with small baseline drift and fast reaction and recovery times of about 5 and 30 s, respectively. This experiment confirms the good gas-sensing characteristics of an epitaxially-grown SnO₂ gas sensor.