H-2 SENSORS USING FE2O3-BASED THIN-FILM

This paper describes the fabrication procedure as well as the sensing properties of new hydrogen sensors using Fe2O3-based thin film. The film is deposited by the r.f. sputtering technique; its composition is Fe2O3, TiO2(5 mol%) and MgO(0-12 mol%). The conductance change of the film is examined in various test gases. The sensitivity to hydrogen gas is enhanced by treating the film in vacuum at 550 degrees C for 4 h and then in air at 700 degrees C for 2 h. The sputtered Nm is identified to be polycrystalline alpha-Fe2O3 based on X-ray diffraction patterns. However, the surface layer is considered to be changed to Fe3O4 after heating in vacuum and then to gamma-Fe2O3 after heating in air. The film is thus a multilayer one with a thin gamma-Fe2O3 layer on an alpha-Fe2O3 layer. The sensing mechanism is discussed based on measurements of the physical properties of the film, such as the temperature dependence of the sensor conductance, X-ray diffraction pattern, surface morphology, RBS (Rutherford backscattering) spectrum and optical absorption spectrum.