Mixed In/Fe oxide thin films for ppb-level ozone sensing

For the purpose of ozone detection, thin-film gas-sensor based on mixed In/Fe oxides were developed by sputtering and thermal treatment according to the RGTO technique. Preparation of the film was optimized by varying the In-Fe ratio in the sputtering target and electron microscopy analyses were carried out in order to correlate the microstructural features of the nanosized layers with the electrical properties. The nanostructured films exhibit homogeneous morphology and high degree of porosity. Annealing resulted in higher stoichiometry but did not promoted exaggerated coarsening for the grains. A mixed In₂O₃ and Fe₂O₃ composition was determined by electron diffraction. The effect of iron is to decrease working temperature for optimal ozone detection down to 250°C. The sensing layers with higher iron content are capable to detect 30 ppb of O₃ with a relative response ΔG/G of 3.5. Response towards CO, NO₂, ethanol and methanol was also investigated. A good response towards 0.1 ppm of NO₂ was observed at 250°C. Also in this case the best performances are observed for the film with higher iron content.