Generally, thin film sensors based on semiconductor oxides (In₂O₃, SnO₂, Fe₂O₃) are characterised by improved performance when detecting gases of acceptor nature (NO_x, O₃) and C₂H₅OH. Sensitivity of thin films to reducing gases is extremely low. In order to improve the characteristics of thin films to flammable gases, oxide layers are commonly been doped with noble metals. It is essentially, that gas-sensitive features of Fe₂O₃ are strongly determined by its structural features like phase composition, dispersity, defectiveness, morphology etc. γ-Fe₂O₃ is used as an individual layer and as a component of a multi-layer structure of ceramic sensors for detection of flammable gases. In the present work we report a study of gas-sensitive behaviour of γ-Fe₂O₃ thin films deposited on Si-substrate. The sensitive layers were formed from the stabilised sol of Fe₂O₃ prepared by the sol-gel rout. The sol was deposited onto micromachined Si-substrates of new design. Structure of the material was studied by XRD, HR-TEM, DTA/TG, FT-IR and Mössbauer spectroscopy. The applied conditions of Fe₂O₃ synthesis allow to obtain thin-film γ-Fe₂O₃, which is metastable at r.t. As it follows from the DTA/TG data, thus prepared γ-Fe₂O₃ remains stable up to 485 C. TEM characterisation gives spherical particles of size as high as 3-9 nm. Non-uniformity of the grain size distribution provides good quality of the films and close contact between grains. Thin film sensor, based on highly dispersive γ-Fe₂O₃, is characterised by high sensitivity to CH₄. Suitable sensitivity of the sensor to 100 ppm of CH₄ is reached at 350-425 C. Besides, the dynamic response profiles are well reproducible under repeated exposition of CH₄. Optimal operating temperature, at which the sample shows maximum response, fastest dynamics and linear response vs. concentration dependence, is found to be 425 C. This work was supported by the GASMOH project (2000-10041).

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