Influence of microstructure of tungsten oxide thin films on their general performance as ozone and NOx gas sensor

Olena Berger; Thomas Hoffmann; Wolf-Joachim Fischer; Valeri Melev

doi:10.1117/12.501930

24 April 2003 Influence of microstructure of tungsten oxide thin films on their general performance as ozone and NO_x gas sensors

Olena Berger, Thomas Hoffmann, Wolf-Joachim Fischer, Valeri Melev

Author Affiliations +

Proceedings Volume 5116, Smart Sensors, Actuators, and MEMS; (2003) https://doi.org/10.1117/12.501930
Event: Microtechnologies for the New Millennium 2003, 2003, Maspalomas, Gran Canaria, Canary Islands, Spain

Abstract

Tungsten oxides thin films were obtained by electron beam deposition and annealed in the temperature range 350-800°C for 1-3 h. The structure, morphology and phase composition of the as-deposited and annealed films were characterized by X-ray diffraction and AFM. The electrical response towards NO₂ and O₃ was studied both experimentally and theoretically. In order to interprete the kinetic characteristics of tungsten oxide thin films upon exposure to different gases a model, based on surface adsorption/desorption processes coupled with bulk diffusion was used. A link between the geometrical and chemical heterogeneities of the tungsten oxide film surfaces and their performance characteristics as gas sensors was established. It was shown that the nature and the amount of the surface adsorption sites of the different non-stoichiometric phases (W_nO_3n-2or W_nO_3n-1) or WO₃, and their conductive mechanism are defined from: the phase composition of the film, the crystallographic and electronic structure of the phases, the orientation of the crystallites within the film, and the geometrical form and dimensions of the crystallites. All tungsten oxide thin films investigated in this work are suitable to detect very low concentrations of NO₂ (0.05-0.5 ppm in N₂ and synthetic air) and ozone (25-90 ppb) at very low working temperatures (80-160°C). The films annealed at 400°C for 1-2 h are very selective to ozone and the films annealed at 400°C for 3 h and at 800°C for 1 h are very selective to NO₂.

Citation Download Citation

Olena Berger, Thomas Hoffmann, Wolf-Joachim Fischer, and Valeri Melev "Influence of microstructure of tungsten oxide thin films on their general performance as ozone and NO_x gas sensors", Proc. SPIE 5116, Smart Sensors, Actuators, and MEMS, (24 April 2003); https://doi.org/10.1117/12.501930

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