| In the last few years, much attention has been attracted to micro gas sensors and electronic noses in the field of gas sensing technology. The micro gas sensor, in which a heater, a temperature detector, electrodes and sensitive thin film are integrated by microelectronic, micromachining and thin film technology, is a new generation of gas sensor with the advantages of low power consumption and ease of integration. So the semiconductor oxide thin films gradually become the main development direction in the researches of sensitive thin film.As a member of the novel semiconductor materials, tungsten oxide has been under an extensive research in recent years for its unique physicochemical properties. It has been widely used in many different applications, such as electrochromic windows, optical devices, fuel cells, gas sensors, and photocatalyst materials, etc. In this work, WO3 films and Ti-doping WO3 films were deposited on glass substrates by reactive magnetron sputtering technology, we first got the p-type Ti:WO3 films. Pd-doping WO3 films were prepared by sol-del method, which is used as the sensitive thin film in optical gas sensors.The crystal structure, optical properties, surface morphologies and surface compositions of WO3-based films was studied by X-ray diffraction (XRD), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), Hall Effect measurement and spectrophotometer. The changes of their optical properties and structure after annealed as well as the effect of the Ti-doping on the performances and structure were analyzed. The results show the relationship of crystal phases and annealing temperature. In addition, the process parameters on the WO3-based sensitive films were discussed.The optical constants and optical band gap were calculated in this paper by the single oscillator model and transmission envelope method. The band gap of as-deposited WO3 film is about 3.14eV and the refractive index is 2.0 to 2.3 between 400nm to 2400nm. The impact of annealing temperature and Ti-doping on optical constants and optical band gap of WO3 films are investigated, too.Results of the test of film gas sensors based on WO3 and Ti-doping WO3 are discussed in this paper, too. Sensor properties were investigated using resistance measurements upon test gas exposures. The experiments were performed at different operating temperatures as well as on different gas concentrations. The pure WO3 films deposited under 20% oxygen pressure and annealed at 450℃showed excellent sensitivity to 1ppm NO2 gas, the sensitivity exceed 15. While p-type Ti:WO3 films showed excellent sensitivity to PLG gas and the response curve almost show the square-wave figure. The sensor character and gas sensitive mechanism are analyzed. The change of transmissivity of Pd-doping WO3 films have been investigated in H2 gas with different concentration. The gas sensitivity and response time have been studied, too. The transmissivity change mechanism of gas sensitive thin films was explained based on the theory of optical transfer. The theory study was consistent with the experiments and can be used to analyze other n-type optical gas sensor thin films.At the end of this paper a short conclusion for the past work and the goal for future research are made.
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