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Study of Room Temperature WO3Gas-sensing Thin Film Based on Rapid Thermal Annealing and Led Radiation

Author: JiaDingLi
Tutor: HuMing
School: Tianjin University
Course: Microelectronics and Solid State Electronics
Keywords: Room temperature gas sensor Tungsten oxide thin film Rapid thermal annealing LED
CLC: TP212
Type: Master's thesis
Year: 2012
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Abstract


With the development of modern industry, the environmental problems areincreasingly apparent, and that is a great threat to human health and safety. A largeproportion of air pollution gas is nitrogen oxides such as NO2. Environmentalmonitoring and protection cause widespread concern worldwide. In many fields, suchas the environment, energy, automotive industry, food safety, medical and so on,demand for various types of high-performance gas sensors increased. Therefore, thestudy of various types of gas detection with rapid reversible response, which candetect the gas of low concentration especially nitrogen oxide, become an increasinglyprominent issue. Many semiconducting metal oxides can be utilized as solid-state gassensors materials and have been widely used for NO2detection. Among thesesemiconducting metal oxides, WO3is considered to be one of the most attractivematerials for making semiconducting metal oxides gas sensors. Due to slow andappreciable interaction of the surrounding gas with the surface of sensing layer atroom temperature (RT), the working temperature of WO3thin film gas sensor reacheshigh up to about200oC. The heating element is required, thus would increase powerconsumption, and would also be not conducive to the integration with siliconsubstrate. What’s more, the high temperature could even trigger the explosion in somecondition. Therefore, there is an essential need for the development of gas sensors thatcan be operated at lower temperature (even at RT) with enhanced response.This paper creatively used Rapid Thermal Annealing (RTA) to make WO3thinfilms on Al2O3substrate and to combine LED light irradiation to NO2gas sensing test.The general process is as follows: using magnetron sputtering method, interdigitalplatinum electrodes and nano-WO3film were deposited on the clean Al2O3substratesuccessively, and then after rapid thermal annealed, the morphology of all thesamples was investigated by scanning electron microscope (SEM) and atomic forcemicroscope (AFM), the crystallization structure and phase identification werecharacterized by X-ray diffraction (XRD). The NO2-sensing measurementexperiments were taken under the LED light at the room temperature. Compared with conventional thermal annealed WO3thin film, the WO3through RTA exhibitedmarkedly high sensitivity to NO2and short recovery time at RT under the100lx LEDirradiation due to the high specific surface area and the small grain size. Comparisonof different samples helps to find the best rapid thermal parameters for WO3thin filmgas sensors.The results show that Samples after the RTA have the smaller grain size, themore porous the surface of the structure, the larger specific surface area and thenarrower band gap. The initial resistance occurred to reduce under the LED irradiation,thus greatly improved on the NO2sensing property, and provided a guideline to therealization of the high performance room temperature gas sensor to NO2.

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