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Study on Gas Sensors Based on Inerratic Porous WO3Film

Author: ShenWanJiang
Tutor: QinYuXiang
School: Tianjin University
Course: Microelectronics and Solid State Electronics
Keywords: porous WO3film gas sensor rapid annealing metal doping metal oxide
CLC: TP212
Type: Master's thesis
Year: 2012
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Abstract


With the development of modern industry, poisonous and harmful gases areproduced in great quantities, which endanger people’s health and environment. Thus,it is of vital realistic meaning to develop different kinds of gas-sensing material andequipment. Of all the sensitive materials at study, WO3has shown prospectiveapplication for gas-sensing.In this thesis, we use AAM as the template and substrate, and then utilizemagnetron sputtering process to generate inerratic netted WO3film of high activesurface onto it; and then, based on this substrate, deposit a metal oxide layer or ametal layer of a few nanometer thick by means of magnetic reaction sputteringprocess or rf sputtering process, respectively, titanium oxides, copper oxides, and Pt.We inquire into the template-assisted depositing process, two different kinds ofthermal annealing process as well as depositing process of double composite films,namely, metal oxide doped process. And investigate how the structure and sensibilityof WO3film responds to templates of various thickness and aperture characteristic,two different kinds of thermal annealing treatment and metal oxide dopant. It turnsout that WO3films sputtering-deposited on AAM templates can duplicate the porousstructure of the template to form inerratic nano aligned WO3film. From AAM ofsmaller aperture, we can get WO3films of more inerratic porous structure. Betterduplicating can be achieved by the films of larger pores. The optimal workingtemperature of WO3film to explore NO2is150℃, under which the porous filmexhibit best sensitivity and selectivity to NO2. Sputtering time can affect the thicknessand sensitivity of netted WO3film. The longer sputtering time is, the thicker films are,and the more compact the structure after anneal we get, in the end, less sensitive toNO2the film is. After rapid annealing treatment, we can get inerratic nano alignedWO3film of smaller grain size, more uniform grain density on the surface of it. Somore oxygen vacancy form, more surface state oxygen there is, thus, better responseto NO2, namely, higher gas response sensitivity it has. However, comparison of thefilms prepared by conventional annealing treatment and rapid annealing treatmentrespectively turns out that the film after rapid thermal annealing treatment has fasterresponse recovery time when it is explored to NO2. The optimal annealingtemperature of inerratic nano aligned WO3film is500℃, under which the porousfilm exhibit best sensitivity and rapid response and recovery time. The porous WO3films doped with metal oxide or metal show better gas sensor property when it isexplored to NO2compared to the films undoped, but do not obviously improveresponse and recovery time. The porous WO3films doped with copper oxides showbest sensitivity to NO2among three samples doped with titanium oxides, copperoxides, and Pt, respectively. According to this theory, we get a gas sensor that it hassuperhigh sensitivity to NO2gas. When the sensor is explored to lower concentrationof NO2gas, such as33ppb, its sensitivity still can reach8.55.

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