There are many types of gas sensor, due to the different working structure form between gas and material, the physical, chemical and biology reaction are also different, so the classification methods are various, by types of gas: oxygen sensing component, ammonium sensing component and alcohol sensing component; by basis material: metal oxide, organic polymer semi-conductor, solid electrolyte; by working method: dry type and wet type; by structure: sintered, thin-film and thick-film; by working mechanism: resistor type, capacitive type and electrochemistry type.
WO3 is a kind of N structure metal oxide semi conductor material, when it gets contact with the testing gas, the resistance changes which results in the change of output signal in order to test gases. WO3 has a good sense for H2S、Sox and NOx, so it has great potential. Deposition technology for WO3 thin film and related deposition parameter have great influence on sensitivity for thin film gas sensor. Due to the different producing method and condition, defective density in thin film material would be different. Also when making heat treatment of material, grain size also changes, it has big influence on electrical property and gas reaction time for WO3.