Study On The Conductivity Sensitivity Of Tungsten Oxide Gas Sensors

With the development of society and the improvement of people's living standards,the air quality has gradually become the focus of people's attention.Gas sensors are increasingly becoming important components for detecting toxic and harmful gases.The tungsten oxide gas sensor with high sensitivity,fast response recovery speed,low working temperature and other excellent characteristics,has shown a wide range of potential applications.With the development of sensitive materials,the response types of sensitive materials have become a new research point.The research on the response types of metal oxide sensors plays an important role in understanding the gas sensing mechanism and thus accelerates the rapid development of gas sensors.WO₃ is an N-type semiconductor material,but WO₃ nanowires exhibit a P-type semiconductor response.In this paper,W films were deposited by magnetron sputtering and followed by two-step thermal oxidation to prepare tungsten oxide nanowires on different substrates.The effects of preparation conditions on the growth of tungsten oxide nanowires crystallinity,oxidation degree and microstructure was studied.The tungsten oxide nanowires were characterized by scanning electron microscopy,transmission electron microscopy and X-ray diffraction.The effects of preparation conditions on the response types were investigated.Finally,the P-type response mechanism of tungsten oxide nanowire gas sensors was analyzed.The substrate has a great influence on the growth of tungsten oxide nanowires.The tungsten oxide nanowires with higher density and longer length are uniformly grown on the smooth surface by tube furnace thermal oxidation,while the distribution of nanowires on the surface of porous silicon is sparse and the length is shorter.WO₃nanowires is fully oxidized after annealing treatment.Tungsten oxide nanowires have higher sensitivity to NO₂ gas at room temperature and show P-type response.Nanowires after different annealing time was studied.The morphology of tungsten oxide nanowires recrystallized during long time annealing,and the nanowires gradually transformed into nanoparticles and nanorods.The sputtering time of W film has a significant effect on the growth of tungsten oxide nanowires.When the sputtering time is 5 min,the nanowires become sparse and the oxidation process is relatively complete.The samples at 8 min and 10 min have higher nanowire densities and are not completely oxidized.Annealing temperature has a greater impact on tungsten oxide nanowires.After annealed at 480°C,all of the thinner nanowires were transformed into nanorods or nanoparticles,and the crystal was WO₃ phase.NO₂ gas sensing performance was observed N-type response type at room temperature.The samples annealed at 460°C and below has the nanowires main structure,with insufficient crystallization and P-type response at room temperature.The formation of inversion layer caused by oxygen adsorption in the air made the WO₃ nanowires show P-type response type.