Influence Of Doping On Gas Sensing Properties Of Metal Oxide Gas Sensor

As the typical semiconductor gas sensor, the metal oxide semiconductor is dominantin the research and applications for its high sensitivity, fast response, low cost, convenientin detection and so on. However, along with the social development, people have anincreasing demand for gas detection. As we know, doping with extrinsic dopants is animportant and effective way to improve gas-sensing performance toward the target gases.So, it is necessary to study the influence of doping on gas sensing properties of metaloxide gas sensor.In this paper, WO₃thick films were prepared using screen printing technique andthen doped with Pd using micro-injection. The doping amount was controlled by changingconcentration of PdCl2solution. The results showed that the gas sensing properties of thedoped WO₃thick films to toluene were superior to those of the undoped ones. Especially,the10-9mol Pd-doped WO₃thick films（inject0.1μL,0.1mol/L PdCl2solution） possessedlarger response, better selectivity and lower operating temperature. Moreover, the bestsensitivity of gas sensor with doping amount toward different gases was different.The Pd-doped WO₃gas sensitive materials were prepared using different dopingtechniques. The gas sensing properties of the gas sensors to ppb NO₂were investigated.The Pd-doped WO₃gas sensors possessed larger and faster response than those of theundoped ones. And gas sensing properties of gas sensors depended on doping technique.Compared solution blending technique with soaking technique, the Pd-WO₃（Ⅰ） gassensors using the first doping technique had larger and faster response. And the responseof Pd-WO₃（Ⅰ） gas sensors to50and500ppb NO₂were7.17and198.82respectively atlow operating temperature（100℃）. Finally, the Pd-WO₃（Ⅰ） gas sensors prepared usingscreen printing technique are very suitable for detecting NO₂at relatively low operatingtemperature.The SiO₂nanoparticles doped ZnO gas sensors were prepared, and tested for theirmethanol and ethanol gas sensing properties. The results showed that SiO₂-doped is quiteeffective in restraining the growth of ZnO grains. In the range of the operating temperatures studied, from400to450℃, SiO₂-doped enhanced the sensitivity of gassensors. However, the sensitivity of SiO₂-doped ZnO gas sensors was restrained from200to350℃. Furthermore, the response time of the doped gas sensors was always longer thanthe pure ZnO.