Study On Preparation Of Micro Gas-sensitive SnO₂ Sensor By Laser Micro-cladding

With the development of gas-sensitive sensors for more miniaturization,higher integration and better performance, more and more rigid requirements have been brought forward by researchers focusing on fabrication of Micro-gas sensors. At present, the micro gas-sensitive sensors are mainly prepared by thin-film methods, which contain photolithography,sputtering,doping,etching and so on, with complicated process,rigid fabrication circumstance and high cost. It has a profound practical meaning to developing the process to prepare micro gas-sensitive sensor .By using of the equipment for micro laser-cladding developed by our laboratory , a novel MEMS method was brought forward to preparing micro gas-sensitive SnO2 sensor based on micro laser-cladding.We got the gas-sensitive paste by dissolving the SnO2 Nano powder in ethanol and then evaporating it .The paste was steady, with the sedimentation being 0.5 mm high. Under the circumstance of spinning velocity of 6000r/min,spinning time of 30s,Nd-YAG laser scanning velocity of 1mm/s and 0 bias off the focus ,we prepared the SnO2 layer on the 96% board of Alumina . From the SEM photos, we find that in the gas-sensitive layer the SnO2 grains were global with large specific surface area, whose diameters were about 1μm. We prepared the micro-heater on the other side of alumina board. The micro-heater prepared by Micro-pen has the perfect performance of heating with the consumption of power of 3.5W,the heating response time of no more than 20s and the central temperature of 335℃.We prepared arrays of series-wound and shunt-wound gas-sensitive resistors .Through many times of experiments, we found that as for CO and CH4,the narrower and shorter the gas-sensitive films were, the more sensitive the films were and the shorter the time of response and recovery was. The optimum size is 500μm long and 200μm wide, at which the sensitivities were respectively 4.5,7 and 9.5 as for CO,CH4 and ethanol, the optimum working temperatures were 300℃,300℃and 260℃respectively, the response time were 15s,10s and 10s respectively ,and all the recovery time were 20s.