Research On MEMS MOS Gas Sensor For Gas Recognition

Gas recognition plays an important role in many fields such as environmental pollution,home safety,agricultural production,biomedicine and food health.MEMS MOS gas sensor has a wide detection range,low power consumption and low cost,which is very suitable for miniaturization,portable and other intelligent applications of gas recognition technology.For practical application of gas recognition,the high selectivity and low power consumption of MEMS(Micro-electromechanical Systems)MOS(Metal Oxide Semiconductor)gas sensor array is critical.However,the cross-sensitivity of MEMS MOS gas sensor restricts its development in gas recognition.In addition,with the structural design of higher integration,the size of MEMS MOS gas sensor arrays is getting smaller and smaller.To achieve mass production,a material preparation process compatible with MEMS process is necessary and and has practical significance.To solve the problems above,this work designs and fabricates a low-power,high-integration cantilever-type MEMS MOS gas sensor array,and uses the magnetron sputtering method based on semiconductor technology to prepare a variety of gas-sensitive material films.The selectivity of the gas sensor has been improved in terms of different material system and temperature modulation,and food classification has been realized.This research mainly includes the following contents:In order to realize the array and high integration of MEMS MOS gas sensor,a microcantilever-type sensor,a bridge-type sensor and a single-chip quadrangle sensor with four channels,which are based on suspended beam structure,were designed.The main structure of the microcantilever-type gas sensor is on the cantilever beam,and the material area is located at its free end.The power consumption is extremely low,and the sensor can reach 450℃ at about 5.81mW.The main structure of the bridge-type gas sensor is on the suspended bridge,and the sensing area is located in the center of the suspended bridge.Its structural stability is higher than that of the single-cantilever gas sensor,and it can reach 420℃ at about 12.17 mW.The main body of the quadrilateral sensor is a quadrilateral structure composed of four bridges.Four channels are integrated in the center of each edge,which share a quadrilateral heater.The quadrilateral gas sensor has high integration,high structural strength,and low power consumption,which is suitable for use in gas recognition technology.In order to improve the selectivity and response of gas-sensitive materials,noble metal modification and sputtering atmosphere regulation were performed on metal oxide semiconductor materials.The "sandwich" structure of MOS material/noble metal/MOS material is proposed,and the influence of pure oxygen and pure argon sputtering atmosphere on the gas-sensitive properties of the material is studied.It is found that the construction of "sandwich" structure makes the surface of the material have more adsorbed oxygen and reaction sites,and the sputtering atmosphere of oxygen reduces the grain size of the material,which greatly enhanced the response of the sensor to ethanol.The sensitivity of ZnO/Au/ZnO materials prepared by sputtering under 30 sccm oxygen to 100 ppm ethanol reaches 15(Rair/Rgas).In addition,the co-sputtering method is also proposed to dope the noble metals.The selectivity of Pd/SnO2 and Pd/Co3O4 prepared by co-sputtering is greatly improved to ethanol,hydrogen sulfide and hydrogen.On this basis,the selectivity of quadrilateral sensor is further improved from the two aspects of material system and temperature modulation,and food is successfully classified.For the first time,Au/In2O3,Au/SnO2,Cu/SnO2 and Au/WO3,four co-sputtering sensing materials are simultaneously realized on a single-chip quadrilateral sensor,forming four different sensing channels in the true sense.And three kinds of rotten meat(pork,beef and shrimp)are classified by combining recognition algorithm PCA and SVM.Furthermore,based on the quadrilateral structure,a self-temperature-modulated quadrilateral gas sensor is proposed.By designing the different metal widths of the heater on the four edges,a temperature gradient is 50-110℃ between channels of adjacent temperatures when the power consumption of the sensor is 29.90 mW,which can achievie natural temperature modulation on the single-chip sensor.The sensor takes into account low power consumption,small size,and different gas selectivity of different channels,which can effectively distinguish between fruit,vegetables,and meats.