Design And Preparation Of Doped Improved SnO₂ Methane Sensor

Methane is a kind of gas without color and smell,widely distributes in coal mine,biogas digesters,ice gas fields in deep sea and other energy mining areas.Due to its flammable and explosive characteristic,it may bring harm to the safety to people's lives and property.So,it has received high attention from researchers.By using methane gas sensors,we can maintain the environmental safety in industrial production and realize environmental methane concentration real-time monitoring.SnO₂ methane gas sensor has stable performance,low cost,good gas sensitive response and simple preparation process.These characteristics make it become the earliest gas sensor put into research and production.At present,SnO₂ methane sensor has the problems of high working temperature,small response and high energy consumption.In order to solve the problems of high working temperature and low response,doping SnO₂ gas sensing material is used to reduce the optimum working temperature and improve the gas sensing response;In order to solve the problem of high energy consumption,this paper designs MEMS structure micro hot plate.Compared with the traditional heating device,the corresponding temperature can be obtained at a lower heating voltage,and the power consumption of the device is lower.The main content of the dissertation is as follows:1.Pd doped SnO₂ methane sensor was prepared and studied.Firstly,Pd doped SnO₂composites were prepared by a simple hybrid grinding process.Secondly,the gas sensing layer was prepared on the heated plate electrode by a brush coating process.The gas sensing properties of Pd doped SnO₂ gas sensor to methane at different temperature and relative humidity were studied.The results show that Pd doping can improve the gas sensing performance of SnO₂ and reduce its working temperature.Among them,the sensor with 2 wt%Pd doped SnO₂ has the best gas sensing performance,and the gas sensing response to 500 ppm methane can reach 3.43 at the optimal operating temperature(200?),and the sensitivity is increased 45.67 times(50–1000 ppm).Finally,the sensitive mechanism model of Pd doped SnO₂ Composite film to methane gas was established based on the characterization and gas sensing performance test results.2.The micro hot plate of MEMS structure is designed by COMSOL simulation.MEMS micro-hot plate has the size of 100?m×100?m and a three-layer structure.After optimized design,the size of the micro-hot plate is as follows:Pt heating electrode's width is 7?m and thickness is 300 nm,Si₃N₄ isolation and medium layer's thickness is 500 nm,Au test electrodes'thickness is 300 nm.Simulation of three-layers structure refers to the micro hot plate fork electrode area under the condition of optimum parameters of temperature and thermal stress of displacement shows that on both ends of the electrode is 0.22-0.34 V voltage,the temperature in electrode area up to 178-321?and stable,comply with temperature conditions needed for methane gas sensitive sensor testing.Compared with the traditional four-layer micro-hot plate sensor,the specific heat capacity is lower and the temperature of the device is higher under the same heating voltage,which can effectively reduce the power of the device...