The Research Of Tin Oxide Gas Sensors

With the development of economy and society, there is a growing emphasis on the monitoring of toxic gases, and’tin oxide gas sensors have been used widely because of their high sensitivity, low cost, and good performance of response and recovery. In this paper, based on literature survey and scientific experiments, we use tin oxide nano-materials as sensitive material and study gas sensing properties of gases such as ethylene and ethanol.Firstly, we study gas sensing properties of ethylene using SnO2 gas sensors. SnO2 powder materials were prepared by chemical precipitation. After SEM, XRD and other means of characterization, we find the size of powder particles is about 10nm, and the distribution of particles is uniform.10 ppm of ethylene was tested by pure SnO2 gas sensors. The maximum sensitivity is about 2.2 in the working temperature of about 200℃ (heating current is 140mA), and the response and recovery performance is good, the response is Is, the recovery time is 5s. Then we doped 3wt%AgNO3、PdCl2 and CuO respectively in SnO2 materials, and made gas sensors. The results show that the device doped of 3wt% PdCl2 getting better performance, the maximum sensitivity is from 2.2 to 2.7, and the optimum operating temperature decreased from 200℃ to 160℃. Also its response and recovery performance is good with 1s of response time and 9s of recovery time. After a test of several repeated times, the resistance can also return to the initial state. The gas sensors achieve good linearity relatively at different concentration of ethylene. The performance of device is stable.Secondly, we study gas sensing properties of ethanol using SnO2 gas sensors. The powder material is also prepared by chemical precipitation. After testing 100ppm ethanol, we find the maximum sensitivity is approximately 19 at the operating temperature of 120 ℃. But its recovery performance is poor, the recovery time is more than 500s. Then we doped 0.5,% and 1% graphene in SnO2 materials, the results show that the recovery performance of gas sensors was improved a lot, and the stable performance of the device is good.Thirdly, we explore the gas sensors based on micro-channel plate (MCP) of silicon with macro porous structure. The Si-MCP was prepared by electrochemical etching with photo assisted. The Si-MCP has arrays of 3μm × 3μm, and the depth is about 200 μm. We prepare the sol with SnCl2 as the precursor and deposit the SnO2 thin films on a substrate to determine the thin film deposition process. Then Si-MCP was acted as the structure of gas sensors after thermal oxidation, and several methods were used to deposit thin films on the inner walls of SiO2-MCP, such as soaking, spin coating, dispensing and liquid flowing. The results show that the methods of spin coating and liquid flowing perform better, a uniform thin film can be deposit on the inner walls of SiO2-MCP, and the thickness is between 100m and 200nm. Finally, we design the heating module of the gas sensors based on SiO2-MCP, and the subsequent gas sensing test is still in progress.This work was sponsored by Shanghai Pujiang Program (No.14PJ1403600), Shanghai Fundamental Key Project (No.11JC1403700), National Natural Science Foundation of China (No.61176108), PCSIRT, and Research Innovation Foundation of ECNU (No.78210245).