| Most of the semiconductor gas sensors are made from MOS (metal oxide semiconductor).When the gas adsorbed on the MOS's surface, the electronic property (such as conductivity, etc.) can be changed, which is widely used for the purpose of detecting harmful gases. As one of the most important N type MOS materials, SnO2 is one kind of broad-spectrum type gas-sensing materials, and thereby have been well studied and put into wide application. In recent years, the development trend of semiconductor gas sensors is miniaturization, integration and multifunction. Combined with microelectronics technology, the thin film technology makes them possible. It is the reason that the study of thin film gas sensors has attracted increasing attention nowadays.Pt doped SnO2/Pt film and CeO2 doped SnO2/CeO2 film were fabricated by powder sputtering method in this article. Two kinds of films were tested and analyzed, respectively. We discussed the influence of the thickness on the gas-sensing property, including response time, resume time and sensitivity. We also investigated the relationship between the sensitivity and temperature. We found that the component made from the Pt doped SnO2/Pt film existed an optimum working temperature, the optimum working temperature depends on the doping and the kind of detected gases. The component would have an excellent performance within its optimum working temperature range.Experiment results indicate that powder sputtering bulk doped SnO2 / Pt (Pt's concentration is 1Wt %) film exhibit high sensitivity to CO gas. The film sensitivity highly depends on the film thickness. The appropriate film thickness is about 70 - 80 nm, and the optimum working temperature is low, with the value of about 160℃. The response time of SnO2/Pt film is quite short. The response time and resume time both are about 10s.The result show that Pt doping in the SnO2 film not only increases the sensitivity to CO but also lowers the working temperature effectively. This film had high sensitivity to ethanol above 300℃. But in the range of sensitive temperature to CO gas, the film's sensitivity to ethanol is lower, about 50% of that to CO. Therefore, the SnO2/Pt film is a promising material for the application as CO sensor.The gas sensors made from CeO2 doped SnO2/CeO2 film shows good response to the ethanol. The working temperature is in the range of 350- 460℃, the response time of the component is rather short which is about 5 s. When it comes to CO, the device is not sensitive to CO at the working temperature above. Only when the working temperature is lower than 200℃, does the sensitivity to CO become high. Therefore, the SnO2/CeO2 film is a promising material for the application as alcohol sensor.In the experiments, we found that the temperature of gas-sensors component chips would rise when they reacted with the deoxidize gas(C2H5OH, CO, CH4 etc.).The temperature of the gas sensors goes higher along with the increasing of thegas concentration. We called it reaction temperature change (△trea). We found that thetemperature would rise about 4 -10℃when we tested ethanol with the concentration of 200×10-6, using the component whose sensitivity S(100×10-6) >150. High sensitivity component's△trea in high concentration deoxidize gas could damage thegas sensor greatly. In this article, the change of the reaction temperature was also discussed. |
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