Study On Design And Characteristics Of Micro-structure Gas Sensor Based On Silicon Substrate

Portable smart devices are increasingly popular nowadays as the rapiddevelopment of science and technology. While people enjoy the convenience of theInternet, they eager to set up a more comprehensive network-the Internet of thingswhich can include actual objects surround their usual life. Therefore, more and moreMEMS devices with special features are integrated into smart devices. MEMS gassensor is just such a device which can be used to detect gas composition.This paper presents the recently study on structural design of micro devices andsemiconductor material at first. Then, a micro-heater design process based on ANSYSis generalized and a new Si-based micro sensor is designed by this process. Later,study on improving the performance of α-Fe₂O₃by reforming the synthesis processand doping is showed. Finally, a micro gas sensor is made up by the micro-heater andthe sensitive material. The specific innovative research results of this paper are mainlyon structural design of micro-heater and sensitive material （α-Fe₂O₃） performanceoptimization, as follows:（1） A complete specification design process for micro-heater is proposed basedon ANSYS. And a new Si-based micro heater is designed according the process. Inthe new design, the electrode is only20μm to reduce power consumption with abalance surface temperature distribution; the heating electrodes and the signalelectrodes are arranged on a same layer in order to lower the difficulty and cost ofproduction; A pit is etched in the Si substrate so as to cut down the heat loss. The newmicro-heater’s power consumption is reduced down from390mW to170mWcompared with the commercial one at340℃and its surface temperature distributionis more uniform which is very important for sensitive material.（2） The synthesis process is reformed to improve α-Fe₂O₃gas sensitivecharacteristics at first. FeOOH is prepared by thermal precipitation and divided into5groups by processing temperature for comparison. From the gas sensing performance,it’s easily to find that the group of processing temperature at200/400℃is muchbetter. For this group, its sensitivity for100ppm ethanol reaches to the highest11and the response and recovery time are about30s and150s. Therefore, this group（200/400℃） is chosen to dope carbon nanotubes （MWNTs） to improve its sensitivecharacteristics further. In the second step, α-Fe₂O₃is divided into6groups again bydoping amount. From the gas sensing performance,0.5wt%MWNTs/Fe₂O₃is thebest one of all. The sensitivity for100ppm ethanol reaches to be19much higher thanthe formal11. The response and recovery time are also improved to be20s and120s.At last, some mechanism analysis is introduced to spread the two ways into othersemiconductor materials for gas sensing performance improving.（3） Micro gas sensor which is used to detect ethanol （100ppm） is made up withthe micro-heater and MWNTs/α-Fe₂O₃material. By comparison with traditionaldevices, the static power consumption can be reduced obviously （Iheat=60mA, Heatpower drops from590mW to300mW）. Although the micro sensor’s sensitivity dropsto10.7from16.7as the sensitive material coated on the micro-heater is less. Thesensor’s response and recovery time are improved significantly to5s and90s. WhenIheatis65mA, the micro sensor also can be used to detect formaldehyde.In summary, the researches about this paper provide some ideas and experienceon micro gas sensor.