Micro-structure Gas Sensors And Electronic Nose

In the last few years, much attenion has been attracted tO micro gas sensors andelectronic noses in the field of gas sensing technology. The micro gas sensor, inWhich a heater, a temperature detector, electrodes and sensitive then film areintegrated by microelectronic, micromachining and thin filmn technlogy, is a newgeneration of gas sensor with the advantages of low power consumption and ease ofintegration (into array or with circuitry. In this thesis, a first membrane-tyPe microgas sensor in China was fabricated successfully; its power consumption is <75 mWwhe operated at 300℃. The structural design and the key of preparation processwere discussed.The resisthee-temperature relation (R-T pattern) of SnO₂, film in temperature-pulsed operation mode was measured, for the first time, using a membrane-typemicro gas sensor, whose temperature can be modulated between room temperatureand 450℃. It is found that from the R-T pattern, it is possible to separate the effectsofthermally activated processes and the surface chemistry on the film resistane. It isthe resistance change due to the surface chemistry that reflects the response processof the film. Therefore, the measurement of R-T patterm in temperature-pulsed modebecomes an approach for the analySis of electrical properties and gas responsemechanism of SnO₂-based or other metal oxide thin films.The 3 deposition processes of SnO₂ thin films (the RGTO technique, from thethermal oxidation of DC-sputtered Sn film at room temperature and RF sputtering inan Ar/O₂(8:2) mixture) in micro gas sensors have been comparatively examined. It isfoun tha the SnO₂ thin film deposited by RF sputtering is very sensitive to organicvapors, and the film is deposited at room temperature, which compatible Wth the lift-off tecnique. Therefore, the RF sputtering is an ideal process for the preparation ofSnO₂, thin films in micro gas sensors.The electrical and gas sensitive properties of SnO₂ and SnO₂-based thin filmshave been studied in detail. The results indicate that the SnO₂, film, deposited by theRGTO technique and doped with Pt, has high sensitivity towards CO and longstability; SnO,-Ag,O then film has good selectivity and high sensitivity towards H,S,its perfOrmance is bCtter than SnO,-Ag and SnO,-CuO then films.An eleCtrOnic nose is an inStrUment, Which comPrises an array of gas sensorswith partial SPecificity and an aPpropriate pattem recoghtion system, caPable ofrecoghzing simPle and comPlex odors. The data acquisition from tin dioxide gassensor array, samPling control, sigllal preProcessing (featUr eXtfaCon), and pattemrecognition tecboques torincipal comPonents analysis and bact4opagation,,Jnetwrks) .in electronic noses were also stUdied in this thesis. A nose systemconStrUotd has good performance in the idelltification of differen Chinse riceWs, orghac vaPors and gasoline grades and is getting closer tO practicalaPPlications.