| Metal-oxide semiconductor (MOS) gas sensors is one of the most important toolsfor people to obtain gas information, it have been playing an indispensable role inenvironmental monitoring and protection, chemical process control, security detection,et al. However, there are some difficulties in obtaining stable analysis result in theapplication since its low sensitivity to low concentration gas, poor selectivity andhigh heating power, which directly lead to the negative influence to the precision ofgas detection. This paper focuses on several key issues related to the design oftesting&analysis instrument, micromodule fabrication, signal recognition method andperformance enhancement method. Major tasks of this paper are as follows:Improved sensor testing&analysis instrument with specialized hardware andsoftware for gas sensor testing has been made to solve several typical problems inMOS sensor application include the design of enclosed structure, overcominguncertain errors by artificial operation, automatic testing process is implemented toovercome traditional artificial repeated and tedious operation, making the processmore easier and credible. It can also ensure the instrument accuracy, response speedand test range in changing environment. Improve the shift mechanism to ensureweak signal (10pA magnitude) acquisition with1.7%precision in each simultaneoustest, it support the research of sensitive material, micromodule and test methods.In the research of gas sensitive materials, this paper reveals the effect of mixingratios of FeCl3and urea on Fe2O3-based gas sensor performance. Tests shows itsperformance of a gas sensitive materials produced by a of a1:3ratio of FeCl3and ureaand in a nano microspheroidal microstructure, is better than those materials in ananorod structure with a1:1ratio, and far superior to ordinary Fe2O3precursormaterial. The contrasting of these test results of the toxic gas emissions with NO, SO2，NO2，CO and H2S, shows that the materials in a1:3ratio are with high sensitivity andgood selectivity. Test using and commercial sensors are suffered from a large size andhigh-power cost, a new micro sensor has been designed, which is in a1.6mm1.6mmmicro-heating plate structure and packaged by a standard SMD ceramic pedestal.Finite element simulation and experimental tests show that the power in which asensor can reaching its working desired temperature is25mW, and h eat transfer rateand thermal efficiency of the sensor are far superior to those ordinary ceramic tubesensors. Also the whole volume of the sensors is greatly reduced，and suit for miniaturization applications.This article analyzes and investigates the principles and features of the detectionon various gas or mixed gas by using single sensor with temperature modulationtechnique, it proposes the sample method of transient response of temperaturechanging and the stable-state response of each voltage step section by using stairshape heating voltage, which is helpful to get the comparatively overallcharacteristics. According to the redundant sample characteristics dimensions as wellas the redundant problem inevitably caused by characteristics relevance, it proposesand proves the sample characteristics optimization method based on cover rough setand adaptive cover-generation method. Comparison experiments of feature extractionin time domain and wavelet time-frequency domain indicated this simplified featureset method possesses better classification recognition accuracy and regressionprediction accuracy than ranking method by using maximum value of the distances ofinternal class and interclass. The extracted sample characteristics set is presented bydisjunctive form and can be configured by the actual needs with more flexibility.On the basis of the analysis on MOS gas sensor oxygen-ion model, it is foundthat after the new type sensor contacts with the gas, the consumption speed ofionization oxygen is much higher than its generation speed. Therefore, it proposes toincrease the objective gas volume fraction to react with ionization oxygen within ashort time and quickly replace the electron for the compressed gas source test methodwhile the conductivity materials are temporally increased. And thus it raises theconception of concentration responsiveness. In accordance to the micro heating platetype element and new gas sensing materials, it designs and produces an improved testmachine with the function of compressing little space gas source. It is demonstratedfrom the test results that this method is effective for the sensing enhancementdetection with extremely low volume fraction, and as to H2S, a four-time polynomialfitting model is established with average derivation5.834%in modeling repeatabilityand the maximum sample derivation7.9%. |
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