Design And Performance Of Formaldehyde Thin Film Gas Sensor Based On Ln FeO₃(Ln=La,sm)

With the rapid development of industry and construction,the amount of polluting gases discharged into the atmosphere by human is increasing.However,the side-heating gas sensors based on various sensitive particulate materials still suffer from poor reproducibility,which limits the practical applications of this kind of gas sensors.Meanwhile,the rapid development of thin technology and semiconductor technology provides a feasible method for mass production of gas sensors,and the high-performance gas sensor suitable for mass production can be prepared by sol-gel spin coating method combined with electron beam evaporation technology.In this work,La Fe O₃and SmFeO₃ materials are used for research objects and the sensing performance towards HCHO were measured respectively.And the related technology of preparing high performance thin film gas sensor was explored.1.La Fe O₃ thin film was prepared by sol-gel spin coating after annealing.The crystal structure and surface morphology of film were characterized by a series of experiments and characterization,so as to determine the best process for preparing a uniform La Fe O₃ thin film.It can be found that the film was uniform and compact.Then,the La Fe O₃ thin film gas sensor was fabricated by electron beam coating instrument.The results of experiments and characterization show that a uniform film can be obtained by rotating the precursor of 0.4 M La Fe O₃ at 500rpm for 15s,and then at 4500rpm for 30s.In addition,the sensing performance of La Fe O₃ thin film gas sensor was tested.The results show that the the trace detection capacity of LFO thin film gas sensor is as low as 50 ppb,.The performance repeatability of thin film gas sensor was further studied.It was found that the initial resistance value of the film gas sensor of different batches of thin film gas sensors fluctuated in the range of 3.17-3.35 M?,and the response value toward 1 ppm HCHO was between 1.29-138.The corresponding initial resistance value and response value were 5.4%and 6.5%,respectively,which shows excellent performance repeatability.Finally,the sensing mechanism of La Fe O₃thin film gas sensor was discussed based on the theory of depletion layer and electron interaction of target gas on the material surface.Therefore,this research will pave the way on designing high-performance La Fe O₃thin film gas sensors.2.The film formation quality of SmFeO3 film was explored by adjusting the speed and rotation time of spin coating.Then,the crystal structure and the morphology of the film were characterized by means of X-ray diffraction(XRD)and atomic force microscopy(AFM).The thin film gas sensor based on SmFeO₃ was fabricated by electron beam coating instrument,and the gas sensing performance of SmFeO₃ thin film gas sensor was explored.The results show that the detection limit of SmFeO₃ thin film gas sensor is as low as 100 ppb,and it has good favorable selectivity at low concentration(100 ppb-1 ppm)HCHO.Finally,the gas sensing performance of the gas sensor was compared with that of the thin film gas sensor based on Ln Fe O₃,and the enhancement mechanism of Ln Fe O₃ was explored.