15267

1479 دكتري

دكتري

الكترونيك

اصفهان : دانشگاه صنعتي اصفهان

1398

بيست، 109 ، 10ص.: مصور (رنگي)، جدول، نمودار

وحيد غفاري نيا

محمود تبريزچي، عليرضا علافچيان

مسعود سيدي، اصغر غلامي

1398/08/14

كتابنامه

مهندسي برق

مهندسي برق و كامپيوتر

1398/08/14

2575364

1 Modeling of the effect of reducing gases on the electrical conductivity of semiconducting metal oxides Soudeh Barami s barami@ec iut ac ir September 2019 Isfahan University of Technology Isfahan 84156 83111 Iran Degree PhD Language FarsiSuperviser Dr Vahid Ghafarinia Ghafarinia@cc iut ac irAdvisor1 Prof Mahmud Tabrizchi m tabriz@cc iut ac irAdvisor2 Dr Alireza Allafchian allafchian@cc iut ac irAbstractChemiresistive metal oxides are widely used in the fabrication of gas sensors The theory of gas sensitivity ofmetal oxide sensors has been developed based on the gas solid interactions on the metal oxide surface Theseinteractions led to a charge transfer that is well described by the Poisson Boltzmann equation The receptorfunction of metal oxides can be modelled based on this differential equation Here precise results of numericalsolution of Poisson Boltzmann equation and the more general Poisson Fermi Driac equation show thelimitations of approximated solutions and found even where the accumulation layer created near the surface ofmetal oxide grains the Poisson Boltzmann approximation is not valid anymore and the Poisson Fermi Diracequation must be used Here the combination of Poisson Boltzmann relation surface reactions and gasdiffusion has been solved numerically to derive an exact solution for temporal variation of the sensorconductivity The established model can be used for both thin and thick oxide layers The model has beensimulated with different combinations of effective parameters Among the results the significant effect ofdecreasing the grain size and the thickness of the sensitive layer on increasing the sensitivity of the sensor canbe noted Also using the presented equations the ultimate electrical potential limit for each grain was estimated For example for spherical grains with a diameter of 50 nm the surface potential will not exceed 0 3 volts whenthe doping level is 2 5 1017cm 3 To experimentally investigate the model a thin film sensor was fabricated byRF sputtering of ZnO on quartz substrate The transient response of the sensor to an oxygen pulse was recorded The results showed that the proposed model for the transient response of the metal oxide gas sensor is in goodagreement with the experimental responseKey Words Gas sensor metal oxide transient response electrical potential Poisson Fermi Dirac sensor modeling IntroductionThe chemiresistive behavior of metal oxides and their utility for gas detection wasintroduced in early 1960s 1 Since then metal oxides have been the subject of study innumerous researches 2 High sensitivity low cost and simple fabrication process havemade them popular in most of gas sensing applications 3 From the beginning of thisindustry it was required to understand and model the sensing mechanism of metal oxidegas sensors to further improve their performance 4 Hence many research papers havedealt with the receptor function and transducer function of metal oxide films to derive aconduction model for their gas dependent response Error Reference source not found These models could explain the experimental findings in most of important cases

وحيد غفاري نيا

محمود تبريزچي، عليرضا علافچيان

مسعود سيدي، اصغر غلامي