电子技术专业英语教学课件作者何茗unit7.ppt

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1、Unit7SemiconductorDevicesThepropertiesandperformanceofintegratedcircuitsaredependentonthedevicesusedtoconstructthem.ThemostdevicesaremadebybipolartransistorsandMOStransistors.下一页返回Unit7SemiconductorDevicesBipolartransistorsThestructureofaverticalnpntransis

2、torisshowninFigure1.7.1.Thetransistorisformedbygrowingalightlydopedntypeepitaxiallayeronaptypesubstrate.Thislayerbecomesthecollector.TheptypebaseisdiffusedintotheepitaxialcollectorandthentypeemitterisdiffusedintothebaseasshowninFigure1.7.1.Aptypeisolationwe

3、ll(ISO)isdiffusedfromthesurfacetothesubstrate.Duringcircuitoperation,thesubstrateisbiasedatthelowestvoltageinthecircuit.下一页上一页返回Unit7SemiconductorDevicesThisreversebiasesthecollectorisopnjunctionisolatingthecollectorepi.Innormaloperationthebaseemitterpnjunc

4、tionisforwardbiasedandthebasecollectorpnjunctionisreversedbiased.Sincetheemitterismoreheavilydopedthanthebase,theforwardcurrentacrossthebaseemitterjunctionisdominatedbyelectrons.Theelectronsinjectedintothebasecauseanelectronconcentrationgradientinthebasetha

5、tresultsindiffusionofelectronsacrosstheptypebase.下一页上一页返回Unit7SemiconductorDevicesCollectorcurrentThelawofthejunction,equation(2.31),expressestheelectronconcentrationinthebaseattheedgeofthebaseemitterdepletionregion,asafunctionofthevoltageappliedtothebas

6、eemitterjunction.Italsoexpressestheelectronconcentrationinthebaseattheedgeofthebasecollectordepletionregionasafunctionofthevoltageappliedtothebasecollectorjunction.Inthebaseattheedgeofthebaseemitterdepletionregion,theelectronconcentrationis下一页上一页返回Unit7Sem

7、iconductorDevicesTheelectronconcentrationinthebaseattheemitterismanyordersofmagnitudegreaterthantheequilibriumconcentration.InthebaseatthecollectortheelectronconcentrationisWhereVbeisthevoltageappliedtothebaserelativetothecollector.Innormaloperationthecolle

8、ctorisbiasedpositiverelativetothebase,soVbeisanegativevoltage.Theexponentinequation(7.2)isalargenegativenumberandtheelectronconcentrationinthebaseatthecollectorapproacheszero.ThisisillustratedinFigure1