最新BJT双极型晶体管课件PPT.ppt

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1、BJT双极型晶体管8.1IntroductiontotheBJTICisanexponentialfunctionofforwardVBEandindependentofreverseVCB.ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)NPNBJT:N+PNECBVBEVCBEmitterBaseCollector2Common-EmitterConfigurationQuestion:WhyisIBoftenpreferredasaparameteroverVBE?ModernSemiconduc

2、torDevicesforIntegratedCircuits(C.Hu)38.3BaseCurrentSomeholesareinjectedfromtheP-typebaseintotheN+emitter.Theholesareprovidedbythebasecurrent,IB.pE'nB'WEWB(b)emitterbasecollectorcontactIEICelectronflow–+holeflowIB(a)contactModernSemiconductorDevicesforIntegratedCircuits(C.Hu)7Isalar

3、geIBdesirable?Why?8.3BaseCurrentemitterbasecollectorcontactIEICelectronflow–+holeflowIB(a)contactModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Forauniformemitter,88.4CurrentGainHowcanbFbemaximized?Common-emittercurrentgain,bF:Common-basecurrentgain:ItcanbeshownthatModernSemic

4、onductorDevicesforIntegratedCircuits(C.Hu)9EXAMPLE:CurrentGainABJThasIC=1mAandIB=10mA.WhatareIE,bFandaF?Solution:WecanconfirmandModernSemiconductorDevicesforIntegratedCircuits(C.Hu)108.4.1EmitterBandgapNarrowingEmitterbandgapnarrowingmakesitdifficulttoraisebFbydopingtheemitterveryhe

5、avily.ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)ToraisebF,NEistypicallyverylarge.Unfortunately,largeNEmakes(heavydopingeffect).SinceniisrelatedtoEg,thiseffectisalsoknownasband-gapnarrowing.DEgEisnegligibleforNE<1018cm-3,is50meVat1019cm-3,95meVat1020cm-3,and140meVat1021cm-

6、3.11TofurtherelevatebF,wecanraiseniBbyusinganepitaxialSi1-hGehbase.Withh=0.2,EgBisreducedby0.1eVandniE2by30x.8.4.2Narrow-BandgapBaseandHeterojuncionBJTModernSemiconductorDevicesforIntegratedCircuits(C.Hu)12AssumeDB=3DE,WE=3WB,NB=1018cm-3,andniB2=ni2.WhatisbFfor(a)NE=1019cm-3,(b)NE=1

7、020cm-3,and(c)NE=1020cm-3andaSiGebasewithDEgB=60meV?(a)AtNE=1019cm-3,DEgE50meV,(b)AtNE=1020cm-3,DEgE95meV(c)EXAMPLE:EmitterBandgapNarrowingandSiGeBaseModernSemiconductorDevicesforIntegratedCircuits(C.Hu)13Ahigh-performanceBJTtypicallyhasalayerofAs-dopedN+poly-siliconfilmintheemitt

8、er.bFislargerduetot