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1、6.012-ElectronicDevicesandCircuitsLecture11-TheMOSCapacitor-Outline•AnnouncementsHandout-LectureOutlineandSummaryExams-WillbereturnedinrecitationnextWed.•Qualitativedescription-MOSinthermalequilibriumDefinitionofstructure:metal/silicondioxide/p-typeSi(Example:n-MOS)Electro
2、staticpotentialofmetalrelativetosilicon:fmZerobiascondition:Sisurfacedepletediffm>fp-Si(typicalsituation)Negativebiasonmetal:depletiontoflat-bandtoaccumulationPositivebiasonmetal:depletiontothresholdtoinversion•Quantitativemodeling-MOSinthermalequilibrium,v=0BCDepletionapp
3、roximationappliedtotheMOScapacitor1.Flat-bandvoltage,VFB2.Accumulationlayersheetchargedensity,qA*3.Maximumdepletionregionwidth,XDT4.Thresholdvoltage,VT5.Inversionlayersheetchargedensity,qN*•MOSwithbiasappliedtotheadjacentn+-regionImplicationfordepletionregionwidthImpactont
4、hresholdvoltageClifFonstad,10/03Lecture11-Slide1Anotherviewofbipolartransistoroperation:ChangingthepotentialenergybarrierbetweenemitterandcollectorwiththeB-EvoltageEmitterBaseCollectorThep-typebaseregionplacesapotentialenergybarrierforelectrons,qf,betweenthen-btypeemittera
5、ndcollectorUnbiasedregions.Whenthecollectorisbiasedpositiverelativetotheemitterisbecomesattractivetoelectrons,Vapplied,CEbuttheelectronsarestillblockedqvV=0CEBEfromflowingtothecollectorbythepotentialbarrierattheEBjunction.qvEBElectronscanonlyflowfromtheemittertothecollecto
6、rwhenthispotentialbarrier,qf,isreducedbyBiasedinbqvapplingaforwardbiasonthebase-ForwardCEemitterjunction.[ItisreducedtoActiveq(f-v).]RegionbBEx0wBClifFonstad,10/03TailoredafterFig.10.1inthecoursetext.Lecture11-Slide2GMOSSvGS+vDSDstructures–iGiDn+n+p-SivBS+iBAnn-channelMOSF
7、ETBInann-channelMOSFET,wehaveton-regions(thesourceandthedrain),asinthenpnBJT,withap-regionproducingapotentialbarrierforelectronsbetweenthem.Inthisdevice,however,itisthevoltageonthegate,v,thatmodulatesthepotentialbarrierheight.GSTheheartofthisdeviceistheMOScapacitor,whichwe
8、willstudytoday.ToanalyzetheMOScapacitorwewillusethedepletionapproximationthatweintroduced
