《半导体器件物理》4

2020/2/27PhysicsofSemiconductorDevices1MOSFETANDRELATEDDEVICE2020/2/27PhysicsofSemiconductorDevices2OUTLINEThePowerMOSFETTheMOSDiodeMOSFETFundamentalsMOSFETScalingCOMSandBiCOMSMOSFETonInsulatorMOSMemoryStructure2020/2/27PhysicsofSemiconductorDevices3SiO2metalsemiconductorSiO2semiconductordOhmiccontactTheMOSDiodeisofparamountimportantinsemiconductordevicephysicsbecausethedeviceextremelyusefulinthestudyofsemiconductorsurfaces.2020/2/27PhysicsofSemiconductorDevices4TheIdealMOSDiode2020/2/27PhysicsofSemiconductorDevices5AnidealMOSdiodeisdefinedasfollows:a)Atzeroappliedbias,02BEmsmmsqqqqqqgb)Theonlychargesthatexistinthediodeunderanybiasingconditionsarethoseinthesemiconductorandthosewithequalbutoppositesignonthemetalsurfaceadjacenttotheoxide.c)Thereisnocarriertransportthroughtheoxideunderthedirectcurrentdc)-biasingconditions,ortheresistivityoftheoxideisinfinite.2020/2/27PhysicsofSemiconductorDevices6OperationModes2020/2/27PhysicsofSemiconductorDevices7EnergyBandDiagramsAndChargeDistributionAccumulation:2020/2/27PhysicsofSemiconductorDevices8Accumulation:QmQS-dxChargeDistributionkTEEiPFienPxE(X)ElectricFieldAnaccumulationofholesneartheoxide-semiconductorinterface.2020/2/27PhysicsofSemiconductorDevices9Depletion:EFVg0EFEvEcEiWqNQAscChargeDistributionE(X)xElectricFieldxwQm-d)(x2020/2/27PhysicsofSemiconductorDevices10StrongInversion:kTEEipiFenn2020/2/27PhysicsofSemiconductorDevices11StrongInversion:xwmQm-dQnQscChargeDistributionmAnscnsWqNQQQQElectricFieldxE(x)Oncestronginversionoccurs,averysmallincreaseinbandbendingcorrespondingtoaverysmallincreaseindepletion-layerwidthresultsinalargeincreaseintheQnintheinversionlayer,sothesurfacedepletion-layerwithreachesamaximum,Wm.)(x2020/2/27PhysicsofSemiconductorDevices12TheSurfaceDepletionRegionisthebandbendingwithboundaryconditions0inthebulkands)0(EFEiSemiconductorsurfaceECEvEgBqsqOxidexP-typesilicon)(xq0s2020/2/27PhysicsofSemiconductorDevices13Atthesurfacethedensitiesare:kTqipBsenn)(kTqipsBenp)(IntheMOSdiode,thefollowingregionsofsurfacepotentialcanbedistinguished:0sAccumulationofholes(bandsbendupward)0sFlatbandcondition0sBDepletionofhole(bandsbenddownward)BsMidgapwithns=np=ni(intrinsicconcentration)BsInversion(bandsbenddownward)2020/2/27PhysicsofSemiconductorDevices14Thepotentialasafunctionofdistancecanbeobtainedbyusingtheone-dimensionalPoisson’sequation:ssxdxd)(22Afterusingthedepletionapproximationthatweemployedinthestudyofp-njunctions.21WxsThesurfacepotentialsis:SAsWqN2222020/2/27PhysicsofSemiconductorDevices15Thecriterionoftheonsetofstronginversion:iABsnNqkTinvln22)(Themaximumwidthofthesurfacedepletionregion:AiAsABsmqNnNkTqNWln2)2(2and)2(2BAsscNqQ2020/2/27PhysicsofSemiconductorDevices16SurfaceChargevs.SurfacePotential2020/2/27PhysicsofSemiconductorDevices17TherelationshipbetweenWmandtheimpurityconcentrationforsiliconandgalliumarsenide,whereNBisequaltoNAforP-typeandNDforn-typesemiconductor.2020/2/27PhysicsofSemiconductorDevices18CapacitanceinaMOScapacitorSmallsignalcapacitanceMOScapacitanceisdefinedassmallsignalcapacitanceandismeasuredbyapplyingasmallacvoltageonthetopofadcbiasdtdVCdtdVdVdQdtdQIGGGGG2020/2/27PhysicsofSemiconductorDevices19C-VCurves2020/2/27PhysicsofSemiconductorDevices20FrequencyEffectThefrequencyofacsignalplayanimportantroleinthecapacitanceofaMOSCapacitor(afterGrove,etal.)2020/2/27PhysicsofSemiconductorDevices21IdealMOSCurvesQm0VDepletionregionxw-d-Qn-qNA)(xsEFECEi0qV0VBqsqjxEFInversionregionEvQSNeutralsregionBanddiagram(p-typesubstrate)Chargedistribution2020/2/27PhysicsofSemiconductorDevices22)(x-d0wx0oxsQElectric-fieldDistribution-dv0vswx0)(xPotentialDistributionTheappliedvoltagewillappearpartlyacrosstheoxideandpartlycrossthesemiconductor.sVV0000CQdVS2020/2/27PhysicsofSemiconductorDevices23CapacitanceatLowFrequencyLowfrequencyorquasi-staticMajorityandminoritycarriercanrespondwithacsignalandreachatequilibriumconditionP-typesubstrateAccumulation)2exp(kTqQsssgoxsSoxVqkTCddQCC211111oxCVQCSiCoxCQQ2020/2/27PhysicsofSemiconductorDevices24DepletiondsisasisddWqNdQdC2)(soxsaisoxdagCqNCWqNV2)2(12asigoxoxqNVCCCoxCDCQQW2020/2/27PhysicsofSemiconductorDevices25InversionoxCinvCsgoxsSoxVqkTCddQCC211111QQwdmOncetheinversionlayerforms,thecapacitancestartstoincrease,sincecsiisnowgivenbythevariationoftheinversionchargewithrespecttowhichismuchlargethanthedepletioncapacitancess2020/2/27PhysicsofSemiconductorDevices26Inlowfrequency,thegeneration-recombinationratesinthesurfacedepletionregionareequaltoorfasterthanthevoltagevariation,thentheelectronconcentration(minority)canfollowthealternatingcurrent(ac)signalandleadtochargeexchangewiththeinversionlayerinstepwiththemeasurementsignal.Theincrementalchargesappearsattheedgeofthedepletionregioninhighmeasurementfrequency.2020/2/27PhysicsofSemiconductorDevices27MOSFETFundamentals2020/2/27PhysicsofSemiconductorDevices28Structureof