半導(dǎo)體器件物理

2023/9/2PhysicsofSemiconductorDevices1OUTLINE

ThePowerMOSFET

TheMOSDiodeMOSFETFundamentalsMOSFETScaling

COMSandBiCOMS

MOSFETonInsulator

MOSMemoryStructure2023/9/2PhysicsofSemiconductorDevices2SiO2metalsemiconductorSiO2semiconductordOhmiccontactTheMOSDiodeisofparamountimportantinsemiconductordevicephysicsbecausethedeviceextremelyusefulinthestudyofsemiconductorsurfaces.2023/9/2PhysicsofSemiconductorDevices3TheIdealMOSDiode2023/9/2PhysicsofSemiconductorDevices4AnidealMOSdiodeisdefinedasfollows:Atzeroappliedbias,Theonlychargesthatexistinthediodeunderanybiasingconditionsarethoseinthesemiconductorandthosewithequalbutoppositesignonthemetalsurfaceadjacenttotheoxide.Thereisnocarriertransportthroughtheoxideunderthedirectcurrentdc)-biasingconditions,ortheresistivityoftheoxideisinfinite.2023/9/2PhysicsofSemiconductorDevices5Operation

Modes2023/9/2PhysicsofSemiconductorDevices6EnergyBandDiagramsAndChargeDistributionAccumulation:2023/9/2PhysicsofSemiconductorDevices7Accumulation:QmQS-dxChargeDistributionxE(X)ElectricField

Anaccumulationofholesneartheoxide-semiconductorinterface.2023/9/2PhysicsofSemiconductorDevices8Depletion:EFVg>0EFEvEcEiChargeDistributionE(X)xElectricFieldxwQm-d2023/9/2PhysicsofSemiconductorDevices9StrongInversion:2023/9/2PhysicsofSemiconductorDevices10StrongInversion:xwmQm-dQnQscChargeDistributionElectricFieldxE(x)Oncestronginversionoccurs,averysmallincreaseinbandbendingcorrespondingtoaverysmallincreaseindepletion-layerwidthresultsinalargeincreaseintheQnintheinversionlayer,sothesurfacedepletion-layerwithreachesamaximum,Wm.2023/9/2PhysicsofSemiconductorDevices11TheSurfaceDepletionRegionisthebandbendingwithboundaryconditionsinthebulkandEFEiSemiconductorsurfaceECEvEgOxidexP-typesilicon2023/9/2PhysicsofSemiconductorDevices12Atthesurfacethedensitiesare:

IntheMOSdiode,thefollowingregionsofsurfacepotentialcanbedistinguished:Accumulationofholes(bandsbendupward)FlatbandconditionDepletionofhole(bandsbenddownward)Midgapwithns=np=ni(intrinsicconcentration)Inversion(bandsbenddownward)2023/9/2PhysicsofSemiconductorDevices13Thepotentialasafunctionofdistancecanbeobtainedbyusingtheone-dimensionalPoisson’sequation:Afterusingthedepletionapproximationthatweemployedinthestudyofp-njunctions.Thesurfacepotentialis:2023/9/2PhysicsofSemiconductorDevices14Thecriterionoftheonsetofstronginversion:Themaximumwidthofthesurfacedepletionregion:and2023/9/2PhysicsofSemiconductorDevices15SurfaceChargevs.SurfacePotential2023/9/2PhysicsofSemiconductorDevices16TherelationshipbetweenWmandtheimpurityconcentrationforsiliconandgalliumarsenide,whereNBisequaltoNAforP-typeandNDforn-typesemiconductor.2023/9/2PhysicsofSemiconductorDevices17CapacitanceinaMOScapacitorSmallsignalcapacitance

MOScapacitanceisdefinedassmallsignalcapacitanceandismeasuredbyapplyingasmallacvoltageonthetopofadcbias2023/9/2PhysicsofSemiconductorDevices18C-VCurves2023/9/2PhysicsofSemiconductorDevices19FrequencyEffectThefrequencyofacsignalplayanimportantroleinthecapacitanceofaMOSCapacitor(afterGrove,etal.)2023/9/2PhysicsofSemiconductorDevices20IdealMOSCurvesQmDepletionregionxw-d-Qn-qNAEFECEiEFInversionregionEvQSNeutralsregion

Banddiagram(p-typesubstrate)Chargedistribution2023/9/2PhysicsofSemiconductorDevices21-d0wxElectric-fieldDistribution-dv0vwx0PotentialDistribution

Theappliedvoltagewillappearpartlyacrosstheoxideandpartlycrossthesemiconductor.2023/9/2PhysicsofSemiconductorDevices22CapacitanceatLowFrequencyLowfrequencyorquasi-static

MajorityandminoritycarriercanrespondwithacsignalandreachatequilibriumconditionP-typesubst rateAccumulation

2023/9/2PhysicsofSemiconductorDevices23Depletion

W2023/9/2PhysicsofSemiconductorDevices24Inversion

wdmOncetheinversionlayerforms,thecapacitancestartstoincrease,sincecsiisnowgivenbythevariationoftheinversionchargewithrespecttowhichismuchlargethanthedepletioncapacitance2023/9/2PhysicsofSemiconductorDevices25Inlowfrequency,thegeneration-recombinationratesinthesurfacedepletionregionareequaltoorfasterthanthevoltagevariation,thentheelectronconcentration(minority)canfollowthealternatingcurrent(ac)signalandleadtochargeexchangewiththeinversionlayerinstepwiththemeasurementsignal.Theincrementalchargesappearsattheedgeofthedepletionregioninhighmeasurementfrequency.2023/9/2PhysicsofSemiconductorDevices26MOSFETFundamentals2023/9/2PhysicsofSemiconductorDevices27StructureofMOSFET2023/9/2PhysicsofSemiconductorDevices28TypesofMOSFET2023/9/2PhysicsofSemiconductorDevices29Non-equilibriumCondition2023/9/2PhysicsofSemiconductorDevices30LinearRegion&

SaturationRegion2023/9/2PhysicsofSemiconductorDevices312023/9/2PhysicsofSemiconductorDevices32CurrentsinLinearRegion2023/9/2PhysicsofSemiconductorDevices33OperationRegionsActingasaresistor.LinearRegion(VD<<VDsat)2023/9/2PhysicsofSemiconductorDevices34Pinch-offPointThethicknessofinversionxi(y=L)=02023/9/2PhysicsofSemiconductorDevices35CurrentinSaturationRegion2023/9/2PhysicsofSemiconductorDevices36AMOSFETcanbedividedintomanycapacitorfragmentsVCdecreaseinthisdirection…………vcSourceSidePinchoffDrainSideVc=0meansnochargesinducedElectroncurrentflow2023/9/2PhysicsofSemiconductorDevices37SaturationRegion(VD>VDsat)ID=constantLL’2023/9/2PhysicsofSemiconductorDevices38

Theuppercharacteristicscanbederivedunderthefollowingidealconditions:ThegatestructurecorrespondstoanidealMOSdiode.Onlydriftcurrentconsidered.Carriermobilityintheinversionlayerisconstant.Dopinginthechannelisuniform.Reverse-leakagecurrentisnegligibly.Thegradualchannelapproximation.2023/9/2PhysicsofSemiconductorDevices392023/9/2PhysicsofSemiconductorDevices40

IdealizeddraincharacteristicsofMOSdiode2023/9/2PhysicsofSemiconductorDevices41nMOST的輸出特性曲線2023/9/2PhysicsofSemiconductorDevices42從另一方面來看，溝道漏端VDS=VDsat=VGS-VT時，Qn(L)=0這種情況叫做漏端溝道夾斷。

現(xiàn)在一般用溝道漏端夾斷來解釋長溝道器件VDS>VDsat時的漏極電流飽和現(xiàn)象。這需要從幾個方面來加以說明。

首先VDS超過VDsat以后，溝道夾斷點的電勢始終都等于VGS-VT。設(shè)想夾斷點移動到y(tǒng)=L’，則有很容易看的出來由此得出結(jié)論，未夾斷區(qū)的電壓將保持等于VGS-VT不變。2023/9/2PhysicsofSemiconductorDevices43溝道漏端夾斷的nMOST2023/9/2PhysicsofSemiconductorDevices44

其次，當VD>VDsat時，超過VDsat的那部分外加電壓，即VDS-VDsat，降落在夾斷區(qū)上。夾斷區(qū)是已耗盡空穴的空間電荷區(qū)，電離受主提供負電荷，漏區(qū)一側(cè)空間電荷區(qū)中的電離施主提供正電荷，它們之間建立沿溝道電流流動方向（y方向）的電場和電勢差，漏區(qū)是高摻雜的，漏區(qū)和夾斷區(qū)沿y方向看類似于一個N+P單邊突變結(jié)，結(jié)上壓降增大時空間電荷區(qū)主要向P區(qū)一側(cè)擴展。所以當夾斷區(qū)上電壓降（VDS-VDsat）增大時，夾斷區(qū)長度擴大，有效溝道長度L’縮短。

對于長溝道MOST，如果在所考慮的VDS范圍內(nèi)始終是<<L，那么在VD>VDsat情形下，未夾斷區(qū)的縱向及橫向電場和電荷分布基本上與VD＝VDsat時相同，從溝道點到源端之間的電阻因而也保持不變?？紤]到VD>VDsat未夾斷區(qū)壓降始終等于VGS-VT，所以漏極電流恒定不變，這就是電流飽和。2023/9/2PhysicsofSemiconductorDevices45ionimplantationintothechannelregion2023/9/2PhysicsofSemiconductorDevices46VaryingtheoxidethicknessTheVTofthefieldoxideistypicallyanorderofmagnitudelargerthanthatofthethingateside.2023/9/2PhysicsofSemiconductorDevices47Substratebias2023/9/2PhysicsofSemiconductorDevices48TheSubthresholdRegion

Vg<Vt2023/9/2PhysicsofSemiconductorDevices49Thedraincurrentisdominatedbydiffusion2023/9/2PhysicsofSemiconductorDevices50Subthresholdswings,S

ExceptforaslightdependenceonbulkdopingconcentrationthroughCdn,Sisratherinsensitivetodeviceparameters.2023/9/2PhysicsofSemiconductorDevices51VoltageTransferCharacteristicSymmetryDesignConceptNoiseMargin2023/9/2PhysicsofSemiconductorDevices52DynamicOperation

2023/9/2PhysicsofSemiconductorDevices53PowerDissipationPowerdissipation:DynamicandstaticDynamicpowerconsumptionForaninverterPowersupply:VDDLoadcapacitance:CDynamicPowerPower:Energystoredinc:EnergydissipatedbyQp:

EnergyinCwillbeconsumedbyQNindischargeperiod2023/9/2PhysicsofSemiconductorDevices542023/9/2PhysicsofSemiconductorDevices55DIBLleadstoasubstantialincreaseinelectroninjectionfromthesourcetothedrain.Subthresholdcurrent2023/9/2PhysicsofSemicondu