Finfet技术(3D晶体管)详解-Intro-to-FinFet

IntroductiontoFinFetHaiyingZhaoWhatdoesFinFetlookLikeBulknmosSilicononinsulatorFinFetWhatdoesFinFetlooklike3DviewofFinFET3Dviewofmulti-finFinFETWhatdoesFinFetlooklikeMoore’slawandscalingtheoryIdealscaling:ReduceW,LbyafactorofaReducethethresholdvoltageandsupplyvoltagebyafactorofaIncreasingallofthedopinglevelsbya(W,L,tox,VDD,VTH,etc,arescaleddownbyafactora)Foraidealsquare-lawdevice,Idisreducedbya,butgmandintrinsicgainGm*roremainthesame.Asscalingintosubmicronregion,ShortChanneleffectspreventfurtherscaling.Barrierloweringincreasesaschannellengthisreduced,evenatzeroapplieddrainbias,becausethesourceanddrainformpnjunctionwiththebody,andsohaveassociatedbuilt-indepletionlayersassociatedwiththemthatbecomesignificantpartnersinchargebalanceatshortchannellengths,evenwithnoreversebiasappliedtoincreasedepletionwidthShortChannelEffects:DIBLDIBL:draininducedbarrierlowering.DIBL=d(Vth)/d(Vds)ShortChannelEffects:SubthresholdswingBiasinganmosinsubthresholdresgion,VgsVth,Vdsislargeenough.Id=uCdW/L(KT/q)^2(exp(Vgs–Vth)/M))Cdiscapacitanceofthedepletionlayerundergate.M=(1+Cd/Cox)*KT/qId=f(Vgs-Vth)Toturnoffthetransistor,Howmuchreductionof(Vgs-Vth)couldleadtoasmallenoughId.SubthresholdSwingS=d(Vgs)/d(log(Id))=2.3KT/q(1+Cd/Cox)ThesmallerSis,thebetteritis.BadSubthresholdSwingwillresultinhigheroff-statecurrentiftheVgsappliedtoturnoffthetransistoristhesame.V=uE(Eissmallenough)V=Vsat(Eisstrongenough)AsVgsincreases,thedraincurrentsaturateswellbeforepinch-offoccurs.ShortChannelEffects:VelocitySaturationBarrierloweringincreasesaschannellengthisreduced,evenatzeroapplieddrainbias,becausethesourceanddrainformpnjunctionwiththebody,andsohaveassociatedbuilt-indepletionlayersassociatedwiththemthatbecomesignificantpartnersinchargebalanceatshortchannellengths,evenwithnoreversebiasappliedtoincreasedepletionwidthShortChannelEffects:DIBLDIBL:draininducedbarrierlowering.DIBL=d(Vth)/d(Vds)ConclusionToreduceshortchanneleffects,weneedtoreduceXd(channeldepletionlayerthickness),Xj(Junctiondepletionwidth),Xox(oxidelayerthicknessundergate).ThescalelengthofbulkMOSFETisanindicationofLg.LgDealingwithShortChannelEffectsinbulkMOSFET1.Increasingbodydopingconcentration2.UsinghaloimplantHighdopingdensityresultsin:Lowercarriermobility;hightunnelingeffectwhichincreasesoff-statecurrents;Largerdepletioncapacitorsleadingtohighsubthresholdswingwhichincreasesoff-statecurrents;Largerparasiticcapacitance,Cgd,Cds.DealingwithShortChannelEffectsinFullydepletedSilicononInsulator(SOI)Useultra-thinfilm(tsiissmall)astheconductingbody,depletionlayerisconfinedinthefilm.(Xd=tsi).Eliminatethejunctionparasiticcapacitors.Cuffofftheleakagecurrentpathfromdraintosubstrate.FromFD/SOItoFinFETBendupthegateandnarrowthegate.Finwidth=2*filmthicknessTheeffectbodythicknessisreducedby2.XdcanberegardedasFinwidth/2.ToobtaingoodcontrolofSCE,Leff1.5*Wfin(Finwidth).Finfetcanoperateattwomode,singlegateanddoublegate.FinFetcharacteristicsLg=15nmLg=30nmThresholdVoltage=0.196VSubthresholdSlope=72mV/decadeOffCurrent=70A/mDIBL=64.67mV/VSomevalues:ApproximatedcI-Vequations?Squarelaw?OnewayisusingnthpowerlawtocomputertheFinFetcurrent.FinFet:ChallengesorOpportunitiesCarriermobility:Lightlydopedorundopedfinbodyincreasescarriermobility.Shortchannellengthenablesvelocityovershoot,whichincreasesmobility.LowVthdecreasestheverticalelectricfield,whichincreasescarriermobility.Tunnelingeffects:Gatetochanneltunneling,BandtobandtunnelingatPNjunctionFinFet:ChallengesorOpportunitiesParasiticresistance:araisedsource/drainstructurecanbeusedtoreducetheparasiticresistance.However,theoverlapcapacitanceisincreased.Prasiticresistanceisthemainadversefactorwhichpreventsfinfets’application,whichleadstolowerspeedandhighnoise.FinFet:ChallengesorOpportunitiesFinFet:bigadvantages1.Havingexcellentcontrolofshortchanneleffectsinsubmicronregimeandmakingtransistorsstillscalable.Duetothisreason,thesmall-lengthtransistorcanhavealargerintrinsicgaincomparedtothebulkcounterpart.2.MuchLoweroff-statecurrentcomparedtobulkcounterpart.3.Promisingmatchingbehavior.Applications1.Lowpowerdesignindigitalcircuit,suchasRAM,becauseofitslowoff-statecurrent.2.Poweramplifierorotherapplicationinanalogareawhichrequiresgoodlinearity.