MOS电容器.ppt

ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 1 Chapter5MOSCapacitor MOS Metal Oxide Semiconductor SiO2 metal gate Sibody Vg gate P body N MOScapacitor MOStransistor Vg SiO2 N Slide5 2 Thisenergy banddiagramforVg 0isnotthesimplestone N p o l y s i l i c o n S i O 2 P S i l i c o n b o d y Chapter5MOSCapacitor ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 3 5 1Flat bandConditionandFlat bandVoltage E0 VacuumlevelE0 Ef WorkfunctionE0 Ec ElectronaffinitySi SiO2energybarrier c SiO 2 0 95eV 9eV E c E f E v E c E v E f 3 1eV q y s c Si E c E f q y g c Si E 0 3 1eV V fb N poly Si P body 4 8eV 4 05eV E c E v SiO 2 Thebandisflatattheflatbandvoltage q ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 4 5 2SurfaceAccumulation MakeVg Vfb fs surfacepotential bandbendingVox voltageacrosstheoxide ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 5 5 2SurfaceAccumulation ModernSemiconductorDevicesforIntegratedCircuits C Hu Vg Vt Slide5 6 ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 7 5 3SurfaceDepletion Thisequationcanbesolvedtoyieldfs ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 8 5 4ThresholdConditionandThresholdVoltage Threshold ofinversion ns Na or Ec Ef surface Ef Ev bulk or A B andC D ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 9 ThresholdVoltage Atthreshold ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 10 ThresholdVoltage ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 11 5 5StrongInversion BeyondThreshold Vg Vt ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 12 InversionLayerCharge Qinv C cm2 ModernSemiconductorDevicesforIntegratedCircuits C Hu Vg Vt Vg Vt Slide5 13 5 5 1ChoiceofVtandGateDopingType Vtisgenerallysetatasmallpositivevaluesothat atVg 0 thetransistordoesnothaveaninversionlayerandcurrentdoesnotflowbetweenthetwoN regions P bodyisnormallypairedwithN gatetoachieveasmallpositivethresholdvoltage N bodyisnormallypairedwithP gatetoachieveasmallnegativethresholdvoltage ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 14 Review BasicMOSCapacitorTheory fs 2fB Vfb Vt Vg accumulation depletion inversion Wdep W dmax accumulation depletion inversion f s 1 2 W dmax 2 e s 2 f B q N a 1 2 Vg Vt Vfb ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 15 Review BasicMOSCapacitorTheory 0 Vg accumulation depletion inversion Qinv accumulation depletion inversion a b accumulation depletion inversion c Qs 0 accumulation regime depletion regime inversion regime totalsubstratecharge Qs Qacc Vg Vg Qdep qNaWdep Vt Vfb slope Cox slope Cox Vt Vfb Vt Vfb qNaWdep qNaWdmax Vg Qinv slope Cox Vfb Vt ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 16 5 6MOSCVCharacteristics ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 17 5 6MOSCVCharacteristics Qs 0 Vg accumulation regime depletion regime inversion regime Qinv C Vfb Vt Cox accumulation depletion inversion Vg Vt Vfb slope Cox ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 18 CVCharacteristics Inthedepletionregime ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 19 Wdep C ox gate P substrate Wdmax N DCandAC SupplyofInversionChargeMaybeLimited Accumulation Depletion Inversion Inversion Ineachcase C ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 20 CapacitorandTransistorCV orHFandLFCV ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 21 Quasi StaticCVofMOSCapacitor Thequasi staticCVisobtainedbytheapplicationofaslowlinear rampvoltage 0 1V s tothegate whilemeasuringIgwithaverysensitiveDCammeter CiscalculatedfromIg C dVg dt ThisallowssufficienttimeforQinvtorespondtotheslow changingVg ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 22 1 MOStransistor 10kHz Answer QSCV 2 MOStransistor 100MHz Answer QSCV 3 MOScapacitor 100MHz Answer HFcapacitorCV 4 MOScapacitor 10kHz Answer HFcapacitorCV 5 MOScapacitor slowVgramp Answer QSCV 6 MOStransistor slowVgramp Answer QSCV EXAMPLE CVofMOSCapacitorandTransistor DoestheQSCVortheHFcapacitorCVapply ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 23 5 7OxideCharge AModificationtoVfbandVt ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 24 Typesofoxidecharge Fixedoxidecharge Si Mobileoxidecharge duetoNa contaminationInterfacetraps neutralorchargeddependingonVg Voltage temperaturestressinducedchargeandtraps areliabilityissue 5 7OxideCharge AModificationtoVfbandVt ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 25 EXAMPLE InterpretthismeasuredVfbdependenceonoxidethickness ThegateelectrodeisN poly silicon Solution Whatdoesittellus Bodyworkfunction Dopingtype Other ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 26 fromslope N typesubstrate ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 27 5 8Poly SiliconGateDepletion EffectiveIncreaseinTox Gauss sLaw IfWdpoly 15 whatistheeffectiveincreaseinTox ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 28 EffectofPoly GateDepletiononQinv Howcanpoly depletionbeminimized W dpoly E c E f E v E c E f E v q f poly P gate N substrate Poly gatedepletiondegradesMOSFETcurrentandcircuitspeed ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 29 EXAMPLE Poly SiliconGateDepletion Vox thevoltageacrossa2nmthinoxide is 1V TheP poly gatedopingisNpoly 8 1019cm 3andsubstrateNdis1017cm 3 Find a Wdpoly b fpoly and c Vg Solution a ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 30 b c Isthelossof0 11Vfromthe1 01Vsignificant EXAMPLE Poly SiliconGateDepletion ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 31 5 9InversionandAccumulationCharge LayerThickness QuantumMechanicalEffect Averageinversion layerlocationbelowtheSi SiO2interfaceiscalledtheinversion layerthickness Tinv n x isdeterminedbySchrodinger seq Poissoneq andFermifunction ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 32 ElectricalOxideThickness Toxe Tinvisafunctionoftheaverageelectricfieldintheinversionlayer whichis Vg Vt 6Tox Sec 6 3 1 Tinvofholesislargerthanthatofelectronsbecauseofdifferenceineffectivemass Toxeistheelectricaloxidethickness ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 33 EffectiveOxideThicknessandEffectiveOxideCapacitance ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 34 Equivalentcircuitinthedepletionandtheinversionregimes a b c d Generalcaseforbothdepletionandinversionregions Inthedepletionregions Vg Vt Stronginversion ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 35 5 10CCDImagerandCMOSImager Deepdepletion Qinv 0 Exposedtolight 5 10 1CCDImager ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 36 CCDChargeTransfer ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 37 two dimensionalCCDimager Thereadingrowisshieldedfromthelightbyametalfilm The2 Dchargepacketsarereadrowbyrow ModernSemiconductorDevicesforIntegratedCircuits C Hu Slide5 38 5 10 2CMOSImager CMOSimagerscanbeintegratedwithsignalprocessing