VLSI DevicesThe DiodeDepletion RegionForward BiasReverse BiasDiode CurrentModels for Manual AnalysisJunction CapacitanceDiffusion Capacitance (Forward Bias)Secondary EffectsDiode Model (Manual Analysis)SPICE ParametersWhat is a Transistor?The MOS TransistorMOS Transistors - Types and SymbolsThreshold Voltage: ConceptThe Threshold VoltageThe Body EffectCurrent-Voltage RelationTransistor in LinearTransistor in SaturationCurrent-Voltage Relations Long-Channel DeviceA model for manual analysisCurrent-Voltage Relations: Deep-Submicron FETVelocity SaturationPerspectiveID versus VGSID versus VDSA unified model for manual analysisSimple Model versus SPICEA PMOS TransistorTransistor Model for Manual AnalysisThe Transistor as a SwitchSlide 34Slide 35MOS Capacitances Dynamic BehaviorDynamic Behavior of MOS TransistorThe Gate CapacitanceGate CapacitanceSlide 40Diffusion CapacitanceSlide 42Linearizing the Junction CapacitanceMOS Capacitances in 0.25/0.5 mm CMOS processesThe Sub-Micron MOS TransistorThreshold VariationsSub-Threshold ConductionSub-Threshold ID vs VGSSub-Threshold ID vs VDSSummary of MOSFET Operating RegionsParasitic ResistancesLatch-upFuture PerspectivesProblems HW3© Digital Integrated Circuits2ndDevicesVLSI DevicesVLSI DevicesIntuitive understanding of device operationFundamental analytic modelsManual ModelsSpice ModelsSecondary and deep-sub-micron effectsJunction Diode and FETResistor and Capacitor© Digital Integrated Circuits2ndDevicesThe DiodeThe DiodenppnB ASiO2AlABAlABCross-section of pn-junction in an IC process One-dimensionalrepresentation diode symbolOccurs as parasitic element in Digital ICs© Digital Integrated Circuits2ndDevicesDepletion RegionDepletion Regionhole diffusionelectron diffusionp nhole driftelectron driftChargeDensityDistancex+-ElectricalxFieldxPotentialVW2-W1(a) Current flow.(b) Charge density.(c) Electric field.(d) Electrostaticpotential.© Digital Integrated Circuits2ndDevicesForward BiasForward Biasxpn0np0-W1W20pn(W2)n-regionp-regionLpdiffusionForward Bias usually avoided in Digital ICs© Digital Integrated Circuits2ndDevicesReverse BiasReverse Biasxpn0np0-W1W20n-regionp-regiondiffusionDiode Isolation Mode© Digital Integrated Circuits2ndDevicesDiode CurrentDiode Current)1(/kTVsDDeII© Digital Integrated Circuits2ndDevicesModels for Manual AnalysisModels for Manual AnalysisVDID = IS(eVD/T – 1)+–VD+–+–VDonID(a) Ideal diode model (b) First-order diode model)1(/kTVsDDeII© Digital Integrated Circuits2ndDevicesJunction CapacitanceJunction Capacitance© Digital Integrated Circuits2ndDevicesDiffusion Capacitance Diffusion Capacitance (Forward Bias)(Forward Bias)© Digital Integrated Circuits2ndDevicesSecondary EffectsSecondary Effects–25.0 –15.0 –5.0 5.0VD (V)–0.1ID (A)0.100Avalanche Breakdown© Digital Integrated Circuits2ndDevicesDiode Model (Manual Analysis)Diode Model (Manual Analysis)IDRSCD+-VD© Digital Integrated Circuits2ndDevicesSPICE ParametersSPICE ParametersTransit time models charge storage© Digital Integrated Circuits2ndDevicesWhat is a Transistor?What is a Transistor?Resistor is poor model in saturation– current sourceSource and Drain are symmetricN-channel: Source is most negative of the twoP-channel: Source is most positive of the twoFour Modes:Off (leakage current only)Sub-Threshold (exponential)Linear (Resistive)Saturation (Current Source)VGS  VTRo nSDA Switch!© Digital Integrated Circuits2ndDevicesThe MOS TransistorThe MOS TransistorPolysiliconAluminum© Digital Integrated Circuits2ndDevicesMOS Transistors -MOS Transistors -Types and SymbolsTypes and SymbolsDSGDSGGSD DSGNMOSEnhancementNMOSPMOSDepletionEnhancementBNMOS withBulk Contact© Digital Integrated Circuits2ndDevicesThreshold Voltage: ConceptThreshold Voltage: Conceptn+n+p-substrateDSGBVGS+-DepletionRegionn-channel© Digital Integrated Circuits2ndDevicesThe Threshold VoltageThe Threshold Voltage© Digital Integrated Circuits2ndDevicesThe Body EffectThe Body Effect-2.5 -2 -1.5 -1 -0.5 00.40.450.50.550.60.650.70.750.80.850.9VBS (V)VT (V)© Digital Integrated Circuits2ndDevicesQuadraticRelationship0 0.5 1 1.5 2 2.50123456x 10-4VDS (V)ID (A)VGS= 2.5 VVGS= 2. VVGS= 1.5 VVGS= 1. VResistive SaturationVDS = VGS - VTCurrent-Voltage Relation Current-Voltage Relation© Digital Integrated Circuits2ndDevicesTransistor in LinearTransistor in Linearn+n+p-substrateDSGBVGSxLV(x)+–VDSIDMOS transistor and its bias conditions© Digital Integrated Circuits2ndDevicesTransistor in SaturationTransistor in Saturationn+n+SGVGSDVDS > VGS - VTVGS - VT+-Pinch-ofRegion© Digital Integrated Circuits2ndDevicesCurrent-Voltage RelationsCurrent-Voltage RelationsLong-Channel DeviceLong-Channel Device© Digital Integrated Circuits2ndDevicesA model for manual analysisA model for manual analysis© Digital Integrated Circuits2ndDevicesCurrent-Voltage Relations:Current-Voltage Relations:Deep-Submicron FETDeep-Submicron FETLinearRelationship-4VDS (V)0 0.5 1 1.5 2 2.500.511.522.5x 10ID (A)VGS= 2.5 VVGS= 2. VVGS= 1.5 VVGS= 1. VEarly Saturation© Digital Integrated Circuits2ndDevicesVelocity SaturationVelocity Saturation (V/µm)c = 1.5n (m/s)sat = 105Constant mobility (slope = µ)Constant velocity© Digital Integrated Circuits2ndDevicesPerspectivePerspectiveIDLong-channel deviceShort-channel deviceVDSVDSATVGS - VTVGS = VDD© Digital Integrated Circuits2ndDevicesIIDD versus V versus VGSGS0 0.5 1 1.5 2 2.50123456x 10-4VGS (V)ID (A)0 0.5 1 1.5 2 2.500.511.522.5x 10-4VGS (V)ID (A)quadraticquadraticlinearLong ChannelShort Channel© Digital Integrated Circuits2ndDevicesIIDD versus V versus VDSDS-4VDS (V)0 0.5 1 1.5 2 2.500.511.522.5x 10ID (A)VGS= 2.5 VVGS= 2. VVGS= 1.5 VVGS= 1. V0 0.5 1 1.5 2 2.50123456x 10-4VDS (V)ID (A)VGS= 2.5 VVGS= 2. VVGS= 1.5 VVGS= 1. VResistiveSaturationVDS = VGS - VTLong Channel Short Channel© Digital Integrated Circuits2ndDevicesA unified modelA unified modelfor manual analysisfor manual analysisSDGB© Digital Integrated Circuits2ndDevicesSimple Model versus SPICE Simple Model versus SPICE 0 0.5 1 1.5 2 2.500.511.522.5x 10-4VDS (V)ID (A)VelocitySaturatedLinearSaturatedVDSAT=VGTVDS=VDSATVDS=VGT© Digital Integrated Circuits2ndDevicesA PMOS TransistorA PMOS Transistor-2.5 -2 -1.5 -1 -0.5 0-1-0.8-0.6-0.4-0.20x 10-4VDS (V)ID (A)VGS = -1.VVGS = -1.5VVGS = -2.VVGS = -2.5V© Digital Integrated Circuits2ndDevicesTransistor Model Transistor Model for Manual