拉扎维《模拟集成电路设计》第二版课件 .ppt

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1、Chapter17:Short-ChannelEffectsandDeviceModels17.1ScalingTheory17.2Short-ChannelEffects17.3MOSDeviceModels1BackgroundThesquare-lawcharacteristicsderivedforMOSFETsprovidemoderateaccuraciesfordeviceswithminimumchannellengthsofgreaterthanseveralmicrons.Asdevicedimensionscontinuetoscaled

2、own,reachingbelow12nm,higherordereffectsnecessitatemorecomplexmodels.Ourobjectivehereistoprovideabasicunderstandingofshort-channeleffectsandreviewsomeoftheSPICEmodelsdevelopedtoreflectsuchphenomena.WefirstdescribetheidealscalingtheoryofMOStransistors.Next,westudyshort-channeleffects

3、.2ScalingTheoryThetwoprincipalreasonsforthedominanceofCMOStechnologyintoday’ssemiconductorindustryarethezerostaticpowerdissipationofCMOSlogicandthescalabilityofMOSFETs.Theidealscalingtheoryfollowsthreerules:reducealllateralandverticaldimensionsbyα(>1)reducethethresholdvoltageandthes

4、upplyvoltagebyαincreaseallofthedopinglevelsbyα3Constant-fieldscalingSincethedimensionsandvoltagesscaletogether,allelectricfieldsinthetransistorremainconstant,hencethename“constant-fieldscaling.”NotethatW,L,tox,VDD,VTHandthedepthandperimeterofthesourceanddrainjunctionsscaledownbyα.Sa

5、turationdraincurrentofasquare-lawdeviceafterscaling:Weobservethatthecurrentcapabilityofthetransistordropsbyafactorofα.4AdvantagesofScalingTheadvantageofscalingliesinthereductionofcapacitancesandpowerdissipation.Thetotalchannelcapacitanceis:Tocalculatethesource/drainjunctioncapacitan

6、ce,wefirstanalyzetheeffectofidealscalingonthetotalwidthofthedepletionregion.Recallthatthiswidthisgivenby:WhereNAandNDdenotethedopinglevelsofthetwosidesofthejunction.5Depletionregioncapacitance6S/DjunctioncapacitancesThebottom-platecapacitanceoftheS/Djunction(perunitarea),Cj,increase

7、sbyafactorofα.Thesidewallcapacitance(perunitwidth),Cjswremainsconstant,asthedepthofthejunctionisreducedbyα.Allofthecapacitancesthereforedecreasebythescalingfactor.7Delay8Effectofidealscaling9Effectofidealscaling10Short-ChannelEffectsInordertoappreciatetheneedforsophisticateddevicemo

8、dels,webrieflystudy