Table Of ContentANALYSISANDMODELINGOFNONLOCALANDDYNAMICFLOATING-BODY
EFFECTSFORAPPLICATION INSCALEDSOICMOSTECHNOLOGY
By
SRINATHKRISHNAN
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHLOSOPHY
UNIVERSITYOFFLORIDA
1996
UNIVERSITYOFFLORIDALIBRARIES
ACKNOWLEDGEMENTS
Ithasbeenamatterofgreatpleasureandhonorformetohaveworkedfor,andmore
importantly,with,myadvisor.ProfessorJerryPossum.Hisconstantencouragement,com-
binedwithprofoundtechnicaldiscussions,wereinstrumentalforsuccessfulcompletionof
thiswork.Hisdemandforexcellence,inqualityandcontent,inanyworkwillalwaysbea
sourceofinspirationtome.Ihavebeenenrichedbyhisassociation,personallyandprofes-
sionally,andferventlywishthatatleastatinyportionofhisoutstandingqualitieshave
rubbedontome.Icannotfindwordstoexpressmygratitudetohim,butsupposeaheart-
feltthanksisinorder.Ialsowishtoexpressmysincerethankstothemembersofmy
supervisorycommittee.ProfessorsTimothyAnderson,RobertFox,MarkLaw,ShengLi
andToshikazuNishida,fortheirinterestinthiswork,andtheirpatienceinreadingthis
manuscript.
IamgratefultotheSemiconductorResearchCorporationandtoTexasInstruments
andIBMforfinancialandtechnicalsupportofferedtowardsthiswork.Iwouldalsoliketo
thankDrs.TedHoustonandLisaSu,andMr.MarioPelellaforprovidingmostofthemea-
sureddatausedinthiswork.
Iwasextremelyfortunatetohaveinteractedonadailybasisformostofmygraduate
studenttenurewithDrs.DongwookSuhandPing-ChinYeh,andGlennWorkman.Not
only didI greatly benefitfrom stimulating technical discussions with them, but also
immenselyrelishedtheirwarmcompanyduringnumerousconferencetrips.Iwouldalso
11
liketothankmycolleagues,someofwhomIcountonasfriendstoo,whohavehelpedme
onseveraloccasionswithonethingoranother.Throughtheiramiablepersonalities,happy
hours,andsportsduringsomeoftheweekends,theywereresponsibleformyhavinga
well-roundedgraduateschoolexperience.Icannotnamethemall,butmustdefinitelylist
Drs.ChetanParikhandKeithGreen,JonathanBrodsky(whosesincereone-minuteques-
tionsoftenresultedinthought-provokingthree-hourdiscussions!),SteveCea,Ming-Yeh
Chuang,OmerDokumaci,DougWeiser,andDavidZweidinger.Aspecialthanksgoesto
MaryTurner,ourenormouslypatient,yetefficientsecretary,forherinfiniteordealswith
me,beitindealingwitheleventhhourdeadlinesforabstracts,orpreparingpostersatthe
verylastminute,nothanksinlargeparttomyprocrastination.
IwasextremelyluckyduringmystayinGainesvilletohavefoundnear-perfectroom-
matesturnedgreatfriends:SamirChaudhrywhohasputupwithmyworstandbest(ifat
allany!),andisasdependableandreliableasarock;GanapathyMahalingam,anintrigu-
ingartistandarchitectwithagoldenheart;andNoshirTarapore,theeternalentertainer
whocouldalwayslightenupyourmood.Iwillalwaysdeeplycherishthememoriesofmy
timewiththem.ItwouldbeinexcusabletonotmentionZareenTarapore,fornotonly
countlessdinners,andbutalsoforopeningmyeyesinmorethanoneway.Iamproudto
saythatIhaveevolvedasapersonconsiderablyoverthepastfewyears,thanksinlarge
parttointeractionwithher.IwouldalsoliketothankRalfEdelman,mytennispartner,
whoisoneofthenicestpersonsIhaveevermet.Thisacknowledgmentwouldbeincom-
pletewithoutthementionofPeram,forhisunselfishfriendshipeversinceIhaveknown
him,and,Pradeep,themagnitudeofwhosefriendshipwillnotdiminishwithtimenorthe
physicaldistancebetweenus.
Inthemidstofthis,Icannotforgettothankmyextendedfamily,theJaganMohanites.
Inparticular,Iamdeeplygratefultomygrandfatherforhisconstantwordsofwisdomand
patiencewithmysometimesfrivolousattitudes;mygrandmother,oneofthemostamaz-
ingladiesIhaveeverknown,forherdeepanduncompromisinglove;Peripa,Perima,
Vijay,Amit,Jayshree,andSusieforalwayswelcomingandprovidingmeahomeaway
fromhomeinCalifornia;SumeetaandSangitafortheirconstantlittlenotesofencourage-
mentthroughe-mails;andmylittlenephewsandnieces,Adeeti,Ishan,Tarini,Shriya,and
Sriram, whothroughtheirinnocenceandinfectious laughter,haveshownmehowto
appreciatethesimplerthingsinlife.Lastly,butmostimportantly,Icannotthankenough
mymotherMalathiKrishnan,fatherR.Krishnan,andsisterVidhya,whothroughtheir
undyinglove,commitment,andendlesssacrificeshaveprovidedthefoundationformy
emotionalwellbeing.
IV
TABLEOFCONTENTS
E^e
ACKNOWLEDGEMENTS
ii
ABSTRACT viii
CHAPTERS
INTRODUCTION
1 1
2 ASTUDYOFCARRIERVELOCITYSATURATIONANDOVERSHOOTIN
DEEP-SUBMICRONSOIMOSFETs 9
2.1 Introduction 9
2.2 EffectsofVelocitySaturationontheCurrentDriveofSOIMOSFETs 10
2.2.1 Analysis 10
2.2.2 ResultsandDiscussion 14
2.3 VelocityOvershoot 20
2.3.3 ModelDevelopment 21
2.3.3.1 ConceptofEffectiveSaturatedDriftVelocity 23
2.3.3.2 ChannelCurrent 25
2.3.4 ModelImplementationWerification 26
2.3.5 ResultsandDiscussion 28
2.3.6 EffectofOvershootonImpactIonization 30
2.4 Conclusions 33
3 NON-LOCALIMPACTIONIZATIONINSOIMOSFETs:MODELING,
VERIFICATION,ANDAPPLICATION 34
3.1 Introduction 34
3.2 ModelDevelopment 35
3.2.1 Strong-InversionAnalysis 37
3.2.1.1 ChannelRegion 38
3.2.1.2 LDD 39
3.2.1.3 Drain 41
3.2.2 Weak-InversionAnalysis 41
3.2.2.1 FD/SOI 42
3.2.2.2 PD/SOI 44
3.2.3 Moderate-InversionAnalysis 44
3.3 ModelImplementation 45
V
1
3.4 VerificationandDiscussion 47
3.5 ModelApplicationtoDevice/CircuitDesignOptimization 55
3.6 Conclusions 58
4 FLOATING-BODYKINKSANDDYNAMICEFFECTSINFULLYDEPLETED
SOIMOSFETs 60
4.1 Introduction 60
4.2 DeviceMeasurements 61
4.3 Analysis 64
4.4 Modeling 70
4.4.1 Introduction 70
4.4.2 ModelDevelopment 71
4.5 ApplicationtoDesign 73
4.6 Conclusions 76
5 PARASITICBIPOLARJUNCTIONTRANSISTORINSOIMOSFETs:BiMOS
MODELING,VERIFICATION,ANDAPPLICATIONTORELIABLECIRCUIT
DESIGN 77
5.1 Introduction 77
5.2 TheTransientBipolarEffect 78
5.3 BiMOSModeling 82
5.3.1 Introduction 82
5.3.2 AQuasi-2DModelfortheParasiticBipolarTransportCurrent 82
5.3.2.1 BITTransportModeling:1-Dor2-D? 84
5.3.2.2 IgppinTopPortionofSOIFilm(0<x<tb) 89
5.3.2.3 IbjtinBottomPortionofSOIFilm(tj,<x<tj^tb) 95
5.3.2.4 TotalIgjjintheSOIFilm 96
5.3.3 ChargeModeling 96
5.3.3.1 TopPortionoftheBody(o<x<tb) 97
5.3.3.2 BottomPortionoftheBody(tj,<x<t^tj,) 98
5.3.3.3 Quasi-NeutralSource 99
5.3.3.4 ChargeAllocation 99
5.3.4 RecombinationCurrent 100
5.3.5 ParasiticBITModelingfortheFD/SOIMOSFET 100
5.3.6 SignificanceofBiMOSModeling 101
5.4 ModelImplementation 101
5.5 ModelVerificationandDiscussion 102
5.5.7 Introduction 102
5.5.8 Verificationwith2-DMEDICISimulations 102
5.5.9 Igj-j-DependenceonFallRate:SignificanceofDiffusionCapacitance 107
5.6 DesignInsight 110
5.7 SummaryandConclusions 11
VI
6 SYSTEMATIC,PHYSICS-BASEDPARAMETER-EVALUATION
METHODOLOGYFORUSEWITHSOISPICE 114
6.1 Introduction 114
6.2 GeneralApproachtoParameterEvaluation 115
6.3 ParameterEvaluationforFD/SOIMOSFETs 116
6.3.1 SubthresholdRegion 120
6.3.1.1 CalibrationBasedonSubthresholdSlope 120
6.3.1.2 CalibrationBasedonSubthresholdCurrent 124
6.3.2 Strong-InversionRegion 125
6.3.2.1 CalibrationBasedonLinear-RegionCharacteristics 125
6.3.2.2 CalibrationBasedonOutputCharacteristicsatHighDrainBias 126
6.3.3 ApplicationtoActualFD/SOITechnologies:Example1 127
6.3.4 ApplicationtoActualFD/SOITechnologies:Example2 131
6.4 ParameterEvaluationforPD/SOIMOSFETs 139
6.4.5 SubthresholdRegion 143
6.4.5.1 CalibrationBasedonSlope/CurrentatLowDrainBias 143
6.4.5.2 CalibrationBasedonSlope/CurrentatHighDrainBias 145
6.4.6 Strong-InversionRegion 146
6.4.6.1 CalibrationBasedonLinear-RegionCharacteristics 146
6.4.6.2 CalibrationBasedonOutputCharacteristicsatHighDrainBias 146
6.4.7 ApplicationtoActualPD/SOITechnologies:Example1 147
6.4.8 ApplicationtoActualPD/SOITechnologies:Example2 149
6.4.9 ExtensionofPD/SOIMethodologytoCalibratetheTransientBipolar
Effect 155
6.5 Summary/Conclusions 156
7 SUMMARYANDSUGGESTIONSFORFUTUREWORK 159
7.1 Summary 159
7.2 SuggestionsforFutureWork 161
APPENDIXA 163
DERIVATIONOFSIMPLIFIEDENERGY-BALANCEEQUATION 163
APPENDIXB 167
WEAK-INVERSIONFIELDCHARACTERIZATIONFORFD/AND
PD/SOIMOSFETs 167
REFERENCES 170
BIOGRAPHICALSKETCH 177
vii
AbstractofDissertationPresentedtotheGraduateSchool
oftheUniversityofFloridainPartialFulfillmentofthe
RequirementsfortheDegreeofDoctorofPhilosophy
ANALYSISANDMODELINGOFNONLOCALANDDYNAMICFLOATING-BODY
EFFECTSFORAPPLICATIONINSCALEDSOI/CMOSTECHNOLOGY
By
SrinathKrishnan
August1996
Chairman:Prof.JerryG.Fossum
MajorDepartment:ElectricalandComputerEngineering
Thisdissertationfocusesonmodeling,anditsapplicationthereof,ofeffectsthatare
importantinscaledsilicon-on-insulator(SOI)CMOSdevices.Thefirstpartofthedisser-
tationconcernsmodelingofnon-localeffectssuchasvelocityovershootandimpaction-
ization.Thebasisforthenon-localmodelinghereisthesimplifiedenergy-balance(EB)
equation.TheEBequationkeepstrackofthecarrierkineticenergy,orequivalentlythe
carriertemperature,giventhelocalelectricfield,andhencephysicallyaccountsforthe
temperaturelaggingthefield.A“quasi-steady-state”approximationoftheEBequationis
usedtotransformthefield-dependentmobilityandionizationratetotheirequivalentnon-
localcounterparts.Thetransformedmobilityisthenusedtomodelcarriervelocityover-
shoot,whilethetemperature-dependentionizationrateisusedtoevaluatethenon-local
multiplicationfactor(defined asthe integratedionization rate). As aprecursortothe
velocityovershootanalysis/modeling,acomprehensivestudyofvelocitysaturationonthe
currentdriveofSOIMOSFETsiscarriedout.
ThesecondpartdealswitheffectsinherentintheSOItechnologyduetothefloating
body.Itisshownthatinhighlyscaledfullydepleted(FD)devices,animpactionization-
drivensubthresholdkinkcanoccur.Thephysicaloriginofthiskinkisexplained,andis
attributedtotheback-surfaceoftheSOIfilmbeingonlymildlydepleted.Themeaningof
FD/SOIishencequalified.Incertaintransients,independentofimpactionization,thepar-
asiticbipolartransistorisknowntobeactivatedinSOIMOSFETsduetodynamicbody
charging.Acomprehensivequasi-2DBiMOSmodelforthebipolartransistor,including
the(transient)transportcurrentandtheassociatedcharges,isdevelopedandimplemented
inSOISPICE.Themodelingisbasedonthestandardintegralcharge-controlrelationship,
butismodifiedextensivelytoaccountforthegate-dependentholedensityalongtheverti-
caldirection(variableGummelnumber),whichcanbeimportantincertainapplications.
Anoveldesignconcepttosuppressthebipolareffect,whichistoenhancethediffusion
capacitance,ispresented.
Forsystematicmodelverification,aswellasreliableevaluationofmodelparameters
foragiventechnology,aphysics-basedparameter-evaluationmethodologyisoutlinedin
the final part ofthe dissertation. This algorithm relies on the physical modeling in
SOISPICE,andishencerelativelystraightforward.Itisshownthatthemodelparameters
evaluatedfromthis processcanprovide insightintotechnology duetotheirphysical
nature.TheutilityofthisalgorithmisdemonstratedbyapplicationtoactualscaledSOI
CMOStechnologies.
IX
CHAPTER
1
INTRODUCTION
Theevolutionoftheintegratedcircuit(IC)industryoverthepast25yearsfromlarge-
scaleintegratedcircuits(LSI)topresentdayultralarge-scaleintegratedcircuits(ULSI)
hasbeentrulyphenomenal[Dav95].Theprimarydriverforthisgrowthhasbeenthecon-
stantneedforhigh-performancesystemsatreducedcost/benefit-per-functionfortheend
user[Sem94].Complementarymetal-oxide-semiconductor(CMOS)hasbeentheunani-
moustechnologyofchoiceforrealizingthesehigh-performancesystems.Inordertomeet
improvedperformancespecifications,CMOStechnologyhasbeen,andcontinuestobe,
scaled. Therulesofscaling, whichinvolveshrinkingcriticaldimensionsofthebasic
MOSFET,werefirstproposedbyDennardetal.[Den72],andlaterextendedbyBrewset.
al. [BreSO].Uponimplementation,theseruleshavebeenmoreorlessin accordwith
Moore’slaw[Moo75],whichpredictsthenumberoftransistors/chiptoroughlydouble
everyyear.Thesescalinglaws,however,arenotideal.Theconceptofidealscaling,which
involvesmaintainingconstantelectricfieldsintheMOSFET,whileuseful,hasnotbeen
popularduetoreluctancetodepartfromstandardizedvoltagelevels [Dav95]. Conse-
quently,thetrendofscalingtoyieldhigh-performancesystemshasbeenonewherethe
supplyvoltageishardly,orveryslowlyscaled.
Recentlyanewshiftintheparadigmistakingplaceintheinformationindustry,which
willallowanddemandfasterscalingofthesupplyvoltage [Dav95].Themainforces
behindthischangearetheabilitytoproducecomplexsystemsinachip,combinedwith
1
