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LimitationstoMiniaturizationofMagneticComponents
EyalAklimi,Ph.D.May2017
EyalAklimi,2017
Outline
•Background:WhyMiniaturizePowerElectronics?•FromDiscretetoIntegratedInductors• Fabrication• Structures• Limitations• Comparison
•AdvanceTopicsandInnovativeReports
EyalAklimi,2017
ImproveEnergyEfficiencythroughMiniaturization
• Efficiency isgainingincreasedinterestasmoreelectronicsrunoffofindispensablesources(batteries)andhigh-conversionratioasDCmicrogrids emerge.
D.Nenni,2011
Size∝ Speed
• MakingDC-DCconverterssmaller,faster,moreefficient,andwithhigherconversionratioiskeytoachievingmanydesirableimprovementstoelectronics:• DeeperPDNreducesI2Rlosses,volume,weight,andheatdissipationmanagementrequirements• Techniquesthatrequirebetterconverters:DVS|Cycleandterminatepower|Fasterresponse|Sub-threshold
• Therearesimilaritiesbetweenultra-lowpowersystemsandvery-highpowersystems
EyalAklimi,2017
MiniaturizingDC-DCConverters
POL
PSiP/PMIC
IVR
EricssonBMR450
AlteraEN5364QI
E.Burton,etal.,APEC2015
SizeTrend|I/Ocount
EyalAklimi,2017
MiniaturizingDC-DCConverters- Terminology
• Integratedvoltageregulator(IVR)bringsthelaststageofvoltageconversionintoICpackage• FullyIVR(FIVR)referstomonolithicintegration,whereconverterswitchesareimplementedusingsametransistorsasloadIC• Pros:easyintegration,significantlyreducedinterconnectsparasitics
• Cons:limitedtolowinputvoltagesascorevoltagesdecrease
EyalAklimi,2017
Miniaturizing DC-DCConverters
Whatpreventsswitchingpowersuppliesfromshrinking(POL→ IVR)?• ThreemajorelementsofSMPS(inorderlarge→ small):
• Magneticcomponent(inductor)– biggestchallenge• Switches• Controller,switchesgatedrivers
• Lossesandsizeareintertwinedthroughswitchingfrequency:• Smallerswitches→ higherconductionlosses• Largerswitches→ higherswitchinglosses
𝐿$%&,($% ∝ 1 𝑓+,
Copperalsomatters,ofcourse
• Highfrequencyisoftenlimitedbyinterconnectsparasitics,which,constantlygetsbetter(lower)withbetterintegration
DiscretePackage-integratedChip-integrated
Control
POL/PSiP/PMIC
Integrated
DeadZone
D.W.Lee,2008
EyalAklimi,2017
• Inductorsrequirecurrentcarryingwinding (typicallycopper),and:• Nocore (“aircore”)• Highpermeabilitycore (yoke)
DiscreteandIntegratedMagneticComponents
Integrated(andmicro-magnetic)
Coilcraft,2014
D.Harburg,2012
K.L.Shepard,2012
P.McCloskey,2014
Vishay,2017
Discrete
EyalAklimi,2017
MagneticCoreinInductors
• Themotivationforaddinghigherpermeabilitysoftmagneticmaterialcore,istoincreaseinductancedensity;magneticfluxishowinductorsstoreenergy(comparetocapacitorsthatstorecharge)andhigherflux→ higherenergystoragecapacity• Thecoreprovideslowreluctancepath(“concentration”)forthemagneticflux
AMI,2017
• 𝐵 ∝ 𝜇/𝐻 magneticfieldisamplifiedbythecoretohigherlevelsofmagnetizationflux
EyalAklimi,2017
• Largesizemicroelectronicsmethodologies,usinghardmaterials
• Sputtering:veryslow,difficulttopattern/etch
• Multipleoptions(outsidethescopeofthistalk)
• Materials:solid,powderedmetals,etc.• Techniques:machining,sintering,laminationpressing
FabricationComparison
• windingcopperwire:aroundbobbin/core,orselfsupported
• Sizelimited,Mustbeabletoswivel• Serialproduction
• SameasBEOL:fabricationinlayers,patterningbylithography,withvias/spacers
• SizeandvolumelimitedCopp
erWire-wound Planar
DiscretecomponentCo
ilcraft,201
4
J.–B
.Yoo
n,200
2
Integratedcomponent
FabricationStructuresLimitationsComparison
Magne
tics
• Electroplating:Throughmask/PR
• Chipconscious!
D.S.Gardner,2010
EyalAklimi,2017
Micro-MagneticComponentsStructures
Pseudo-planar(layered)integratedinductorstructures• Spiralair-core(uselessforpowerapplications),orsingle/veryfewturns
• Cladded (race-track)usuallyelongated;multiturnsorsingle(alsostripline,orslab)
• Solenoid (toroidal)• Meander
D.W.Lee,2008
F.Zhang,2008
B.Estibals,2005
E.A.Burton,2014
N.Wang,2012E.Aklimi,2016
J.Kim,2015
FabricationStructuresLimitationsComparison
EyalAklimi,2017
MajorIntegratedMagneticsLimitations
Coppercross-sectionissmall→ highinductorresistance (ESR)Solutions:• Depositasthickaspossiblecopper• Designveryfewturns:
• Copperresistance𝐸𝑆𝑅 ∝ 𝑁 (numberofturns)andinductance𝐿 ∝ 𝑁5 soitisvery temptingtodesignmoreturns
• Significantcopperlossesareusuallynotacceptable.Exceptions:• Onehigh-conversion-ratioconverterreplacesmany2:1converters• Ifefficiencyinlessofapriority
FabricationStructuresLimitationsComparison
Mostlimitationsarenotuniquetointegratedmagnetics,butsomeareratheracute
EyalAklimi,2017
MajorIntegratedMagneticsLimitations
Smallcoressaturatefastatlowcurrents(=permeabilitynon-linearity)
Solutions:• Depositthickmagneticcores.Butstill,itisverydifficulttogoaboveafew𝜇𝑚• Electroplatingisinferiorbutgivesgoodrates• Sputterdepositionisveryslow(@0.1Å/𝑠𝑒𝑐,each1𝜇𝑚 takes±28hours)
• Designveryfewturnstoreducemagneticflux• Lowinductance
BiasCurrent(mA)
COMSOL,2013
E.Aklimi,2016Frequency[Hz]
Indu
ctance[H
]
FabricationStructuresLimitationsComparison
EyalAklimi,2017
MajorIntegratedMagneticsLimitations
Solutions:• Increaseelectricbulkresistivity(SputteredCoZrTa 100µΩ-cm,ElectroplatedCoWP >100µΩ-cm),versuslowresistivityNiFe 45µΩ-cm
R.Clarke,2008
Eddycurrentsgiverisetosignificantlossesathighfrequency,andskin-effect
• Laminate• Cannotelectroplatelaminations.Mustsputter-deposit:layersarethin
• laminatewiththickness≅ skindepth• Decreasefrequency
• Higherinductanceisneeded
FabricationStructuresLimitationsComparison
EyalAklimi,2017
MajorIntegratedMagneticsLimitations
Otherchallenges:• Hysteresislossofmagneticyoke∝ 𝑓• Integratedinductorsareverythin,typically100’sof𝜇𝑚laterallybutonlyafew𝜇𝑚 thick
• Difficultyclosingmagneticlooplaterallywithsmallstructures• Solution:add2nd magneticlayer(claddedstructure)
• Analyticalinductorsdesignformulasandexpressionsvarytoomuchfromactualbehavior.Requires:• Simulationstoestimateinductorparametersandbehavior• Fabricatinginductorscatalogandfitmodelsparametersusingmeasurementresults
R.Clarke,2008
𝐿 =𝜇𝑁5𝐴𝑙
Topview Cross-section
D.W.Lee,2008
FabricationStructuresLimitationsComparison
EyalAklimi,2017
MajorIntegratedMagneticsLimitations
Gainsfromaddingmagneticmaterialstoinductorsarecomplicatedandrequiretailoringinductorandarchitecturetogether;Forexample:• Qualityfactor𝑄 = CDEF indicatesinductor’sperformance
𝑄GH = 𝜔 D𝐿JH + Δ𝐿
𝑅JH + 𝜔 D𝜇′′𝜇′ D Δ𝐿
D.W.Lee,2008
D.S.Gardner,2009
• Increasinginductancebyaddingmagneticmaterialislimitingbothpeakqualityfactor,andthefrequencybandinwhichitisobtained
FabricationStructuresLimitationsComparison
EyalAklimi,2017
MajorIntegratedMagneticsLimitations
Existingmetricspaintaconfusingpictureofinductors’usefulnessinthecontextofanactualconverter (e.g.Q-factorlackinginfooncurrentsaturation!)• Examples:Inductance𝐿[𝐻] |Inductancedensity 𝑛𝐻 𝑚𝑚5⁄ |QualityFactor|PeakQualityFactor|CurrentDensity𝐼TUV 𝐴 𝑚𝑚5⁄ |EffectiveInductorEfficiency𝜂E_XYY |𝐿JH 𝑅TH⁄ 𝑛𝐻 Ω⁄
Non-linearbehavioralmodelsarerequiredtoaccountforlargecurrentsdistortion• Lumpedmodel(L)→non-ideallinearmodel(S-parameters)→ non-linearmodel(X-parameters)
D.S.Gardner,2009
N.Sturcken,2015N.Sturcken,2015
FabricationStructuresLimitationsComparison
EyalAklimi,2017
IntegratedMagneticComponents- Comparison
MagLayers
CuLayers
Inductance Copperlosses
Currentsaturation
IntelFIVRSinge turnaircore
none 1+1via
LOW LOW HIGH(none)
Intelw/magneticMulti-turnracetrack cladded
2+1via
1+1via
HIGH MED LOW
IBMWatson(racetrack)Single-turnracetrackcladded
2+1via
1+1via
MED LOW MED
Ferric(toroid w/magnetic)
1 2+1via
HIGH MED LOW
ColumbiaCore-Clad(Multi-turn cladded)
2+1via
2+1via
HIGH MED MED
E.T.Burtonetal.,2015
D.S.Gardner,2010
N.Wang,2012
N.Sturcken,2013
E.Aklimi,2016
InductorStructures FabricationStructuresChallengesComparison
EyalAklimi,2017
IntegratedMagneticComponents- Comparison
E.T.Burtonetal.,2015
Lowcopperlosses(onlyoneturn)Nocurrentsaturation(aircore)LowfabricationcomplexityLowinductance
EyalAklimi,2017
IntegratedMagneticComponents- Comparison
D.S.Gardner,2010
HighinductancedensityMediumcopperlossesMediumfabricationcomplexityLowsaturationcurrent
EyalAklimi,2017
LowcopperlossesMediumtolowinductanceMediumsaturationcurrentMediumfabricationcomplexity
IntegratedMagneticComponents- Comparison
N.Sturcken,2013
N.Wang,2012
Note:versionsofthistopology(stripline,slab)havebeenproposedbymanyothers(Intel,Tyndall,etc.)
EyalAklimi,2017
IntegratedMagneticComponents- Comparison
N.Sturcken,2013N.Sturcken,2015 K.L.Shepard,2012
HighinductancedensityMediumfabricationcomplexityMediumcopperlossesLowsaturationcurrent
EyalAklimi,2017
400%
IntegratedMagneticComponents- Comparison
Core-Clad(top)
Traditionalsolenoid(bottom)
Singleinductor
E.Aklimi,2016
E.Aklimi,2016
HighinductancedensityMediumcopperlossesMediumsaturationcurrentHighfabricationcomplexity
EyalAklimi,2017
AdvancedTopics
Influenceofprojecteddigitalmicroelectronicstrends• Availabilityofchipreal-estateforInductors↓astransistorsdensity↑• IVRcurrentrequirements↑aspowerdensity↑• IntegratedinductorsshareICrealestatewithI/O,soareaforinductors↓ asI/Odensity↑.Nonetheless,IVRusuallymeans↑powerwith↓I/O
EyalAklimi,2017
AdvancedTopics
• Betterhighfrequencybehaviorisdemonstratedwhenmagneticfluxisalignedwithhardaxis(HA)ofthecore(becausedomainmagnetizationrotationdominatesoverdomainwallmotion)• Elongatedrectangularshapesusuallyinduceeasyaxis(EA)shapeanisotropytothelongedgeofas-depositedfilms
HA
EA
200𝜇𝑚
E.Aklimi,2016
• Anisotropymustbeinduced:• In-situ:thisisanewdepositiontoolsrequirementforbothPVD-sputtering,andelectroplating• Post-depositionbyannealinginstrongmagneticfield:limitedbythermalbudgetofICsfront-end
• CladdedstructuresarebetterataligningfluxwithHAthroughoutthecore
EyalAklimi,2017
AdvancedTopics
• Magneticsfilmsareparticularlychallengingtopattern(evenincomparisontothickAl/Cumetallization):• Additive:photoresistlift-offofthicksputteredlayers• Additive:through-maskelectroplating• Subtractive:hard-maskdeposition,andetchofferrousalloys• Subtractive:damascenerequiresCMP
• Worsewithlaminations
N.Sturcken,2013
EyalAklimi,2017
CreativeWaystoMakeInductors
Microtube inductorsProcessesin2Dbutfunctionsin3D
X.Yu,2015S.-Y.Wu,2015
MoldedinductorsSerialmethod,notsuitableformass-production
EyalAklimi,2017
• ReducingSoC PowerConsumptionusingIntegratedVoltageRegulators,DanielNenni,2011http://www.semiwiki.com/forum/content/694-reducing-soc-power-consumption-using-integrated-voltage-regulators.html
• BMR450TechnicalSpecification,Ericsson,2011• EN5364QIDatasheet,Altera(formerlyEnpirion),2013• FIVR—Fullyintegratedvoltageregulatorson4thgenerationIntel®Core™SoCs,EdwardABurton,GerhardSchrom,FabricePaillet,JonathanDouglas,WilliamJ
Lambert,Kaladhar Radhakrishnan,MichaelJHill,APEC2014• Electronicsatitsbest,workingvoltageratingsforinductors,Coilcraft 2014https://kenvins.wordpress.com/2014/10/09/working-voltage-ratings-for-inductors/• DanHarburg,DartmouthThayerSchoolofEngineering,Microfabricated Inductors,2012http://engineering.dartmouth.edu/microeng/inductors%20full.jpg• RecoveryAct:IntegratedDC-DCConversionforEnergy-EfficientMulticoreMicroprocessors,FinalTechnicalReport,2012
https://www.osti.gov/scitech/servlets/purl/1073611• IntegratedMagneticsforPwrSiP andPwrSoc,PaulMcCloskey,Tyndall,PSMA2014http://www.psma.com/sites/default/files/uploads/tech-forums-
packaging/presentations/is26-integrated-magnetics-pwrsip-and-pwrsoc.pdf• PSCHighFrequencyRFSpiralInductorforWireBondedAssemblies,Datasheet,Vishay2017http://www.vishay.com/docs/61050/psc.pdf• AssemblyMasters(AMI),http://www.assemblymasters.com/air-core-inductors-air-coils.cfm• D.W.Lee,etal.EmbeddedIntegratedInductorsWithASingleLayerMagneticCore:ARealisticOption,PWRSOC2008• Designandrealisation ofintegratedinductorwithlowDC-resistancevalueforintegratedpowerapplications,• F.Zhang,etal,Voltage-ControlledOscillatorintheCoil,2008http://www.cisl.columbia.edu/grads/frank/TEST_CHIP/Chip2/Chip2.html• B.Estibals,Designandrealisation ofintegratedinductorwithlowDC-resistancevalueforintegratedpowerapplications,HAIT2005• E.A.Burton,etal.,FIVR- FullyIntegratedVoltageRegulatorson4thGenerationIntel(R)Core(TM)SoCs,APEC,2014• N.Wang,etat.,Integratedon-chipinductorswithelectroplatedmagneticyokes,JAP,2012• J.Kim,etal.,Anisotropicnanolaminated CoNiFe coresintegratedintomicroinductors forhigh-frequencydc–dcpowerconversion,J.ofphysicsD,2015• E.Aklimi,etal.,Core-CladCMOS- IntegratedInductorswithVerticalMagneticLoopClosure,MMM-Intermag,2016• J.–B.Yoon,CMOS-compatiblesurface-micromachined suspended-spiralinductorsformulti-GHzsiliconRFIcs,IEEEEDL,2002• Chipworks,2011,https://semimd.com/chipworks/page/6/
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EyalAklimi,2017
• COMSOL,2013,https://www.comsol.com/blogs/comsol-4-4-magnetic-saturation-curves/• R.Clarke,2008,http://info.ee.surrey.ac.uk/Workshop/advice/coils/power_loss.html• Powerlossesinwoundcomponents,http://info.ee.surrey.ac.uk/Workshop/advice/coils/power_loss.html• D.S.Gardner,etal.,ReviewofOn-ChipInductorStructuresWithMagneticFilms,IEEETransactionsonMagnetics,2009• N.Sturcken,IntegratedVoltageRegulatorswithThin-FilmMagneticPowerInductors,thesis,2013.• N.Sturcken,etal.,A2.5DIntegratedVoltageRegulatorUsingCoupled-Magnetic-CoreInductorsonSiliconInterposer,IEEEJSSC,2013• N.Sturcken,etal.,MagneticThin-FilmInductorsforMonolithicIntegrationwithCMOS,IEEEIEDM,2015• E.T.Burton,PackageandPlatformViewofIntel’sFullyIntegratedVoltageRegulators(FIVR),APEC,2015• D.S.Gardner,etal,IntegratedOn-ChipInductorsusingMagneticFilms,PWRSOC2010• N.Wang,etal.,Integratedon-chipinductorswithelectroplatedmagneticyokes,JournalofAppliedPhysics,2012• D.V.Schravendijk,PoweringmulticoreprocessorswithmultiphaseDC/DCs,TI,2015https://e2e.ti.com/blogs_/b/fullycharged/archive/2015/08/18/powering-
multicore-processors-with-multiphase-dc-dcs• TI,Howimportantisphase-to-phasecurrentbalanceinmultiphaseconverters?,2015https://e2e.ti.com/blogs_/b/powerhouse/archive/2015/09/18/how-
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EyalAklimi,2017