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1、SolidStateDrivesDataReliabilityandLifetimeWhitePaperAlanR.Olson&DenisJ.LangloisApril7,2008AbstractTheexplosionofflashmemorytechnologyhasdramaticallyincreasedstoragecapacityanddecreasedthecostofnon-volatilesemiconductormemory.ThetechnologyhasfueledtheproliferationofUSB
2、flashdrivesandisnowpoisedtoreplacemagneticharddisksinsomeapplications.Asolidstatedrive(SSD)isanon-volatilememorysystemthatemulatesamagneticharddiskdrive(HDD).SSDsdonotcontainanymovingparts,however,anddependonflashmemorychipstostoredata.Withproperdesign,anSSDisabletopr
3、ovidehighdatatransferrates,lowaccesstime,improvedtolerancetoshockandvibration,andreducedpowerconsumption.Forsomeapplications,theimprovedperformanceanddurabilityoutweighthehighercostofanSSDrelativetoanHDD.Usingflashmemoryasaharddiskreplacementisnotwithoutchallenges.The
4、nano-scaleofthememorycellispushingthelimitsofsemiconductorphysics.Extremelythininsulatingglasslayersarenecessaryforproperoperationofthememorycells.Theselayersaresubjectedtostressfultemperaturesandvoltages,andtheirinsulatingpropertiesdeteriorateovertime.Quitesimply,fla
5、shmemorycanwearout.Fortunately,thewear-outphysicsarewellunderstoodanddatamanagementstrategiesareusedtocompensateforthelimitedlifetimeofflashmemory.FloatingGateFlashMemoryCellsFlashmemorywasinventedbyDr.FujioMasuokawhileworkingforToshibain1984.Thename"flash"wassuggeste
6、dbecausetheprocessoferasingthememorycontentsremindedhimoftheflashofacamera.Flashmemorychipsstoredatainalargearrayoffloatinggatemetal–oxide–semiconductor(MOS)transistors.Siliconwafersaremanufacturedwithmicroscopictransistordimension,nowapproaching40nanometers.FloatingG
7、ateMOSTransistorAfloatinggatememorycellisatypeofmetal-oxide-semiconductorfield-effecttransistor(MOSFET).Siliconformsthebaselayer,orsubstrate,ofthetransistorarray.Areasofthesiliconaremaskedoffandinfusedwithdifferenttypesofimpuritiesinaprocesscalleddoping.Impuritiesarec
8、arefullyaddedtoadjusttheelectricalpropertiesofthesilicon.Someimpurities,forexamplephosphorous,createanexcessofelectronsinthe