材料物理 (8)材料磁性性质课件

MagneticPropertiesofMaterialsI,MagnetizationCurvesFig.MPAa)isthecurveintheabsenceofanymaterial:avacuum.Thegradientofthecurveis4π.10-7whichcorrespondstothefundamentalphysicalconstantμ0.magneticfluxdensity:(A/m,Gs)B=μ0(H+M).M=χmHB=μH=μ0(1+χm)H

,μr=μ/

μ0II,MagneticmomentTheconceptofmagneticmomentisthestartingpointwhendiscussingthebehaviourofmagneticmaterialswithinafield.Ifyouplaceabarmagnetinafieldthenitwillexperienceatorqueormomenttendingtoalignitsaxisinthedirectionofthefield.Acompassneedlebehavesthesame.Thistorqueincreaseswiththestrengthofthepolesandtheirdistanceapart.Sothevalueofmagneticmomenttellsyou,ineffect,'howbigamagnet'youhave.Itisalsowellknownthatacurrentcarryingloopinafieldalsoexperiencesatorque(electricmotorsrelyonthiseffect).Herethetorque,τ,increaseswiththecurrent,i,andtheareaoftheloop,A.θistheanglemadebetweentheaxisoftheloopnormaltoitsplaneandthefielddirection.

τ=

B×i×A×sinθ

τ=B×m×sinθIV,FerromagneticmaterialsThemostimportantclassofmagneticmaterialsistheferromagnets:iron,nickel,cobaltandmanganese,ortheircompounds(andafewmoreexoticonesaswell).Themagnetizationcurvelooksverydifferenttothatofadiamagneticorparamagneticmaterial.V,HysteresisloopMemorydevices1MagneticMemory

Mechanism:MainapplicationsTapeDisketteMagneticdrumMagneticMemorymaterials:-Fe2O3,CrO2,Fe-CoetalRead/writeheads2OpticalMemoryDVD-RWDVDCDApplications:Opticalstoragematerials:PC、PMMA、Epoxyetal.Mechanism:Advantage：lowprice,highstoragedensity;disadvantagelowaccess,largeboxMainapplication:3SemiconductormemoryBasedonsemiconductordevices；Advantage:fastaccess,highdatastorage,lowpower；CachememoryStackedmemoryFlashmemorySemiconductormemoriesCellarrayPeripheralcircuitI/Ounitcircuit

2m+n+k-1CategoriesofSemiconductormemoriesMemorytechnologiesPrimarycategoriesofelectricalmemory:RAM,ROMandFlashNonvolatile:

aftertransitionfromOFFstatetoONstate,deviceremainedinthisstateevenafterturningoffthepower.

Randomaccessmemory(RAM):Trmationislostwhenthepowerremovedfromthedevice.(DRAM,SRAM)Readonlymemory(ROM):Informationisnotlostwhenthepowerisswitchedoff,butthechargestoredinchipcan’tberefreshed.Flash:Thechargecanberefreshedfrequently,andinformationisnotlostwhenthepowerisswitchedoff.

DRAMwriteandreadoperationwritereadROM

MaskROMPROMEPROMEEPROM(Flash)Flash

DielectricTunneloxideMOSFET+FloatingGateThresholdshiftduetotheelectricchargeFlashwrite/erase/readoperationApplyvoltagetocontrolgate(CG)e-tunnelingoccursfromchanneltoFGApplyvoltagetosourcee-transferoccursfromFGtosourceApplyvoltagetoCG.Ife-

presentinFG,noconductionbetweenSandD.Ife-isabsent,conductionhappens.NAND&NORFlashNANDFlash:erasedandprogrammedblock-wise.NORFlash:erasedandprogrammedbyte-wise.PerformanceandrequirementsFastaccessNon-volatilityUnlimitedR/WcyclesLowpowerWidetemperaturerangeLowcostFerroelectricunitHysteresiscurveTwostatesofpolarizationunderappliedfieldcancorrespondtoastored“0”or“1”RemnantpolarizationCoercivefieldFerroelectricmemory(FeRAM)FeRAM(capacitor)Plateline(PL)hasavariablevoltageleveltoenabletheswitchingofthepolarizationoftheferroelectriccapacitor.1T-1CFeRAMoperationTowrite“1”inthecell,BLissettoVDDandPLisgrounded,thenapulseisappliedtoactivatethecelltransistor.Towrite“o”,accomplishedinthesamemannerbutPLandBLareexchangedtoreversethepolarizationofFerroelectriccapacitor.Read:firstBLisgrounded,thenitismadefloating.AfterthecellisselectedbyWL,thePLvoltageisraisedfromGNDtoVDD,raisedvoltageofBLisdependentofthepolarization(data)storedinFeCAP.Electricalbistability:OrganicelectricbistabledevicesAphenomenonexhibittwokindsofdifferentstableconductivestatebyapplyingappropriatevoltage.

TypicalI-VcharacteristicsSiliconmemory:encode“0”and“1”astheamountofchargestoredindevicecell

Organicmemory:storedatebasedonhigh&lowconductivityresponsetoappliedvoltageDevicestructuresCross-BarsShadowmaskDeviceconfigurationsPolyanilinenanofiberGoldnanoparticlesOrganic/nanoparticlessystemMetalcomplex

DonorAcceptorDonor-AcceptorsystemPerformanceandCharacterization

ON/OFFcurrentratioWrite-read-erasecyclesSwitchingtimeRetentionabilityNano-crystalfloating-gatememoryOxidegatetoothinLeakagepathCauseelectronstoredtoleakoutHowtoalleviatethescalinglimitation?

usethinnertunneloxideswithoutsacrificingnonvolatility

oxidethicknessoperatingvoltageoperatingspeedsDielectricTunneloxidePhasechangememoryChangethephasetocrystalline(setorconductive)andamorphous(res