APL95-232101(2009)(2)

非易失性的电阻开关在石墨烯氧化物薄膜

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FIG.2. Coloronline a Theenduranceperformance,and b thedistribu-tionsoftheprogrammingvoltages VSetandVReset oftheCu/GO/Ptmemorycell.

Figure1 b plotsatypicalI-VcurveofaCu/GO/Ptcell.TheinsetofFig.1 b showsthesameI-Vcurveinasemi-logarithmicscale.Duringthemeasurement,thevoltagewassweptinasequenceof0V→1V→0V→ 1V→0Vatarateof0.01V/s.Noformingprocesswasnecessaryforacti-vatingtheresistiveswitchingeffect.Whileincreasingthepositivevoltagesteadily,thecurrentjumpsabruptlyatavolt-agevalueofabout0.8V.Thedeviceswitchesfromthehighresistance state rentLRScomplianceoronstateHRS oroffstate toalowresistancestate10,whichmAinisthiscalledworkthe is“Set”usuallyprocess.neededAcur-dur-ingtheSetprocesstopreventthesamplefromapermanentbreakdown.Bysweepingthevoltagefrom1to 0.4V,thedeviceholdsontheLRS,andstartsswitchingfromtheLRSto Set0.75theHRSprocess.V,the “Reset”ThecellIrecoversprocess-Vcharacteristicsto fromtheHRS, 0.4exhibitandV.Atthevoltageofaholdstypicaluntilbipolarnextswitchingbehavior.ThedeviceyieldoftheCu/GO/Ptstruc-tureismorethan50%.

InordertoinvestigatetheenduranceperformanceoftheCu/GO/Ptmemorydevice,cyclicswitchingoperationswereconducted.Figure2 a showstheevolutionofresistanceofthetwowell-resolvedstatesin100cycles.Theresistancevalueswerereadoutat 0.1Vineachdcsweep.AlthoughtheresistancevaluesofbothHRSandLRSshowsome uc-tuations,theon/offratiosareabout20withoutanyobviousdegradationwithin100cycles.Thedistributionofthepro-grammingvoltages VetertoevaluatethememorySetandVdevice,Reset ,anotherisshowncriticalinFig.param-2 b .V SetandVResetdistributeinarangeof0.3to1VCu/GO/Pt0.9V,respectively.and 0.3tosandwichedThestructureswitchingthresholdvoltagesofthe8,17

arelowerthanthoseofmostreportedRRAMdevices.1,3,4,TheretentionperformanceofthememorycellatRTisshowninFig.3.Thedevicewasswitchedonoroffbydcvoltagesweeping.ThentheresistanceofLRSorHRSwasreadoutatareadingvoltageof0.1V.Thereadoutwasfound

Appl.Phys.Lett.95,232101 2009

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FIG.3. Coloronline RetentionfortheLRSandHRSoftheCu/GO/PtdeviceatRT.

tobenondestructive.BoththeLRSandHRSresistancescanberetainedformorethan104swithoutanexternalelectricalpower,indicatingthatthememorydeviceisnonvolatileandstableatRT.

Weintendtoattributetheobservedresistiveswitchingtothedesorption/absorptionofoxygen-relatedgroupsontheGOsheetsaswellasthediffusionofthetopelectrodes.Asiswellknown,aGOlayercanbeconsideredasagraphenesheetwithepoxide,hydroxyl,and/orcarboxylgroupsattachedtobothsides,andphysicalpropertiesofGOcanbemodulated18,19bythosechemicalfunctionalitiesonthesurface.Weproposethatthedesorptionandabsorptionofepoxide,hydroxyl,andcarboxylgroupsneartheCutopelectrodemayberesponsiblefortheobservedresistiveswitchingintheCu/GO/Ptcell.20,21Whenthereareanamountofepoxide,hydroxyl,andcarboxylgroupsontheGOsurface,theconductanceoftheCu/GO/Ptcellisas-sumedtobelowduetosp3bondingfeature.Asapositivebiasisappliedonthetopelectrode,oxygen-relatedfunc-tionalgroupsinsidetheGOlayer s closetotheCutopelec-trodeareremoved,resultinginanamountofsp2bonds.Theconductanceofthedevicebecomeshigherduetoanincreaseintheconcentrationofinterlayer electrons.Asaresult,thedeviceisswitchedtotheLRS.Whilesweepingthevoltagetocertainnegativevalues,theoxygen-relatedgroupsdiffusetowardGOsheetsandattachtothemagain.Correspondingly,thememorycellreturnstotheHRS.Therefore,thedesorp-tionandabsorptionoftheoxygen-relatedgroupsontheGOsheetscorrespondtotheonandoffstates,respectively.Inaddition,variousmetals suchasAg,Au,andTi astopelectrodesweredepositedonGO lmsandtheI-Vcharac-teristicswereinvestigated.Theresistiveswitchingbehaviorswerealsoobserved.ThedeviceswithCutopelectrodesshowedlargeron/offratioandhigherdeviceyieldcomparedtothosewithAutopelectrodes.Thissuggeststhattheformation/ruptureofmetal lamentsintheGO lmduetothediffusionoftopelectrodesunderanexternalvoltagemayberesponsiblefortheswitchingaswellbesidesthedesorption/adsorptionofoxygen-relatedgroups.Ofcourse,inordertoclarifytherealoriginoftheobservedresistiveswitchingbehaviors,moreinvestigationsareneeded.

Insummary,ableandreproducible/SisubstratesGOresistancebythinvacuum lmsswitching ltrationwerebehaviorsmethod.preparedReli-onPt/Ti/SiO2werefoundintheCu/GO/Ptdevices.TheresistanceratiobetweenHRSandLRSisabout20.Thememorydevicesexhibitedgoodretentioncharacteristicsandlowswitchingvoltages.