BFO中极化转动对电阻态及输运行为的影响

ResistanceandtransportbehavioraccompanyingpolarizationswitchinginBFOPresentedby:RongliGaoGroupM03StateKeylaboratoryofmagnetismInstituteofPhysicsSupervisor:Prof.JirongSun2012-12-24Content1.BackgroundandMotivation2.Experiments3.Resultsanddiscussion4.SummaryBackgroundandMotivationBiFeO3:multiferroicmaterialJPCM20(2008)434220;NatureMaterials5(2006)823(1)G-typeantiferromagneticorder:WithTN~643K;weakferromegnetismJ.Wanget.al,Science.299,1719(2003)(2)Ferroelectricorder:withTc~1100K;LargepolarizationPr~100uC/cm2Polarizationalong(111)directionPseudocubicstructurewithc/a=1.016,H.T.Yiet.al,Adv.Mat.23,3403(2011);SwitchablerectifyingbehaviorandphotovoltaiceffectBackgroundandMotivationC.Wangetal,APL.98,192901(2011);D.Leeetal,PRB84,125305(2011)(1)Rectifyingbehaviorisinterestingduetoitspotentialapplicationinthenon-volatilememorytechnology.(2)However,switchablerectifyingandtransportbehaviorsoccuraccompanyingpolarizationchangesandthepolarizationwereconsideredonlyinfullyupwardorfullydownwardpolarizedstates.(3)Fewworkshavebeenmadeabouttherectifyingandtransportbehaviorandtheintermediatelypolarizedstates.(4)Theinfluenceofpolarizationfatigueprocessonphoto-currenthasnotbeenstudiedyet.BackgroundandMotivationSamplestructures:Ag/Bi0.9La0.1FeO3/La0.7Sr0.3MnO3/SrTiO3AgBLFO-(500nm)LSMO-(30nm)STOExperimentsandResultsMethods:pulselaserdeposition(PLD)(a)LSMOfilmsasbottomelectrodesweredepositedonSrTiO3(STO)substrates.(Temperature:700℃；oxygenpressure:50Pa;depositionfrequencyof1Hz;withthelaserenergyof1.2J/cm2)(b)BLFOfilmsweredepositedonLSMObufferlayer.(Temperature:650℃；oxygenpressure:15Pa;depositionfrequencyof1Hz;withthelaserenergyof1.2J/cm2;cooldowntoRTat2℃/minintheatmosphereof100Pa)(c)AgfilmsweredepositedbyonBLFOasthetopelectrode.(10-4Pa)1.XRDdata(a)BLFOtarget(b)BLFO/LSMO/STOfilmResultsanddiscussion2030405060708090100Intensity2(100)(110)(111)(200)(210)(211)(220)(221)(310)(311)(222)(321)10203040506070802(003)(002)IntensitySTOBFOSTOBFOBFOSTO(001)2.P-EcurvesThe（100）and（110）orientedPrisabout80and95uC/cm2respectively-40-30-20-10010203040-100-80-60-40-20020406080100f=10kHzP(c/cm2)V(V)-30-20-100102030-80-60-40-20020406080P(c/cm2)V(V)f=10kHz(c)BLFO-LSMO/STO-(100)(d)BLFO-LSMO/STO-(110)3.Transportbehaviorsaccompanyingpolarizationswitching,/)()(00RtVtI,/SQPttdttIQ0)(whereSistheareaofthetopelectrodeAccordingtoWecancalculatethePrvalue3.1.Polarizationswitchingprocessdependenceonthepulsevoltages(P~Vcurve)0123456780-10-20-30-40-50-60-70-80-VpulseI(A)t(s)-3V-6V-8V-9V-10V-12V-15V-18V-21V-24V-27V-30V+30V(a)Transientcurrent~time(b)Polarizarion(Pr)~voltage(V)-4-2024-8-6-4-20-30V0-3v-6v-8v-9v-10v-12v-15v-21v-24v-30vI(A)V(v)poledVpulsePP-4-2024-8-6-4-20V(v)I(A)poledVpulse+30V-0V+30V-3V+30V-6V+30V-8V+30V-9V+30V-10V+30V-12V+30V-15V+30V-21V+30V-24V+30V-27V+30V-30V+30VPP024680-20-40-60-80I(A)+30V-30V+30V-27V+30V-24V+30V-21V+30V-18V+30V-15V+30V-12V+30V-10V+30V-9V+30V-8V+30V-6V+30V-3V30V-0V+30Vt(s)024680102030405060708090I(A)t(s)-30V+30V-30V+27V-30V+24V-30V+21V-30V+18V-30V+15V-30V+12V-30V+10V-30V+9V-30V+8V-30V+6V-30V+3V-30V+0V-30V3.2.I-Vcurves(a)I-tcurvefromdownwardtoupward(b)I-tcurvefromupwardtodownward(c)I-Vcurvefromdownwardtoupward(d)I-Vcurvefromupwardtodownward051015202530-2-3-4-5-6-7-8V(v)Imax(A)+Vpulse-30VPP051015202530-2-4-6-8I(A)V(V)PPThecurrentmaximum(resistiveminimum)occursatthecoercivevoltage,bothinupwardanddownwardflipping.Ingeneral,thetransportbehaviorisdeterminedbytheSchottkybarrierformedattheinterface.(a)(b)(c)(d)Therefore,shoulddemonstrateamonotonicvariationwithPr.TheresistanceRshouldvariedmonotonicallywiththepolarization.IndicatingthatPrinducedbarriervariationmaynotlimitedtotheinterfacialbarrier.sbP0/[1]L.Pintilieet.al,JAP.98,124103(2005)Thebarrierheightwasvariedbythepolarization[1]:Where,sbistheseparationbetweensurfacepolarizationchargeandelectrode,isthestaticdielectricconstant,Inordertoillustratethisabnormalrelation,fatiguetestwasperformed.3.3.Polarization-Switchingandfatigueproperties-6-4-20246-24-20-16-12-8-40I(A)V(v)1(+-30V)10(+-30V)50(+-30V)500(+-30V)2000(+-30V)PP(a)alternativepulseRofbothupwardanddownwardpolarizationwasdecreasingwithrepeatingalternativepulses-6-4-20246-4-3-2-10I(A)V(v)1(-30V)10(-30V)50(-30V)500(-30V)2000(-30V)P(b)identicalpulseSchematicofbarrierstructureVacuumlevelAgLSMOBLFO4.26eV3.3eV2.8eV4.8eV(3.3+x)eVEcEvEfEfEfAgLSMOBLFO0.94eVEf2.5eVxThisjustexplainswhythecurrentlevelislow/highunderpositive/negativebias,buttheabnormalresultwasstillunknown.Theimpedancespectrawasstudied.RofbothupwardanddownwardpolarizationwasincreasingwithrepeatingidenticalpulsesLSMOBLFOAgR1R2R3C1C2C3'jZZZZCjM0))(1(20RCRCCCM3.4.impedancespectraanalysis(a)theschematicofthecircuitAccordingtoandForaparallelRCcircuit,themodulusM’’shouldbe1021031041050.01M''f(Hz)1000+30v1000-30v1000+-30vDC=-4V(b)Theimaginarypartofthefrequency-dependenceOnlyasinglepeakcanbedescribedbyasingleRCequivalentcircuit,andthepeakpositionandheighthavetheformof1/RCandC0/2C.0.04.0x1068.0x1061.2x1071.6x10701x1062x1063x1064x1065x1066x1067x1068x106Z''Z'1000*