Semiconductor-Devices-Physics-and-Technology

SemiconductorDevicesSemiconductorDevices--PhysicsandTechnologyPhysicsandTechnology--NanoHybridThinFilmsLab이병훈OutlineOutlineƒHistoryofThinFilmTransistorƒBandStructureƒƒCarrierTransportPhenomenaCarrierTransportPhenomenaƒElectricalPropertiesofJunctionElectricalPropertiesofJunctionƒMetal-Oxide-SemiconductorField-EffectTransistor(MOSFET)ƒJunctionFieldEffectTransistor(JFET)ƒThin-FilmTransistors(TFTs)ƒOrganicThin-FilmTransistors(OTFTs)HistoryofThinFilmTransistorHistoryofThinFilmTransistorNanoHybridThinFilmsLabHistoryofThinFilmTransistorHistoryofThinFilmTransistorAluminumoxideAluminumCoppersulfideFigure1Diagramofthefirstfield-effectelectronicdevicezThe1930s•MostauthorshavecreditedLilienfeldwiththefirstinventionoffield-effectdevice,ina1934patent.Inhisfavoristhefactthathisexampleembodiment,showninfigure1,hasappropriateexamplematerials,namely,asemiconductoractivelayer(Cu2S),aninsulator(Al2O3),andametalgate(Al).Figure2Diagramofanearlyfield-effectdevice.•Shockley’soriginalthinking,in1939,wasbaseduponhisunderstandingofshottkydiode,i.e.,ametal-semiconductorcontact.Herealizedthatadjacenttothemetalthesemiconductorwasdepletedofmobilechargeandthattheextentofthedepletionregiondependedupontheappliedvoltage.HistoryofThinFilmTransistorHistoryofThinFilmTransistorzThe1950s•Source-Thenegativeterminalofanelectronchanneldeviceorthepositiveterminalofaholechanneldevice•Drain-Theoppositeterminal•Gate-Theinsulatedfieldelectrodep-typegatep-typegateSourceDrainFigure3Schematicofthespacechargeregiononajunctionfield-effecttransistor.HistoryofThinFilmTransistorHistoryofThinFilmTransistorzThe1960sInsulatingsubstrateSourceDrainSemiconductorInsulatorControlgateFigure4SchematicdiagramofWeimer’stop-gatestaggeredCdSTFTstructure.•ThehistoryoftheTFTaseveryoneknowsittodayreallybeganwiththeworkofP.K.WeimeratRCALaboratoriesin1962.•Heusedthinfilmsofpolycrystallinecadmiumsulfide,togetherwithinsulatingfilmssuchassiliconmonoxide,inwhichwouldnowbecalledastaggeredstructure,withthesourceanddraincontactsintheoppositesideofthefilmfromthegate.•Onaglasssubstrate,sourceanddrainelectrodesareformedbyevaporatinggoldthroughashadowmask.TheCdSfilmisnextevaporated,alsothroughashadowmask,followedbySiOandfinallyasecondgoldevaporationforthegate.IntrinsicsiliconSourceDrainHeavilydopedregionThermallygrownsilicondioxideGateConductingchannelFigure5Schematiccrosssectionofaninsulated-gatefield-effecttransistor(IGFET)incrystallinesilicon.HistoryofThinFilmTransistorHistoryofThinFilmTransistorzThe1970s•In1979anewmaterialwasintroduced,withprofoundimplication.LeComber,Spear,andGhaithdescribedaTFTusingamorphoussiliconastheactivematerial.Hydrogenatedamorphoussilicon•Ithadpreviouslybeendiscoveredthathydrogenatedamorphoussilicon,incontrasttopureamorphoussilicon,couldbedopedwithdonorsoracceptorstoinducen-orp-typeconductivity.•CdSeexhibitsmuchhighermobilitiesthanamorphoussilicon,butCdSeisapolycrystallinecompound;itspropertiesareinfluencedbygrainsize,grainboundaryinterfacestates,stoichiometry,etc.,anditcanbesensitivetoambientgasessuchasH2Oandoxygen.Amorphoussiliconhasnograinboundariesandisself-passivating.DischargeSi3N4:dielectriclayerDischargesilicon:activelayerOncurrent:severalmicroamperesOFFcurrent:1nAHistoryofThinFilmTransistorHistoryofThinFilmTransistorzThe1980ssubstrateSourceSemiconductorInsulatorGateDrainBasecoatFigure6Schematiccrosssectionoftheinverted-staggeredCdSeTFTstructure.GlasssubstrateSourceDrainGatesInsulatorsCdSelayerFigure7Schematiccrosssectionofthedouble-gatestructureusedbyLuoetal.toachievelow-leakagecurrentsinCdSeTFTs.•Despitetheexcitementgeneratedbythearrivalofthea-SiTFT,significantimprovementsinCdSeTFTsemergedin1980.Mobility:140cm2/V-sOn/OFFratio:106Thresholdvoltage:2VExcellentsaturationupto12V•Alsoin1980,F.C.Luoetal.ofXeroxreportedalow-leakageCdSeTFT.OFFcurrent0V:2.5pATheactivelayerwaslessthan100Åthick•ThisTFTwasengineeredforusewithliquidcrystalsasapixelTFT.HistoryofThinFilmTransistorHistoryofThinFilmTransistorzThe1980s•Luederandhiscoworkersin1979-81introducedanewapproachtoTFTfabricationusingphotolithographyinsteadofshadowmasks.-gateinsulatormaterial:Ta2O5•Theyear1980sawtheintroductionaswellofthepolysiliconTFT,inareportbyDeppetal.ofIBM.-Thesewerehigh-temperaturepolySiTFTs,employingasgateinsulatorSiO2grownthermallyat1050℃.-Glasscannotbeused.•By1982,boththeIBMgroupandNishimuraetal.ofMissubishiwereusinglaserrecrystallizationofpolySitoimprovemobilitiesandlowerthresholdvoltage,achievingvaluesashighas400cm2/V-sforelectronmobility.•ThatsameyearsawreportsofTFT/LCdisplaysemployinga-Siaswellastellurium.Figure8Schematiccrosssectionofaninverted-staggeredTeTFT.GlasssubstrateGate(Ta)Drain(Ni)Source(Ni)Gateinsulator(Ta2O5)Semiconductor(Te)On/OFFratio:106HistoryofThinFilmTransistorHistoryofThinFilmTransistorzThe1980sCrgateAlgatebus-line1st.SiNxGate-insulatorITOpixel2nd.SiNxCrdrain(bus-line)Aldrain(bus-line)a-SiSiNxpassivationAlsourcen+-a-SiCrsourceFigure9Schematiccrosssectionofana-SiTFTofthe“etch-stopper”orinsitutrilayer,type.•Moriyamaetal.ofNEC-MinimumcontaminationzThe