电子器件场效应晶体管(3)课件

6.4.3Effectsofrealsurfaces

alkalimetalions碱金属离子sodium(Na+)ion钠离子mobilecharge可动电荷trappedcharge陷阱电荷interfacecharge界面电荷fixedcharge固定电荷effectivepositivecharge有效正电荷heavilydopedpoly-silicon重掺杂多晶硅MOSStructure

Poly-silicon-OSStructureIdealMOScapacitanceRealSurfaceEffects:Workfunctiondifference&interfacechargeNon-idealcapacitance(1)workfunctiondifference

semiconductoroxiden+polysilicon(多晶硅)ms=m-sn+poly-nSin+poly-pSi(EFm-EFs)=(qs-qm)

V=s-mVG=VFB(平带电压)=-V=m-s=

ms

(2)InterfacechargeGenerally,therearefourtypesofchargesinapracticalMOSstructure.MobileionicchargeQm可动离子电荷OxidetrappedchargeQot氧化物陷阱电荷OxidefixedchargeQf氧化物固定电荷InterfacetrapchargeQit界面陷阱电荷IdealInterfacechargeEffectsofrealsurface6.4.4ThresholdvoltageToachievetheflatbandToaccommodatethedepletionchargeToinducetheinvertedregionQd=-qNaWm(nchannel/P-sub)Qd=qNdWm(pchannel/N-sub)Whenisthethresholdvoltageofp-channelMOSFETgreaterthan0?Howtodo?1）flatbandvoltage2）thresholdvoltage3）depletionmodebecauseVT<0CiCsTomeasurethecapacitance,wemustsuperposethesmalla-csignaltothevoltage.ThatisVG=V+dVG.HeredVGusedtomeasurethecapacitancewillcausethesmallchargechangeoftheMOScapacitorHighfrequency6.4.5MOScapacitance-voltageanalysisVT~SubstrateDopingTypeC-VGPerformance~SubstrateDopingTypeTomeasurethedopingdensityofsubstrateTomeasuretheinterfacestateTomeasurethemobilechargewithintheoxideShowunderflatbandcondition(2)TomeasurethefastinterfacestateDit(3)Tomeasurethemobilechargewithintheoxide

Fig.6-226.4.7Current-voltagecharacteristicsofMOSgateoxides

Tounderstandtheleakagecurrentthroughtheoxide

Fig.6-24(Somethingwrong,seeEnglishtextbookandpage233(chinesetextbook)

)Summary(1)实际器件与理想情况存在偏差：实际情况要考虑功函数差及界面电荷效应。(2)实际情况下存在平带电压，从而使