電子器件場(chǎng)效應(yīng)晶體管(3)課件

6.4.3Effectsofrealsurfaces

alkalimetalions堿金屬離子sodium(Na+)ion鈉離子mobilecharge可動(dòng)電荷trappedcharge陷阱電荷interfacecharge界面電荷fixedcharge固定電荷effectivepositivecharge有效正電荷heavilydopedpoly-silicon重?fù)诫s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(平帶電壓)=-V=m-s=

ms

(2)InterfacechargeGenerally,therearefourtypesofchargesinapracticalMOSstructure.MobileionicchargeQm可動(dòng)離子電荷OxidetrappedchargeQot氧化物陷阱電荷OxidefixedchargeQf氧化物固定電荷InterfacetrapchargeQit界面陷阱電荷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)實(shí)際器件與理想情況存在偏差：實(shí)際情況要考慮功函數(shù)差及界面電荷效應(yīng)。(2)實(shí)際情況下存在平帶電壓，從而使