電子器件場效應(yīng)晶體管

電子器件場效應(yīng)晶體管第1頁/共27頁MOSStructure

Poly-silicon-OSStructureIdealMOScapacitanceRealSurfaceEffects:Workfunctiondifference&interfacechargeNon-idealcapacitance第2頁/共27頁(1)workfunctiondifference

semiconductoroxiden+polysilicon(多晶硅)ms=m-sn+poly-nSin+poly-pSi第3頁/共27頁IdealNon-ideal第4頁/共27頁(EFm-EFs)=(qs-qm)

V=s-mVG=VFB(平帶電壓)=-V=m-s=

ms第5頁/共27頁

(2)InterfacechargeGenerally,therearefourtypesofchargesinapracticalMOSstructure.MobileionicchargeQm可動離子電荷OxidetrappedchargeQot氧化物陷阱電荷OxidefixedchargeQf氧化物固定電荷InterfacetrapchargeQit界面陷阱電荷第6頁/共27頁IdealInterfacecharge第7頁/共27頁Qi第8頁/共27頁Effectsofrealsurface第9頁/共27頁6.4.4ThresholdvoltageToachievetheflatbandToaccommodatethedepletionchargeToinducetheinvertedregion第10頁/共27頁Qd=-qNaWm(nchannel/P-sub)Qd=qNdWm(pchannel/N-sub)Whenisthethresholdvoltageofp-channelMOSFETgreaterthan0?Howtodo?第11頁/共27頁第12頁/共27頁1）flatbandvoltage第13頁/共27頁2）thresholdvoltage第14頁/共27頁3）depletionmodebecauseVT<0第15頁/共27頁(4)MOSCapacitor(ideal)Capacitance-voltagecharacteristics(電容電壓特性）CiCsBecauseCsisdependingonVG,theoverallcapacitancebecomesvoltagedependent.第16頁/共27頁CiCsTomeasurethecapacitance,wemustsuperposethesmalla-csignaltothevoltage.ThatisVG=V+dVG.HeredVGusedtomeasurethecapacitancewillcausethesmallchargechangeoftheMOScapacitorHighfrequency第17頁/共27頁第18頁/共27頁6.4.5MOScapacitance-voltageanalysisVT~SubstrateDopingTypeC-VGPerformance~SubstrateDopingTypeTomeasurethedopingdensityofsubstrateTomeasuretheinterfacestateTomeasurethemobilechargewithintheoxide第19頁/共27頁(1)Tomeasurethewidthofoxidelayer,dopingdensityofsubstrate,VFBandVTFig.6-16Tomeasurethecapacitance,wemustsuperposethesmalla-csignaltothevoltage.ThatisVG=V+dVG.HeredVGusedtomeasurethecapacitancewillcausethesmallchargechangeoftheMOScapacitor第20頁/共27頁Showunderflatbandcondition第21頁/共27頁(2)TomeasurethefastinterfacestateDit第22頁/共27頁(3)Tomeasurethemobilechargewithintheoxide

Fig.6-22第23頁/共27頁6.4.6Time-dependentcapacitancemeasurements

Tomeasurethegenerationlifetime

第24頁/共27頁6.4.7Current-voltagecharacteristicsofMOSgateoxides

Tounderstandtheleakagecurrentthroughtheoxide

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

)第25頁/共27頁Summary(1)實際器件與理想情況存在偏差：實際情況要考慮功函數(shù)差及界面電荷效應(yīng)。(2)實際情況下存在平帶電壓，從而使閾值電壓偏