9 MOSFET I-V Characteristics

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1、6.012-MicroelectronicDevicesandCircuits-Spring2003Lecture9-1Lecture9-MOSFET(I)MOSFETI-VCharacteristicsMarch6,2003Contents:1.MOSFET:cross-section,layout,symbols2.Qualitativeoperation3.I-VcharacteristicsReadingassignment:HoweandSodini,Ch.4,§§4.1-4.3Ann

2、ouncements:Quiz#1,March12,7:30-9:30PM,WalkerMemorial;coversLectures#1-9;openbook;musthavecalculator.6.012-MicroelectronicDevicesandCircuits-Spring2003Lecture9-2Keyquestions•Howcancarrierinversionbeexploitedtomakeatran-sistor?•HowdoesaMOSFETwork?•Howd

3、oesoneconstructasimplefirst-ordermodelforthecurrent-voltagecharacteristicsofaMOSFET?6.012-MicroelectronicDevicesandCircuits-Spring2003Lecture9-31.MOSFET:layout,cross-section,symbolspolysilicongatebodysourcedraingaten+p+n+n+pinversionlayergateoxidench

4、annelnp+pn+n+n+n+Keyelements:•inversionlayerundergate(dependingongatevoltage)•heavily-dopedregionsreachunderneathgate⇒in-versionlayerelectricallyconnectssourceanddrain•4-terminaldevice:bodyvoltageimportant6.012-MicroelectronicDevicesandCircuits-Sprin

5、g2003Lecture9-42CircuitsymbolsTwocomplementarydevices:•n-channeldevice(n-MOSFET)onp-Sisubstrate(useselectroninversionlayer)•p-channeldevice(p-MOSFET)onn-Sisubstrate(usesholeinversionlayer)DDIDnIDnSS+++VDS>0VSGVSBGG__BB++GBGBVGSVBSVSD>0__S−S−IDpD−−IDD

6、p(a)n-channelMOSFET(b)p-channelMOSFETDrainn+Sourcep+GatepBulkor GatenBulkor BodyBodySourcen+Drainp+6.012-MicroelectronicDevicesandCircuits-Spring2003Lecture9-52.QualitativeoperationWateranalogyofMOSFET:•Source:waterreservoir•Drain:waterreservoir•Gate

7、:gatebetweensourceanddrainreservoirsVDSVGSIDGVGSSDwaterVDSn+n+inversionlayerdepletionregionpBsourcegatedrainWanttounderstandMOSFEToperationasafunctionof:•gate-to-sourcevoltage(gateheightoversourcewaterlevel)•drain-to-sourcevoltage(waterleveldifference

8、betweenreservoirs)Initiallyconsidersourcetieduptobody(substrateorback).6.012-MicroelectronicDevicesandCircuits-Spring2003Lecture9-6Threeregimesofoperation:2Cut-offregime:•MOSFET:VGS0.•Wateranalogy:gateclosed;nowatercanflowregardlessof