Amit Chaudhry Fundamentals of Nanoscaled Field Eff ect Transistors Fundamentals of Nanoscaled Field Effect Transistors Amit Chaudhry Fundamentals of Nanoscaled Field Effect Transistors AmitChaudhry UniversityInstituteofEngineeringandTechnology PunjabUniversity Chandigarh,India ISBN978-1-4614-6821-9 ISBN978-1-4614-6822-6(eBook) DOI10.1007/978-1-4614-6822-6 SpringerNewYorkHeidelbergDordrechtLondon LibraryofCongressControlNumber:2013932710 ©SpringerScience+BusinessMediaNewYork2013 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionor informationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped.Exemptedfromthislegalreservationarebriefexcerpts inconnectionwithreviewsorscholarlyanalysisormaterialsuppliedspecificallyforthepurposeofbeing enteredandexecutedonacomputersystem,forexclusiveusebythepurchaserofthework.Duplication ofthispublicationorpartsthereofispermittedonlyundertheprovisionsoftheCopyrightLawofthe Publisher’s location, in its current version, and permission for use must always be obtained from Springer.PermissionsforusemaybeobtainedthroughRightsLinkattheCopyrightClearanceCenter. ViolationsareliabletoprosecutionundertherespectiveCopyrightLaw. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexempt fromtherelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. While the advice and information in this book are believed to be true and accurate at the date of publication,neithertheauthorsnortheeditorsnorthepublishercanacceptanylegalresponsibilityfor anyerrorsoromissionsthatmaybemade.Thepublishermakesnowarranty,expressorimplied,with respecttothematerialcontainedherein. Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Dedicated to Almighty Preface This book is an outcome of my research publications during my teaching and researchcareer. ThebookisaboutbasicunderstandingoftheMOSFETdevicesandtheirphysics atnanometerscale.ThetopicisalsoimportantbecausetheMOSdeviceshavebeen usedforthepast60yearsandhavebeenscaleddowncontinuouslyfortheirusein verycomplexanaloganddigitalcircuits.Inthisbook,asimpleandlucidtreatment tothe topic has been givenwhichwillenableastudenttofulfillhis/her desiresto learnabouttheMOSdevicesatnanoscale.Therearevariousissueswhichmakethe nanoscaleMOSFETsdifferentfromtheconventionalMOSFETssuchasquantum mechanical tunneling and inversion layer quantization. These issues along with their solutions such as alternate devices structures, strained-Si technology, high-κ technology, etc., require a thorough discussion and presentation in a book form whichispresentedhere. The book will be primarily for students studying in post graduate and under- graduate in electronics, microelectronics, physics, and nanoelectronics as a refer- encebook. Thebookhasbeenorganizedasfollows: ThebookstartswithintroductorychapteronMOSPhysicsandscaling.Scaling laws, models, and short channel effects have been presented in this chapter. In Chap. 2, the quantum mechanical tunneling in ultra thin gate oxide MOSFETs hasbeenpresentedthroughsomemodels.InChap.3,anotherquantummechanical effect such as inversion layer quantization in substrate has been given and some models have been described. In Chap. 4, the use of high-k dielectrics in the advanced MOS transistors has been outlined. In Chap. 5, the use of alternate materials such as germanium in the MOS substrate and some models has been given. In Chap. 6, the use of biaxial strained silicon technology and some case studiesfornchannelMOSFETandpchannelMOSFETmodelinghavebeentaken. In Chap. 7, another advanced approach of enhancing the carrier mobility and the performanceoftheMOSFEThasbeendiscussed.Thisistheapplicationofuniaxial strainonthe MOSFET.InChap.8,somenovelstructuresofMOSFET havebeen presented which can replace the conventional bulk MOSFET in the near future. vii viii Preface Lastly in Chap. 9, the morerecenttechnology such as graphene based field effect transistorshavebeendiscussed. Theauthorwouldliketoacknowledgethoseindividualswhocontributedtothe writingofthisbookandtotheresearchonwhichitisbased. Though every care has been taken in presenting the facts and figures, the comments of my learned readers are most welcome on the issues related to thematerialpresentedinthisbookforitsfurtherimprovement. Chandigarh,India AmitChaudhry Contents 1 ScalingofaMOSTransistor. . .. . . .. . . .. . . .. . .. . . .. . . .. . . .. 1 1.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 InternationalTechnologyRoadMap forSemiconductor(ITRS)andItsProjections. . . . . . . . . . . . . . 2 1.3 MOSFETPhysics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3.1 MOSFETOperation. . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3.2 Accumulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3.3 Depletion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3.4 ChannelCreation(Inversion). . . . . . . . . . . . . . . . . . . . 5 1.3.5 InversionChargeDensity. . . . . . . . . . . . . . . . . . . . . . . 6 1.3.6 WeakInversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3.7 StrongInversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.3.8 ExplicitSurfacePotential. . . . . . . . . . . . . . . . . . . . . . . 7 1.3.9 ThresholdVoltage(V ). . . . . . . . . . . . . . . . . . . . . . . 8 Th 1.3.10 SubstrateBiasEffect. . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.3.11 DrainCurrent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.4 I-VCharacteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.4.1 ChargeSheetModel. . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.5 GateCapacitance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.6 ScalingofMOSFETs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.6.1 ConstantFieldScaling. . . . . . . . . . . . . . . . . . . . . . . . . 13 1.6.2 ConstantVoltageScaling. . . . . . . . . . . . . . . . . . . . . . . 14 1.7 ShortChannelEffectsorPenaltiesofScaling. . . . . . . . . . . . . . . 14 1.7.1 CarrierFieldMobilityReduction. . . . . . . . . . . . . . . . . 14 1.7.2 ChannelLengthModulation(CLM). . . . . . . . . . . . . . . 15 1.7.3 DrainInducedBarrierLowering(DIBL). . . . . . . . . . . . 16 1.7.4 GateOxideTunneling. . . . . . . . . . . . . . . . . . . . . . . . . 16 1.7.5 InversionLayerQuantization. . . . . . . . . . . . . . . . . . . . 16 1.7.6 ImpactIonization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.7.7 SourceandDrainResistanceEffect. . . . . . . . . . . . . . . 17 1.7.8 Poly-SiDepletionLayerEffect. . . . . . . . . . . . . . . . . . . 17 ix