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UT Arlington EE 5340 - Semiconductor Device Theory

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Slide 1Fully biased n-MOS capacitorMOS energy bands at Si surface for n-channelComputing the D.R. W and Q at O.S.I.Q’d,max and xd,max for biased MOS capacitorFully biased n- channel VT calcn-channel VT for VC = VB = 0Fully biased p- channel VT calcp-channel VT for VC = VB = 0n-channel enhancement MOSFET in ohmic regionConductance of inverted channelBasic I-V relation for MOS channelI-V relation for n-MOS (ohmic reg)Universal drain characteristicCharacterizing the n-ch MOSFETSubstrate bias effect on VT (body-effect)Body effect dataLow field ohmic characteristicsMOSFET circuit parametersMOSFET circuit parameters (cont)MOSFET equivalent circuit elementsMOS small-signal equivalent circuitMOS channel- length modulationAnalysis of channel length modulationChannel length mod- ulated drain charImplanted n-channel enhance-ment MOSFET (ohmic region)Ion implantation*“Dotted box” approx**Calculating xi and DVTIf xi ~ xd,maxCalculating VTImplanted VTMobilities**Substrate bias effect on VT (body-effect)Body effect dataM&K Fig. 9.9 (Eq. 9.1.23)Subthreshold conductionM&K Fig.9.10 (p.443)M&K Fig. 9.11 (p.444)Subthreshold current dataMobility variation due to EdeplVelocity saturation effectsReferencesEE 5340Semiconductor Device TheoryLecture 27 – Spring 2011Professor Ronald L. [email protected]://www.uta.edu/ronc©rlc L27-28Apr20112Fully biased n-MOScapacitor0yLVGVsub=VBEOx,x> 0AcceptorsDepl Reg e- e- e- e- e- e- n+ n+VSVD p-substrateChannel if VG > VT©rlc L27-28Apr20113MOS energy bands atSi surface for n-channelFig 8.10**©rlc L27-28Apr20114Computing the D.R. W and Q at O.S.I.ExEmaxxaSixNqdxdE aSBpSidqNVVx)(22,max)(2SBpVVarea ,maxda,maxdxqNQ ©rlc L27-28Apr20115Q’d,max and xd,max forbiased MOS capacitorFig 8.11**xd,max(mm))2-d,max(cmqQ'©rlc L27-28Apr20116Fully biased n-channel VT calc  0V ,qNVV22x ,xNqQ' ,0NnlnVVV'C'Q2VVVVV :substratepaCBpd,maxd,maxad,maxaitpFBOx,maxdpFBCTTthreshold at ,G©rlc L27-28Apr20117n-channel VT forVC = VB = 0Fig 10.20*©rlc L27-28Apr20118Fully biased p-channel VT calc  0V ,qNVV22x ,xNqQ' ,0nNlnVVV'C'Q2VVVVV :substratendBCnd,maxd,maxdd,maxidtnFBOx,maxdnFBCTTthreshold at ,G©rlc L27-28Apr20119p-channel VT forVC = VB = 0Fig 10.21*©rlc L27-28Apr201110n-channel enhancementMOSFET in ohmic region0< VT< VGVB < 0EOx,x> 0AcceptorsDepl RegVS = 00< VD< VDS,sate-e- e- e- e- n+ n+ p-substrateChannel©rlc L27-28Apr201111Conductance ofinverted channel•Q’n = - C’Ox(VGC-VT)•n’s = C’Ox(VGC-VT)/q, (# inv elect/cm2)•The conductivity sn = (n’s/t) q mn•G = sn(Wt/L) = n’s q mn (W/L) = 1/R, so•I = V/R = dV/dR, dR = dL/(n’sqmnW)  WdV VVV'CdLInTCGL0VVOxDS ©rlc L27-28Apr201112Basic I-V relationfor MOS channel     2TGOxnsatDDTGsatDSDSsatDSDDnTGsatDSDSTGDS2DSDSTGOxnDVVL2CWIIso VVVV for ,VI by given be I let soSat0LyQ' VVVV AtVVV VVVV2L2CWI'.,,',,,,©rlc L27-28Apr201113I-V relation for n-MOS (ohmic reg)   2TGSOxnsat,Dsat,DSDSLys,sat,DSsat,DSTGDS2DSDSTGOxnDVVLW2'CIVV for const iscurr. channel that assume0n' ,V Atphysical.-non is result ,VVVVfor Note .VVVV2LW2'CIIDVDSVDS,satID,satohmicnon-physicalsaturated©rlc L27-28Apr201114Universal draincharacteristic9ID1ID4ID1ID1VGS=VT+1VVGS=VT+2VVGS=VT+3V2DSOxnsat,DVLW2'CIVDS 2Oxn1DV1LW2'CI saturated, VDS>VGS-VTohmic©rlc L27-28Apr201115Characterizing then-ch MOSFETVDIDDSGB 2TGSOxnsat,DTGSDSTGSDSVVLW2'CIso , VVV0V , VVVGSVTDILW2'CslopeOxn©rlc L27-28Apr201116Substrate bias effect on VT (body-effect)    pSBpOxaSiSBTSBTTaSBpmaxd,Oxmaxd,apFBSTT2V2'CNq20VVVVV so , qNV22x where , 'CxNq2VVVSource to relative be ncalculatio V Letting©rlc L27-28Apr201117Body effect dataFig 9.9**©rlc L27-28Apr201118Low field ohmiccharacteristics    DSVVVGSDOxnDSTGSDSTGSOxnDTGDS2DSDSTGSOxnDVLWKPdVdI'C KP , VVVLWKPVVVLW'CIthat so ,VVV let e,Furthermor region. ohmic for, VVVV2LW2'CITGDS©rlc L27-28Apr201119MOSFET circuitparameters region ohmic ,VVL'CWgsaturation ,VL'CWgVIgcetancTransconduTGSOxnmLDSOxnmsVGSDmDS©rlc L27-28Apr201120MOSFET circuitparameters (cont) ohmic ,VVVL'CWgsaturation ,0gVIgeconductanc drain or OutputDSTGSOxndLdsVDSDdGS©rlc L27-28Apr201121OxOxOxgdOxgs'WLCC ,C31C ,C32C Fig 10.51*MOSFET equivalentcircuit elements©rlc L27-28Apr201122MOS small-signal equivalent circuitFig 10.52*©rlc L27-28Apr201123MOS channel-length modulationFig 11.5*©rlc L27-28Apr201124Analysis of channellength modulationDDsat,DSDSDSsat,DSpDSsat,DSpaSiILLL'IVVVV2VV2qN2Lmod length the as same theis change DR the Assume©rlc L27-28Apr201125Channel length mod-ulated drain charFig 11.6*©rlc L27-28Apr201126e-e- e- e- e- + + + + + + + + + + + + Implanted n-channel enhance-ment MOSFET (ohmic region)0< VT< VGVB < 0EOx,x> 0AcceptorsDepl RegVS = 00< VD< VDS,sat n+ n+ p-substrateChannele- channel ele + implant ion©rlc L27-28Apr201127Si & SiO2AlSi3N4Si Al & SiO2Si3N4RangeDRPIon implantation*©rlc L27-28Apr201128“Dotted box” approx**©rlc L27-28Apr201129curve dottedunder area curve dashedunder area iaiimplXNdxN 0'oxiitiaitCxqNΔV so xand Nget implant to desired, as Vget ToFBTmaxd,iV V then , x xIf diiaiiiibeforessssxQQNNNN qN 'impl ,' Calculating xi and DVT©rlc L27-28Apr201130  aiaiSBppsaiaimsxdaiaidaaiipsadNNxqVqNxqNxqNxqNQNNxqNx22,222If xi ~ xd,max©rlc L27-28Apr201131 iidiathiiaiathpsaiaiSBppsaOxpspOxiaiOxssmsTnxNNVnxNNVNNxqVqNCCxqNCQVlnor , ln2122''''Calculating VT©rlc L27-28Apr201132Implanted VTVt per Eq. 9.1.23 in M&K for a MOSFET with an 87-nm-thick gate oxide, Qf/q = 1011 cm-2,


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