Bdm a 77 071 Tr, Spice2 Mos Modelling Hdbk

8/13/2019 Bdm a 77 071 Tr, Spice2 Mos Modelling Hdbk

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6 Kay 1977 1 COInputercode represent a sIgnificant ImproVelhent over the mod1 ls Included inearl ier verstons of SpreE and most other computer , l ldeddesign t.odes.In order to successfully utt1 Ize the models, the desJgnermust befamit iarwtth the model formulation and the parameterization procedures requitedfor model spec i f e ti on.. Th i 5 report p resents thedesigl le >wfth t:ldescription of thmodel topology, the model parameterS, and thephysical basis forthemathemat ica 1 formulation,

The spa CE2 HOS model described here fs appropriate for tneversionof the Code maintained t SandiaL.aboratorJes, Albuquerque,NewHexieo.Readers who are using other versions of the code shouldreferto theupdate cards in appendix A to insure that the code modifications indicatedthere have been Incorporated In their version.

TheSP I CE2HOS model has been designed for a max rmum o f par rne te rizatlon f lex ib i l i ty . Conceptually, that f lexIbi l i ty can be s tbe r e -fleeted by considering a separation of the model into an analyticalsection and an empirical section. These two sect ions can be IJsedseparately or in various combinations. Tncdis t lnct ion between the twosections is made purely to faci l I tate disClJssion a n d d o e s n o t i ~ p l y adifference in model uti l i z a t i ono ra rigId boundary betw.een the two.The analytical model re:1ies heavily on p:-ocessing parameters to predictthe e lectr Ica lcharac te r l s t cs. The des rgner speel f i e sva 1ues forbackground dopingconcentration . urface s ta te density. h s t sur.hcestate density, e tc . and the code calculates values for thresholdvoltage. drain currer:t. etc. Tneaccuracy of .themodel depends onthe appropr'i aleness of the mathe:matt cal formulation and tneaccuracyof the input data.

The empirical model simulates the electr ical characterist ics of theHaS t ransiStor by using parameters based .00 measured operational characteri s t ics . For example, the empirical model uses a measured value for thethreshold voltage. The accuracy of the model s based on the ab i l l tyof

1 1


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8DM CORPORATIONthe designer to match the electrical characteristics of the component inquestion with the model parameters available. The empirical model isvery similar to the model used In the original Berkeley version ofSPICE2..

SPICE2. s use of the empirical or analytic31 model is determined bythe parameters specified. If the substrate doping concentration isincluded In the model variable l i s t , the analytical model witl beutilized even though a val ue for threshold vol t a ~ ~ may have been specifled inadvertantly. Some mixing of the models Is possible in that.under certain circumstances, a required parameter value ~ be calculatedfor use in the empirical model i f a parameter based on measured data isnot available. Also, some empirical model parameters will overrideanalytical parameters if both are specified. (Note that an empiricalvalue for threshold voltage will not override the analyti=atly calculatedvalue If substrate doping is specified.) In general, SPICE2. strives toattain a consistent set of model parameters. As a last resort, i t willrevert to a table of default parameter values if the required input data

a r ~ not supplied. The default values have been chosen to produce acomputable MOS model. They are not necessarily represe tative of aparticular device or a particular OS technology.

Figure 1 1 is a diagram of the MOS model topology used in SPICE2.The polarity indications represent the convention or forward bias. Forexample, a positive drain-to-substrate voltage tends to turn on thedrain-to-substrate diode. The diagram is for an NMOS transistor. Thepolarity conventions are reversed for a PMOS device. SPICE2. performsali c a l c u l a t i o ~ with sign conventions appropriate for N channel devicesand then reestablishes the proper direction of current flow In PMOSdevices. For this reason, all the equations In subsequent chapters wiltcarry signs appropriate for NMOS. The model is perfectly bilateral,hence, I t requires no rigid dIstinction between the source and drainterminals in applying It to a circuit analysis.

Figure 1-2 presents a simplified flowchart of the relationship ofthe MOS model to the SPICE2 program. The model parameters from an Inputdeck are init ial ly processed by the MOD HK subroutine which performsseveral preliminary calculations and prints out a device model summary.

,1-2


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8DM CORPORATION

G

\V 'CGa CGS CGO

< YGO.

VaS t-/ \0

S Dr J ~ ~ t rd- \I S -; ' b ~V S

as J Cso

a

Fj gure I I . SP ICE HOSFET l'Iode I

/-3


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8 M CORPORATION

1MODL CARDS

I MODCHKSPICE

t MOSFET

ONE TIME IMODEL PARA

CONTROLS CMOS DEVICE

FETLTM

PNJLIM

MOSEQN

MOSCAP

lifiGR8

NPUT PROCESSING OFMETERS

Of1PUTAT ION OFS

LIMITS CHANGE IN NONLINEAR='ET VOLTAGES

LI ITS CHANGE IN NONLINEARJUNCTION VOLTAGES

IMPLEMENTS MOS EQUATIONS

COMPUTES MOS OVERLAP CAPACITANCEAS A FUNCTION OF VOLTAGE

P R F O ~ H S NUMEP I CAL I :TEGRAT I

Figure 1-2. Sinptified FlowchClrt of MOS :1odel Relacionsnlp to SPICE ?rogr/-l


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80M CORPORATION

After the in i t ia l parameter processing. control of the KOS model passesto the executive subroutine HOSFET I t interfaces with the main SPICE2program, insures the correct current and voltage polar i t ies for bothHMOS and PMOS mode 1s t and calls other sub rout Ines associ ated wJth theKOS model. The functions of the other subroutines are indh:ated Infigure 1-2. The MOS QH subroutine imptementsthe model equatioM forcalculat ing drain current In each region of operation i .e . , cutoff ,subthreshold, l inear, and sa turued .

In chapter II , deflnit lons are provided or all parameters used inthe empirical and analytical models. The deflnlt ionsln:: lude the unitsin which the parameter must be specified and Identify whether theanalytical or empirical parameter overrides If both are spec.ifled Chapter t I contains a discussion of the physical characteristlc:.s whichthe analytical model attempts to predict and the empirical model attemptsto simulate. Emphasis is placed on providing the designer with somephysical l.nsight Into the impact of Individual parameters on modelcurrt.nt/vol tage character is t ic:s. Chapter IV demonstrates the impactof selected parameter variat ions on the prediction of output character is t ics of MOS inverter.


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80M CORPORATIONCH PTER II

HODEL P R METER DEFINITIONSA total of 29 parameters can be specified by the designer Ir. t h ~

variable l i s t of the HOS model. Some of these parameters are usedsolely with the empIrical model and others are used solely with theanalytical model. In some cases, one parameter overrides another or 15redundant i f another Is specified. Table 11-1 provides a listing ofpossible parameters and which model uses them. The table also Indicateswhen a parameter Is overridden and gives the ~ ~ ; u l t value. The fol-lowing paragraphs give a brief discussion of each line entry in thetable and refer the desIgner to the appropriate section of chapterfor further Information on the parameter's Impact on model character-Istlcs.

A. VTO - ZERO BIAS THRESHOLD VOLT GE .The threshold volnge specified as VTO will only be used i f thebackground doping concentration is not 5peclfied. It should be speci-fied i f the designer wIshes to use the empirical model. In addition todetermining the boundary between the off region and the linear region oftransistor operation, the value of VTO is used in calculation of sub-strate bias effects, weak inversion effects. mobility degradation, andtemperature effects. A d scuss ion of these effects may be found inchapter III , sections St 0, F, and G.

If a value for VTO is not specified and NSUB is specified (thea n a l y t t c ~ J model). the thresh01d voltage Is calculated from equation11-1.

where

/ q N VTO V + 2, 2 v S I SUB fFB f CQSSVFB - flatband voltage ms - -C-ox

11-1

oxEq. 11-1


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TABLE I f I . SPICE2 II00El PARAI1ETERSI'AI\AAffll otfl'uUMAAt 0[$ (:III I'1I OM [ ,, CAl flOOEl AHAUTI(Al HODEl OYUIDIHC tlOOEL UNitS VALuEno lUO liAS usn SI'((I(I[O [Al(ULATD AllALYTlCAl nY1UIru VOLts -0.1 (,.",II/CAl

t H ~ S f l O l t YOl1A&( Oil DEfAULT If NSUI IS SI'[(lfl[OVTO V 2 V'" l>IIC SUB :-_ .

AlVINUIIISlC usn sPtClfl[o usn Sl'fOrl[O S,tttfltD VAlot D V [ P . ~ I D [ S 2 . ~ Z [oS AKAllTltAtT ~ S C O H D U C T ~ C t DHAIIU Oil AllAlYTltAl; OfAUlT OCCIIIIS t.O t-5 (1 11 1 II 'CAL

KI' otO'l. If 0 < 0 tOl 0.. . . tulk l UIt( IU IISU U'[ClfltO IISII $1'[ClflO Oil Sl'tClflEO VALUE OY[1I1110$ v-liZ 0.0 ["""IICAlI'MAtlUn OfAULT CAI\I1A ..,----V c I""SUI- ~ O l l

I',1t S T ~ O H C I I I V ~ S I D I C USU 'I'[ClfltO OS[II SI'EC,'IEO nil SI'(lfl(O VAluE OV[IIAIO[S , .r. ( lAICALSlIlIrAtt I'OTN Al Ot O(fJ\uLT '0 ll. ,. (" )q ,lAl410A ClWllltl HHGTK usn SI'ClfltC usn SPtclrtfD 011 Sr((IrlfD VAlllt OV1I1110[S y-I II. 0 t ill CALI IOOUlATt Otf Oil 'tlfAUtl

lMDA- - { v ~ ~ ; . ~ v ~ }:'AII.AIIUU lO;'YDSliD 0111\111 OW1tt USE SI'ttlflEO U S [ ~ S'((lrl(O Oil SP(ClflO vAlur OVEIIIIIOtS OttlS 0.0IIES'SfAltU Oil OUAUlf DEfAuLTliS S O l 1 ~ C OfIIttC IIsn s , t u f i n USEII 5'(( l f l [0 C* 5'((lrlD _ALuE OVERIIIOES OttIS 0.0

A U I S T ~ I t C Oft O[rAUU DEfAULT(CiS CAn-SOultt[ usn SP((lrt[D us(1I 5Pc,r/(D Oil S"EClflrD VAlUE J)VIIUDU Hr.. 0.0OY[lIlA1' A t A I T ~ C E Oft OHAUU . OEfAuLt'[11 eM or ~ H [ lVIOl"(CD tAfr-OftAlH /)VEALAI un $.I'(lflO U S f ~ SI'[CI'I(O 011 SPEClflCD VALliE O Y f t ~ I D S f i t . 0_0CAr'''' ITAllet Plk 0" DHAULT OHAulf. :.. or (IIAMIIU VIOTH


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TAbLE I I - I . SPICE2 HODEl PARAHETERS (Cont Inued)0

P.UAMUU DE'AUlT[11f II ICAL ttOO[L IMAttl I ) (SUI ' OIf AHAl n iCAl OOEl OY[I\I\'DIIIC ~ [ l I UNITS YALOr(ea CATt-IUU. u s n S'ECfFlD USO 51 ' (Cfr ln SI'CI'IEO VAlur OY[ftl\IDis flc , 0.0OV[I\tA' [AI'ACITAHt( 01\ D(rAULT Olt OHAUtT..Eft c_ CHAttHtl

lICfH2'110 l UoI l ASSUl STMf ( - u s n $,tI r I [0 USEI\ S'ECU'rEO SI'[CIF'EO VALUE Oy(I\I\IO S rIc 0.0SOUI\I: [ JUII(11011 (AI' A- 01\ DHAULT 01\ OHAUlTC fAIICf'(Il c ,l orJUNCTlOIf MtA

tas ZEI\O liAS SUISTI\ATE- ustll s , u r r l t o u s n $ ' [ [ ' ' ' r o SI'[(lflO YAlU[ OyI\I\IO S r ao2 0.0OMIN JUNCTION CAI'A- 01\ OEfAULT 11 DEfAUllCHAlltE 'IIu.2 orJUNCTIOM AIIA

TOIt OUOt TlltCkHlSS USUI S 'Ul r l [ O USEII S'UIFI[O S'[Clrl[O VALUE OYEIIIIIO S e , - ttP t AI CALCOHSISHHT IIItH tOHSlSHIIT IIHH 10-5 AlfAUtlCAlkI' Oil Dlr Ull 1(1 Oil DEf AUtT. IUU JUNC f I Of u s n SPUl tHO UUIl S' fCl f l ro S'EClr l [O YAlUr OVERRIDES Y .8CONtACT POT[NtIAl OR DEFAULT 01\ DEFAUlt

JS IUU: JUMCTlOIf u s n S'[[IFIO u s u $'((IFI[O S,[CI ' IO VAlU[ OYIlIl10S Ale . 1.0(-8II[Y(IIS( SAluMIION 011 DHAULT 01\ DHAULTCURR[IIT ' t i l c- orJUIIC fI Of ~ l A

HSUI Svas T lAf t>Oft IIIIi 00 1I0f SPECIfY USEII SI'HlflD A AlYTICAl If .SUI S' tCI- c. . 0.0If [KP'llIltAL OOl OI'lOHAU U t l [O Oft I YTG-OIS DtSfll[O

IISS I [CTIY SUllfACE IIOT ItQUIIlEO u s n CI EO SP[CIFI[1 VAlu[ O Y { I t ~ I O [ 5 : z 0.0oSTAn O(NS DtfAULT 011 OHAUl T I'AflAKEfI-UHU5(O IN (Mrlltl-tAL KOO[l..,s UnCTI( fAST usn 5'Ulnn UHk SPEC II srCI'IO VAlUt o v t ~ I t ' O $ e . 2 0,0 lUO VAtU[SUUAC[ STAT[ Oil OEFAULT Olt DEfAUlT H'K'HAfHIIHSH., \/fAil: IHV(ItS,Off

CHAUCTUISTICS


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S u ~ f A C [ flOIIllTT

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TABLE - I . SPICE2 HOOEl PARAMETERS (Continued)

( I ICAL l10DHUS [1\ SI'(C ., I)OlOHAuLT

USEII SI'[IUIEO11 DEFAULT

ItOT Il[QOIlODEfAUlt

1I0T IlEQOIII[O

USR 51'(CfflOCONSISHNl \ TH1\1' 11 HAULT

U S E ~ SPEC 1(0Ol DEfAULT

UHII SP(CIfIEOOil DEFAULT

US [II i '( t f 1 0UII DEfAIlLT

ANALYTICAL ..colUSEII S'C If I)OR DEfAULT

USR 51'[C IOOil DEfAUlt

US(II src [0OR DEfAULT

USU SrClfIU1 1'0lAIIITT OI'I'OSltE

S U S T ~ H-I r O l A ~ I T T SAPIE ASSUaUItAH11 DEfAULT

USII SI ' (Clr tU(ONSISHNT \lItHKI 11 DEfAULTustR srClfIDOil DEfAUlT

usn S'[CIFI(ODEFAULT

U'>lk SI'(IFIDOil OEfAULT

OVIII110IHC flOOEl UNITSS'Clfl(O VALUE OVIII110(S

Sl ' [ ( I ' I [O VALUE OV[AAIOES; ~ a -I'AlM[TEl UNUSED IN [tIP,-R CAl flOOllSPECIFI(O VALUE OVIIIIID[5'AlMEIEII UNUSED IN (tIP,A eAl fIOOl

S'(( IFI[O YAlUS or 1\1' ~ t / v .O'/HRlDS uoSP[CIrifO VALUE OV[IIlIO(S Y/ca

spEClrl(O VALUE OY(R IO(S

~ f [ ( , , l O VAlUE OYI 'U(S

OHAULTVALUE

0.0 100 'ALU(HlflUIATULAHULOlfrUSION (FrItts

0 0 UO ,Atut(L IIAT SLAT[ IIAtOlfrUSION (fr[CTS

AlCAH

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1.0\

0.1) 1[110 vAtll(HlfllNATUMalliTYO{CIIA )ATlONlHUh

, U l O VAl UlH'fllllATtSTH( INflUENC[or lAHIIAlVOllACt OROI'AlOHC tH((HAHHEl OMfIOlillTTorCIIAOAflON


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Af

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OESn I I ' ll 11r l luu MOIUCOHffettN'

Hltl lR HOI$tn,QfI(HTfOIlVAIIOIUS HOHIOtAlJUtltTJOHCAl'AC IT AHcrCOEfFICIENt

TADLE It-I . SPICE2 flOOEt PARAt'ETERS (Concluded)

[ IAItAl fIOon AHAUT 1 AL 'IOOU OVEARIDING ~ [ lUSEIl SOI'I'llUl OStll SI' r t lf 10 S'(ClflO vAtOE OYERltlDtS011 DEFAULT OItO(fAULf

US[I\ 5 ( ( If 10 UHII SI ' re tFlU Sl'tClfltO vAlur OY(IIIt O(SOlt O[fAOll 01\ OHAOlTu s n S'[ClrtEO UStft I ' [(1f 1[0Oft otAUlt 11 OHAUlT

UlCITSDrUUlT

YAlUrD.C lUG VAlur

(LU MAnfIOlS[ Hf[CTS1 0

.5


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BDM CORPORATIONE

ms t\eta 1 semiconductor work function m - SO _ ....2_ fq~ Hetat gate work function (specified internal to SPICE as 1>2 . vlss Oxide charge N *q55

C Oxide capacitanceox

SI-Si02. work function (specified internal to SPICE as 3.25 VSilicon bandgap ~ s p e c l f l e d internal to SPICE2. as 1.12 V at27.C

kT Bulk Fermi level - 11 \qk Boltzman s constantT - Temperature OK

~ S U B

f Intrinsic carrier concentration (specified internal to SPICE as1.45 x 1 1 em- 3 at 27C}

NSUB Substrate doping concentrationesi Permittivity of silicon (specified internal to SPICE as

11.7 x 8.854 x 10. 14 Flam)The SPfCE2 empirical model assumes that a specified value of VTO is

also described by equation II-I . To insure proper operation of the nOdel.VTO should be determined from an extrapolation of the drain conductanceversus gate voltage curve to zero conductance. The experimental datashould be taken wi th zero substrate-source bias. Note that the threshold voltage is temperature dependent due to variations in n Eg , andT.B. KP INTR I NS I C TRANS CONDUCTANCE

The intrinsic transconductance. KP, maybe specified for eitherthe ~ p i r i c l or analytical model. A specified value overrides anycalculation or default value in either model. H ~ ~ v e r failure of theuser to define a value results n a default value in the empirical

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8 M CORPORATION

mod l, but I t results in either a calculated o ~ default value In then l ~ c l model. If positive, nonzero values for mobility UO) and

oxide thickness TOX) re specified, the analytical model will determineKP from equation 11-2.

UO C UO coxox rex CEq. 11-2)If zero or negative values re specified for UO and TOX then the defaultvalues of these parameters will be used In equation 11-2 to yIeld theanalytical default values listed in table II-t . If a value is specified'for KP, any subsequent value specified for the nondegraded surfacemobility, UO. will be ignored by SPICE2. When usIng the analyticalmodel, the designer should usually specify UO and TOX and eliminate KPfrom the variable l ist For the empirical model, KP is the experimentaltransconductance Jivided by the width to length ratio (aspect ratio).I LIt shoul d be deternli ned from the s lope of the curve of 0

VOSWversus VGS for small v.lues of VOS and zero VBS A further discussion of KP as influenced by mobility degradation effects is included inchapter III.F.C GAtiMA - BULK THRESHOLD PARAMETEr

Gamma may be specified for either the empirical or analyticalmodel. I t is the coefficient of the tenms accounting for substrate biaseffects in the equation for drain current originally developed by Ihantola 2and given in equation 3 below.

{ VOs[VGS VDSJ- 2 - V - - -f Fe 2 (Eq. 11-3)

~ _ ;; _ ~ ~ vos 2.( - vet2 - (2.( - Ves ) 3 2] }GAMMA

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8DM CORF> RATION

In the analytical model, the designer will usually not specify a valuefor GAMMA, since SPICE2 will calculate a value from other parameters.In the empIrical model, the value ofG tIJiI1A should e determined from thestope of a plot of threshold voltageversus.jv eS -2 'f xpertmen taldetermination of GAMMA may be difficult for short channel devices.Chapter 111.e contains a more complete discussion of the Influence ofshort channel effects on GAMMA.o PHI - SURFACE POTENTIAL AT STRONG INVERSION

The surface potentIal at strong lnversion, PHI. may be specified foreither the empIrical or the analytical model. If the value is specified,i t is assumed to equal twice the Fermi levet. -In the analytical model,a value or PHI will not usually be speclf ed, since I t is calculatedfrom equation II-It if no value is indicated in the variable l is t

PHI 2+( ~ T t o ( N ~ B ) (Eq. IHThe analytical model uses half of the specified or calculated value ofPHI for the Fermi level in subsequent calculations. In the empi ricalmodel. failure to specify PHI results in a default value of 0.6 volts.

The values of the quantities PHI, NSUB GAMMA, and VTO are mathematically combined at several points in the SP1CE2 implementation of.the analytical and empirical models Therefore, the user should ~ x -cise care to insure that these parameters are conststent with eachother. Note that PHI is temperature dependent through variations in Tand Nt

E LAMBDA - CHANNEL LENGTH MODULATION PARAMETERThe channel length modulation parameter, l..AI tBOA, may be specified

or either the empirical or analyttcal model. A specrffedvalue willtake precedence in either the empirkal model or the analytical model.Lambda must be specified tn the empirical model If channel length modulation Is to be included. For the analytical model. i f no value or a zero

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8 M CORPOR TION

value is specified, ~ P I C E 2 will c.lculate L MBD from the equation I f 5._ t i t s Vos - VSAT v.+ VOS-VOSAT)2 )112o VOS qN SUB It 4

Eq. 11-5)Lambda Is used to calculate the effective channel length as the depletionregIon spreads Into the channel. The expression used for the effectivechannel length Is

L - AL .Any specIfied value of A must be consistent with thIs equation. For amore complete description of the effect of A on channel length modulationeffects see chapter III.E.

F. RO Aim RS - DRAIN AND SOURCE OHMIC RESISISTAUCEThe draIn and source ohmic resistance RD and RS, may be specified

for either the analytical or empirical model. If they are not specified,they are defaulted to zero values for both models.

G. CGS AND CGO - SOURCE ANO DRAIN OVERLAP CAPACITANCESThe g a t e t o s o ~ r c e and gate-to-drain capacitances, CGS and CGO, may

be specified in either the empirical or analytical modei. Failure tospecify the parameter results in a zero value. If values are specified,they must be in units of farads per em of channel width since SPICE2multiplies the quantities by the channel width to determine total capacitance.The overlap capacitance represented by CGS or eGO Is a fixed value.SPICE2 automatically attributes a variable percentage of the gate-to-channel capacitance to the gate-to-drain and gate-to-source.capacitances.Th percentage depends on the operatIng region of the HOS transIstor. Amore complete explanation of the capacitance calculation procedures iscontained in chapter III.H

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BOM SORPORATION

H eGa - GATE BULK OVERLAP CAPACITANCEThe gate bulk overlap capacitance, eGa, may be specified for either .

the empiric:.11 or analytical model. Fatlure to specify the parame.terresults in a zero value. If the value is specified, t must be in unitsof farads per cm of channel length. SPICE multiplies the quantity bythe channel length to determl ne tota J capac t tance. The CGa term representsa fixed value of capacItance.I caD AND cas - ZERO BIAS SUBSTRATE - DRAIN AND SUBSTRATE - SOURCEJUNCTION CAPACITANCE

The zero bias substrate-drain and substrate-source capacitance maybe specifled n either the empirical or analytical model. Failure tospecify the quantity results tn a zero value. CBO and CBS must bespecified In units of farads/cm2 SPlCE2 multiplies the values by thedrain or source area as appropriate. CBO and CBS are used with theparameters PB and FC In the voltage variable junction capacitance equations indicated below.

CBSTOTAL - (Eq. I I-G)

FOl 'Wa rd Bias

CBSTOTAL - VBS]2PB (Eq. 11-7)

The reverse bias equation is the familiar form associated with thecapacitance of a step Junction. The forward bias equatton s reminiscentof a dlffusfon capacitance equation that has been formulated to insurecontinuity with the reverse bias equation and to prevent any possibilityof a division by zero. When the default values of Fe (.5) and PB .C)are used, almost perfect continuity is achieved between the two equations.

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CORPORATION

J . TOX' OXIOE THICKNESS

The. gate oxide thickness, Tox' may be specIfied for either theempt.ricat or analytical 'model. If no vatue Is speclfted, the analytical

model defaults l to value of 1 At and the empirical model effectivelyoxdefaults i t to a value of Infinity (actually the value of C is set tooxzero). An Infinite value of Tox Cox Q) enmln.tes substrate biaseffects, weak. Inverston effects, and variable mob' It ty effects from themodel.K PB - BULK JUNCTION POTENTIAL

The bulk. Junction potential, PB t may be specified for ei ther theempirical or analytical model. If not specified. i t assumes the defaultvalue of .8 volts in both models. The parameter represents the PJunction contactpotentJal for the source-tosubstrate and drain-tosubstrate Junctions. It Is used n the CBOand CBS Junction capacftanceequations. The designer should refer to subsectlon I of this chapterfor a discussion of those equations.L JS BULK JUNCTION ~ V R S SATU R ATION CURRENT

The Junction reverse saturation current, JS, may be specified ineither the empirical or analytIcal models. If not specified, i t assumesthe default value of 10 nA/cm2 in both models,. The parameter representsthe coefficient of the diode equation whfch simulates the current/voltagecharactedstics of the drain-tosubstrate and source-tosubstrate diodes.ft must be speCified in units ofA/cm2 slnceSPIC:2 wit I automaticallyscale t by the appropriate. dra.in r soure.eJunctlon area. The diodeequatIon used in SPICE2 hg lven below

whereSS JS[ x p ~ ~ S ) .. 1] (Eq. f -3)

yr. .q


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80M CORPORATION

The substrate-to-source and substrate-to-drain diode modals contain aresistance In parallel with the current generator described above. Thisshunt resistance has a value of 1 12 ohms. It prevents current sourcecut sets from occurring in some model conffguratlons.H SUB - EFFECT I VE SUBSTAATEDOPI NG CONCENTAATION

The effective substrate doptng concentration,NSUB, should only bespecified f the analytical model Is desired. The speetflcation of NSUSwill cause the analytIcal model to override the empirical model. Ifneither a value for VTO nor NSUB Is specified, the default value of VTOwill be assigned, and the empirIcal model will be used. The equationused to calculate the thresheld voltage i f NSUB is specified was givenpreviously in section A of thIs chapter. Although the SPlCE2 User sHanual Indicates that NSUB Is the effective substrate doping concentration, there is no need to specify a value other than the actual substratedoping. The analytical model Is formulated to simulate the two-dimensionaleffect on threshold voltage In short channel devices. In less sophisticatedmodels a value of effective doping concentration must be specified tocorrectly simulate the threshold voltage as a function of backgate bias.A more complete discussion of the calculation of threshold voltage inthe analytical model is included in chapter III , sections Band tN. NSS EFFECTIVE SURFACE STATE DENSITY

The effective surface state density, NSS should only be specifiedi f the designer wishes to use the analytical model. No errors wIllresul t if NSS is spec fled in the emp i ri cal mode , but NSSwi not beused in any of the calculations, and i t couid lead to some confusion i fi t Is needlessly specIfied. In the analytical model, NSS is used in thecalculation of VTO discussed previously In section II.A.

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80M CORPORATIONO. NFS - EFFECTIVE FAST SURFACE STATE DENSITY

The effective fast surface state density NFS, may be specified foreither the empirical or analytical model. If not specified a zerodef.ult value is assigned. The parameter is used In both models for theweak Inversion characteristics. If NFS equals zero the weak inversioneffects s e c t i o ~ of the model is bypassed. A nonzero value of NFSproduces some dratn current for ,values of Ves VTO A completediscussion of the weak inversion characterlstfcsof the iOOdeTTs--::-ln-c '71-u-: dedin section 111.0.P. ~ - METALLURGICAL JUNCTION DEPTH

The metallurgical junction depth XJ, may be specified for eitherthe empirical or analytical model. f not specified a zero value isassigned. The value of XJ is used in conjunction with the lateraldiffusion coefficient. LO, to determine the effective channel length.

where L -2*LO*XJM

Lo Effective channel lengthLM Mask defined channel lengthLO Lateral diffusion constantXJ - Metallurgical Junction depth

(Eq. 11-9)

The effective channel length is used in atl calculations requiring thewiqth-to-length ratio. Failure to specify either XJ or LO results inthe use of the m.sk defined channel length throughout the model.Q. LO - LATERAL DIFFUSION COEFFICIENT

The lateral diffusion coefficient LO, may be specified or eitherthe analytical or empirical model. As discussed in the section above.

11-13


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8DM CORPORATION

LO is used in conjunction with XJ to define the effective c ~ n n e l length.Failure to specify either LO or XJ results In the USe of the mask definedchannel length throughout the model. It should be noted that the defaultvalue of tD has been changed from 0.8 as specified In the SPlCE2manua I to zero.R. NG TE ND TPS - POLYSILICON G TE DOPING ND TYPE OF POtYSlllCON

The polyslltcon gate dopIng, NGATE, and the type of poiystl1con,TPS, should be specIfied only If the analytical model isused. Specifica-tion of these parameters In the empirical model w111 not result in anerror, but they witt not be used in Iny calculations. For the empiricalmodel, the value of VTO will not be modified further bytne specificationof NC TE and TPS. In the analytlcal model, these parameters are used tocalculate the metal/semIconductor work function from equation 11-10.

where

- - TPS (FERHIG) - (FERHIS)ms

TPS - I for NG TE opposite doping from NSUB- - I for NG TE same doping as NSUB

Eq. I 1- JO

Thus, the two fermI levels are additive if the gate doping is of oppositepoladty to the substr7ate, and they aresubtracti\.le i the gate andsubstrate are of the same doping polaricy. The value for msls updatedfor t e m p ~ r t u r e variations specified wlth a TEMP card.

11-14


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s. UO, UCRIT,UEXP,AND UTAA - SURFACE MOBILITY, CRITICAL E FIELD.VARIABLE totOSILITY EXPRESSION EXPONENT, AND TRANSVERSE FIELDCOEFFICIENT-The surface mobility, UO and the other parameters assoctated wIth

the vartable mobility modeling capability of SPICE2 may be specIfied foruse with either the analytical or empirical model. If both KP and UOare specifted, KPwtt1ause UO to be Ignored. If neither KP ncr UO are .specified a default value of 700 em2/V-S Is assigned for both MHOS andPMOS transistors.

The equation for mobil tty varIation Is given In equation 11-11.

J UO .[UCRIT C S1 ] EXP

5 Cox Ves - VON - UTRA V DS ) Eq. 11-11If values for UCRIT, UEXP, and UTAA are unspecified, default values ofI x 104 v/em 0, and 0 are respectively assigned. A zero value for UEXPeffectively removes all variable mobility effects from the model. Novariable mobil ity effects are simulated untl I the value of the denominatorof equation I I I I exceeds that of the numerator. A more thorough discussionof the variable mobility model is provided in chapter 111.F.T. KF and AF - FLICKER NOISE COEFFICIENT AND FLICKER NOISE EXPONENT f J e ~ N~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ f < :oj The flicker noise coefficient and the flicker notse exponent areused in conjunction with ac analysis portion of SPICE2. In using thiscapability to characterhe the noise performance, a current generator Isconnected between the drain and source with a value defined by equatIon11-12.

Eq. 11-12)

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8 M CORPOR TION

where -0 drain current9 small signal transconductancemf frequency

U. Fe - FORW RD BIAS tlOHIDEAL JUUCTION CAPACITANCE COEFFICIENTThe forward bias nonldeal Junction capacitance coefficient, FC, may

be specified in i t h ~ r the empirical or analytical model. Along withPS, t determines the transition between the use of the reverse biasJunction capacitance equation and a forward bias diffusion capacitanceequation. The appropriate equations were previously given in section 1of this chapter. If no value is specified the default value of 0.5is used. For most eases the default will give satisfactory performance.

11-16


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8 M CORPORATIONCHAPTEI\ I I I

IHPLEHENTATION OF FII\ST ND SECOND ORDER ~ T R I C L EFFECTSIN THE SPICE2 HOS HODEL .

A INTI\ODUCTIONIn chapter II, a brief description was gIven of each of the parameters

Involved In utrlizlng the SPICE2 HOS model. The material In this chapter.describes the relationship between these parameters and the Implementationof the major f irst and second order electrical effects In the model.The purpose of the chapter Is to foster a quantitative appreciation ofthe influence of parameter values on HOS transistor characteristics.The descriptIon is divided into discussions of: 1) substrate biaseffects, 2) two-dimensional effects on threshold voltage, 3) weakinversion effects, 4) channel length modulation effects, 5) variablemobility effects, 6) temperature effects, and 7) variable capacitanceeffects. Wherever appropriate, parametric studies are presented to

Idemonstrate the Influence of Incremental parameter variations on tran-sistor electrical characteristics. These studies are performed with theanalytical model. Table 111-1 provides a l st of parameter values whichserve as the starting point for all examples. The parameter values weredevetoped for the simulation of a particular CHOS inverter. They areused here for illustrative purposes and are not necessarily advocated astypical values.

T BLE 111-1. EX MPLE NHOS ND PMOS

TRANSISTOR ANALYTICAL HODEL P R METERS

NHOS-RS-.769 nC B o 5 . ~ 3 X t o 8 F/em2JS-3.82XIO- tl A/cm2

XJ-2XIO-4 emUEXP-.l

CGS-9.0SXIO-12 F/emCBS-S.43Xl08 F/em2NSUa-2Xlo I6 em-)LO-O.OUTRA-.3

111- t

-12CGD-9.0SXIO F/em-6TOX-7.0Xl0 emNSS-IXIO cm-22UO-700 em IV SFe-.s

CGa-o.o F/cmPB-.9 VNFS_1Xl0 em- 2UCRIT-1Xl04 V/cm1\0-.769 n


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BOM CORPORATION

PMOS-R.S-9.74 ohms-8 2CBO-l.86x10 F/cmJS-;.82X10 11 A/cm2..4XJ-2X)0 emUEXP-.241 5

CGS-t4.76XIO-J2 F/cm tGD-14.76Xl0-12 F/cm CGS-D.O F/emCBS-l.86XI0 B F/cm2. TOX-7XI0-6 cm PS-.9 VNSUB-2X10 5 em-; NSS_IX10 11 cm-2 NFS_IX10 11 cm- 2Lo-O.O UO-166 emZ/V-S UCR.IT-jXI04 V cmUTR.A-.3 FC-.S R.0-9.74 ohms

8. SUBSTR ATE BIAS EFFECTS

Consider the HOS transistor as a four terminal device with a reversebiasIng potential between the source and substrate (VBS). The effect ofthis voltage s to increase the arrount of charge stored in the depletionregion. It resut ts In a decrease in the drain current for a fixed gateto-source voltage. The substrate bias effect ts included in the SPICE2.model by adding VBS to the quanttty 2.tf as shown in equation 111-1 whichdefines drain current in the triode region of operation.

10 e {(VGS - VrB - 2 f - V ~ s VOS(2 f - v ) 3 Z1t Yo [


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r _ NHOS OUTPUT CH R CTERISTICS F VBS) .-.I I I I IV 0.0 V8S - V 2.0 VV V/ 85 I II I I I I I

-Q . I I I , V ".0 V851/ , I zw:Ju

1/ I I I / ' y 6.0 y'( II 8S S " . - -- - - V Y 8.0 y/ / / IS A-I V YIS 10.0 VJ J I I . ; 'Z . . H I I V--c I V/ I / La IIIJ I "' / VIII ,,/ ' /3 lJ 11/I ll, II/WI('''(11I. (ffI Yes 10.0 YW 2.0 11111 t -lo 0.2 MilI , .f-jt- " - t.a L D . A N Y D L TA (VOL fs . J

Figure III-I(a). HHOS Drain Characteristics Demonstrating Substrate Bias Effects

:mmono:o:o


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r

.......V IA-x:0(..........:IfIII. :.:)u:If...-c. :a

.-

.......I......

H

.H''''A; I -

H

'S

.H'

1 1f

......

I

I

I

,

I

, t

, .PHOS OUTPUT CHARACTERISTICS FCVBS

... ......-:: ~ .E:=:ii p- vas - 0.0iI'\: v~ ~ If I\ - vIIS 2. 0 V r- ::::; :::oil . . \ I::;.:: \ ' -iI , ves It. ) VIIJ' \ I I[.d; \ 1\ , .- v i ~ 6.0 vI a \ \ . .Vas b.O Vi ' --Vas 10.0 VJ

J ;16,Lr

I, f- r - J ves IQ.O V - -f f--- W 11111 -_. J . - -La 0.2 ,II l. -.. -. ,- _. - I - -

.. - - . . -. _ . .-...... . . -- - - .- - - -. i- - , - ...L ,IN VDLT.I VOLTS)

figure III-I b). PHOS Drain CharacteristIcs Demonstrating Substrate Bias Effects

-ImCona:D-a:a2


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r

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r

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DM CORPORATION

C, TWO-DIMENSIONAL EFFECTS ON THRESHOLD VOLT GE

As the c ~ a n n e l length of an MOS transistor is shortened to lessthan 5 ~ m the amount of depletion layer charge which is effective interminating the E field lines due to the gate-to-substratepotential issignificantly decreased. The result is a lower threshold voltage and asofter t u ~ n - o n characteristic than would normally be expected. Thesimple one-dimensional analysis, which is the usual basis for MOS models,is not sufficient to predict the varIation of threshold voltage withchannel length. However, Pocn3 has developed an analytical expressionwhich can be used to modify the usual expression for threshold voltageto account for two-dimensional effects.

The basis of Pocn s analysis is shown in figure 111-3. He assumesthat only the charge contained within trapezoid BCD is effective interminating the gate to substrate E field lines. He also assumes thatthe width of the depletion regton under the source and drain is the sameas that under the channel. The ratio of the area of trapezoid ABeD to arectangle wtth sides of length Wand L gives the percentage of thesubstrate charge which influences the threshold voltage. Figure 111-3gives a summary of the mathematics.

The resultant expression for threshold voltage as implemented inthe SPICE2 MOS model is given in equation 111-2.

VT VFB + 2 ~ f + f V BS) ~ D (Eq. 111-2)- oxor

whereW - depletion l a y e ~ width -

111-7


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8DM CORPORATION

\ - B

/

GATE

SUBSTRATEX+X.)2.J

x Xj R - /lJ0. \,/: :B [ L Xj M )]

[ X . . ~- r V j - )]Figure 111-3. Development of Two Dimensional Effects on

Threshold Voltage

111 8


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8 M CORPORATION

\liiI\Ie

The modification of the depletion region charge by f(V is carriedthrough expressions for the drain cur: ent in all regions of operation.o t ~ that the quantity J tS i qllsuacox is the parameter GAMMA and tne

quantity XJ Is the parameter XJ In the MOS model variable l is t . The twodimensional effect on threshold voltage can be eliminated by spectfylngeither CAKKA or XJ as zero.

The effect of the modeled two-dImensional effect on turn-on characterIstics is shown in figure I I I - ~ . A series of drain conductance curves isdisplayed for MOS transistors with the same aspect ratio (W/LoIO) butdifferent values of channel length. All other model parameters are thesame as these given in table 111-1.O. WEAK INVERSION EFFECTS

Host HOS models assume that conduction begins abruptly once thegate voltage exceeds the threshold voltage. The threshold voltage iscalculated for a surface potential. s . which is equal to twice the bulkFermi level (+,. 2 f . This is the classic strong i n v ~ r s i o n approximation. It results in a drain conductance versus gate voltage characteristisuch as that shown by the solid curve in figure 111-5. In actuality,some conduction occurs in the weak inversion region ( s < 2 f .Swanson and e i n d l ~ have developed a technique for simulating performancein this region. The dashed curve In figure 111-5 qualitatively describesthe relationship between the classic model and the weak Inversion model.Conduction begins below the threshold voltage and drain conductanceincreases exponentially with gate voltage unttl i t i n t e r s i : C ; ~ , , ~ ~ t b e _ ~ s ~ ~ t : ' _ ~ ~ ?

t ~ ~ , ~ ~ : , , ~ , i ~ ~ w ~ ~ ~ ~ ~ ' W ~ ~ " ~ ~ ~ ~ ~ ~ w : w , ~ ~ Q N ~ ~ ~ ( ) ~ ~ _ : ~ ~ ~ w w : ~ : e s h o I / Proper s imu 1 ltion of weak Inversion characteristics can e of'sTgw Tficant importance/IIA modeling devices whose threshold voltage has been lowered by ion /

tmplanfation and in modeling devices where surface state density halbeen Increased by ionizing radiation. %/////1

I\',' , % ' ' ' ' ~ ' ' ( ' ~ ' ' ' ~ ' ' V , ' ' ' ' ' ' ' ' W , ~ , , , , , , , , ' ' ' ' ' ' ' ' % 9 .

I r r 9


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r

.......'wuzoC...U::Jazauz-C

L

....... NHOS DRAIN CONDUCTANCE FCll, -Vos .. 2.0 V..... Yes 0.0 v\lILo to.O V Lo 0.2 111 .1 I I I ViJlo O . ~ mil \i I I IVILo .;. 0.8-1.2-1.6-2.0 m \ i' J.- IVIVIh .

/J'. f ( I1/1, f / l17. .r.- /. riJA

/ , rV ~/ r_. /.. .

rI...: 'I'._It

...... i I ........

........ - - .. - .IATt: fOLTA.t: tvoL1\fFigure I I I - ~ ( a ) . NMOS DraIn Conductance Characteristics DemonstratingTwo-Dimensional' 'eshold Vo1tage Effects

.,.

-, .,I I{ I

..

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r

--It0-

uz'U:::Jazauz-t:a

L

.--110

. M,,_;;;r

H

..... , ,- ,

VDS 2.0 VWlLo lu.o VVas 0.0 V

PHOS DRAIN CONDUCTANCE FCll

t

l

Lo 0.2 mil .Ilp - 0. mil ,o 0.a-I.2-1.6-2.0 mil /\1

11\. J1/{j

J[/jII.,rIJIh,

. it 2 ~ c >.A Tf VOL T A (VOLTS)

Figure 111-4(b). PMOS Drain Conductance Characteristics DemonstratingTwo-Dimensional Threshold Voltage Effects

'-,

T .6_I

-:mCono:o


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8 M CORPORATION

90S

VO

Figure 111 5. escription of eak Inversion Effects


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8 M CORPORATION

To implement the weak inversion model SPICE2 defines a turn onvoltage. VON' as shown In equation 111-3.

. /2'f kT ( QNFS YO JON, VFB .f YO - Vas - q Cox 2 2 ' fV . . .

Classica 1 Threshold Vol tage Eq. 111-3)

VON corresponds to the point of intersection between the exponentialcurve and straight line in figure 111-5. Its dependence on temperature.number of fast.surface states. and substrate bias is readily apparentfrom an examination of the equation. For atl gate to source voltagesless than VON' the drain current is given by the expression

2VDS - 3 YO [ ( 2 , - V V ) V2f S OS

Eq. I I I - 4 )

EXP

T ~ e coefficient of the exponential term has been chosen to insurecontinuity between the current predicted in the weak Inversion regionand that predicted in the linear region. The expression for the linearregion drain current is

111-13


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1 B l[' CS - VFB 2. f V ~ ]-(2. f Yes r 2] Eq. It 1:"5)

The portIon of the ft IC::>4el simulating weak inversion is only IncJudedwhen both TOX and NFS have been speC:ifted. If NFS is specified both the .

caTaria the empi ri ca 1 model wi exhibit conduction below thethreshold voltage.

The result of the weak inversion effects in the SPICE2 I10S :nodecan be seen 1n f rgure 111 6 where the d ra n conductance versus gatevoltage Is plotted for a variety of fast surface state densities.E. CHANNEL LENGTH HOOULATION

HOS transistors with relatively shortehannel lengths 10.0 wn) oftenexhibit finite drain-to-source conductance i . ~ . t an imperfoect satura-tion characteristic) for drain-tosource voltages greater than pinchoff.

~ h J l l l l L C : ~ ~ ' 1 ~ ~ , L c : ~ ~ l - e r : l ~ i l l ~ ~ n ~ - w ~ w l , ~ L % ~ L ~ b ~ ~ . l s 1 2 "d with a subsequent shortening ofFigure 111 7 gives a schematic demon

stration of this effect. To determine the effective channel length ifthe parameter LAMBDA is not specified. the depletion layer width aroundthe drain Is calculated from equation 111-6.

toL

TERM 1..--...- TERM 2

v::1 YS Yom +I +(VO\- VOSAT nEq. 111-6)

The second term tn the equation is a departure from the usual method ofcalculating the drain depletion width which would use (Vas - VOSAT)1/2.


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r NHOS O F NFS) .-,

--I0wuz


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r

1 10

wuZ


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80M CORPORATION

This formulation has been chosen to insure a smooth transition in currentbetween the linear and saturated regions of operation. However, notethat for values of VOS approaching zero and small values of VOSAT VOSAT - Vc - VT, a significant value of AL can be calculated by themodel. For example, i f VOS - .1 V, VT - 2 V.and Ves - 3 V Jthe value ~ fAL Is 1.0 for a background doping concentration of I x 10 S em-3This aspect of the model could cause a problem for the user simulating acircuit where the device experiences low g ~ t e voltages and low drain tosource voltages simultaneously.

The channel shortening effect is implemented by multiplying thetaspect ratio ~ / L o ) by I-LAMBDA VOS The following equation shows theresult of the multiplication

J [Lo I-LAMBDA VDS (Eq. 111-7)

Note that if LAMBDA is specified i t must be defined as the ratio of thedepletion width to the channel length times the drain to source voltage.If LAMBDA is specified, t is not varied as a function of VBS The channel shortening effect cannot be eliminated tn the analyticalmodel by specifying LAMBDA as zero. If a value for NSUB is specified, avalue for LAMBDA will be calculated by SPICE2. If the user wishes toeliminate the effect he should specify a small value (.001) for LAMBDA

Figure 111-8 shows the channel shortening effect on the drain characteristics with the parameters except LAMBDA taken from table III-I.The upper curves were generated with LAMBDA calculated by the SPICE2model, and the solid curves were generated with LAMBDA - 001 i .e. ,channel Shortening effects eliminated).F. VARIABLE MOBILITY EFFECTS

The surface mobility, ~ s which appears s term tn the currentexpression for the subthreshold. linear, and saturated regions ofoperation is not equal to the mobility in the bulk material. In fact.

111-18


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r

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:ItWe::JU:II-oC

0 7

...# (;>,

.M0

10

...0

tt,0

...

()(

b

5

f

::1

,Dq;t

... ,00

vas' 0.0 v 'w 2.0 IIJILo 0.2 mil

11V/i f

I

IILj1-- II- . -

-.....lI ~ ,t . . t- ,) , 0

,.N OS OUTPUT CH R CTERISTICS ~ ( l A H B D A II I I I 1 JI IJ l l lA CALCULATED ..1 I I Ves 10.0 Y , : : t -1, . H .001VV ILIL I

j / IL1 1.lIJ

rL

-I t -

A CALCULATED. ...L

Ves 5.0 V _ r- .,.A .001 .I .1I I J 1.f r - I I I Ir A - CALCULATED 2.0 V f-..t - .. 1-- I ...l ...l ...l -1 1 .. .1 __ -. .001... I . ..'1.0 ( ,0 Olt IN YO L T A ' r (VOLTS) . ,1;0 D ( ) 1 7 , ( ) 1 ) 0 I ~ , vFigure II -O(a). N OS Drain Characteristics DemonstratingChanne1 Shortening Effects

mon


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r .......1617 I- Ves 0.0 vw 2.0 III f....... - L0 0.2 mildYe. I I I-.........-. ,OIY' -x: - -(t- .......:It oil .wiICIe:JU .......,0 I)Z-CIe Ia ,00'1 ,I /....... 111

,0 t>( ,fJrI.......00 / I- ,....... I ''''.0 0 ).

- , L : ~.0lil~ ,- l d. jfigure 11I-3(b).

PHOS OUTPUT CHARACTERISTICS F(LAHBOAj-I I I I r -

-t

II :\t,,1- ., ,. ..,1. ...0.1 tt-\.t\)\} 'l- ' - ~, . Vi.--'

It- -

I r1/ V S 10.0 V W/ I/ I' 1/ 1 . ~ O l -I

J /, / r- -1/ . // -1 1/I -1-1-1-- - I-1

I -i...1, I CA,lCUlATED: .1 . ~ O l

I , I J - tVes 5.0 V - - l

Ves 2.t? V1 CALCULATED I I I 1 .-. .... ~ 6 . 0 a .A I M YOLTAI ' (VOLTS)8,0 'C/o / .7 .0 1


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80M CORPORATION

~ s is a function of gate-to-source voltage. substrate to source voltage.and drain to source voltage. The theoretical relationship betweensurface mobility and the E fields resulting from these applied voltagesis ~ t well defined. Therefore. the SPICE2 model utilizes an empiricalrelationship which is sufficiently flexible to simulate the results ofmobility var ation. The equation implementing variable mobility isshown below:

UEXPus - (Eq. I I I -b

The transition to the variable mobility expression is not made untilVGS - VON - UTRA VOS is greater than UCRIT t .~ ;..f.

Figure 111 9 is a plot of the llS ICox [ UCRIT t S Jratio UO versus C Y -Y -UTRA Vox GS ON OSwith UEXP as a variable. It should prove useful in selecting values ofUEXP to give desired variations in mobility. Clearly, specification ofUEXP - 0 eliminates all variable mobility effects. The influence oftransverse E fields on mobility degradation has been reported to be spercent effect for HOS transistors with channel lengths in the vicinity of5.0 ~ 5 Therefore. the parameter UTRA should normally be used in finetuning the variable mobility simulation. The parameter UCRIT is effective(n determining the va.lue of VGS where variable mobility effects areinitiated in the model.

Figure 111-10 compares the drain characteristics of an NHOS andPHOS transistor with and without yariable mobility included in the model.The upper curves represent a constant U which was achieved by settingsUEXP - O. The lower curves represent the results achieved with the mobilityparameters given in table 111-1.

111-21


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a OM CORPOR TION

c:0 0. ....:l

C'IoU

0 1 >....C ) - 0c.n 00 :::>

: :: CJ-..... < 0r:l- a:::111 IIoU :::l II:>0 ott ... -z: 0\.. 01 1> 11 1:::l

U'\ 11 1>c.n


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r:

.....VIQ.ZI I IJUZ-c

L

......-01 .l vas 0.0 v

......,0/1

,.....,ooi

.....0 0 ,

I :P If

I.....,0 0 .

2.0 11111Lo 0.2 11111

IIJi/

1 IIII

Jif1/ Vh VJ

j'/

VV

N OS OUTPUT

I

CHARACTERISTICS FJUEXP)

UEXP 0 Ii

V I - I/ ves 10; VV II

UEXP .1 :V ""1/

UEXP 0UEXP .1 ViS 5.0 v

-,

UEXP 0 . . Ves 2 .0 V e . :1..0 /,0 UEXP a_ N VO r A I VOLTS)

b. O 0 10, D 2.., D Y. 0Figure ' - IO(a) . NHOS Drain Characterist ics Oemonstratln:J VarIable

Hobl J I ty Effects

.-. )

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......VIQ.~ ...ZW;UZ-c

,DOl

......003

......,oo; .

100

Vas 0.0 V --W 2.0 ,II

l o 0.2 , I '- 1-- >- 1-. - or- -- ---fo- 1- -

f0- r-

- l- i- - - - - - -.. i

I- I- 1/r - - f- -- I- I~

- -. -- ... ....- r- f-V. - .- . - > -1 - ....- -.-. - ~. . - r - ....

- -- Vf-'I --1/~ .1 - -,., t '}.,oFigure 111-IO(b).

,-PMOS OUTPUT CHARACTERISTICS FCUEXP-- f- - - r-

.... ~- UEXP 0.0 L . ../ .........

:,...- t- ' 'V~

V/ Ves 10.01/

J1/ -- UEXP 2 ~ I S .... pot - ...... ........ .[....00I-' '- .- r-'" r-v

Iv, - r- - t- r - .- r - UEXP 0.0 -- ._-1

_UEXP 21tIS_ Ves -S.o-....-I- r- t ~ ~ l- r- .....-- - r - -I- - --r- ... .- I-t- .... t - r- .. T f. t- . . - ..- - ._ . t- .- .. tVes .':'; .OV It II . I:0 '-co OR IN YOLTAef:(vOLTS)8', 0 I 0, 0 I t / y: Cl / 0

PHOS Drain Characteristics Demonstrating VariableHob IIlty EH,

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80M CORPOR TION

C TEMPERATURE EFFECTS

The temperature d e p ~ n d e n c e of MOS transistor characterIstics isIncluded in the SPICE2 model through appropriate variations in thequantity VON VON was dIscussed previously under the sections on weakinversion and variable mobility. A detal1ed examination of i ts definingequation reveals the appropriate temperature dependencies.

Eq. 111-9)

All_.terms in the equation Including the Fermi level are updated fortemperature dependence. Naturally all terms multiplied by I are alsoqupdated. For silicon gate devices, the silicon gate work function (theterm m in aluminum gate devices) is aiso updated for temperature effects.

Figure III-II shows a comparison of drain characterists at 12SC.2SC, and -55-C. Figure 111-12 shows a comparison of drain conductanceplots over the same temperature range.H VARIABLE CAPACITANCE EFFECTS

Figure 111-13 shows five capacitive elements associated with the MOSmodel topology. The capacitances Cas and CaD are standard voltagevariable Junction c a p a c i t a n c ~ s These were discussed sufficiently inchapter 11.1. The remaining three elements represent various gatec a p a c i t a n ~ e s and contain both fixed and variable terms. The fixed termsare specified as the parameters CGS. eGo and eGe in the model variablel is t They represent metallization ovedap capacitances. A variableportion of the gate-to-channel capacitance is added to each of thesefixed va.1ues depending on the region of transistor operation. Thevalues of each of the capacitances in each region of operation is illus-

trated quat i tatively in figure 111-1,3. In the region below cutoff. theentire gate-to-channel capacitance is assigned to eGe As the device

11/ 25


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r.

........VI0:r~ WUZ .... ~ ,If

NHOS OR IN CONDUCT NCE -,

-55 'I+25J Ic

I II I L .. 25c, ' ifL/I It'~ IIf,

/i//,

/ / ~ Il...- ' J I.... . . V / /.... ..... . ..- - ... . - '

. .. .... , ... I., . I ... .... to ...,/.. eAT VOLTAe VOLTS) -.J1 0 J / ~ 1.'1 II . /11 p e>

,g-Figure ' - I I ( a ) . NIIOS Drain Charart.eristics Demonstrating Temperature Effects

(

ImCo~noJoJ

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.0figure ' - I I (b) . PHOS Drain CharacterIstics DemonstratIng Temperature Effects

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r ......10 1.,

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...........~ ,0/7---..zw ...- 010IUZ ......- , ~

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ves 5.0 V

ves 2.0Voa I VOLTA.f VOLTS) _.. a /0 0 J, a Y. 0 0Figure t l ' -12(a) . ,IOS Drain Conductance Characteristics Demonstrating Temperature EFfects

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,.

r ...... PHOS OUTPUT CHARACTERISTICS -, I CU.3 _ vas 0.0v 2.0 11111-lu 0.2 IIIlr

,.i,...- .. .-55 C .,. ,. ....

-.il .,. i0..lC ...... I.: ......-..IE 100;2I I I::1 ,/r/ ,/ ves-lo.OUIE

' /1/ +25OC :-.- j - >- " . -- II / '..., I

[/ '

--- / +125/)C 1- - r-- ... .../ v - - - .../ --0 0 1 / ......I //[7 , -55C

/ , l ,I yes-- I 7 ; +25OC. , ' - -5.0V'/ -- -- +125 C - - - - - - - - .- .- --1 .::; ....... _.- ''/ * , . ...l D_A N YDLTA., (VOLTs) ..J

) f 0 , 0 12. 0 I Y,. /6, C1 .0 10

t ,()Figure 111-12 b). PHOS Drain Conductance Characteristics Demonstrating Temperature Effects

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\ \ \\\

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SATURATION

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Figure 111-13. Cite Capacitance Variations111- 0


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operation transitions into the saturated region, up to two-thirds of thechannel capacitance is transferred to C The equation governing thetransit ion is

Eq. 111-10)

The transition from saturated into linear operation is governed by theequat ions

2

Eq . I I I - 11 )he transition points between the capacitance equations in the fourregions of transistor operation are shown in figure 111-13.

The discussion of capacitance variations concludes the descriptionof the physical characterist ics s.mulated by the model.


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t::H f\:l COHPOHAJ lur ICHAPTER IV

PARAMETERIZATION FROM INVERTER OUTPUT CHARACTERISTICSIn some cases the analyst may be confronted with a lack of parameter

Ization data. If he does not have access to individual HOS transistorterminals the output characteristics of lin inverter may be beneficial inestimating parameter values. In figure IV-I a series of MOS Inverteroutput characteristics have been plotted f o r SPlCE2 Inverter model basedon the parameter values previously specified in table Ill I. Indtvlduar---parameters have been varied to.demonstrate their Influence on the shape andmagnitude of the predicted output characteristics. The data points +)were taken from a MOS inverter and re presented for comparison purposes.With appropriate variations in parameter values the analyst can closelysimulate experimental data with the SPICE2 model.

IV l


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....I

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. ... ::.... 'f ' V Iflo0oi to1 I"f1 / jV + + + HEASURED OUTPUT CHARACTERISTICS. . 7


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8DM CORPORATION

REFERENCES1. Cohen, E. Program Reference for SPICE2, Electronics ResearchLaboratory Memorandum University of California, Berkeley, June 14,1976.2 Ihantola, H. K J . Design Theory of a Surface Field EffectTransistor, Stanford Sol id State Electronics Lab., Stanford University, Tech Rpt 1661-1, September 1961.3. Poon, H. c., L. D. Yau and R. C. Johnston. D.C. Hodel for Short-Channe1 IGFET I S , Abstracts of tnternat i ona 1 So 1I d State C rcu itsConference, 1973.4. Swanson, Richard H. and J. D. Heindl. ilion-Implanted Complementary

OS Transistors in Low Voltage Circuits, IEEE Journal of Solid StateCircuits, vol. SC-7, no. 2, AprIl 1972, pp. 146-153.5. Herckel, Gerard, J. Borel, and N. Z. Cuplez. An Accurate LargeSignal MOS Transistor Hodel for Use In Computer Aided Design. IEEETransactions on Electron Devices, vol. EO-19. no. 5. Hay 1972.681-690.

IV-3


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APPENDIX A.SPICE2 MODEL CHANGES

c n IS IHPOItUNT TO HOTE THAT fHIS IS '40T A .. UPDATE OECI{.: IT; IS 'C O .LY'A LIST'OF CHAHGrS T",AT 'HAVE iE;:" IUOE TO S'ICCYS'ZO;Z' ' '--IOEHT SINDrA . DE LE TE " :IS EQ {;l" f.--.. . . .. . . ... .---. . .. ----...--.-.-- ...-......_...C PREiENT ERttOR MtsS1C[ "liEN 'ReEl" IS Y RT. LUGE AND HEGATIVE.' IETA'Tii ' I) IF IARCEXP.GT.t-SO'. )) 8ETlZ BETll.EXPtARG XPJ. Co. ......... . . . . . ............................................................... - - .....---- .......... - ........- ..............OELETE NOSCON.36C . COq:tECT "OBIlITY' DEGUnutoNHobEt.: ' Slr"n Ir'A}fuHcnO{("ar-_-'c THQSHOln VOLTAGE [NSTEID OF Yet.- -YGST . - v t f =VOHc DELE T HOS CA";t . . . . . . c C O ~ ~ E C T ERROR IN MOSCAP 8Y r N T E K C H I N ~ I H G CaVLGS lNO CDVLCO , .. ' . SUOl:tOUTIH HOSCAf" (VGS.veo' .COVL.e S ,COVlt:;O, COVLI;B'CC s . , ' o ~ a w-----c

- - r N $ r l f T - K O ( j , . . , e ' H ~ K . , . . ...,t.,.orlld------------------------c C O R ~ E C T THE HOSHT 11001. P A ~ A H T E R I..IST SO THE ~ A L U E OF THRESHOLDC VOLTAGE PRINT[O OUT tS THE ~ ~ l u E i J S E C e Y S P l e ( : - - IF CVALUEI .OCV"U.NE.J.GI I(PRHY-l-1NSEII'T HOOCHI(.ZIrtS . , . . .. . .. _. _ . . . . _ . _u ..IF ' K P ~ N T . Q . l O . I O . E Q . ~ ' _RITE".999)999 FOt 1U' f H ~ . " 7 H U n 1s IHc:Jt;SlsrNT TO'"$l'E'cn"i'VTowHli"1iSuQ t

" ? ~ S SPtCIFIED. VTO IS CAlCUlATtO 6Y S P I C ~ . , 1 . 1 X .2 SlH . . . TtI1S CALCULATED VAL.UE: IS S .. OWH IN THE ABOVEU81.E:."f' .DELETE ~ ? D C H ( . l Q l . H O O C H K . 1 Q 3VALI)E (LOeV. l -VALUE (LOCV" 3 ~ J .TypE VAt,.'utU:OCV'::U _ 1 SQRTlVALUEllOCV.""C

-DELETE ~ O D C H ~ . 1 " OC ALLJW N E ~ T I V VALUES OF TPS &tiD NSS: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .s ; IF IVALtJflLOCV+U.LToIQ.OJ, GO TO 51"l"lStIlT M"OCIoII(.1 .. 3 . .

C 57 IF ( ( . E O . Z Z . O P . . I . t ( : . l : . ~ : W . I O . E . : . ' : . ' . ~ ~ . T.o. ...__ __ ..._.OELETE MODCHK.5.C OEFAUI. T Tloit f' OSF :r PA:tAIiET'.t LD TO U:oto .. 2 " .. . : . C . t . J . D . l . l . 1 ~ t . ~ . 1 . v . ~ . 3 C . O .C"DELETE ~ O S E Q N . l l 'C PREvitlT ERROR H::SSAGE W H E ' N ' A ~ H H r " U " v E ~ Y (lRc; "ANO Ntnmt - : - A R G ~ N T - eVGS-VON)/V'ACTOS. o.

C IF (ArcG""" er "'5 Ool.) I,. GOS-:3EU . X . ~ ~ lItGrtNT L ............................OEI..T 50PUPih83C PRE'IElJT ~ O : { O R 'f'lESSACE'WHEH AI\CHNl-rs ' lEU , U G - C f ' O N ~ l n y " r . p.c..r - C H -U I1E U /U U lExprDI't .. :IF ( A P . C ~ T . c E . e - s O O . ' J XPfRH [XP(IRGHf'V1L JEtlOCV+1,) Y1,+'VZ-V1J-'1. '-EXPTR"' .....................- . . . . . . . . ............ f l ~ T E S'RUPU.85.S0RUPO.ARCl'1T.t. a l l-T IME t ) TAiJARCl'1TZ ITZ-TIHE1./TAUZEXPTRI'I1 G.' .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . .EXPTJ"H2 .. O.IF (&P.CHT1.GE.(-$OO;, ' ExPUtl1 - EXP(lRCHT1r . . . . . . . . . . . . . . . . . . . . . . . . .IF C ' R G l ' 1 r l . G . C - S O ~ . ' ) E X P T ~ H Z XP(ARGrtTllltrVAL"'U ftOCViLl V1+ cvz.;vn- U.t-txPilHI1 h (Vr=V2T' 'tr.r-.CYI:rTlurzr-Cc C H l ~ G r S IN HOISE HODEL FOR ~ O S F E T '-INSERT H O I S E . 2 1 ~ ... .. .........- .. .


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X L - Y A L U ~ C L O C V + l ' - Z . : Y A L U ' L O C K + Z C t Y A L U E ( L O C " t 1 9 'XW-vALUE Cl.OCVtZ) .. ... . . . . . . . ; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -.. -..COX-VALUECLOCKtll,Cox XL Xw- COX. XL -XM ..-. - -.. - ... .-- ..-.-.-. - .-OELErE HoISE.301- -VNa ItTKHH ravTE:HP -Fmt- ~ : o r r F 1 l l T l C 1 1 i : T CP.CTT7 [ FR::.Co n t ... rJ wTI

C- tDENT CO::tTUPD ., ...... .... -.-.--.. .-.-- -. ..C C O ' t ~ f C T E R ~ O R S IN SUS.tOUTItlt T"PUPO ASSOCUTO WInt re:..pERITURC .COl1ltENSA T ON EFFECT ............_-.-.OELETE "OOCH(.69-C--""HOCIFY ')ANOGAp-ro''TSSU E I < A T U ~ COI1PEtlSA lION OF T H ~ E S H O L . O Voe.. TACE.TY? ~ O : P L C { L O C . Irp:o. V4LUECLCCY+ZZI _.- - .._._. -VF' Y A L U E ( 1 . 0 C V + J _ I - T Y P E - O I . C ~ I ,

V S T ~ I P VF".ti .,TypE-OLOPH . ........_-.-...... -.. . . ... -.. .IF ( V A L U C L O C V + Z l 1 . " ( . ( ~ . J " GO TO .15VST' IP .. VSTRIP+O .5 - (Ol.Oe:Ci-EGFET, .. .. . . . . . . ... . . . . .. .- . . .GO TO .Z- - - 1 5 C O T r N U ~ ~ ~ - - - - - - OLOCiAT OI.DVT-,LOCeVAI.UECLJCV+Z1J/0l.OXHr,'ATNE" VT-'1.0CiCVAI.U (LOCV+ZU IX U . - -- - .- VSTlIP VSTRIP+TYPE-TPS-COI.OCAT-GATHEW'IoZ0 CONTINuE' . . . . . .. . . .VFS VsrRtp-:.5-TYP-PWI ~ A l . U E (LOeV'.)., ' . - VFS+TYPPP'iiIVALUElLOCV+1) V A L U E ( l . O C V . 3 ~ ) + T Y P E - V A L U E C L O : V + l J - S Q ~ T C P M r J-rCENT PLr.aZa .. . . . . . .

-INSERT OVTPVT.2G


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DIMENSION YARR.,(a,. - INSERT 11 T PI r ; 3 .......WRITE (1,%1%' ATITLEZ1Z Foct:tA T X .15Aa, ...... .

-INSERT 0 ~ T P v r . 1 Q 3- - - ' - - - i o I R I T ' 7 - ; } n T " " I i H r I ' p ~ O " ' I T l f I ' Y T - - . ; ; d ' L T ( T ' " R ~ - - - - - - - - - - - - - - - - - - -Z3S ' O R ~ A T elI10)DO 219 1.1.NPOIN . ..- . . . . . . . . . . . . . .

NLOt;ATaLOCYDO 216 ; .1 KHTR ........---.-. ------- -.Y A R ~ A Y C J ' VALUECNLOClr.I, - - - H L O C & " T . N L . o c i . i ' + r ~ P O I H t ' : ; . . : : ; . . . ~ . . . ; ; . ; . - - - - - - - - - - - - - - - - - - -

216 CONTINUE. "'RITE C7;Z1ar YALUE LOCUlr , lURRlYlJ ) ; ' ;{. i,; i iCHTIU" ' '- ' ' ' -- ' ' ' Z19 CONTINUE .. ZlS FOIt 1AT fKiS;4f . . - -- - ..... _- _ - _

-OELETE UP01.Z_ . - PROGP.AH-S'P1C-(f'I'R'l'Ur"ZJ1 .oorpor. Z t fI P, .. INP ) f ' t lpE6. OUTpUT. TlpEn-cELETE UP01.:SC T 1 IF A ,&,101'0:1oa ' .................................. _ ......

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