Chapter 16 Selecting a MOSFET Model

1 : 1 Thu Jul 23 19:10:43 1998 Star-Hspice Manual, Release 16 Selecting a MOSFET ModelNow that you know more about MOSFET models from Chapter 15, Introducing MOSFET . it will be easier for you to choose which type of modelsyou require for your Chapter lists the various MOSFET models, and provides the specificationsfor each Model . The following topics are covered in this Chapter :nLevel 1 IDS: Schichman-Hodges ModelnLevel 2 IDS: Grove-Frohman ModelnLevel 3 IDS: Empirical ModelnLevel 4 IDS: MOS ModelnLevel 5 IDS ModelnLevel 6 and Level 7 IDS: MOSFET ModelnLevel 7 IDS ModelnLevel 8 IDS ModelnLevel 13 BSIM ModelnLevel 27 SOSFET ModelnLevel 28 Modified BSIM ModelnLevel 38 IDS: Cypress Depletion ModelnLevel 39 BSIM2 ModelnLevel 40 HP a-Si TFT ModelnLevel 47 BSIM3 Version 2 MOS ModelnLevel 49 BSIM3 Version 3 MOS ModelnLevel 50 Philips MOS9 ModelnComparing MOS : 2 Thu Jul 23 19:10:43 1998 Level 1 IDS: Schichman-Hodges ModelSelecting a MOSFET Model16-2 Star-Hspice Manual, Release 1 IDS: Schichman-Hodges ModelThis section describes the parameters and equations for the Level 1 IDS:Schichman-Hodges Model .

2 Level 1 Model ParametersThe Level 1 Model parameters Model ParametersName(Alias) Model selector. Level 1 is the Schichman-Hodges capacitance per unit gate area. If COX is notspecified, it is calculated from (BET,BETA)A/V2intrinsic transconductance parameter. If KP is notspecified and UO and TOX are entered, theparameter is computed from:KP = UO COXThe default= (NMOS), (PMOS).LAMBDA(LAM, LA) modulationTOXm1e-7 gate oxide thicknessUOcm2/(V s)carrier : 3 Thu Jul 23 19:10:43 1998 Selecting a MOSFET ModelLevel 1 IDS: Schichman-Hodges ModelStar-Hspice Manual, Release Width and Length ParametersName(Alias) length reduction on each = DEL SCALMLD (DLAT,LATD)mlateral diffusion into channel from source and LD and XJ are unspecified, LD Default= LD is unspecified but XJ is specified, LD iscalculated as: LD Default= XJLD scaled = LD SCALMLDACmThis parameter is the same as LD, but if LDAC is in statement, it replaces LD in the Leffcalculation for AC gate shrink diffusion into channel from bulk along widthWDscaled = WD SCALMWDACmThis parameter is the same as WD, but if WDAC is inthe.

3 Model statement, it replaces WD in the Weffcalculation for AC gate layer and width shrink : 4 Thu Jul 23 19:10:43 1998 Level 1 IDS: Schichman-Hodges ModelSelecting a MOSFET Model16-4 Star-Hspice Manual, Release Voltage junction depth:XJscaled = XJ SCALMXL (DL, (LDEL) for masking and etching effects:XLscaled = XL SCALMXW (DW,WDEL) for masking and etching effects:XWscaled = XW SCALMName(Alias)UnitsDefaultDescriptionG AMMAV1 effect factor. If GAMMA is not specified, itis calculated from NSUB (See CommonThreshold Voltage Parameters on page 15-52).NFS (DFS, NF,DNF)cm-2 surface state densityNSUB(DNB,NB)cm-31e15bulk surface doping. NSUB is calculated fromGAMMA if not inversion potential PH is calculatedfrom NSUB if not specified (See CommonThreshold Voltage Parameters on page 15-52).VTO (VT)Vzero-bias threshold voltage. If not specified, it iscalculated. (See Common Threshold VoltageParameters on page 15-52).)

4 Name(Alias) : 5 Thu Jul 23 19:10:43 1998 Selecting a MOSFET ModelLevel 1 IDS: Schichman-Hodges ModelStar-Hspice Manual, Release Level 1 MOSFET Model should be used when accuracy is less importantthan simulation turn-around time. For digital switching circuits, especially whenonly a qualitative simulation of timing and function is needed, Level 1 run-time can be about half that of a simulation using the Level 2 Model . Theagreement in timing is approximately 10%. The Level 1 Model , however, resultsin severe inaccuracies in DC transfer functions of TTL-compatible input buffers,if these buffers are present in the channel-length modulation parameter LAMBDA is equivalent to theinverse of the Early voltage for the bipolar transistor. LAMBDA is a measure ofthe output conductance in saturation. When this parameter is specified, theMOSFET has a finite but constant output conductance in saturation.

5 IfLAMBDA is not input, the Level 1 Model assumes zero output conductance. Level 1 Model EquationsThe Level 1 Model equations EquationsIn the Level 1 Model the carrier mobility degradation and the carrier saturationeffect and weak inversion Model are not included. This Model determines the DCcurrent as follows:Cutoff Region, vgs vthLinear Region, vds < vgs - vds +()vgsvth vds2------- vds = : 6 Thu Jul 23 19:10:43 1998 Level 1 IDS: Schichman-Hodges ModelSelecting a MOSFET Model16-6 Star-Hspice Manual, Release Region, vds vgs - vthEffective Channel Length and WidthThe Model calculates the effective channel length and width from the drawnlength and width as follows:Threshold Voltage,vthvsb 0vsb < 0 Where the built-in voltage vbi is defined as:orNote: See Common Threshold Voltage Parameters on page 15-52forcalculation of VTO, GAMMA, and PHI if they are not vds +()vgsvth ()2 =LeffLscaledLMLT XLscaled2 LDscaledDELscaled+() +=WeffMWscaledWMLTXW scaled2 WDscaled +() =vthvbiGAMMAPHIvsb+()12/ +=vthvbiGAMMAPHI12 + +=vbivfbPHI+=vbiVTO GAMMA PHI12/ = : 7 Thu Jul 23 19:10:43 1998 Selecting a MOSFET ModelLevel 1 IDS.

6 Schichman-Hodges ModelStar-Hspice Manual, Release Voltage,vsatThe saturation voltage for the Level 1 Model is due to channel pinch off at thedrain side and iscomputed by:In the Level 1 Model , the carrier velocity saturation effect is not = : 8 Thu Jul 23 19:10:43 1998 Level 2 IDS: Grove-Frohman ModelSelecting a MOSFET Model16-8 Star-Hspice Manual, Release 2 IDS: Grove-Frohman ModelThis section describes the parameters and equations for the Level 2 IDS: Grove-Frohman Model . Level 2 Model ParametersThe Level 2 Model parameters Model ParametersName(Alias) Model selector. Level 2 is the capacitance per unit gate area. This parameteris calculated from TOX if not (ESAT) electric field for carrier velocity Grove:electrons 6e4holes zero to indicate an infinite value. ECRIT ispreferred over VMAX because the equation is morestable. ECRIT is estimated as:ECRIT = 100 (VMAX / UO)KP (BET,BETA) transconductance.

7 If KP is not specified andUO and TOX are entered, KP is calculated fromKP = UO COXLAMBDA(LAM, LA) length : 9 Thu Jul 23 19:10:43 1998 Selecting a MOSFET ModelLevel 2 IDS: Grove-Frohman ModelStar-Hspice Manual, Release Width and Length channel charge (fixed and mobile) coefficientTOXm1e-7gate oxide thicknessVMAX(VMX, VSAT) drift velocity of carriers. Use zero toindicate an infinite (Alias) length reduction on each side:DELscaled = DEL SCALMLD (DLAT,LADT)mlateral diffusion into channel from source and LD and XJ are unspecified, LD default= LD is unspecified but XJ is specified, LD iscalculated from: XJ. The default= = LD SCALMLDACmThis parameter is the same as LD, but if LDAC is includedin the . Model statement, it replaces LD in the Leffcalculation for AC gate shrink length referenceLREF scaled = LREF diffusion into channel from bulk along widthWDscaled = WD SCALMName(Alias) : 10 Thu Jul 23 19:10:43 1998 Level 2 IDS: Grove-Frohman ModelSelecting a MOSFET Model16-10 Star-Hspice Manual, Release Voltage ParametersWDACmThis parameter is the same as WD, but if WDAC isincluded in the.

8 Model statement, it replaces WD in theWeff calculation for AC gate layer and width shrink width referenceWREF scaled = WREF junction depthXJscaled = XJ SCALMXL (DL,LDEL) bias accounts for masking and etching effectsXLscaled = XL SCALMXW (DW,WDEL) bias accounts for masking and etching effectsXWscaled = XW SCALMName(Alias) width factor for adjusting thresholdGAMMAV1 effect factor. This parameter is calculatedfrom NSUB if not specified (see CommonThreshold Voltage Parameters on page 15-52).LND length sensitivityLN0 length subthreshold subthreshold factor. Typical value= (Alias) : 11 Thu Jul 23 19:10:43 1998 Selecting a MOSFET ModelLevel 2 IDS: Grove-Frohman ModelStar-Hspice Manual, Release ParametersNFS (DFS,NF, DNF)cm-2 surface state densityNSUB (DNB,NB)cm-31e15bulk surface doping. If NSUB is not specified, it iscalculated from inversion potential. If PHI is not specified, itis calculated from NSUB (see Common ThresholdVoltage Parameters on page 15-52).

9 VTO(VT)Vzero-bias threshold voltage. If it is not specified, itis calculated (see Common Threshold VoltageParameters on page 15-52). Model selectorWND width width sensitivityName(Alias) equation selector. This parameter can be set toMOB=0 or MOB=7. If MOB=7, the Model is changed,which also affects the channel length :MOB=7 operates as a flag. It invokes the channellength modulation and mobility equations of MOSFETL evel modulation. THETA is used only when MOB= typical value in this application is THETA= (Alias) : 12 Thu Jul 23 19:10:43 1998 Level 2 IDS: Grove-Frohman ModelSelecting a MOSFET Model16-12 Star-Hspice Manual, Release mobility parameters are best determined by curve fitting. In most casesUTRA should be specified between and Nonzero values for UTRA canresult in negative resistance regions at the onset of saturation. Level 2 Model EquationsThe Level 2 Model equations EquationsThe following section describes the way the Level 2 MOSFET Model calculatesthe drain current of n-channel and p-channel Region, vgs vth(see subthreshold current) field for mobility degradation, UCRIT.

10 Theparameter is the limit at which the surface mobility UObegins to decrease in accordance with the empiricalrelation given (F2) critical field exponent in the empirical formula whichcharacterizes surface mobility degradationUO (UB,UBO)cm2/(V s)600 (N)250 (P)low-field bulk mobility. This parameter is calculated fromKP if KP is field coefficientNote:SPICE does not use UTRA. HSPICE uses it ifsupplied, but issues a warning because UTRA canhinder (Alias)UnitsDefaultDescriptionIds0= : 13 Thu Jul 23 19:10:43 1998 Selecting a MOSFET ModelLevel 2 IDS: Grove-Frohman ModelStar-Hspice Manual, Release Region, vgs>vthwhereEffective Channel Length and WidthThe Model calculates effective channel length and width from the drawn lengthand width as follows:Ids vgsvbi vde 2--------------- vde23--- PHIvdevsb++()32/PHIvsb+()32/ [] =vdemin vdsvdsat,()= 1 DELTA si 4 COX Weff ------------------------------------ += KPWeffLeff----------- =LeffLscaledLMLT XLscaled2 LDscaledDELscaled+() +=WeffMWscaledWMLTXW scaled2 WDscaled + () =LREFeffLREF scaledLMLT XLscaled2 LDscaledDELscaled+() +=WREFeffMWREF scaledWMLTXW scaled2 WDscaled + () = : 14 Thu Jul 23 19:10:43 1998 Level 2 IDS.