SmartSpice BSIM3 Version 3

UC Berkeley released the final version of the BSIM3v3 model in October, 1995. This model is now available in SmartSpice 1.4.0 in two different variants. The SmartSpice implementation is referred to as MOSFET model level 8. The original Berkeley model is also available within SmartSpice as MOSFET model level 81. Both models produce virtually identical results when commonly acceptable model parameter sets are used. However, these models are not identical since the SmartSpice implementation provides a number of additional parameters currently not supported in Berkeley Spice.

This article describes the SmartSpice BSIM3v3 implementation and the primary differences between the SmartSpice level 8 and level 81 models;

• Standard SmartSpice MOSFET Parameters contains a list of standard SmartSpice MOSFET model parameters not supported in Berkeley Spice.
• Differences between BSIM3v3 Level 8 and Level 81 Parameters lists the level 8 and level 81 parameters with the same names but different default values.
• Additional Parameters in the SmartSpice BSIM3v3 model describes additional SmartSpice level 8 parameters introduced in order to improve the Berkeley BSIM3v3 model.
• Output Device Variables contains a list of the BSIM3v3 output parameters that can be printed, plotted and measured during simulation.
• BSIM3v3 Level 8 Capacitance Model describes the capacitance model in the SmartSpice implementation of the BSIM3v3 model.
• The final section contains an example input deck, illustrating some aspects of the BSIM3v3 model

For further information on the SmartSpice BSIM3v3 implementation, refer to reference [2] and [3] at the end of this article.

Table 1: Standard SmartSpice MOSFET parameters.

a. Parameter TOX will be ignored if the parameter COX is specified. Otherwise COX will be calculated using the value of TOX.
b. If LD is not specified it will be calculated as 0.75* XJ.

Table 2: Standard SmartSpice MOSFET Temperature Parameters.

General Options Supported by BSIM3v3 Level 8

The options listed below are supported by the SmartSpice BSIM3v3 Level 8 model. These parameters can be specified in the .OPTIONS statement.

The options ACM, DEFL, DEFW, DEFAD, DEFAS, DEFPD, DEFPS, DEFNRD, DEFNRS, HDIF, LD, LDIF, SCALE, SCALM and TNOM are standard for all MOSFET models including BSUM3v3 Level8.

The option BYPASS is not currently supported for BSIM3v3.

The option CAPDC = 1 can be specified to calculate BSIM3v3 capacitances for both Level 8 and Level 81. Default 0 (OFF).

The option CONV=num (0<num<5) is supported for BSIM3v3. Default 0.

The conductance GMIN is connected in parallel with the bulk-drain and bulk-source diodes. Default 1e-12.

The conductance DCGMIN is connected between drain and source nodes. Default 0.

The option VZERO = num is supported by the BSIM3v3 Level 8 model. This option defines the MNA formulation in SmartSpice. The option VZERO = 2 is recommended when simulating relatively large circuits, with hundreds or thousands of transistors in the time domain. It accelerates simulation and in some cases increases the accuracy of simulation results. Default 0. For further information regarding the option VZERO, see "SmartSpice Version 1.4.0 Release Notes".

The option EXPERT = 1 can be used to detect discontinuities in the BSIM3v3 model. If EXPERT = 777 SmartSpice will detect negative conductances GM, GDS and GMBS, and negative capacitances. Default 0 (OFF).

For further information regarding the BSIM3v3 Level 8 implementation, see Application Notes:

1. SmartSpice BSIM3 Version 3 Intrinsic Capacitance Models

2. SmartSpice BSIM Version 3 Non-Quassi Static Model

Differences between BSIM3v3 Level 8 and Level 81 Parameters

In Table 3 the junction current and capacitance parameters have different defaults in the SmartSpice (level 8) and Berkeley (level 81) BSIM3v3 models.

Table 3: Default Parameter Values.

Note : In the UC Berkeley implementation, the drain saturation current is calculated as follows;

if AD > 0 then

DrainSatCurrent = JS * AD

else

DrainSatCurrent = 1.0e-14

The parameters IS and JSW are not used.

Additional Parameters in the SmartSpice BSIM3v3 model

Additional parameters were introduced into the SmartSpice level 8 model to resolve conflicting situations in the Berkeley BSIM3v3 implementation, and to improve the convergence properties of the BSIM3v3 model.

TEMPMOD Parameter

The UC Berkeley BSIM3v3 manual [1] (final version) and implementation are not consistent in terms of the temperature dependencies. In the source code they are calculated as functions of the nominal temperature tnom. In contrast the BSIM3v3 manual treats them as functions of the circuit temperature, temp.

In the SmartSpice level 8 model, are calculated at tnom by default. This corresponds to the Berkeley implementation rather that the documentation. The temperature equations described in the Berkeley manual will be used if the model parameter tempmod=2.

Parameter Scaling

In the UC Berkeley BSIM3v3 implementation, some model parameters can be scaled depending upon actual parameter values. These parameters are U0, LU0, WU0, PU0, NPEAK, LNPEAK, WNPEAK, PNPEAK, NGATE, LNGATE, WNGATE and PNGATE.

U0, LU0, WU0 and PU0 Parameters

In the Berkeley BSIM3v3 source code, these parameters can be scaled in two routines, "b3mpar.c" and "b3set.c". In b3mpar.c the scaling is performed independently for each parameter as follows,

In b3set.c the binning parameters LU0, WU0 and PU0 are scaled depending upon the U0 value. In the SmartSpice (level 8) implementation, scaling is performed using the following rule,

if U0 > 1 then

i.e., parameter scaling is based upon the basic U0 value.

NPEAK, LNPEAK, WNPEAK and PNPEAK Parameters

In the SmartSpice BSIM3v3 (level 8) implementation, these parameters are scaled as follows,

if NPEAK > 1e20 then

NGATE, LNGATE, WNGATE and PNGATE Parameters

In the SmartSpice BSIM3v3 (level 8) implementation, these parameters are scaled as follows,

if NGATE > 1e23 then

Smooth Function Parameters

The SmartSpice BSIM3v3 (level 8) model contains a number of smoothing functions that were developed to eliminate discontinuities in the Berkeley BSIM3v3 model. The model parameters used in these functions are listed in Table 3.

Table 4: SmartSpice BSIM3v3 level 8 smoothing parameters.

The parameter ABULKLIM is used to prevent a discontinuity due to the limitations Abulk0 >= 0.01 and Abulk >= 0.01. To disable the Abulk smoothing function let ABULKLIM = 0.0.

The parameter NLIM is used to prevent a discontinuity for n >= 1 in the subthreshold swing parameter n equation. To disable the n smoothing function let NLIM = 0.0.

The parameter LAMBLIM is used to prevent a discontinuity for <= 1 in the equation

= A1 . Vgsteff+A1

and in the polysilicon depletion effect (Ngate) equation. To disable both the Lambda and Ngate smoothing functions let LAMBLIM = 0.0.

The parameter UEFFLIM is used to prevent the denominator in both the µ_eff and A_bulk equations from becoming negative. The µ_eff smoothing function cannot be disabled.

By setting the smoothing parameter flag, SMOOTH, equal to 0, all smoothing functions except for the µ_eff smoothing function will be disabled.

Output Device Variables

Table 5. DC Output Variables for BSIM3v3 Model.

Table 6: Charge and Capacitance Output Variables for BSIM3v3 Model.

BSIM3v3 Level 8 Capacitance Model

The capacitance model in the SmartSpice BSIM3v3 (level 8) model is evaluated in three steps.

• The variable gate, bulk and drain charges, qg, qb and qd respectively, are calculated as functions of the gate, drain, source and bulk voltages. The charge contribution of the overlap, bulk-drain and bulk-source capacitances are not added to qg and qb at this stage. The partitioning ratio of qd to qs is determined using the XPART model parameter. Nine basic "capacitances" (partial derivatives of the qg, qd and qb charges with respect to Vgb, Vdb and Vsb) are calculated as follows;

• The total gate, drain and bulk charges (Qg, Qd and Qb respectively) are calculated. These charges contain the variable gate (qg), drain (qd) and bulk (qb) charges as well as the charge contribution of the overlap, bulk-drain and bulk-source capacitances.
• Sixteen derivatives of the terminal charges with respect to the terminal voltages are computed as follows;

The following BSIM3v3 device parameters can be stored, printed and/or measured using the .save, .probe, .print and .measure statements.

• The variable transcapacitances,
  

• The variable bulk-drain and bulk-source capacitances

• The total gate, drain and bulk charges

Note: To output capacitances during .DC analysis, let the optional parameter capdc = 1 in the .options statement.

Example

Input Deck

* UC Berkeley BSIM3 Version 3 Model

* Model parameter set obtained from

* http://rely.eecs.berkeley.edu:8080/bsim3www/bsim3.html


.OPTIONS RELTOL=1e-4 ABSTOL=1e-16 VNTOL=1e-9


.OPTIONS CAPDC=1 NUMDGT=9 FORMAT NOMOD


.SAVE

+ @mn1[vth] @mn1[vdsat] @mn1[gm] @mn1[gds] @mn1[gmbs]

+ @mn2[vth] @mn2[vdsat] @mn2[gm] @mn2[gds] @mn2[gmbs]

+ @mn1[cggb] @mn1[cgdb] @mn1[cgsb] @mn1[cdgb] @mn1[cddb]

+ @mn1[cdsb] @mn1[cbgb] @mn1[cbdb] @mn1[cbsb]

+ @mn3[cggb] @mn3[cgdb] @mn3[cgsb] @mn3[cdgb] @mn3[cddb]

+ @mn3[cdsb] @mn3[cbgb] @mn3[cbdb] @mn3[cbsb]

* ===================================================


.DC VGG 0 5v 0.05

Vgg gg 0 DC 3

Vdd dd 0 DC 0

Vbb bb 0 DC 0


* SmartSpice BSIM3V3 (Level 8) model; Vds=5V

Vb b bb DC 0

Vd d dd DC 5v

Vs s 0 DC 0

Vin g gg DC 0

Mn1 d g s b NMOS w=4.0u l=0.8u

+ PS=19.50u AS=17.10p PD=19.50u AD=17.10p

* UC Berkeley BSIM3v3 (Level 81) model; Vds=5V

Vb2 b2 bb DC 0

Vd2 d2 dd DC 5v

Vs2 s2 0 DC 0

Vin2 g2 gg DC 0

Mn2 d2 g2 s2 b2 NMOS81 w=4.0u l=0.8u

+ PS=19.50u AS=17.10p PD=19.50u AD=17.10p


* SmartSpice BSIM3V3 (Level 8) model; Vds=1V

Vb3 b3 bb DC 0

Vd3 d3 dd DC 1

Vs3 s3 0 DC 0

Vin3 g3 gg DC 0

Mn3 d3 g3 s3 b3 NMOS w=4.0u l=0.8u

+ PS=19.50u AS=17.10p PD=19.50u AD=17.10p


* UC Berkeley BSIM3v3 (Level 81) model; Vds=1V

Vb4 b4 bb DC 0

Vd4 d4 dd DC 1

Vs4 s4 0 DC 0

Vin4 g4 gg Dc 0

MN4 d4 g4 s4 b4 NMOS81 w=4.0u l=0.8u

+ PS=19.50u AS=17.10p PD=19.50u AD=17.10p


.LET kirhNplus='i(vin)+i(vs)+i(vd)+i(vb)'

.LET kirhNminus='i(vin2)+i(vs2)+i(vd2)+i(vb2)'

.LET kirhPplus='i(vin3)+i(vs3)+i(vd3)+i(vb3)'

.LET kirhPminus='i(vin4)+i(vs4)+i(vd4)+i(vb4)'


.MEASURE DC max_kirhNplus MAX `abs(kirhNplus)'

.MEASURE DC max_kirhNminus MAX `abs(kirhNminus)'

.MEASURE DC max_kirhPplus MAX `abs(kirhPplus)'

.MEASURE DC max_kirhPminus MAX `abs(kirhPminus)'


*

****** SmartSpice BSIM3V3 (Level 8) model

*

.MODEL NMOS NMOS level=8

+ Tnom=27.0

+ nch= 1.024685E+17 tox=1.00000E-08 xj=1.00000E-07

+ lint= 3.75860E-08 wint=-2.02101528644562E-07

+ vth0= .6094574 k1= .5341038 k2= 1.703463E-03 k3=-17.24589

+ dvt0= .1767506 dvt1= .5109418 dvt2=-0.05

+ nlx= 9.979638E-08 w0=1e-6

+ k3b= 4.139039

+ vsat= 97662.05 ua=-1.748481E-09 ub= 3.178541E-18

uc=1.3623e-10

+ rdsw= 298.873 u0= 307.2991 prwb=-2.24e-4

+ a0= .4976366

+ keta=-2.195445E-02 a1= .0332883 a2= .9

+ voff=-9.623903E-02 nFactor= .8408191 cit= 3.994609E-04

+ cdsc= 1.130797E-04

+ cdscb=2.4e-5

+ eta0= .0145072 etab=-3.870303E-03

+ dsub= .4116711

+ pclm= 1.813153 pdiblc1= 2.003703E-02 pdiblc2=

.00129051 pdiblcb=-1.034e-3

+ drout= .4380235 pscbe1= 5.752058E+08 pscbe2= 7.510319E-05

+ pvag= .6370527 prt=68.7 ngate=1.e20 alpha0=1.e-7 beta0=28.4

+ prwg=-0.001 ags=1.2

+ dvt0w=0.58 dvt1w=5.3e6 dvt2w=-0.0032

+ kt1=-.3 kt2=-.03

+ at= 33000

+ ute=-1.5

+ ua1= 4.31E-09 ub1= 7.61E-18 uc1=-2.378e-10

+ kt1l=1e-8

+ wr=1 b0=1e-7 b1=1e-7 dwg=5e-8 dwb=2e-8 delta=0.015

+ cgdl=1e-10 cgsl=1e-10 cgbo=1e-10 xpart=0.0

+ cgdo=0.4e-9 cgso=0.4e-9

+ clc=0.1e-6+ cle=0.6

+ ckappa=0.6

*


***** UC Berkeley BSIM3v3 (Level 81) model

*

.MODEL NMOS81 nmos level=81

+ Tnom=27.0

+ nch= 1.024685E+17 tox=1.00000E-08 xj=1.00000E-07

+ lint= 3.75860E-08 wint=-2.02101528644562E-07

+ vth0= .6094574 k1= .5341038 k2= 1.703463E-03 k3=-17.24589

+ dvt0= .1767506 dvt1= .5109418 dvt2=-0.05

+ nlx= 9.979638E-08 w0=1e-6

+ k3b= 4.139039

+ vsat= 97662.05 ua=-1.748481E-09 ub= 3.178541E-18

uc=1.3623e-10

+ rdsw= 298.873 u0= 307.2991 prwb=-2.24e-4

+ a0= .4976366

+ keta=-2.195445E-02 a1= .0332883 a2= .9

+ voff=-9.623903E-02 nFactor= .8408191 cit= 3.994609E-04

+ cdsc= 1.130797E-04+ cdscb=2.4e-5

+ eta0= .0145072 etab=-3.870303E-03

+ dsub= .4116711

+ pclm= 1.813153 pdiblc1= 2.003703E-02 pdiblc2=

.00129051 pdiblcb=-1.034e-3

+ drout= .4380235 pscbe1= 5.752058E+08 pscbe2= 7.510319E-05

+ pvag= .6370527 prt=68.7 ngate=1.e20 alpha0=1.e-7 beta0=28.4

+ prwg=-0.001 ags=1.2

+ dvt0w=0.58 dvt1w=5.3e6 dvt2w=-0.0032

+ kt1=-.3 kt2=-.03

+ at= 33000

+ ute=-1.5

+ ua1= 4.31E-09 ub1= 7.61E-18 uc1=-2.378e-10

+ kt1l=1e-8

+ wr=1 b0=1e-7 b1=1e-7 dwg=5e-8 dwb=2e-8 delta=0.015

+ cgdl=1e-10 cgsl=1e-10 cgbo=1e-10 xpart=0.0

+ cgdo=0.4e-9 cgso=0.4e-9

+ clc=0.1e-6+ cle=0.6

+ ckappa=0.6

.END

Measurement Results

* UC Berkeley BSIM3 Version 3 model

DC Analysis, 27 deg C,Fri Mar 29 10:03:27 1996

max_kirhnplus = 9.051605833e-19 at = 3.700000000e+00

max_kirhnminus = 5.000000956e-12 at = 3.250000000e+00

max_kirhpplus = 7.999465181e-19 at = 4.950000000e+00

max_kirhpminus = 1.000000639e-12 at = 5.000000000e+00


Figure 1 contains two sets of ids vs vds curves, the first obtained with vds = 5V and the second obtained with vds = 1V. As can be seen, there is no discernible difference between the curves generated using the level 8 BSIM3v3 model and the original UC Berkeley BSIM3v3 model (i.e. level 81) in SmartSpice.

Figure 1. Comparison of ids vs vds curves obtained using the SmartSpice BSIM3v3 level 8 and level 81 models.

Figure 2 contains gm vs vgs curves obtained from two transistors (mn1 and mn2). These transistors have exactly the same bias conditions. The mn1 transistor uses the SmartSpice BSIM3v3 level 8 model, while the mn2 transistor uses the original UC Berkeley model (i.e. level 81). As can be seen a discontinuity exists in the original Berkeley model and this discontinuity has been removed from the SmartSpice BSIM3v3 level 8 model.

Figure 2. Illustration of gm discontinuity in UC Berkeley BSIM3v3 model.

Figure 3 contains the curves generated by some of the capacitance output variables in the SmartSpice BSIM3v3 level 8 model.

Figure 3. Capacitances in the SmartSpice BSIM3v3 level 8 model.

Parameter Extraction

Two versions of BSIM3v3 MOSFET model are supported in UTMOST III and SPAYN. For level 8 and 81, model extraction through curve fit, local optimization and global optimization is available. Worst case Spice model derivation can be done in SPAYN, and is very easy due to the physical nature of the model parameters.

Conclusion

Silvaco now offers a complete tool set for analog Circuit Simulation based on BSIM3v3; a very fast, accurate and convergent SmartSpice, a fully automated parameter extraction UTMOST III and simple, user-friendly worst case Spice model generation SPAYN.

References

[1] BSIM3v3 Manual (Final Version), Department of Electrical Engineering and Computer Science, University of California, Berkeley, 1995.

[2] SmartSpice BSIM3v3 Intrinsic Capacitance Models Applications Note.

[3] SmartSpice BSIM3v3 Non-Quasi Static Model Application Note.