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SPICE MOSFET Declaration

The MOSFET is a 4-terminal device that is specified in the netlist as:

Mname ND NG NS NB ModName <Optional parameters>The optional parameters are:

L= value W= value AD=value AS=value PD=value PS=value NRD=value where:

L,W: gate length and width (in m). Default: 1 meterAD,AS: source and drain diffusion (in sq. m). Default: 0PD, PS: perimeter of the source and drain (in m). Default: 0 meterNRD: number of squares for drain diffusion, for resistance calculations. Default: 1 sq.

M1 1 2 3 4 MyFet L=1u W=10u

1

2

3

4

1

2

3

4

If an optional parameter is omitted the default values are used.Here is an example declaration for the devices at right:

Additional device parameters, including whether the device is NMOS or PMOS, are defined in the MODEL declaration for MyFet (next slide!)

ND

NG

NS

NB

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SPICE MOS Model

The SPICE MOSFET Model is defined in the netlist as.MODEL ModName xMOS (parameters) (xMOS is either NMOS or PMOS)

Some key parameters are:

600cm2/V-sMobility μ0U0

DefaultUnitsDescriptionParameter

∞metersOxide thicknessTOX

0 Farads/metersGate-bulk overlap capacitance/channel widthCGBO0 Farads/metersGate-drain overlap capacitance/channel widthCGDO0 Farads/metersGate-source overlap capacitance/channel widthCGSO0 Volts-1Channel-length modulationLAMBDA0.6 VoltsSurface potentialPHI0 Volts1/2Bulk threshold parameterGAMMA2E-5 Amps/Volts2Transconductance parameter, μ0 CoxKP0 VoltsZero-bias threshold voltageVTO

21 12d gs ds

WI KP V VTO LAMBDA VL

A simple NMOS device with no capacitances or body effects might be specified as.MODEL MyFet NMOS (VTO=1 KP=0.25)

t sbV VTO GAMMA PHI V PHI

0 oxKP C 03.9oxC TOX

In terms of these parameters some of the basic device characteristics are:

If the user specifies U0 and TOX, then KP is computed as:23gs oxC C WL CGSOW dgC CGDOWKey Device Capacitances:

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Level 1 MOS SPICE Parameters

600cm2/V-sMobilityU0

DefaultUnitsDescriptionParameter

0 metersLateral diffusion lengthLD0 metersLateral diffusion widthWD

1 Flicker noise exponentAF0 Flicker noise coefficientKF+ 1 Gate material type: + 1 =opposite of substrate, -1=same, 0=AluminumTPG∞metersOxide thicknessTOX

0 1/centimeter2Fast surface-state densityNFS0 1/centimeter2Surface-state densityNSS0 1/centimeter3Substate doping densityNSUB0 Farads/metersGate-bulk overlap capacitance/channel widthCGBO0 Farads/metersGate-drain overlap capacitance/channel widthCGDO0 Farads/metersGate-source overlap capacitance/channel widthCGSO0.5 Bulk p-n forward-bias capacitance coefficientFC0.33 Bulk p-n sidewall grading coefficientMJSW0.5 Bulk p-n bottom grading coefficientMJ0 Farads/metersBulk p-n zero-bias perimeter capacitance/lengthCJSW0 Farads/meters2Bulk p-n zero-bias bottom capacitance/lengthCJ0 FaradsBulk-source zero-bias p-n capacitanceCBS0 FaradsBulk-drain zero-bias p-n capacitanceCBD0.8 VoltsBulk p-n potentialPB0 Amps/meters2Bulk p-n saturation/current areaJS1E-14 AmpsBulk p-n saturation currentIS0 Ohms/squareDrain-source diffusion sheet resistanceRSH∞OhmsDrain-source shunt resistanceRDS0 OhmsBulk ohmic resistanceRB0 OhmsGate ohmic resistanceRG0 OhmsSource ohmic resistanceRS0 OhmsDrain ohmic resistanceRD

0 Volts-1Channel-length modulationLAMBDA0.6 VoltsSurface potentialPHI0 Volts1/2Bulk threshold parameterGAMMA2E-5 Amps/Volts2Transconductance parameter, μ CoxKP0 VoltsZero-bias threshold voltageVTO

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MOS Devices in MultiSim

Q6

100um 100um

Select “Place→Component…”

A number of “virtual” devices to choose from, here we select the 3-terminal enhancement-mode MOSFET

This will appear in the circuit schematic

Double-click on the component:

Click “Edit Model” to see SPICE Model declaration

This is where we modify the SPICE model parametersIn MultiSim

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Simple NMOS/PMOS Devices in MultiSim

NMOS PMOS

In ECE 2 we will often solve problems assuming a very basic device described by a threshold voltage, transconductance, and output resistance. We can create simple MOS models with these three parameters as follows:

21 12d gs ds

WI KP V VTO LAMBDA VL

After making desired changes in the model, select “Change Part Model”. Only use “Change All Models” if you want the same model to apply to all the FETs in your circuit!

Remember: PMOS enhancement devices have a negative VTO!

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Typical Parameters (Long and Short)

.MODEL 2N7000 NMOS (LEVEL=3 RS=0.205 NSUB=1.0E15 DELTA=0.1 +KAPPA=0.0506 TPG=1 CGDO=3.1716E-9 RD=0.239 VTO=1.000 VMAX=1.0E7 +ETA=0.0223089 NFS=6.6E10 TOX=1.0E-7 LD=1.698E-9 UO=862.425 +XJ=6.4666E-7 THETA=1.0E-5 CGSO=9.09E-9 L=2.5E-6 W=0.8E-2)