SPICE MOSFET Declaration
ND
The MOSFET is a 4-terminal device that is specified in the netlist as:
Mname ND NG NS NB ModName <Optional parameters>
NG
NB
The optional parameters are:
NS
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 meter
AD,AS: source and drain diffusion (in sq. m). Default: 0
PD, PS: perimeter of the source and drain (in m). Default: 0 meter
NRD: number of squares for drain diffusion, for resistance calculations. Default: 1 sq.
If an optional parameter is omitted the default values are used.
M1 1 2 3 4 MyFet L=1u W=10u
3
1
Here is an example declaration for the devices at right:
2
4
3
2
4
1
Additional device parameters, including whether the device is NMOS or PMOS, are
defined in the MODEL declaration for MyFet (next slide!)
© Bob York
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SPICE MOS Model
The SPICE MOSFET Model is defined in the netlist as
(xMOS is either NMOS or PMOS)
.MODEL ModName xMOS (parameters)
Some key parameters are:
Parameter
VTO
KP
GAMMA
PHI
LAMBDA
CGSO
CGDO
CGBO
U0
TOX
Description
Zero-bias threshold voltage
Transconductance parameter, μ0 Cox
Bulk threshold parameter
Surface potential
Channel-length modulation
Gate-source overlap capacitance/channel width
Gate-drain overlap capacitance/channel width
Gate-bulk overlap capacitance/channel width
Mobility μ0
Oxide thickness
Units
Volts
Amps/Volts2
Volts1/2
Volts
Volts-1
Farads/meters
Farads/meters
Farads/meters
cm2/V-s
meters
Default
0
2E-5
0
0.6
0
0
0
0
600
∞
In terms of these parameters some of the basic device characteristics are:
Id 
1
W
KP
Vgs  VTO
2
L

 1  LAMBDA Vds 
2
Vt  VTO  GAMMA

PHI  Vsb  PHI

A simple NMOS device with no capacitances or body effects might be specified as
.MODEL MyFet NMOS (VTO=1 KP=0.25)
If the user specifies U0 and TOX, then KP is computed as:
Key Device Capacitances:
© Bob York
2
C gs  CoxWL  CGSO W
3
KP  0Cox
Cox 
3.9 0
TOX
Cdg  CGDO W
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Level 1 MOS SPICE Parameters
Parameter
VTO
KP
GAMMA
PHI
LAMBDA
LD
WD
RD
RS
RG
RB
RDS
RSH
IS
JS
PB
CBD
CBS
CJ
CJSW
MJ
MJSW
FC
CGSO
CGDO
CGBO
NSUB
NSS
NFS
U0
TOX
TPG
KF
AF
© Bob York
Description
Zero-bias threshold voltage
Transconductance parameter, μ Cox
Bulk threshold parameter
Surface potential
Channel-length modulation
Lateral diffusion length
Lateral diffusion width
Drain ohmic resistance
Source ohmic resistance
Gate ohmic resistance
Bulk ohmic resistance
Drain-source shunt resistance
Drain-source diffusion sheet resistance
Bulk p-n saturation current
Bulk p-n saturation/current area
Bulk p-n potential
Bulk-drain zero-bias p-n capacitance
Bulk-source zero-bias p-n capacitance
Bulk p-n zero-bias bottom capacitance/length
Bulk p-n zero-bias perimeter capacitance/length
Bulk p-n bottom grading coefficient
Bulk p-n sidewall grading coefficient
Bulk p-n forward-bias capacitance coefficient
Gate-source overlap capacitance/channel width
Gate-drain overlap capacitance/channel width
Gate-bulk overlap capacitance/channel width
Substate doping density
Surface-state density
Fast surface-state density
Mobility
Oxide thickness
Gate material type: + 1 =opposite of substrate, -1=same, 0=Aluminum
Flicker noise coefficient
Flicker noise exponent
Units
Volts
Amps/Volts2
Volts1/2
Volts
Volts-1
meters
meters
Ohms
Ohms
Ohms
Ohms
Ohms
Ohms/square
Amps
Amps/meters2
Volts
Farads
Farads
Farads/meters2
Farads/meters
Farads/meters
Farads/meters
Farads/meters
1/centimeter3
1/centimeter2
1/centimeter2
cm2/V-s
meters
Default
0
2E-5
0
0.6
0
0
0
0
0
0
0
∞
0
1E-14
0
0.8
0
0
0
0
0.5
0.33
0.5
0
0
0
0
0
0
600
∞
+1
0
1
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MOS Devices in MultiSim
Select “Place→Component…”
This will appear in the circuit schematic
Q6
100um
100um
Double-click on the component:
This is where
we modify the
SPICE model
parameters
In MultiSim
A number of “virtual” devices to
choose from, here we select the 3terminal enhancement-mode MOSFET
© Bob York
Click “Edit
Model” to see
SPICE Model
declaration
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Simple NMOS/PMOS Devices in MultiSim
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:
NMOS
PMOS
Remember: PMOS
enhancement
devices have a
negative VTO!
Id 
1
W
KP
Vgs  VTO
2
L

 1  LAMBDA Vds 
2
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!
© Bob York
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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)
© Bob York
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