Using Common Threshold Voltage Equations
This section describes the common threshold voltage equations.
Common Threshold Voltage Parameters
The parameters described in this section are applicable to all MOSFET models except LEVELs 5 and 13.
|
Name (Alias)
|
Units
|
Default
|
Description
|
|
DELVTO
|
V
|
0.0
|
Zero-bias threshold voltage shift
|
|
GAMMA
|
V
1/2
|
0.527625
|
Body effect factor. If GAMMA is not set, it is calculated from NSUB.
|
|
NGATE
|
1/cm
3
|
|
Polysilicon gate doping, used for analytical model only. Undoped polysilicon is represented by a small value. If NGATE
<=
0.0, it is set to 1e+18.
|
|
NSS
|
1/cm
2
|
1.0
|
Surface state density
|
|
NSUB
(DNB, NB)
|
1/cm
3
|
1e15
|
Substrate doping
|
|
PHI
|
V
|
0.576036
|
Surface potential. NSUB default=1e15.
|
|
TPG (TPS)
|
|
1.0
|
Type of gate material, used for analytical model only
LEVEL 4 TPG default=0 where
TPG = 0 al-gate
TPG = 1 gate type same as source-drain diffusion
TPG = -1 fate type opposite to source-drain diffusion
|
|
VTO (VT)
|
V
|
|
Zero-bias threshold voltage
|
Calculating PHI, GAMMA, and VTO
The model parameters PHI, GAMMA, and VTO are used in threshold voltage calculations. If these parameters are not user-specified, they are calculated as follows, except for the LEVEL 5 model.
If PHI is not specified, then,
If GAMMA is not specified, then,
The energy gap, eg, and intrinsic carrier concentration for the above equations are determined by:
where,
If VTO is not specified, then for Al-Gate (TPG=0), the work function 
ms is determined by:
where type is +1 for n-channel and -1 for p-channel.
For Poly-Gate (TPG=±1), the work function is determined by:
If the model parameter NGATE is not specified,
Otherwise,
Then VTO voltage is determined by:
where,
If VTO is specified, then,
Star-Hspice Manual - Release 2001.2 - June 2001
