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Compact Models for Small Geometry MOSFETs
5.5 Summary
This chapter presents compact MOSFET models for small geometry devices.
In order to develop accurate small geometry compact model, the different
structural and physical effects are modeled in device threshold voltage. First
of all, the nonuniform substrate doping is modeled in device threshold voltage. Then the model for small geometry effects such as short channel effect,
reverse short channel effect, narrow width and reverse-NWEs are included
in the threshold voltage model. In this chapter, the accurate mobility model
is derived to account for the effect of high gate bias on device performance.
With accurate mobility model, the regional drain current models for the
linear and saturation regions are developed to model high lateral electric
field and velocity saturation due to high drain bias. Finally, the compact
models for hot carrier–induced substrate current for MOSFETs devices are
presented.
Exercises
5.1 Consider an nMOSFET device with channel doping concentration
N a = 1 × 10 18 cm −3 and T ox = 3 nm. Assume Q f = 0, V sb = 0, and n+
degenerately doped poly gate.
a. Calculate the value of long channel threshold voltage V th0 .
b. Derive the expressions for K1 and K2 in terms of the channel and
substrate body effect coefficients and an intermediate substrate bias.
Gate
Igd
Igs
Igcs
Body
Source
Drain
I gcd
Igb
FIGURE 5.24
Gate current model: different components of gate tunneling current in nanometer-scale
MOSFETs.
Compact Models for Small Geometry MOSFETs
5.5 Summary
This chapter presents compact MOSFET models for small geometry devices.
In order to develop accurate small geometry compact model, the different
structural and physical effects are modeled in device threshold voltage. First
of all, the nonuniform substrate doping is modeled in device threshold voltage. Then the model for small geometry effects such as short channel effect,
reverse short channel effect, narrow width and reverse-NWEs are included
in the threshold voltage model. In this chapter, the accurate mobility model
is derived to account for the effect of high gate bias on device performance.
With accurate mobility model, the regional drain current models for the
linear and saturation regions are developed to model high lateral electric
field and velocity saturation due to high drain bias. Finally, the compact
models for hot carrier–induced substrate current for MOSFETs devices are
presented.
Exercises
5.1 Consider an nMOSFET device with channel doping concentration
N a = 1 × 10 18 cm −3 and T ox = 3 nm. Assume Q f = 0, V sb = 0, and n+
degenerately doped poly gate.
a. Calculate the value of long channel threshold voltage V th0 .
b. Derive the expressions for K1 and K2 in terms of the channel and
substrate body effect coefficients and an intermediate substrate bias.
Gate
Igd
Igs
Igcs
Body
Source
Drain
I gcd
Igb
FIGURE 5.24
Gate current model: different components of gate tunneling current in nanometer-scale
MOSFETs.