Extrinsic Model

Bias-Independent Variables

Overlap capacitance

Overlap body factor

Normalized overlap body factor ° °°°°°°

Tunneling current density constant (in )

Channel tunneling current density exponential constant (dimensionless)

Overlap tunneling current density exponential constant (dimensionless)

Auxiliary variable of gate current model

The / conduction band offset

Streamlined Surface Potential Approximation

The availability of the surface potential in the overlap regions is essential to the physical modeling of the charge and gate current components. The streamlined analytical approximation of the surface potential excludes the effects of minority carriers and consequently is even simpler and more efficient than the one employed in the channel region.

Let

and

For , proceed in the follow steps

For , compute

The evaluation of and is carefully ordered to avoid over/underflow problems.

Charge Model

Source overlap region charge

Drain overlap region charge

Bulk overlap region charge

Inner fringe charge correction

Outer fringe charge

Terminal charges

where the superscript (i) indicates that the value for that parameter is taken from the SP intrinsic model.

Gate Current Model

Channel contribution

where F _s is the supply function describing the difference of the population of carriers across the oxide at mid-point and is given by

Source-Drain Partition

The partition of the gate current in the channel area into the source and drain is essential for the MOSFET compact modeling, which is accomplished in SPMOS using the symmetrical linearization method.

The drain portion is given by

and the source portion is given by

Source Overlap Region Contribution

The supply function, , describing the difference of the population of carriers across the oxide in the source overlap region, given by

Drain overlap region contribution

The supply function, , describing the difference of the population of carriers across the oxide in the drain overlap region, given by

By setting SW_IGATE to 0 (default value) gate current model is turned off.

Substrate Current Model

The substrate current of MOSFETs due to impact ionization is given by

Total Terminal Currents

The effect of and on the gate, source, drain and body components are as follows

where , and are terminal currents produced by the intrinsic (core) SPMOS model and

The computation of the impact ionization current be turned off by setting the parameter SW_IMPACT to 0 (default) and turned on by setting SW_IMPACT to 1.