It is widely accepted and confirmed that the effective mobility depends only on the effective electrical field perpendicular to the silicon surface and is independent of the doping level near the interface [91][47][41]. This dependence reflects at the microscopic level the empirical universal mobility model [99][89]. Accordingly the vertical field dependence of P-channel mobility model can be expressed in the following form:
where 
is the channel mobility, 
is
the vertical field along the channel region, 
, 
and 
are
model parameters. The accuracy of (5.1) has been verified
with 
for a wide range of substrate concentration, oxide thickness
and vertical field [47][41]. As device size is reduced and/or
lateral field is increased, the mobility degradation with the lateral
electrical field has the following relationship [91][17]:
where 
accounts for lateral field dependence of channel
mobility, 
is the horizontal field, 
denotes the saturation
velocity and 
is a model parameter.
