N-drift doping concentration has important contribution
in determining the breakdown voltage and on-resistance
of the device. It should be well considered because
higher N- drift doping concentration can minimize the
on-resistance of the device, but also lowering breakdown
voltage of the device that expected to be high. It also has
a proportional relationship with threshold voltage degradation caused by hot carrier injection. So the
variation of N-drift doping concentration can be used to
optimize the VDMOS transistor performance