To achieve a certain
for a given device topography and
source/drain doping the channel doping has to be adjusted accordingly.
In modern deep-sub-micron devices the channel doping is determined
by several parameters - depending on the type of channel
engineering - so that the adjustment for
is not unique.
A practical and very robust approach is to define the channel doping
relative to a certain channel doping level
or relative to
one specific implantation dose. This parameter is then varied to
achieve the off-state current, while the other channel profile parameters
(and so the shape of the profile) remain unchanged.
The advantages of this procedure are that it is very robust and in
an optimization it removes one unknown from the set of parameters
but does not interfere in any other way.
Assuming a uniformly doped long-channel device in weak inversion
the off-state current can be written as follows (cf. (A.14)):