Can
I make a device fabricated in a nm process behave like
a long channel device by making L several microns in length
or even longer? I want to make my
devices follow the square-
law equations.
Nanometer
devices are designed to drop the drain-source voltage
across a very small
distance (see pages 144 and 151 in the 3rd
edition concerning dVDS/dXdl).
Increasing the channel length
simply increases the
amount of inverted charge under the gate
oxide adjacent to the
source, Fig. 6.10. Longer channel length
does not
significantly change the width of Xd in Fig. 6.10 and
thus short-channel
effects (e.g., velocity saturation) are still
present.
As
mentioned throughout the book devices fabricated in submicron
CMOS
process do not (even remotely) follow the square-law
equations and that is why
we don’t use them when we design in
nm CMOS processes.