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.