How do we define VDS,sat for short-channel MOSFETs? On page 297 we see
Eq. 9.54 as Vov = VGS - VTHN is not = VDS,sat. I don't understand this?
As seen in Fig. 6.11 VDS,sat is simply the drain to source voltage on
the border between the saturation and triode regions in either long or
short channel devices (note that no deep thought is required.) In long-
channel devices VDS,sat happens to be the same as the overdrive voltage.
In short-channel devices it's not (as seen in Eq. 9.54).
Q: How do I determine VDS,sat in a nanometer process though?
Ans: You look at the ID-VDS curves, Fig. 9.31 for example. This is why we
use the plots for design in nanometer processes and not equations!
Note don't spend time looking for a simple equation (like VDS,sat = VGS - VTHN).
For example, VTHN is not a constant but rather a function of VDS, VSB, etc.
Another question: Are the short channel effects present for only very small L
transistors? If I choose L = 2 um in 180 nm technology, do the short-channel
effects still exist?
See the previous email response (number 7).