transistor question

[Special K]

There is one thing I never quite understood about the saturation region of a long-channel MOSFET (NMOS) - if the channel does not exist anymore near the drain, how is there still current flowing from the source to the drain? None of my textbooks seem to provide an adequate explanation for this.

It makes sense for the short-channel devices, because it is viewed as a velocity saturated region, rather than a channel that doesn't exist at all.

 

[BrownTown]

The additional voltage added to get into the saturation region is seen a a voltage accross the distance from the end of the pinched off channel to the drain, this voltage provied the energy to accelerate the electrons across the P-type region (NMOS). The resistance of the channel is much lower than the resistance between the pinced off point and the drain, so the majority of the voltage is seen across that point. The the farth your drive the MOSFET into saturation the more voltage is seen across the pinch point and the drain which means there is additional force to accelerate the electrons. I guess at some point you would get enough voltage to achieve breakdown, but hopefully that never happens in real life.

Does that sound right? I'm just reading it out of a text book...