Strain engineering which we will see later on to increase mobility and even
new device structures. there are several new device structures.
I will just show you a couple. One is the ultra thin body on SOI.
SOI I remind you stands for silicon on insulator.
And it looks like this. You have a silicone substrate, an oxide
on top of it and you have a very thin body transistor.
This is the source, this is the body and this is the drain.
And with enough gate voltage here you can deplete the entire body.
Now because you don't have a large body here, it, it can be shown you have fewer
effects with leakage. You have no problem with floating bodies
and things like that. And, this is built on a ultra thin SOI
wafer, which is, somewhat more expensive than a normal wafer, but you achieve
reduced short channel effects. You limit the effect to the degree to
which the source and drain can effect what happens to the channel.
Of a more widely advertised process is the Tri-gate process which a variation of
the Fin, FinFET process. It's currently used by Intel's 22
nanometer technology. And in ops doc form it looks like this.
This is the channel in three dimensions and you have a gate that surrounds the
channel on three sides. The source and drain are thicker here in
order to make contact into them. But, the main channel is this one.
Because now, you surround the device on three sides, you keep better control of
the channel, and you reduce short channel effects.
I remind you, when we discussed charge sharing in particular, we talked about
the fact that the gate competes with a source in the drain In keeping control of
the channel. Here, since the gate hugs the channel in
this way, it gives better control on the channel and the corresponding control of
source and drain on the channel is weaker.
So you have reduced short channel effects this way.
There are many variation, several variations of this structure.
In both of these structures, the channel is fully depleted.
So we have seen in this lecture, a short summary of the scaling process, that used
to carry us from generation to generation years ago.
And, a short, a brief summary of how things are done today in order to produce
high performance devices with very small dimensions.
At this point we have finished our small dimension effects lectures.
Starting next time, we will be talking about CAD modelling.
How all of this can be incorporated into CAD models, and what makes CAD models
good or bad.