Vov vs Vds_sat for short channel devices

[diarmuid]

Hello,

Classically a MOSFET is saturated when Vds > Vgs - Vth ... (Vgs - Vth = vov).

However Ive recently started working on a more modern process where Vds_sat is used to indicate the onset
of saturation and not Vov.

However Vov and Vds_sat are not the same.

Physically I understand that when Vds > Vov the channel is pinched off hence saturated. However I dont
physically understand Vds_sat and why it is different from Vov for small channel devices?

I have seen from previous posts it has something to do with velocity saturation but still dont quite get it.

Any thoughts?

Thanks,

Diarmuid

 

[Dominik Przyborowski]

In Tsividis book about modelling is first order explanation that lower Vdsat is caused by CLM effect. You can check it in chapter 6 of this book.

 

[diarmuid]

Is this the book:

"Operation and Modeling of the MOS Transistor"

... any particular edition?

Txs,

 

[Dominik Przyborowski]

Yes that book. I have a 2nd edition from 1998. At this moment nothing more comes to my mind about this effect. Maybe in ENC, Vittoz book about modelling is something more or in articles from IEEE TED or SSE but You should check it.