Dual Vt and Multi VT technology

[AdvaRes]

Hi guys,

I'm moving to study dual Vt and Multi VT technology for Low power applications. I have no Idea how can we make such transistors,how they are layouted, how they are used to buid circuits and how do we select the threasholds. I need some progressive material that explain this technology and highlights its advantages.
Any reference/material and even a small advice from you are welcomed.
Thanks in advance.

Cheers,
Advares.

 

[diemilio]

Well, if you have access to some PDK that has nominal, medium and native VT devices (like TSMC 0.25, 0.18, 0.13 etc) I will start by going through the spice models, running characterization simulations and generating layout using Pcells (usually native and medium doped devices have an extra layer to block the deposition of extra dopants used to make VT higher); that way you can get a lot of information and an initial idea of where each type of transistor stands with respect to the others.

diemilio

 

[AdvaRes]

Thanks for replying. Before going to layout, the first thing that I wanna know is the fixing of Vt. Is it fixed by the technology or it is possible to the user of the transistor to change them depending on his requirements ?

As far as I knew dual Vt transistors are used to build circuits that can be High speed or Low power this depends on the Vt selected.(2 modes of operations)
Complex blocks can be constructed with these transistors like flip flops. Do this mean that when we buit circuits using dual Vt transistor that we need to buit a logic to select the mode during the circuit running ?

 

[dick_freebird]

I can only speak in generalities, but I do most of my work in
a process that has 4 VTs for both N and PMOS. From logic to
depletion mode. We start with an intrinsic silicon layer.

You get one increment of VT from whether gate poly is doped
same or counter species to S/D/channel (work function). Another
from raw channel doping.

You need low VT to get speed at low gate overdrive (since
Cload remains fixed and current is square-law, lower VT
yields square-law performance improvement. At the cost of
an exponential subthreshold leakage....

You can get a "poor man's" mixed VT by body control, if
you have twin wells anyway. Not something you'd want to
-have- to do, but a trick for the bag.