[SOLVED] Vth relationship with technologies

[kenambo]

Hi all

what is the relationship of Vth with respect to technology scaling.?

As i know Vth is entirely depends on the doping of the substrate.

Is there any dependence regarding scaling.

Thanks

 

[dick_freebird]

VT is what you make it. One conscious choice made in
low voltage technologies is to reduce VT (who wants
a 1V VT with a 1V supply?) and this leads to more concern
about subthreshold leakage and its control.

VT is not necessarily simply substrate / well doping. Many
low voltage flows offer multiple VTs so that one size does
not have to fit all, when some sections want speed and
some, just to not eat a bunch of idle supply current. A
VT adjust implant (pair) would be seen in the layers if
the flow supports this.

 

[Dominik Przyborowski]

The decananometer processes has also pocket/halo implants which strongly modifying Vth.

 

[kenambo]

Ok fine.

consider a 180nM process what is Vth relationship with device length?

And theoretically what happens to Vth when lenth varies?

and i know vth and leakage is correlated. So what are these halo implants?

thanks

 

[Dominik Przyborowski]

Halo implants are additional the opposite type implants added close to source/drain region to avoid threshold voltage decreasing with decreasing channel length. It start to be used in some 130nm nodes and beyond. Now in older processes the channel doping profile is formed to prevent decreasing Vth with smaller L and for almost all current available technologies the relation of Vth is decreasing function of channel length with saturation for L equal a few Lmin.

Of course for short channel fets a DIBL effect also changing the Vth.

 

[dick_freebird]

I've seen halo features even up at 250nm (SOI). I would
not care to make a quantitative prediction about short
channel (or, because everybody has to engineer the hell
out of their devices and then goes over the top) reverse
short channel effects. This is really not a useful question
for anyone but the actual foundry; details matter, and
then only to someone willing to do your analysis for you.

 

[kenambo]

Hi dominick,

So as far as halo implants are concerned they are used to avoid Vth decrease while decreasing the length ..

Am i right..

So if it is true means, how Vth reduces when we increase the Length of the device in a same tecnology..

For example.. let us assume W and Vgs is constant , for l = 40nm my threshold voltage is 550mV
any for l = 1u , my Threshold is 500mV

Can you please justify it?

thanks..

 

[dick_freebird]

That would be reverse short channel effect (VT decrease
with increasing L).

Empirical modeling types will just fit the behavior using
the knobs they've got in the compact model.

The halo implants at long channel do not overlap the
majority of the channel. At short channel they may overlap
and sum somewhat, adding to the body doping of the
entire channel (not just the critical drain region where
the halo is supposed to do its thing (fight DIBL)).