Normalize to drawn or effective width?

By: carop (carop.delete@this.somewhere.org), February 5, 2015 3:40 pm
Room: Moderated Discussions
David Kanter (dkanter.delete@this.realworldtech.com) on February 5, 2015 12:45 pm wrote:
>
> Yes, I am. I've heard a number of people make the argument that it's better to normalize to Weff,
> but the reasoning doesn't make sense to me (why not calculate leakage normalized to Weff?).
> Moreover, most other companies are not disclosing effective width, so it makes things even harder.
>

With the gate wrapping around the fin, you effectively get higher device width per footprint of the device and for a given device footprint (which is typically set by number of metal tracks you allocate to a given standard cell and how much space is wasted to isolate devices and plug gate contacts) you get higher drive current. The catch is that the higher Ion comes at the price of higher capacitance which Intel is not quoting.

>
> I don't find this argument particularly compelling, in part because I heard it mostly from
> companies that aren't disclosing much about their own FinFET process (e.g., TSMC).
>

I believe it was IBM that suggested active current (Ieff) as a metric of speed in an IEDM paper.

The figure is from the STM FD-SOI N10 paper which was presented at IEDM 2014.

- [13] is Intel@VLSI2012
- [14] is Intel@IEDM2012
- [15] is TSMC@IEDM2013

I included the figure for a quick Intel N22 and TSMC N16 device comparison. No, IBM did not normalize drive current to footprint in their IEDM 2014 SOI FinFET paper either. Intel seems to be the only manufacturer normalizing the drive current of their FinFET devices to footprint. I do not want to argue with that, but this is something to bear in mind when benchmarking.

At N22, Intel used a fin height of about 35nm and fin pitch of 60nm. At N14, they increased fin height to 42nm and dropped fin pitch to 42nm. So the shrink from N22 to N14 increased channel width by 70% but drive current by less than 30% (15% nMOS, 41% pMOS). How do you explain this performance difference then?



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                Normalize to drawn or effective width?David Kanter2015/02/05 12:45 PM
                  Normalize to drawn or effective width?carop2015/02/05 03:40 PM
                    Normalize to drawn or effective width?David Kanter2015/02/06 01:44 PM
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