David Kanter (dkanter.delete@this.realworldtech.com) on November 26, 2013 5:25 pm wrote:
> tarlinian (tarlinian.delete@this.gmail.com) on November 26, 2013 12:50 pm wrote:
> > Eric Bron (eric.bron.delete@this.zvisuel.privatefortest.com) on November 26, 2013 12:21 pm wrote:
> > > > we're still looking at over 2,000 mm^2 just for the eDRAM. That seems ... um ... large?
> > >
> > > that will be around 300 mm^2 per 1 GB "MCDRAM" stacked die in the 2nd slide here :
> > > http://vr-zone.com/articles/xeon-phi-knights-series-continues-landing-2015/64112.html
> > >
> > >
>
> > Based on the data Intel has presented on 22 nm eDRAM presentation
> > the minimum size for 8 billion bits in ~232
> > mm^2. (This is just based on naively multiplying the unit
> > cell size times 8 billion, which is obviously grossly
> > optimistic.) If you take the reported 128 Mbit macro density
> > (17.5 Mbit/mm^2), you get ~457 mm^2. These are obviously
> > large areas, but not grossly unrealistic, especially on what will be a very mature 22 nm >process.
>
> How much cheaper do you think the eDRAM process is? They don't need the whole logic stack
> of 9 metal; they could probably get away with 4 metal layers perhaps another layer for
> the thick upper level metal. How much impact on yield and cost does that have?
>
> David

The upper metal layers are rarely yield killers from my understanding (I don't work in any integration related areas, but I'd guess maybe 1-2% yield improvement, max.) Cost reduction is probably not that much in an accounting sense (outside of actual marginal wafer fab costs) because the upper metal layers is probably done with significantly older equipment that is probably fully depreciated for Intel (especially when you consider their traditional CPU process with only a few layers of dense metal, the wafer cost delta over the SoC process is probably more). That marginal cost is maybe $50 a wafer? (CMP and litho materials are usually the most expensive and they probably aren't any more than $10/wafer per pass. These are pretty wild guesses though.