By: tarlinian (tarlinian.delete@this.gmail.com), April 22, 2015 5:28 pm
Room: Moderated Discussions
Paul (paclifton.delete@this.gmail.com) on April 22, 2015 5:20 pm wrote:
> I'm pretty much aligned with Otis' views but feel he could be a bit more adamant on some points.
>
> FinFETs, with a fin width less than 10 nm are already quantum well FETs (QWFETs), and
> entered Intel HVM at 22 nm node. Sorry David Kanter, your predictions 4 and 6 predicting
> the advent of QWFETs at 10 nm (Intel) and 7 nm (the rest) are already fails.
>
> Talk of high mobility materials should be discouraged in the nanometer era. Electron transport is now largely
> ballistic and the old mobility concept is barely relevant any longer. Longitudinal and transverse effective
> masses and band degeneracies are more important considerations now and going forward. Sure, mobility and effective
> mass are linked but we need to get away from the old concepts. Even then more prosaic factors such as contact
> resistance / Rsd might well be the over-riding considerations regarding transistor performance.
>
> David Kanter's statement "classic CMOS behaves poorly at supply voltages below 1V, due to the bandgap
> structure of silicon" is hard to parse: "bandgap structure" itself is an ambiguous term not used by
> device physicists - band gap or band structure? Reducing operating voltage has everything to do with
> optimizing the transistor's subthreshold characteristic and its variability and has almost nothing
> to do with band gap or band structure. I don't think there's an argument that semiconductors other
> than silicon can improve the ability of digital circuits to function at lower voltages, unless one
> invokes tunneling source ideas (not mentioned in the article under discussion here). Maybe he means
> that if low voltage operation could be achieved by superior control of the sub-threshold behavior,
> then a different material could perform better at low voltages? That's a lot of coulds...
>
> To repeat Otis "Last year UCSB reported the first III-V devices that are competitive with 22nm Si". That's
> far from compelling! Anyone seen data showing any nanometer scale III-V
> to strained silicon to make the additional huge effort to bring III-Vs to manufacturing worthwhile? RF performance
> metrics (fT, fmax, gm) don't count in digital CMOS which is dominated by interconnect RC.
>
> The balance of probabilities (~90%) points to silicon channels continuing at least up to the 10 nm node.
> Since germanium offers potential improvements for both n-type and p-type, that is perhaps the only realistic
> contender beyond 10 nm. Co-integration of Ge and III-V materials? Likely not ever (<10%).
I pretty much agree with all of this. Parasitics pretty much dominate scaled transistor performance these days. III-V is more likely to find a place in the first non-MOS transistor or for band engineering purposes in the SD to reduce contact resistance. It's my understanding that lowering operating voltage is pretty much limited by subthreshold swing, not insufficient mobility.
> I'm pretty much aligned with Otis' views but feel he could be a bit more adamant on some points.
>
> FinFETs, with a fin width less than 10 nm are already quantum well FETs (QWFETs), and
> entered Intel HVM at 22 nm node. Sorry David Kanter, your predictions 4 and 6 predicting
> the advent of QWFETs at 10 nm (Intel) and 7 nm (the rest) are already fails.
>
> Talk of high mobility materials should be discouraged in the nanometer era. Electron transport is now largely
> ballistic and the old mobility concept is barely relevant any longer. Longitudinal and transverse effective
> masses and band degeneracies are more important considerations now and going forward. Sure, mobility and effective
> mass are linked but we need to get away from the old concepts. Even then more prosaic factors such as contact
> resistance / Rsd might well be the over-riding considerations regarding transistor performance.
>
> David Kanter's statement "classic CMOS behaves poorly at supply voltages below 1V, due to the bandgap
> structure of silicon" is hard to parse: "bandgap structure" itself is an ambiguous term not used by
> device physicists - band gap or band structure? Reducing operating voltage has everything to do with
> optimizing the transistor's subthreshold characteristic and its variability and has almost nothing
> to do with band gap or band structure. I don't think there's an argument that semiconductors other
> than silicon can improve the ability of digital circuits to function at lower voltages, unless one
> invokes tunneling source ideas (not mentioned in the article under discussion here). Maybe he means
> that if low voltage operation could be achieved by superior control of the sub-threshold behavior,
> then a different material could perform better at low voltages? That's a lot of coulds...
>
> To repeat Otis "Last year UCSB reported the first III-V devices that are competitive with 22nm Si". That's
> far from compelling! Anyone seen data showing any nanometer scale III-V
- logic
> to strained silicon to make the additional huge effort to bring III-Vs to manufacturing worthwhile? RF performance
> metrics (fT, fmax, gm) don't count in digital CMOS which is dominated by interconnect RC.
>
> The balance of probabilities (~90%) points to silicon channels continuing at least up to the 10 nm node.
> Since germanium offers potential improvements for both n-type and p-type, that is perhaps the only realistic
> contender beyond 10 nm. Co-integration of Ge and III-V materials? Likely not ever (<10%).
I pretty much agree with all of this. Parasitics pretty much dominate scaled transistor performance these days. III-V is more likely to find a place in the first non-MOS transistor or for band engineering purposes in the SD to reduce contact resistance. It's my understanding that lowering operating voltage is pretty much limited by subthreshold swing, not insufficient mobility.
