

IBM demonstrates manufacturing process for creating 100GHZ graphene transistors  - ericb
http://www.technologyreview.com/computing/24482/?a=f

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sparky
It should be pointed out, for the edification of those who are not VLSI
people, that transistors with an f_t of 100GHz are not the same thing as
transistors from which one can build a credible 100GHz processor. f_t is the
input frequency at which the gain through the transistor (biased in the linear
region) is unity (1). This has some relation to how fast the transistor can
switch from 0 to 1 when biased in the saturation region (the way digital logic
works), but it is not 1:1. Likewise, the cycle time of a processor is the
delay of the longest path from one flip-flop or latch (storage element) to
another flip-flop that is expected to take 1 clock cycle. The length of this
path is typically expressed as a multiple of the propagation delay of an
inverter driving 4 other inverters (delay grows with output load, or _fanout_
) (FO4 delays <http://en.wikipedia.org/wiki/FO4>). Typically, high-performance
processor microarchitectures are designed with a 5 (Pentium IV) - 25 (slower
but more power-efficient) FO4 delay critical path. Once you account for clock
skew, jitter, process/temperature variation, etc., your processor frequency is
1 to 2 orders of magnitude lower than your transistors' f_t.

The authors of this paper are careful to point out that their graphene
transistors' f_t is higher than CMOS transistors _of the same gate length_
(240nm), but that is comparing with a ~12-year-old CMOS processes. Modern CMOS
processes are faster than this (for instance, this paper
[http://wwwtw.vub.ac.be/elec/Papers%20on%20web/Papers/DLinten...](http://wwwtw.vub.ac.be/elec/Papers%20on%20web/Papers/DLinten/%5BLinten%5Djournal.pdf)
assumes a 90nm RF CMOS process with an NMOS f_t of 150GHz). Graphene can
certainly catch up once they figure out how to shrink the devices, but it will
take more than productizing the current state-of-the-art to compete with CMOS.

~~~
rjurney
I don't know what you just said, but I'm glad someone is on top of this stuff.
Keep up the good work!

~~~
sparky
Haha sorry about that. The short version is:

1) These graphene transistors are faster than CMOS transistors of the same
size, but CMOS transistors of the same size haven't been used for most
purposes in about a decade. Modern CMOS transistors (the kind used in your
Core 2 Duo or Core i7) are roughly twice as fast.

2) 100GHz transistors => ~1-10 GHz processors, not 100 GHz processors.

~~~
rjurney
Thanks!

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anigbrowl
A more detailed examination of these results here:
[http://arstechnica.com/science/2010/02/graphene-fets-
promise...](http://arstechnica.com/science/2010/02/graphene-fets-
promise-100-ghz-operation.ars)

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rms
100-GHz Transistors from Wafer-Scale Epitaxial Graphene

[http://www.sciencemag.org/cgi/content/abstract/sci;327/5966/...](http://www.sciencemag.org/cgi/content/abstract/sci;327/5966/662?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=graphene&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT)

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pwhelan
When this comes to market, the Von Neumann bottleneck compensation techniques
will become obsolete in a way. However I would love to see how this will speed
up computing in throughput, because this clearly is a major achievement.

~~~
thaumaturgy
I predict that no fewer than 16 meta-languages and API layers will be piled on
top of existing development methodologies, and that all future operating
system graphics will be rendered in fully textured 3D, and that development
will consist of drag-and-drop objects.

So, in short, the end-user experience won't change at all.

(Sorry, I'm a little cranky at the moment. Too many slow applications for no
bloody good reason.)

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rauljara
So, about 10 years until they make their way into pcs. Hopefully hard drives
will be fast enough to keep up with these new processors by then. It'd be
really frustrating to have a computer with a processor that's 50x as fast, but
the computer only runs about 1.5x overall.

~~~
bjelkeman-again
I don't think we will have "hard drives" then. The solid state disks are
starting to come down in price and the speed is nice in comparison. But, yes,
I feel your pain.

~~~
goodgoblin
"'Roads?' Where we're going we don't need 'roads'."

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ntoshev
The longest path in a 100 GHz chip would be 3 mm or a signal travelling at the
speed of light won't have enough time to reach the other endpoint.

~~~
andreyf
<3mm cores might be a great idea - as multicore programming evolves, this may
make possible thousands or millions of cores running at very high clock
speeds.

~~~
wmf
Tilera's "KILL" cores are probably a bit under 3 mm x 3 mm, although I don't
think massive multicore is a good idea for many applications.

<http://gamma.cs.unc.edu/EDGE/SLIDES/agarwal.pdf>

~~~
andreyf
_I don't think massive multicore is a good idea for many applications_

But hey now, that's the problem of the applications, isn't it? There's
probably quite a bit of exciting potential with what you can do with massive
multicore architecture - slide 6 of the presentation you linked to being a
very convincing reason why.

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grinich
Just when you thought Moore's law was broken.

