Hi all,
An article in the online edition of _IEEE Spectrum_, available at
<http://www.spectrum.ieee.org/publicfeature/dec00/sup.html>, discusses
the enormous progress that has been made on a device that I've been
reading about since I was in grade school: Josephson junctions. This is
another one of those technologies that's been "just short" of
commercialization, but a second generation of these devices looks like
solving many of the problems with constructing practical circuits that
first-generation devices encountered. The article predicts mainstream
commercial products within five years.
Josephson junctions are essentially superconducting rings broken by a
very thin insulating barrier. These can store and manipulate magnetic
flux, and can thus be used for digital computation. The new developments
concern radically new ways of using these junctions that permit
high-density integrated circuits to be fabricated.
Complex integrated circuits have been fabricated that run at 20 GHz -- a
digital signal processor is one example -- and single flip-flops have
been run at over 750 GHz. Unlike conventional semiconductor devices,
power requirements do not increase significantly with increased clock
speeds. The technology lends itself to extremely accurate
analog-to-digital conversion, opening many more possibilities for
wireless data transmission.
Second-generation Josephson junction, or rapid single-flux quantum
(RSFQ), devices can be fabricated very inexpensively with
photolithographic techniques that are now essentially obsolete, using 1
um linewidths that haven't been seen in microprocessor fabrication for
almost a decade. There are no known physical barriers to using line
widths less than a tenth of this. The article mentions 100,000-device
chips less than 0.5cm^2 dissipating 0.25W and running at 250GHz.
Of course, the downside is the requirement for cryogenic cooling: RSFQ
devices operate at a temperature of 5K (about -450 degrees F or -268 C).
However, because the devices are so small, this requirement can be met
with very small cryocoolers that do not require liquid helium; the
article mentions off-the-shelf systems available today that cost under
$20,000, fit in the lower half of a standard 48cm equipment rack, and
require maintenance only once every 24 months. Obviously, this isn't PC
territory, but it's certainly comfortable for servers.
-- Bruce
--------------------------------------------------------------------------
Bruce Toback Tel: (602) 996-8601| My candle burns at both ends;
OPT, Inc. (800) 858-4507| It will not last the night;
11801 N. Tatum Blvd. Ste. 142 | But ah, my foes, and oh, my friends -
Phoenix AZ 85028 | It gives a lovely light.
btoback AT optc.com | -- Edna St. Vincent Millay
Mail sent to [log in to unmask] will be inspected for a
fee of US$250. Mailing to said address constitutes agreement to
pay, including collection costs.
|
