John Hearns wrote:
BTW, re the discussion on processor frequency scaling,
what finally did happen to Emitter Coupled Logic and gallium arsenide?
GaAs ... the material of the future. And always will be.
As a cub high energy physicist, I devoted many hours to learning about
ECL and Fastbus - it was (still is) the fastest switching technology,
therefore the Fastbus standard was based around it. Ditched now I think
for VMEbus systems.
Sigh. Those big old crates were a reaql sight.
I wonder out loud if any exotic semiconductor plus ECL will be revived
in the future.
The problems with GaAs are economic, and perceived safety (not to
mention the technological problem of controlling defects in the material
... EL2 was/is a fun one). Economic, as Silicon has a huge installed
base, and you can't simply switch materials in the same foundery ...
different materials do require different processes and machines ...
which increases costs. There are no economies of scale for GaAs.
Perceived safety as the high temperature grown GaAs required 5+
atmospheres of Arsenic gas at ~500C or thereabouts (quoting from memory)
to maintain an equilibrated growth. Not too many people want to live
near such a thing. There is a low temperature grown GaAs, though this
has a number of defects you have to get better control over for devices.
Its a shame, as GaAs is a direct bandgap, and is therefore much *faster*
than Si at switching (no phonon mediation of valence<->conduction band
needed, so fewer rate limiting steps are needed). I've heard estimates
(12 years ago) of 3 order of magnitude faster transistors (estimated).
Joe
--
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