Still lower noise radio astronomy (was: low-noise amplifiers for radio astronomy )

In article ,
"John (Liberty) Bell" writes:
With a reasonable sized yield of good room temperature chips,
one might then find a smaller but still reasonable yield of cryogenic
temperature functional chips, within the same batch.

Cryo-CMOS fab lines exist already; they were used to produce the
multiplexers for Spitzer Space Telescope detectors as well as ground-
based infrared detectors used all over the world. No prizes for
guessing who the really big customer is. I've never seen exact cost
figures, but my impression is that cryo-CMOS used to be not
drastically more expensive than standard CMOS... maybe a factor of
two, but not ten. But this could easily have changed if standard
CMOS prices have come down in the last few years, and as I say, this
is just an impression, not actual knowledge.

I don't know whether CMOS produced on standard fab lines would work
or not at cryogenic temperatures. My _guess_ would be probably yes
down to 30 K, probably no below that. (A lot of properties of
silicon change drastically between 25 and 30 K.) But this is just a
guess.

whether FETs that fail at low temperatures do so catastrophically,
or if they start working again when warmed.

The latter, usually. Catastrophic failures occur but are rare. They
are probably more likely in resistors than in FETs, not that I have
seen enough catastrophic failures in any components to make a valid
statistical sample.

If you want a quick test, just dip your parts into liquid nitrogen.
A welding supply company will sell you all you want at pennies per
liter. You can store the stuff temporarily in an ordinary vacuum
bottle, but use the stainless steel ones. The glass ones can fail
catastrophically. (I do have experience with that! There are glass
vacuum bottles designed for holding cryogens, but you won't find them
at your local drugstore.) And don't screw the lid on too tightly.

Of course as I write above, parts that work fine at 77 K won't
necessarily work at all at 15 K or below.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
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