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Cryogenic sorta-HV

Hi, all:-

There's a fair bit of info out there on operation at ~4K of electronics, however most of it is at a few volts.

Anyone have any pointers or experience dealing with MOSFETs handling ~100V?

There's a negative tempco of breakdown voltage to deal with and some other disturbing stuff that goes on that's perhaps related to impact ionization at very low temperatures.

When it comes down to it, I'll just dunk some stuff and try it, but I'd like to get frozen ducks in a row before burning off helium.

Thanks in advance,

Reply to
Spehro Pefhany
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Start by taking things down to 77K and doing some measurements, then extrapolating a bit? LN2 is cheaper than LHe2, I assume.

At those temperatures you may run into interesting quantum effects -- do your FET leads go superconducting at those temperatures, or are they too mundane?

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

Yes it is. It's got much higher heat capacity so the thermal shock more, and there is a bunch of weirdness between the two temperature, but probably worth the double dip.

Most normal materials (except Pb, Nb and Hg) don't go superconducting until lower temperatures than 4K and/or extreme pressure, if at all.

For some reason, copper aluminum and silver don't ever seem to become superconductors, even under high pressure.

Ordinary diodes do weird things like oscillate, carriers freeze out of lightly doped bipolar parts etc.

There are a bunch of new possibilities such as GaN and SiC parts.. possibly nobody has done much work with them yet.

Best regards, Spehro Pefhany

Reply to
Spehro Pefhany

I've heard of jfets and gaasfets being used at helium temps. Bipolars go nuts below about 20K.

One of my customers does cryo electronics for NMR, but they go down to about

40K, so I couldn't get much helpful info out of them. 
--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation
Reply to
John Larkin

Pure tin superconducts at 3.77 K; there's some reason to be concerned with solder (Sn Ag Cu alloy).

Reply to
whit3rd

3.722K according to my info.

What's the reason for concern?

As long as part of a loop is normal, the rest doesn't matter.

--sp

Reply to
Spehro Pefhany

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