MESFETs for cryogenic amplifier

[navarromoral]

Hello,

I am interested in the design of low noise amplifiers intended for cryogenic use at medium frequencies (10MHz). I have found several PhD. thesis where transistors NE25139 or CF739 are used successfully. My problem is I can´t find any model for these transistors to perform simulations, has anybody simulated one of those?
BTW if someone knows a replacement, I am also very interested.

Thank you very much!
Santi

 

[dick_freebird]

It would be kind of surprising that in this day, there is no
company making these FETs and still not offering a SPICE
model, nor any of the various industrial SPICEs (e.g. PSPICE,
LTSpice et al). Maybe you need to dig deeper, research
the equivalents on some parts database and look at the
alternate sources for web site support>models collateral.
Digi-Key, Mouser, Allied / Element14, all of these have tons
of FETs to rake through and likely something that's a match.

Failing that you could rip off a MESFET model that is only
roughly right and refit its params to match what you can
find on the component datasheets.

You want to take some care about what a PhD thesis calls
"success" and what a valued product in a competitive
market situation needs to succeed, if you are in the latter
environment.

But JFETs and MESFETs are suitable for low noise apps
as long as you keep conduction away from the surface
(i.e. Vgs<0 for a NFET). You also need enough source
and channel doping that freeze-out is not an issue, this
is where "been there, it worked" has value - the manufacturers
are almost certainly, none of them, interested in supporting
cryo applications. At some temperature many transistors
deviate from what classical temperature behaviors you'd
expect. Worse, the wider the bandgap, so don't get too
excited about embracing RF GaN MESFETs without pulling
some curves from the dewar first.

 

[D.A.(Tony)Stewart]

Unless you get these in ceramic, I wouldn't hold my breath on how long they will work for cryo temperatures in a plastic sealed case.

That being said, I was surprised once when asked to test a hard disk drive to see if it would fly ( 1um) at -40'C and complete power on self test ... for the military. The bearings squealed a bit, but it worked. ( when tried once or twice)

We have also tried cold-spray on plastic case packages which often are only rated to 0'C in spite of significant improvements over the decades in epoxy seals.

With sufficient molecules of H2O migrating past the plastic seal interface, when frozen, shear stress results in sudden death of the chip.

 

[navarromoral]

Thank you very much for your reply. I know both transistor I mentioned work at cryo temperatures but I still have not been able to get a model...

Thanks