Teflon is great for dielectric absorption and insulation, but its temperature coefficient is ghastly. It goes through a phase change right around room temp.
It's hard to find teflon caps above about 50 pF.
The second ADC that I designed was a dual-slope, and in ignorance I used a mylar cap as the integrator. It was terrible, several per cent error. A tech fixed it for me.
C0Gs are usually good. SiO2 (MIS) caps are superb, but are usually found inside chips. There are some for sale as discretes.
Vacuum capacitors have pretty low DA.
We need a high-K vacuum.
I'd be very surprised if he didn't have to in any event, since the sorts of relaxation processes that give rise to soakage must have fairly dramatic temperature dependences.
Cheers
Phil Hobbs
I found this yesterday, but couldn't really see any prices or specs...
It looks bigger than 50 pF :^)
George h.
If you make the plates out of neutronium, that might help out.
As a bonus, it may be a high temperature superconductor, which is nice.
As a downside, it'll have lower energy storage capacity -- y'know, too much and the whole thing collapses. Pesky, that.
Tim
How do the plates change the permativity of the dielectric?
The empty space between the plates would be intensely curved (high gravitational field), and the geometry non-Euclidian.
Sadly, empty space next to neutronium isn't going to stay empty long - it won't last any longer than the neutronium which doesn't seem to be stable anywhere except inside a star with at least 20% of mass of the sun.
Not really. It would probably explode before you could get the bits close enough together to collapse.
Some sort of multiple-parallel-plate MEMS vacuum cap should be possible, with really tiny plate spacing. But MIS SiO2 caps are really good. Those are used inside ICs to make capacitive ADCs and such.
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