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Electrochemistry in diodes?!

Hi,

I'm doing some diode research, and would like to know of any possible DC voltages produced in the diode due to electrochemical reactions. It's a palladium-silicide diode, part number SMS7630, but also has gold. Over time the atoms could migrate. The SMS7630 is a microwave diode used for small signals. It is not terribly uncommon for the DC voltages produced by small AC signal rectification from such ZBD's (zero bias diodes) to be as low as one microvolt DC. The SMS7630 zero bias resistance is ~ 5400 ohms. Even the slightest *possible* electrochemical reaction is important-- e.g., diode square law detectors.

It seems possible, for example, for silicon atoms migrating some distance into the palladium side to bond with palladium atoms that previously had no such bond-- diffusion.

I would like to build an experiment to measure this DC voltage produced by electrochemical reactions. Does anyone have any idea what DC voltages I could expect? Nano volts, pico volts, etc. The DC voltage produced by a lead acid battery is temperature dependent, where the electrochemical DC voltage decreases with an increase in temperature; -0.022V/=B0C-- ref:

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tery#Electrochemistry

Therefore, how about measuring the change in DC voltage produced by the SMS7630 at say 60F versus 90F? I have a two layer metal shield system (small and medium shields) and an electrometer that produces a few femto amps bias current. It could detect down to 0.5uV DC, but if there's no appreciable chance of these diodes producing up to 0.5uV DC from electrochemical reactions then it could save a lot of research time.

Please see page 3 of this pdf for details on this diodes structure:

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Regards, Paul

Reply to
Paul
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Non-detectable directly. Your only hope is measuring conduction carrier density over time.

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This does not happen over decades, unless they experience high temperatures for extended periods.

I'd plan on looking for an secular increase in applied voltage to drive a given current, or such a decrease in current resulting from an applied voltage.

David A. Smith

Reply to
dlzc

Thanks for reply David. If I understand you correctly, then that's my thought as well; i.e., that the DC voltage produced by this diodes electrochemical reactions would be undetectable. The junction diffusion occurring on the order of decades sounds significant. To all intents and purposes, I'm guessing that would amount to *zero* DC volts. Hmmm, maybe it's a few femto volts, lol. I had no idea commercial diodes diffused at such a slow rate.

Even if it diffused at a faster rate, I'd imagine the electrochemical potentials produced from palladium and silicon would be small, perhaps less than one microvolt.

Correct me if I'm wrong, you're suggesting the electrochemical DC voltage is too small to be directly measured, so it's better to measure the long term change in resistance due to diffusion? That's an interested method that should work. It's a bit time consuming though, waiting for the resistance to change, but at least doable. Although it would be interesting to know what the electrochemical DC voltage would be in such a diode.

Many Thanks, Paul

Reply to
Paul

You will have some sort of "thermoelectric junction" voltage, as you would with a "thermopile", but there are some constraints on the conductors you would use between the two junctions.

You can google: dopant diffusion semiconductor ... to get a better feel for this. Until you get up near something like 200 degC, diffusion is near zero for all intents and purposes.

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You can try using two devices at different temperatures, with identical wiring between them. See if you measure a potential difference. But diffusion will be a *very* small signal.

Let's see what the other folks in the groups you posted to think...

David A. Smith

Reply to
dlzc

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Reply to
Marvin

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