[oasisaimlessly]

MEMS oscillators do use a vacuum, and that's why they're susceptible to helium. A helium atom is tiny compared to an oxygen or nitrogen atom, and can leak through many otherwise-perfect seals.

So, a (badly-designed) MEMS oscillator is basically a region of vacuum enclosed by a membrane that only helium can permeate. Of course exposing it to helium is going to permanently change its behavior! Once the helium gets in, there's no reason for it to leave, due to the vastly higher atmospheric pressure outside.

[fuzzfactor]

Very interesting. Good info about both the gyroscopes and oscillators. I didn't know that much progress had been made.

I remember when MEMS started getting capable of micro fluid handling, but wasn't aware of what they were doing with "lack of fluid" :)

Really bringing the little vacuum chambers out of the big vacuum chamber and onto the street.

Over the decades I have often thought about doing something like that, but not really micro.

Now I'm suspicious about something I hadn't considered before at a previous employer's chem lab. Last month when they called me back in, there was inconsistent oscillation being applied (sometimes not) to a key analog sensor on one instrument which is about the same vintage as the iPhone 6 where the problem showed up from the early MEMS oscillators. These instruments have been there for over a decade and it may be some other electronic problem, but this does coincide with a couple additional gas analyzers they brought in a few months ago which are now wasting about 5x more helium than I was using when I was controlling it. Exhausting into one lab, but not having a completely isolated ventilation system.

Now I know something to try next time and that's not even why they called me in this time.

This could actually be one of those problems that shows up intermittently depending on which way the "wind" blows ;)

Sometimes the best way to fix things is to wait until you're smarter :0

Thanks to all for very valuable info and links.