Discussion:
MEMS oscillators
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Adrian Godwin
2018-10-30 10:50:12 UTC
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How sensitive to atmospheric environment are MEMs oscillators ?

https://www.reddit.com/r/sysadmin/comments/9si6r9/postmortem_mri_disables_every_ios_device_in/


It gets closer to time-nuts territory in the earlier discussion - see
captaincool's contribution some way down :

https://www.reddit.com/r/sysadmin/comments/9mk2o7/mri_disabled_every_ios_device_in_facility/
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jimlux
2018-10-30 12:44:14 UTC
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Post by Adrian Godwin
How sensitive to atmospheric environment are MEMs oscillators ?
https://www.reddit.com/r/sysadmin/comments/9si6r9/postmortem_mri_disables_every_ios_device_in/
It gets closer to time-nuts territory in the earlier discussion - see
https://www.reddit.com/r/sysadmin/comments/9mk2o7/mri_disabled_every_ios_device_in_facility/
The helium leak sounds a bit sketchy, especially when you're talking
about a system that has large RF and magnetic fields. Why would a MEMS
resonator care about what gas it is surrounded by.

That said, I recall someone telling me about problems with early MEMS RF
switches and needing some trace amount of water vapor to make them work
- work fine on the bench, but them into thermal vacuum testing and after
some amount of time they stop working, as the H2O diffuses out of the
(non-hermetic) packages.



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Bob kb8tq
2018-10-30 13:53:30 UTC
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Hi

More than sketchy, it sounds a bit crazy.

MEMS are not a lot different than any IC in that you can get packaging issues. Put them
in a high pressure “bomb” test and you will see the same issues that you do on any IC.
The gotcha is that an IC is die coated and a MEMS oscillator likely is not. They should
get packaged accordingly (= a low leakage package).

Getting anything into a package at normal atmospheric pressure … not so much.

Bob
Post by Adrian Godwin
How sensitive to atmospheric environment are MEMs oscillators ?
https://www.reddit.com/r/sysadmin/comments/9si6r9/postmortem_mri_disables_every_ios_device_in/
It gets closer to time-nuts territory in the earlier discussion - see
https://www.reddit.com/r/sysadmin/comments/9mk2o7/mri_disabled_every_ios_device_in_facility/
The helium leak sounds a bit sketchy, especially when you're talking about a system that has large RF and magnetic fields. Why would a MEMS resonator care about what gas it is surrounded by.
That said, I recall someone telling me about problems with early MEMS RF switches and needing some trace amount of water vapor to make them work - work fine on the bench, but them into thermal vacuum testing and after some amount of time they stop working, as the H2O diffuses out of the (non-hermetic) packages.
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Paul Alfille
2018-10-30 14:07:24 UTC
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Helium is lower density, a feature used to reduce turbulence in patients
with airway stenosis. Perhaps the lower density changes the resonant
frequency of the MEMS oscillators. (Though the penetration and
concentration are rather suspect in this description.)

Paul Alfille
Post by Bob kb8tq
Hi
More than sketchy, it sounds a bit crazy.
MEMS are not a lot different than any IC in that you can get packaging issues. Put them
in a high pressure “bomb” test and you will see the same issues that you do on any IC.
The gotcha is that an IC is die coated and a MEMS oscillator likely is not. They should
get packaged accordingly (= a low leakage package).
Getting anything into a package at normal atmospheric pressure … not so much.
Bob
Post by jimlux
Post by Adrian Godwin
How sensitive to atmospheric environment are MEMs oscillators ?
https://www.reddit.com/r/sysadmin/comments/9si6r9/postmortem_mri_disables_every_ios_device_in/
Post by jimlux
Post by Adrian Godwin
It gets closer to time-nuts territory in the earlier discussion - see
https://www.reddit.com/r/sysadmin/comments/9mk2o7/mri_disabled_every_ios_device_in_facility/
Post by jimlux
The helium leak sounds a bit sketchy, especially when you're talking
about a system that has large RF and magnetic fields. Why would a MEMS
resonator care about what gas it is surrounded by.
Post by jimlux
That said, I recall someone telling me about problems with early MEMS RF
switches and needing some trace amount of water vapor to make them work -
work fine on the bench, but them into thermal vacuum testing and after some
amount of time they stop working, as the H2O diffuses out of the
(non-hermetic) packages.
Post by jimlux
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Post by jimlux
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