> > > wonder how flash drives hold up over time

This is probably largely academic but ......

In a PIC specifically, is the relationship between endurance and
retention simply the state of the cell oxide ?

Flash/EEPROM retention is > 40 years (although MChip say
they test for 200 years retention @ 55degC) and endurance
is > 100,000 writes

So the Flash/EEPROM is written to just once at programming
time, and you might expect some deterioration after 40 years

Can the Flash/EEPROM re-fresh itself before then ( at 35 years ?)
to get another 35 years working life ? After all, "endurance", in
terms of write cycles, has hardly been touched. And I understand
that the retention deterioration is due to oxide breakdown (break-
down time is related to programming/erase voltage), but is that
oxide breakdown reversible (like an electrolytic capacitor) ?

Perhaps not, and refreshing, by applying a high voltage to the cell,
might actually complete the breakdown. Is that what I should infer
from this -

http://www.seas.upenn.edu/~ese570/1244.pdf

There are some PIC applications that might stay in service for
a long time. I've been using the 16F84 since it came out (and
"C" PICs before that), so some of my old stuff out there, which
is still working fine thank you, is get on a bit now. But if I
planned for a device to be in service for, say, 100 years, can
it periodically re-new itself every 35 years to live that long and
more ?

I'm also thinking perhaps of some of these spacecraft (eg Voyager)
that might have a very long life. Do they not use EPROMs of the
day ? If so, what's to stop their programming just fading away - or
are they not expected to retain it anyway and are simply space junk
with some transmitting capability ? Do they have special long-
retention NASA cells ?

Alan ?

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