awg
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I agree with the other posters, however, there is another thing that occurs when you subject EEPROMs to radiation - the charge on the floating gate can be degraded.
Radiation has a certain amount of energy associated with it (the amount depends on a few factors that escape me at the moment.) Well, this small amount - on the order of a few eV is enough to cause tunneling and thus affect the charge. It sounds like this could have also led to your part now working at a lower temperature only, in addition to Vt threshold changes, etc. The eV level required to upset the floating-gate charge is based on the tunnel oxide thickness; the thinner the oxide, the less energy required to affect the floating gate charge.
We generally don't our EEPROMs to be irradiated...
Joe W.
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