Hallo Erik,

may be my respond does not answer your question.

During 'write' and 'erase' procedure extremely high electric fields are applied to memory cell. Tunneling process needs this high electric field strength. Only by this a sufficient number of electrons can be pushed onto insulated gate or removed from. This extremely high electric field strength is heavily stressing the whole silicon crystal with it's many doped areas, and is highly determining 'life time' of memory cell. Applied electrical field strength is so high, that even memory cells in the environment are affected and can be damaged.

Effect of extreme high electric field strength is mostly a wandering of doping ions or other charged particles into highly isolating layer surrounding gate of memory cell. So, some unpredictable path of leakage current can be fabricated, making any further 'write' or 'erase' procedures impossible and making the gate of memory cell uncapable of holding charge for longer periods. Means, 'endurance' and 'data retention' are affected.

So, in most cases, a memory cell which undergoed a big number of 'write' or 'erase' cycles cannot be expected to show a predictable behaviour at 'end' of lifetime.

Bye,
Kai