Flash Memory – Understanding Failure Modes of FLASH Memory


What is the failure mode of flash memory? I've got some chips rated for 10,000 cycles – what happens after 10k cycles? Do the chips stop writing properly, do you get read errors, etc.? Does it also happen to EEPROMs?

Best Answer

Flash memory degrades as a function of the number of write-erase cycles it is subjected to. Essentially the dielectric structure of the memory cell degrades and becomes unable to maintain a 'low' state. (Think of a N-channel MOSFET - a high on the gate turns the device on, which makes the drain-source resistance low. If the gate is damaged, the drain-source channel can never be established.)

There is often a mechanism to 'mask' these bad blocks once they're identified (usually by a verify operation failing after a write) preventing them from being used - a bad block table, essentially.

See here and here for more details on the physics of it all.