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C90FL Flash erase operation

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C90FL Flash erase operation

C90FL Flash erase operation consists of multiple steps as shown in Figure 1 which is

implemented by the C90FL Flash memory controller hardware. First, all bits in the selected

Flash block(s) are programmed in order to verify the level that allows the erase function to

start at consistent state. Then the erase step deletes all bits. Since the erase is a bulk

operation in which an erase pulse moves all the bits in a Flash block, some bits are over-

erased, for example, under the compaction of check up or under a software program of

verify level. At the compaction step the over-erased columns are compacted back to reduce

column leakage. And finally all the bits below software program verify level are

reprogrammed with very low gate, in order to avoid overshoot of erase verify level for any

bits. As a result, when an erase operation is completed, all the bits in the selected blocks

have their threshold voltage within a pre-defined window, between erase verify level and

software program verify level.

Figure 1. C90FL Flash erase operation flow