Characterization of the Over-Erase Algorithm in FN/FN embedded NOR Flash arrays

The over-erase algorithm is the state of the art procedure exploited in NOR Flash architectures to increase the memory reliability against the over-erase phenomenon mainly caused by either fast or erratic bits. In FN/FN architectures, since the soft-programming operation involved in the algorithm uses the same physical mechanism of the erase operation, its execution potentially triggers additional failures. In this paper, a detailed characterization of the soft-programming failures is provided by categorizing their statistical occurrence in order to capture their relationship with the failures exposed after the execution of the algorithm. A model of the failure rate is then derived to provide a rough guideline for over-erase algorithm optimization in terms of performance and reliability.