Characterization of the Over-Erase Algorithm in FN/FN Embedded <sc>nor</sc> Flash Arrays

Abstract

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.

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“…), the Fully Fowler-Nordheim (FN/FN) concept stands out due to its lower energy consumption required in the programming operation and a relative ease of integration for large density products [33]. However, from the pure reliability viewpoint, the erase operation has always been an issue for every NOR Flash technology so far [37]. In the last decades, special emphasis has been put on the reduction of the standard erase failure mechanisms by implementing either proper correction algorithms or failure screening techniques aiming at a memory fail rate reduction below 1 ppm [38].…”