Reliability of erasing operation in NOR-Flash memories

The erase operation in NOR-Flash memories intrinsically gives rise to a wide threshold voltage distribution causing various reliability issues: read margin reduction; increase of total bitline leakage current and electrical stress during reading and programming. This paper will address and review the erasing operation by analyzing the causes, the reliability issues and the possible solutions of the erased threshold voltage distribution width, the presence of ultrafast bits, the erratic erase phenomenon, the presence of a significant tail (extrinsic behavior) in the erased distribution and the intrinsic oxide degradation during cycling (oxide aging).