A reliable bi-polarity write/erase technology in flash EEPROMs

The authors describe a technology for scaling down the flash E²PROM cell, which has a conventional self-aligned double poly-Si stacked structure. It is clarified experimentally that a flash memory cell written and erased by Fowler-Nordheim (F-N) tunneling has ten times the retention time of the conventional cell, which is written by channel-hot-electron (CHE) injection and erased by F-N tunneling. This difference of data retentivity between these two write/erase (W/E) technologies is due to decreasing the thin gate oxide leakage current by bi-polarity F-N tunneling stress. This improvement in data retention becomes more pronounced as the gate oxide thickness decreases. Therefore, a bipolarity F-N tunneling W/E technology, which enables a flash E²PROM cell to scale down its oxide thickness, shows promise as a key technology for realizing 16 Mb flash E²PROMs and beyond.