Improvement of Multiple-Level Cell Endurance of NAND Flash Memories Using HfO2/ZrO2 Charge Storage Layer
Gang Zhang, Won Jong Yoo · ECS Transactions · 2007
The endurance reliability of multiple-level cell (MLC) using a Si3N4 and high-k HfO2/ZrO2 charge storage layers (CSL) has been investigated. It is found that the base level disturbance, which is resulted from over-erasure or under-erasure, is one of the major degradation factors of the endurance reliability for MLC using a Si3N4 CSL. Programming/erasing (P/E) offsets and thermally-induced base level disturbance significantly limit the Si3N4 MLC endurance reliability over the 104 - 105 P/E cycles. In contrast, HfO2 and ZrO2 CSLs effectively suppress over-erasure, resulting in a strong resistance to P/E offsets or thermally induced base level variation. The MLC endurance reliability is thus effectively improved, and level merge is prevented for 105 P/E cycles.