Investigation of Reliability Issues in a Nitride-Based Localized Charge Storage Flash Memory Cell

• Main Authors: Tsai, Wen-Jer, 蔡文哲
• Other Authors: Wang, Tahui
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/m48b7b

博士 === 國立交通大學 === 電子工程系所 === 93 === Reliability issues in a trapping nitride, localized charge storage flash memory cell are comprehensively investigated in this dissertation. Though the use of a thick bottom oxide and trapping storage concept provides excellent intrinsic charge retention, data loss is found after program/erase (P/E) cycling. Our study shows that trap generation in the bottom oxide during P/E cycling plays a central role. Vt loss in a program-state cell is due to the escape of trapped electrons in the nitride via Frenkel-Poole emission and subsequent oxide trap-assisted tunneling. Interface state annihilation during high-temperature baking would be another source of the observed Vt loss. Vt drift-up in an erase-state cell is the outcome of the tunnel detrapping of cycling-induced positive oxide charges. Furthermore, these positive oxide charges could enhance channel electron tunnel injection and channel-hot-electron injection into the nitride during read operation and thus cause read disturb. Stress-induced interface state growth and transient substrate current are good indicators of cell’s retentivity. All the above regard the charge transport along the vertical direction. On the other hand, lateral migration of excess holes in the trapping nitride dominates the Vt loss in an over-erased cell. Finally, erase speed degradation is studied. It is found that neighboring junction bias would suppress the hot-hole injection efficiency in a nearly punch-through cell. Besides, a cell is hard-to-erase if more electrons reside in the central channel region. Those far electrons are prone to be injected as its neighboring bit is programmed or after P/E cycling.