The Investigation of Endurance and Data Retention for U-Shaped MTP SONOS Flash Memory

• Main Authors: Wang, Han-Tsun, 王漢樽
• Other Authors: Chung, Steve S.
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/15611013420055927906

碩士 === 國立交通大學 === 電子工程學系 電子研究所 === 102 === Recently, SONOS Memory has become more popular because of its simplicity in structure, process, and scalability by comparing with conventional floating gate cells. In this study, a U-MTP (U-Shaped Multi-Time-Programming) SONOS flash memory with an effective shrinking of the storage node size has been proposed. Nowadays, the requirements of flash memory, low voltage operation, low power consumption, and high speed are becoming increasingly important. By using the conventional programming scheme of channel hot electron injection and erasing scheme of band-to-band tunneling hot hole injection, we can achieve these requirements. But the mismatch of the injected electrons and holes could cause the endurance issue. The gated-diode method has been employed to investigate the cause of window degradation after P/E cycling. The charge loss in nitride based charge trapping memory has also been a major reliability issue. The charge loss mechanisms have been published and uncertain whether the leakage path is along the lateral or vertical direction, since it is impossible to separate the two directions loss for conventional structure. In this paper, we propose a method to investigate the charge loss path. By monitoring the change of RTN and threshold voltage shift after different baking times of the U-MTP structure SONOS, the electron or hole distribution can be identified, and the lateral and vertical retention loss can be separated. It was observed that the vertical leakage is the main cause of retention loss. Finally, we introduce an operation scheme, FBEI (Forward Bias induced Electron Injection) for the cell programming. Comparing to conventional schemes, this FBEI scheme has better endurance and data retention as a result of the better match of programming/erasing scheme and lower nitride/oxide damage.