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<p>This study investigates the improvement in retention characteristic in the reprogram scheme of 3D NAND Flash memory using a physical model. The silicon-oxide-nitride-oxide-silicon (SONOS) structure is employed, and the charge-trap layer (CTL) is analyzed according to trap levels. Traps inside the CTL are categorized into shallow trap levels (STL) and deep trap levels (DTL), with multiple levels sampled according to the distribution of trap concentration as a function of trap depth. Charge loss during the reprogram interval is analytically calculated based on electron emission, and the relative contributions of shallow and deep traps are compared after the second program operation. The results demonstrate that the electron trap distribution shifts toward a higher DTL concentration compared with the one-shot program. Furthermore, a trade-off relationship is proposed, in which retention characteristic can be tuned by adjusting the interval time between two program operations. The results were calibrated against measurement data and validated with technology computer-aided design (TCAD) simulations, and a voltage biasing scheme is proposed to enhance reliability.</p>

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Investigation of retention characteristic improvement in reprogram process based on a physical model for 3D NAND flash memory

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月7日

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  • Jooyoung Lee,
  • Hyungcheol Shin

摘要

This study investigates the improvement in retention characteristic in the reprogram scheme of 3D NAND Flash memory using a physical model. The silicon-oxide-nitride-oxide-silicon (SONOS) structure is employed, and the charge-trap layer (CTL) is analyzed according to trap levels. Traps inside the CTL are categorized into shallow trap levels (STL) and deep trap levels (DTL), with multiple levels sampled according to the distribution of trap concentration as a function of trap depth. Charge loss during the reprogram interval is analytically calculated based on electron emission, and the relative contributions of shallow and deep traps are compared after the second program operation. The results demonstrate that the electron trap distribution shifts toward a higher DTL concentration compared with the one-shot program. Furthermore, a trade-off relationship is proposed, in which retention characteristic can be tuned by adjusting the interval time between two program operations. The results were calibrated against measurement data and validated with technology computer-aided design (TCAD) simulations, and a voltage biasing scheme is proposed to enhance reliability.