Impact of Band-to-Band Tunneling in the Charge Trap Layer of NAND Flash Memory

This article investigates the impact of band-to-band tunneling (BTBT) occurring in the charge trap layer (CTL) of vertical NAND (V−NAND) flash memory under excessive erasure conditions and aggressive program operation. Strong local electric fields induce BTBT within the CTL, generating electron–hole pairs that cause trap charge loss, inter-cell interference, and early threshold voltage (V <tex-math notation="LaTeX">ₜₕ </tex-math>) reduction. The generated holes accelerate the loss of trapped electrons near the programmed target cell, degrading incremental step pulse programming (ISPP) characteristics, whereas laterally redistributed electrons induce Vth shifts in adjacent cells. In addition, the time-dependent accumulation of BTBT-generated carriers contributes to initial threshold voltage shift (IVS) during retention. These results show that BTBT in the CTL provides reliability issues in V−NAND flash memory, such as short-term Vth instability and inter-cell interference.