Optimizing De-Trap Pulses in Gate-Injection Type Ferroelectric NAND Cells to Minimize Read After Write Delay Issue

The ferroelectric (FE) NAND flash, featuring metal-interlayer-FE-interlayer-silicon (MIFIS) gate stacks, leverages both charge trapping and polarization (P) switching to achieve a broad memory window (MW) and low operation voltage. These remarkable advancements establish it as a viable contender for future NAND flash technologies. However, the read-after-write-delay (RAWD) problem during program/erase (PGM/ERS), caused by channel-injected interface trapped charges ( ${Q}_{\text {it}}$ ) between the FE layer and the channel interlayer (Ch.IL), leading to short-term Vth variations, remains unexplored in MIFIS FE-NAND cells. This letter presents the first analysis of RAWD in FE-NAND cells, including the experimental optimization of a de-trap pulse that effectively eliminates ${Q}_{\text {it}}$ whereas preserving both gate-injected interface trapped charges ( ${Q}_{\text {it}}$ ’) and P. Consequently, the FE-NAND cell exhibits a narrow MW of 3.45 V at a delay time ( ${t}_{\text {Delay}}\text {)}$ of $1~\mu $ s between PGM/ERS and read operations, expending to 7.40 V at a tDelay of 1 s. This variation is attributed to the generation of ${Q}_{\text {it}}$ and the subsequent de-trap process, affecting channel conductivity. To thoroughly address the RAWD, various pulse widths and amplitudes are experimentally explored immediately post-PGM/ERS to optimize the de-trap pulse for selective ${Q}_{\text {it}}$ removal. Upon applying the optimized de-trap pulse, the stable wide MW (7.40 V) is consistently maintained regardless of ${t}_{\text {Delay}}$ . This work is meaningful as it brings attention to previously unexplored issues in next-generation ferroelectric (FE) NAND cells and suggests practical operational solutions.