Adaptive Pulse Program Scheme to Improve the Vth Distribution for 3D NAND Flash
Shuang Li, Zhichao Du, Yu Wang, Fei Liu, Qi Wang, Zongliang Huo · 2020
As the demand of multi-bit/cell NAND flash devices is increasing rapidly, getting a narrow cell Vth distribution becomes more challenging and necessary. To overcome this challenge, an adaptive pulse program (APP) scheme is reported that can tighten the Vth distribution in this work. Compared with conventional incremental step pulse program (ISPP) scheme, this proposed scheme uses adaptive program pulse to the cells with different program speed, which targets to prevent the extension of Vth distribution's upper tail. Our experimental result demonstrates that APP scheme achieves ~15% improvement for reducing cell Vth distribution width. This comparison of APP scheme and general ISPP scheme is performed by the FPGA platform using 64-layer 3D charge-trapping NAND flash chip.