An innovative structure to improve erase characteristics using p-doped polysilicon in ferroelectric 3D NAND flash with IGZO-channel

Abstract In this paper, we propose an innovative structure using p-doped polysilicon in front of a word line (WL) in ferroelectric FETs based vertical NAND (Fe-3D NAND) flash to improve the negative cell V th characteristics of indium gallium zinc oxide (IGZO)-channel based 3D NAND flash. The proposed structure significantly improved the negative V th characteristics compared to the metal-ferroelectric-interlayer-silicon, band engineered-metal-interlayer-ferroelectric-interlayer-silicon structures-based 3D NAND flash single cell, and improved the positive V th characteristics with the optimization of the structure and operation [Kang et al., Proc. SSDM, 2025]. Additionally, we conducted a study to improve the negative V th characteristics of the 3D NAND flash single cell based on IGZO channel structure and to analyze the characteristics with the 3D NAND flash single cell based on the poly-Si channel structure, and improved the positive V th characteristics with the optimization of the structure. The proposed structure is characterized by electrons that are injected from a WL into the charge trap nitride (CTN) layer while operating negative voltage at the WL, and the holes are injected from p-doped polysilicon into the CTN layer while operating positive voltage at the WL. However, it was found out that the positive cell V th characteristics are degraded due to an increased tunneling barrier for electrons by adding the p-doped polysilicon. Accordingly, the positive cell V th characteristics were improved by scaling the thickness of the p-doped polysilicon, gate interlayer O/N/O and other layers. The cell characteristics of the proposed structure were compared with that of a polysilicon and IGZO channel structure. The proposed Fe-3D NAND structure with p-doped polysilicon in front of the WL and structural optimization significantly improved the negative cell V th characteristics. As a result, we secured a large MW of 6.23 V.