NAND Flash Memory String with Localized Buried Oxide Layer
Young Min Kim, Il-Hwan Cho, Jong‐Ho Lee · Japanese Journal of Applied Physics · 2009
A cell structure without a source/drain (S/D) could be very promising for scaled NAND flash memory beyond the sub-40-nm node, which utilizes the fringing electric field from control gates. In this work, we propose a new NAND string structure where cells have localized buried oxide layers (L-BOXs) and no S/D. The L-BOX is formed in the space between gates. When comparing the proposed cell string with the conventional cell string without the L-BOX, the former forms a field-induced layer more easily in the space, causing the threshold voltage in the space to decrease. Owing to not only the effect of the fringing field from the control gates (CGs) but also the additional effect due to the L-BOX, the proposed structure shows a wider threshold voltage window (Δ V th ) and a higher bit-line current ( I bitline ) during the read operation than the structure without the L-BOX when peak channel doping is uniform along the NAND string.