New read schemes using boosted channel potential of adjacent bit-line strings in nand flash memory

New schemes of read operation using boosted channel potential of adjacent bit-line (BL) strings are proposed for improving on-state current of a cell string in nand Flash memory. The channel resistance of pass cells in a cell string under read operation is decreased by the electric field due to the boosted channel potential of adjacent BL strings, which increases on-state current of the cell string. Proposed schemes give much smaller read disturbance compared with conventional ones because the boosted channel potential of unselected BL strings prevents soft programming in cells of the unselected BL strings. It was also shown that new read operation of #2 scheme leads to suppress the background pattern dependence by ∼58%, as compared with the conventional read operation scheme.