Selective Word Line Erase In 3D Non-Volatile Memory

摘要

An erase process for a 3D stacked memory device allows a portion of a block of memory cells to be erased. In one approach, in a U-shaped NAND string configuration, memory cells in the drain- or source-side columns are erased. In another approach, such as in a U-shaped or a straight NAND string configuration, memory cells in a portion of a column of memory cells are erased, and a dummy memory cell is provided between the erased and non-erased memory cells. A dummy memory cell can be on either side (e.g., above and below) of an erase memory cell, or on either side of a non-erased memory cell. A dummy memory cell is ineligible to store user data, but prevents a downshift in the threshold voltage of an erased memory cell from changing the threshold voltage of a non-erased memory cell, due to capacitive coupling.

主权项

1. A method for performing an erase operation in a 3D stacked non-volatile memory device, comprising:
identifying selected and unselected columns of memory cells of U-shaped NAND strings in a stacked non-volatile memory cell array, in connection with an erase operation, the stacked non-volatile memory cell array comprising word line layers alternating with dielectric layers, each word line layer comprising a selected word line layer portion in communication with memory cells in the selected columns of memory cells, but not with memory cells in the unselected columns of memory cells, and an unselected word line layer portion in communication with memory cells in the unselected columns of memory cells, but not with memory cells in the selected columns of memory cells; and while providing an erase voltage (Verase) to an end of each selected column of memory cells: allowing a voltage (Vw1-float) of at least one of the selected word line layer portions, to float, while providing a fixed voltage (Vw1-fixed) for each of the unselected word line layer portions, and subsequently, lowering the voltage of the at least one of the selected word line layer portions.