Reducing read failure in a memory device

摘要

Read failure is reduced by increasing the drain current through a serial string of memory cells during the read operation. In one embodiment, this is accomplished by using a higher read pass voltage for unselected word lines when the selected word line is within a predetermined distance of the drain side of the memory block array. If the selected word line is closer to the source side, a lower read pass voltage is used. In another embodiment, the cells on the word lines closer to the drain side of the memory block array are erased to a lower threshold voltage than the memory cells on the remaining word lines.

主权项

1. A method for reducing read failure in a memory device having a memory array with a drain side and a source side, the method comprising:
determining if a selected word line is closer to the drain side or the source side; and biasing unselected word lines with a first voltage if the selected word line is closer to the drain side, with a second voltage if the selected word line is closer to the source side, and with a third voltage if the selected word line is closer to a middle of the array between the source side and the drain side; wherein biasing unselected word lines with the third voltage comprises biasing an unselected word line on a drain side of the selected word line and an unselected word line on a source side of the selected word line with the third voltage; wherein the first voltage is greater than the second voltage; and wherein the drain side is at a higher potential than the source side.