Detecting Programmed Word Lines Based On NAND String Current

摘要

A number (Nwl) of programmed word lines in a block of NAND strings is determined by measuring a reference combined current (Iref) in the block when all of the memory cells are in a conductive state. Subsequently, to determine if a word line is a programmed word line, an additional combined current (Iadd) in the block is measured with a demarcation voltage applied to the selected word line. The selected word line is determined to be programmed word lines if Idd is less than Iref by at least a margin. Nwl can be used to adjust an erase-verify test of an erase operation by making the erase-verify test relatively hard to pass when the number is relatively small and relatively easy to pass when the number is relatively large. Or, Nwl can be used to identify a next word line to program in the block.

主权项

1. A method for operating a non-volatile memory device, comprising:
measuring a combined current through a plurality of NAND strings as a reference combined current (Iref) while applying a read pass voltage (Vpass) to a plurality of word lines, the plurality of NAND strings comprise a plurality of memory cells and the plurality of word lines are connected to the plurality of memory cells; and identifying one or more selected word lines of the plurality of word lines which are programmed word lines, the identifying comprises, for each of the one or more selected word lines: measuring an additional combined current (Iadd) through the plurality of NAND strings while applying a demarcation voltage (Vdem) to the selected word line and applying the read pass voltage to remaining word lines of the plurality of word lines, and determining whether the additional combined current is less than the reference combined current by at least a margin.