| CPC G11C 16/3445 (2013.01) [G11C 16/0483 (2013.01)] | 18 Claims |

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1. A memory device, comprising:
a plurality of memory blocks each including a plurality of cell string groups;
a peripheral circuit configured to perform an erase verify operation on a memory block selected from among the plurality of memory blocks; and
an erase operation controller configured to control the peripheral circuit to perform the erase verify operation in units of cell string groups within the selected memory block,
wherein the erase operation controller controls the peripheral circuit to apply, during the erase verify operation, different erase verify voltages to the selected memory block whenever the erase verify operation is performed on each of the cell string groups.
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