Nonvolatile memory device and method of detecting defective memory cell block of nonvolatile memory device

A memory device comprising:

• a voltage generating circuit configured to apply an off-cell detection voltage that is different from a read reference voltage to a target memory cell to perform a hard off-cell detection operation on the target memory cell after the memory device performs an erase operation;
• a sensing amplifier configured to receive an output current from a target cell string based on the off-cell detection voltage;
• and
• a control circuit configured to output a first signal indicating that the target memory cell is a hard off-cell based on the output current of the target memory cell being less than a threshold current.

A method of detecting a hard off-cell comprising:

• applying an off-cell detection voltage that is different from a read reference voltage to a target memory cell to perform a hard off-cell detection operation on the target memory cell after a memory device performs an erase operation;
• sensing an output current from the target memory cell based on the off-cell detection voltage;
• and
• outputting a first signal indicating that the target memory cell is the hard off-cell based on the output current of the target memory cell being less than a threshold current.