Memory device and operating method for performing pre-program operation on over-erasure cells

A memory device comprising:

• a plurality of memory cells connected to each word line, among a plurality of word lines;
• a peripheral circuit configured to perform a program operation on selected memory cells that are connected to a selected word line among the plurality of word lines;
• and
• a control logic configured to control the peripheral circuit to perform the program operation on the selected memory cells after performing a pre-program operation that programs a threshold voltage of over-erasure cells, among adjacent memory cells that are connected to an adjacent word line, having a threshold voltage of an over-erasure state that is lower than a threshold voltage of an erasure state, to the threshold voltage of the erasure state,
• wherein the adjacent word line is a word line that is next to the selected word line,
• wherein the control logic performs an over-erasure cell sensing operation before the pre-program operation on the over-erasure cells, and
• wherein the over-erasure cell sensing operation:
• senses threshold voltages of the adjacent memory cells;
• and
• determines memory cells that have threshold voltages that are lower than an over-erasure verify voltage as the over-erasure cells among the adjacent memory cells.

A method of operating a memory device comprising a plurality of memory cells connected to each word line, among a plurality of word lines, and performing a program operation on selected memory cells that are connected to selected word lines, among the plurality of word lines, the method comprising:

• sensing threshold voltages of adjacent memory cells that are connected to an adjacent word line, wherein the adjacent word line is a word line that is next to the selected word line;
• determining memory cells that have threshold voltages that are lower than an over-erasure verify voltage as over-erasure cells, among the adjacent memory cells, wherein the over-erasure cells have a threshold voltage of an over-erasure state that is lower than a threshold voltage of an erasure state;
• performing a pre-program operation that programs the over-erasure cells to the erasure state;
• and
• performing the program operation on the selected memory cells.