Memory device and operating method thereof

A method for operating a memory device, the method comprising:

• setting an address of a buffer page according to a physical structure of strings included in a selected memory block;
• applying a program allow voltage through a bit line connected to a selected string among the strings;
• applying a program inhibit voltage through a bit line connected an unselected string among the strings;
• turning on a first buffer cell connected between memory cells of the selected string;
• turning off a second buffer cell connected between memory cells of the unselected string;
• with respect to the first and second buffer cells, applying a first pass voltage to unselected word lines of a region in which a selected word line is included and applying a second pass voltage lower than the first pass voltage to unselected word lines of the other region;
• and
• when an electrical characteristic of the memory cells is changed, resetting the address of the buffer page according to the changed electrical characteristic.

A memory device comprising:

• a first select transistor and a first sub-block, which are sequentially stacked above a source line;
• buffer cells stacked above the first sub-block;
• and
• a second sub-block, a second select transistor, and a bit line, which are sequentially stacked above the buffer cells,
• wherein memory cells which are included in the first and second sub-blocks and are included in different strings are commonly connected to word lines,
• wherein gates of the buffer cells are connected to different buffer lines,
• wherein the buffer cells are configured to be selectively turned on or turned off according to a turn-on voltage or a turn-off voltage, which is applied to each of the buffer lines.