| CPC G11C 16/12 (2013.01) | 20 Claims |

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1. A method of operating a memory device, comprising:
performing a first program loop of increasing threshold voltages of first memory cells selected by a first drain select line among a plurality of memory cells coupled to a word line;
performing a second program loop of increasing threshold voltages of second memory cells selected by a second drain select line among the plurality of memory cells; and
alternately repeating the first program loop and the second program loop such that respective threshold voltages of the first memory cells and the second memory cells are increased to respective threshold voltages corresponding to respective target program states.
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