| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To improve data write speed by speeding up verification operation. <P>SOLUTION: A memory cell MC stores one value among four values. A control circuit 7 sets the threshold voltage of a memory cell to voltage from the first threshold voltage to the first threshold voltage or a second threshold voltage (first threshold voltage<second threshold voltage) by first write operation, to the first threshold voltage or a third threshold voltage (first threshold voltage<third threshold voltage) when the threshold voltage of the memory cell is the first threshold voltage by second write operation, to a fourth threshold voltage (second threshold voltage≤fourth threshold voltage) or a fifth threshold voltage (fourth threshold voltage<fifth threshold voltage) when the threshold voltage of the memory cell is the second threshold voltage, and increases a program voltage byΔVpgm each time in first and second write operation to repeat program and verification operation for write operation. TheΔVpgm in the first write operation is larger than that in the second write operation. <P>COPYRIGHT: (C)2008,JPO&INPIT</p> |
