| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To speed up a verifying operation and increase a data writing speed. <P>SOLUTION: A control circuit 7 causes a threshold voltage of a memory cell to be a first threshold voltage or a second threshold voltage from the first threshold voltage by a first writing operation (the first threshold voltage is lower than the second threshold voltage), and, by a second writing operation, causes the threshold voltage of the memory cell to be the first threshold voltage or a third threshold voltage (the first threshold voltage is lower than the third threshold voltage) when the threshold voltage of the memory cell is the first threshold voltage, and to be a fourth threshold voltage (the second threshold voltage is equal to or lower than the fourth threshold voltage) or a fifth threshold voltage (the fourth threshold voltage is lower than the fifth threshold voltage) when the threshold voltage of the memory cell is the second threshold voltage. The control circuit performs program and verifying operations repetitively in the second writing operation, and sets a maximum value to the number of times of the verifying operations that verify whether or not the third threshold voltage is reached, and when the number of times of the verifying operations reaches the maximum value, the verifying operation for verifying whether or not the third threshold voltage is reached is skipped. <P>COPYRIGHT: (C)2011,JPO&INPIT</p> |
