| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To improve a readout margin for a nonvolatile semiconductor memory. <P>SOLUTION: In a first write operation, a memory cell current for a write reference memory cell is selected as a write reference current, and data is written to the memory cell and either a first or a second memory cell. In a second write operation following the first write operation, a read reference current, which is a mean current for the first and the second reference memory cell, is selected as a write reference current and the data is written only to the memory cell. After the second write operation, the difference between the read reference current and the memory cell current for the memory cell can be expanded because threshold voltages for the memory cell is distributed to one side of the first or the second reference memory cell as a border. Resulting from this, the data can be read without fail. The readout margin can be improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI</p> |
