| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a nonvolatile memory in which high speed of writing-erasure operation or the reliability in information security can be selected and information security is further improved. <P>SOLUTION: A flash memory (1) has a plurality of nonvolatile memory cells (2) where electrical writing and erasing are possible and a control circuit (5). In response to the kind of a command supplied from outside, the control part (5) controls writing and erasing to the nonvolatile memory cells and verifying of them to vary an interval of threshold voltage distribution of the nonvolatile memory cells obtained by verifying. For example, when the width of the threshold voltage distribution is made to be smaller with the increase of the interval of the threshold voltage distribution by the instruction of a writing command, voltage stress due to writing can be reduced to improve the reliability in information security. When the width of the threshold voltage distribution is increased by reducing the interval of the threshold voltage distribution on the other hand, the pulse width of pulse voltage for writing can be increased to secure the high speed of writing operation. <P>COPYRIGHT: (C)2007,JPO&INPIT</p> |
