| 摘要 |
<p>PURPOSE:To improve a margin of the drain-disturbance strength by a method wherein, before or after a plurality of blocks composed of a plurality of nonvolatile memory cells are erased, a refreshing operation by which data in the memory cells are read and re-written is performed. CONSTITUTION:After '0's' are written in all memory cells in an erased block, an address Ad in the block is set at '0' and then an erasing operation is performed for 10ms and then a verification is performed. If it is confirmed that all the data which are re-read by the verification are erased to be '1's', the incremental operation of the address Ad in the block is performed and the verification follows. If all the addresses Ad in the block are verified, a refreshing operation follows. That is, the data of the memory cells are read and the same data are re-written. With this constitution, the data which is gradually lost by a drain-disturbance can be recovered.</p> |
