| 摘要 |
<p>PROBLEM TO BE SOLVED: To suppress variation of threshold voltage in a memo erasing state by setting all word lines of a memory cell array in the non-selective states after an erasing operation is executed and detecting whether every memory cell has its threshold voltage of a normal erasing state or an excessive erasing state that is lower than a prescribed level, as compared with the normal erasing state. SOLUTION: Address initialization is executed after an erasing operation and it's decided whether or not any memory transistor TR of an excessive erasing state exists. If a memory TR of an excessive erasing state is detected, a reversing operation is executed to reset the threshold voltage at a prescribed level and the presence of an excessive erasing state is discriminated. Only a bit line, including a memory TR of an excessive erasing state, has a reversing operation with use of a leak detection means which detects an excessive erasing state. Thus, the variation is suppressed in the erasing state of a memory cell, and the reliability is improved for a nonvolatile semiconductor storage device.</p> |
