| 摘要 |
<p>PURPOSE:To reliably rewrite data without causing excessive erasure by setting the threshold voltage of a memory cell when a floating gate is in neutral state to a value between both threshold values when the memory cell is erased and is written. CONSTITUTION:A floating gate memory cell where a floating gate and a control gate are formed is provided on the channel region of a semiconductor substrate. The threshold voltage when the floating gate is in neutral state 'initial' is set to a value between a threshold voltage when the memory cell is in erased state '0' and that when the memory cell is in writing state '1'. For example, the threshold value in the writing state '1' and the erasure state '0' are set to approximately 7V and 2V, respectively, and the threshold value when the floating gate is in the neutral state 'initial' is set to approximately 4V, thus drastically reducing the number of memory cells in excessive erasure state and reliably achieving rewriting.</p> |
