| 摘要 |
<p>PROBLEM TO BE SOLVED: To improve reliability of a tunnel film without increasing erasing time. SOLUTION: When erasing operation is performed, a voltage Vcg applied to a control gate 17 is reduced as time passes. Thereby the potential difference Vsf between a source and a floating gate 15 is not reduced in the case that quantity of electrons accummulated in the floating gate 15 is reduced with the progress of erasing operation and floating gate potential Vf is increased, and erasing operation time is not increased. For increasing the erasing speed, it is unnecessary that the potential difference Vsf between the source and a control gate is made high voltage, so that intensity of an electric field applied on a tunnel film 14 can be reduced when erasing operation is started, and damage to the tunnel film 14 can be prevented. Further, it is excluded that hot holes which are generated in a source diffusion layer 12 during erasing operation are injected in the tunnel film 14 and reliability of the tunnel film is deteriorated.</p> |
