| 摘要 |
<p>PURPOSE:To make occurrence of over erasing hard by controlling an erasing power source thereby controlling an erasing current as prescribed in an electrically rewritable non-voltage semiconductor memory such as a flash memory and the like. CONSTITUTION:A erasing current of high level current Ia from a first erasing power source 4 is supplied to a source of a memory cell of a memory cell array 1, and erasing of a memory cell is performed. And the power source 4 is switched to an erasing power source 5 through a counter circuit 7, a switching control circuit 6 and an erasing power source switching circuit 3 in an erasing time zone near the end of erasing, the erasing current is switched to a low level current Ib. Thereby, tilt of the curve (a) of threshold value voltage Vth becomes gentle, quantity of variation of the voltage Vth is small and accurate measuring control can be performed. Consequently, over erasing is made hard to occur, electrons and positive holes are made hard to trap by a gate oxidized film, and the number of rewriting can be increased.</p> |
