| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To solve the problems that deterioration of reliability characteristic such as endurance durability and retention characteristic and increase of writing time after erasing arise because erasing data in non volatile memory cells such as a conventional EEPROM causes the same erasing voltage to be applied continuously until erasing all the memory cell groups in an arbitrary block is finished and then distribution of memory cell thresholds after finish of erasing tends to broaden to the extent of excessive erasing. <P>SOLUTION: The semiconductor memory device is provided with means 31 and 32 for erasing and means 21 and 22 for detecting finish of erasing specifically for respective memory cell areas 11 and 12 segmented in the memory block 10 whose data is erased simultaneously, and memory cell stress is lowered by alleviating application of erasing voltage to the memory cell area when the threshold of at least one memory cell in the memory cell area reaches the level for finish of erasing and finishes erasing. Excessive erasing of the memory cells, whose thresholds have already reached the level for finish of erasing, can be suppressed and highly reliable or high speed writing can be achieved. <P>COPYRIGHT: (C)2008,JPO&INPIT</p> |
