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US 5,708,605 AGranted
Nonvolatile semiconductor memory device having variable writing and erasing time periods
AssigneeNEC Corporation
InventorToshiya Sato
Life of this patent
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Abstract
In a nonvolatile semiconductor memory device, a nonvolatile counter is provided to store a number of erasing operations. A time period of a writing operation upon a memory cell is changed in accordance with the number of erasing operations. Also, a time period of an erasing operation upon memory cells is changed in accordance with the number of erasing operations.
Claims10
A nonvolatile semiconductor memory device, comprising:
- a nonvolatile counter for storing a number of erasing operations;
- and
- means for performing a writing operation upon a memory cell for a time period which is changed in accordance with the number of erasing operations stored in said nonvolatile counter.
A nonvolatile semiconductor memory device, comprising:
- a nonvolatile counter for storing a number of erasing operations;
- means for determining whether or not the number of erasing operations stored in said nonvolatile counter has reached a certain value;
- means for performing a first writing operation upon a memory cell for a first time period, before the number of erasing operations stored in said nonvolatile counter reaches said certain value;
- and
- means for performing a second writing operation upon said memory cell for a second time period, after the number of erasing operations stored in said nonvolatile counter has reached said certain value,
- said second time period being larger than said first time period.
3 more elements
A nonvolatile semiconductor memory device, comprising:
- a nonvolatile counter for storing a number of erasing operations;
- and
- means for performing an erasing operation upon memory cells for a time period which is changed in accordance with the number of erasing operations stored in said nonvolatile counter.
A nonvolatile semiconductor memory device, comprising:
- a nonvolatile counter for storing a number of erasing operations;
- means for determining whether or not the number of erasing operations stored in said nonvolatile counter has reached a certain value;
- means for performing a first erasing operation upon memory cells for a first time period, before the number of erasing operations stored in said nonvolatile counter reaches said certain value;
- and
- means for performing a second erasing operation upon said memory cells for a second time period, after the number of erasing operations stored in said nonvolatile counter has reached said certain value,
- said second time period being larger than said first time period.
3 more elements
Dependencies are inferred from the claim text.