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US 6,788,580 B2Granted
Nonvolatile semiconductor storage device and data erasing method
AssigneeFujitsu Limited
InventorSatoshi Takahashi
Life of this patent
Estimating the term…
Abstract
A nonvolatile semiconductor storage device includes a memory cell array and a reference cell providing a reference level with which data of the memory cell array is compared with so as to determine whether the data of the memory cell array is in an over-programmed state.
Claims11
A nonvolatile semiconductor storage device, comprising:
- a memory cell array;
- a reference cell providing a reference level with which data of said memory cell array is compared so as to determine whether the data of said memory cell array is in an over-programmed state;
- and
- a control circuit performing an erasing operation on a memory cell in the over-programmed state in said memory cell array when a result of the comparison shows the over-programmed state.
1 more element
A method of erasing data in a nonvolatile semiconductor storage device, the method comprising the steps of:
- (a) programming all of a plurality of memory cells in a region to be erased in a memory cell array;
- (b) determining, with respect to each of the memory cells, whether the memory cell is in an over-programmed state by comparing data of the memory cell with a predetermined reference level;
- (c) causing the over-programmed state of a memory cell determined to be in the over-programmed state to disappear by performing an erasing operation on the memory cell;
- and
- (d) erasing all the memory cells in the region to be erased in the memory cell array after eliminating the over-programmed state from the entire region to be erased.
2 more elements
Dependencies are inferred from the claim text.