NONVOLATILE STORAGE

摘要

PROBLEM TO BE SOLVED: To provide a nonvolatile storage that realizes high precision erasing in a short period of time and stabilized operations at a low voltage.

SOLUTION: This nonvolatile storage performs erasing by discharging the charges accumulated by writing in the floating gate to the source. It has an automatic erasing circuit which performs the following four operations sequentially. The first operation readouts the memory cells which are the erasing units, and pre-writes to the nonvolatile components whose floating gates are not accumulated with charges. The second operation erases the nonvolatile components of the above erasing units at high speed en bloc by applying comparatively a large amount of energy at a comparatively high erasing reference voltage. The third operation reads all the above erased nonvolatile components and writes on the components having comparatively low threshold voltages. The forth operation erases the nonvolatile components of the above erasing units at low speed en bloc by applying comparatively a small amount of energy at a comparatively low erasing reference voltage.

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