NONVOLATILE SEMICONDUCTOR STORAGE DEVICE AND PRODUCTION METHOD THEREFOR

摘要

A nonvolatile semiconductor storage device not likely to cause variations in electric characteristics among individual memory cells. A floating-gate electrode provided on a substrate consists of at least two kinds of materials having different carrier trapping efficiencies, carriers are accumulated in this floating-gate electrode to store data to thereby produce an area where a threshold voltage does not change substantially, and cell-to-cell variations and a fast operation are implemented with the small-variation portion used as a margin for a circuit operation.