Method of programming a semiconductor nonvolatile memory cell and memory with multiple charge traps

Abstract

A semiconductor nonvolatile memory has a memory cell array in which each memory cell has a pair of charge traps and each charge trap stores data with at least three possible values. Different data values produce different read current values. To store data, a controller and a voltage supplying unit in the semiconductor nonvolatile memory successively program and verify the charge traps that require programming, using higher programming voltages for data values that must produce lower read currents. This operation is iterated on the charge traps that have not yet attained their necessary read current values, until no such charge traps remain. The programming voltages are set so that all charge traps require substantially the same number of programming iterations, regardless of the data being stored.