A non-volatile semiconductor memory device includes a non-volatile memory cell and a write circuit that is adapted to write data to the memory cell by supplying a write voltage and a write control voltage to the memory cell to change the write state of the memory cell, changing the supply of the write...http://www.google.de/patents/US7468908?utm_source=gb-gplus-sharePatent US7468908 - Non-volatile semiconductor memory device adapted to store a multi-valued in a single memory cell
