To enable one non-volatile memory cell to store four-value information, three different kinds of threshold voltages are serially applied to a word line in a verify operation to execute a write operation, the threshold voltages of the memory cell are controlled, and two-value (one-bit) information corresponding...http://www.google.com/patents/US7245532?utm_source=gb-gplus-sharePatent US7245532 - Nonvolatile semiconductor memory device which stores multi-value information
Nonvolatile semiconductor memory device which stores multi-value information
