Method for Operating a High Density Multi-Level Cell Non-Volatile Flash Memory Device

A Method for operating a high density multi-level cell non-volatile flash memory possesses the following operating steps:

• (a) a localized trapping memory cell with initial threshold voltage of about 2 V˜3 V is erased to a new initial level of about −2 V˜−1 V, after erasing, stored bits at each side of a cell have a same threshold level, and a uniform charge distribution in a nitride layer along the channel is obtained;
• (b) with the state of the negative threshold voltage of about −2 V−˜1 V as a new initial state, a MLC programming operation for the localized trapping memory is performed, a channel hot electron CHE injection is used with a positive substrate bias to suppress a secondary electron injection, or a pulse agitated substrate hot electron injection (PASHEI) programming method to implement the charge localized storage;
• (c) By changing a gate or a drain voltage or a programming time, more than eight programming states, i.e. more than eight threshold voltage levels can be achieved.