A novel symmetrical split-gate structure for 2-bit per cell flash memory

A fully self-aligned symmetrical split-gate cell structure for 2-bit per cell flash memory with a very competitive bit size is presented. One common select gate is located between two floating gates and a pair of source/drain junctions are shared by the 2 bits. The fabrication method utilized here to create a self-aligned structure is to form a spacer against the prior layer without any additional mask. Although the cell consists of three channels in a series, the attributes from conventional split gate flash are still preserved with appropriate bias conditions.Program and erase operation is performed by using a source side injection(SSI) and a poly-to-poly tunneling mechanism respectively.