New ultra high density EPROM and flash EEPROM with NAND structure cell

In order to realize ultra high density EPROM and Flash EEPROM, a NAND structure cell is proposed. This new structure is able to shrink cell size without scaling of device dimensions. The NAND structure cell realizes a cell as small as 6.43 µm
²
using 1.0 µm design rule. As a result, cell area per bit can be reduced by 30% compared with that of a 4M bit EPROM using the conventional structure and the same design rule. It is confirmed that each bit in a NAND cell is able to be programmed selectively. This high performance NAND structure cell is applicable to high density nonvolatile memories as large as 8M bit EPROM and Flash-EEPROM or beyond.