A highly reliable NAND structure flash memory capable for low voltage operation

For the first time, a new flash cell, called buried bit-line AND (BiAND), is proposed. Buried bit-line AND flash can achieve low voltage programming/erase. The major difference of the current flash cell from the conventional AND flash is the special design of a bit-line contact. With the use of the buried bit-line, the required high program/erase voltage for FN tunneling can be divided between the word-line and bit-line such that lower voltage operation is feasible. Further, the comparison of the cell reliability for different schemes, i.e., high voltage F-N (HV F-N) and Bi F-N operating schemes, has been studied. Results show that the BiAND scheme gives much better endurance and data retention characteristics. This makes it successful for a low voltage and high reliability design.