Demonstration of Split-Gate Type Trigate Flash Memory With Highly Suppressed Over-Erase

The functional split-gate type trigate flash memory cell transistors have successfully been fabricated for the first time, and their threshold voltage (V
_t
) variations before and after NOR-mode program/erase cycle have systematically been compared with the stack-gate ones. It was experimentally found that split-gate type cell transistors with the same control gate length (L
_CG
) of 176 nm show much smaller Vt distribution after erase compared to those of stack-gate ones. Moreover, the measured source-drain breakdown voltage (BV
_DS
) is higher than 3.1 V even the L
_CG
was down to 76 nm. This indicates that the developed split-gate type trigate flash memory is very effective for scaled NOR-type flash memory with highly suppressed over-erase.