A Highly Stackable Thin-Film Transistor (TFT) NAND-Type Flash Memory

For the first time, a successful TFT NAND-type flash memory is demonstrated using a low thermal budget process suitable for stacking the memories. A TFT-SONOS device using bandgap engineered SONOS (BE-SONOS) (Lue, et al. 2005) with fully-depleted (FD) poly silicon (50 nm) channel and tri-gate P⁺-poly gate is integrated into a NAND array. Small devices (L/W=0.18/0.09 mum) with good DC performance are achieved, owing to the good control capability of the tri-gate FD structure. Successful NAND array functions are demonstrated, with more than 1 muA read current for a 16-string NAND array and good program disturb immunity. This new device also shows good endurance and data retention, and negligible read disturb. These results are very encouraging for future 3D flash memory