Band engineered tunnel oxides for improved TANOS-type flash program/erase with good retention and 100K cycle endurance

We demonstrate for the first time improved program, erase, and endurance for charge trap flash TaN-Al
₂
O
₃
-Si
₃
N
₄
-ldquoTunnel-oxide (TO)rdquo-Si MOSFETs through band engineered tunnel oxides (BETO). Several high-K dielectrics (HfO
₂
, HfSiO, Al
₂
O
₃
, Si
₃
N
₄
) and tunnel stack sequences (SiO
₂
-high-k, SiO
₂
-high-k-SiO
₂
) are compared. New results are as follows: SiO
₂
/Al
₂
O
₃
(OA) BE-TO and SiO
₂
/Si
₃
N
₄
/SiO
₂
(ONO) BE-TO DeltaVth windows improve >300% vs. standard SiO
₂
-TO. Both OA and ONO stacks endure P/E cycles to at least 100 K cycles maintaining a window >4V. Results are consistent with a model based on high-k conduction/valence band offsets. Increased erase efficiency for BE-TO enables improved endurance without sacrificing P/E window due to lower P/E voltage stressing. These large, enduring windows are favorable for multi-level cell application and may extend TANOS flash beyond the 20 nm node.