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-Al₂O₃-Si₃N₄-ldquoTunnel-oxide (TO)rdquo-Si MOSFETs through band engineered tunnel oxides (BETO). Several high-K dielectrics (HfO₂, HfSiO, Al₂O₃, Si₃N₄) and tunnel stack sequences (SiO₂-high-k, SiO₂-high-k-SiO₂) are compared. New results are as follows: SiO₂/Al₂O₃ (OA) BE-TO and SiO₂/Si₃N₄/SiO₂ (ONO) BE-TO DeltaVth windows improve >300% vs. standard SiO₂-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.