Charge trapping in alumina and its impact on the operation of metal-alumina-nitride-oxide-silicon memories: Experiments and simulations

We investigate the electron/hole trapping phenomena in alumina blocking oxide and their impact on the program/erase operations and retention of TaN/Al₂O₃/Si₃N₄/SiO₂/Si (TANOS) memory devices. For this purpose, we perform simulations using a physical model that reproduces the charge injection/trapping in TANOS devices, which is extended in order to account for the charge trapping phenomena in the blocking layer. We derive the electrical characteristics of both electron and hole traps in Al₂O₃ by reproducing the measured program, erase, and retention transients. Our results show that the amount of electron charge trapped in the alumina during a program operation strongly depends on the stack composition and program voltages and can account for up to 25% of the total threshold voltage shift, whereas hole trapping during erase is negligible. Finally, we investigate the degradation of retention caused by the electron trapping in the alumina blocking layer, which is shown to result in an accelerated charge loss.