A study of the memory characteristics of Al₂O₃/Y ₂O₃/SiO₂ multi-stacked films with different tunnel oxide thicknesses

Conventional SONOS (poly-silicon/oxide/nitride/oxide/silicon) type memory is associated with a retention issue due to the continuous demand for scaled-down devices. In this study, Al₂O₃/Y ₂O₃/SiO₂ (AYO) multilayer structures using a high-k Y₂O₃ film as a charge-trapping layer were fabricated for nonvolatile memory applications. This work focused on improving the retention properties using a Y₂O₃ layer with different tunnel oxide thickness ranging from 3 nm to 5 nm created by metal organic chemical vapor deposition (MOCVD). The electrical properties and reliabilities of each specimen were evaluated. The results showed that the Y₂O ₃ with 4 nm SiO₂ tunnel oxide layer had the largest memory window of 1.29 V. In addition, all specimens exhibited stable endurance characteristics (program/erasecycles up to 10⁴) due to the superior charge-trapping characteristics of Y₂O₃. We expect that these high-k Y₂O₃ films can be candidates to replace Si₃N₄ films as the charge-trapping layer in SONOS-type flash memory devices.