Electrical properties of HfO₂ charge trap flash memory with SiO₂/HfO₂/Al₂O₃ engineered tunnel layer

The program/erase (P/E) characteristic of tunnel barrier engineered charge trap flash (TBE-CTF) memory with MAHOS (Metal/Al₂O₃/HfO₂/SiO₂/Si) structure and MAHAHOS (Metal/Al₂O₃/HfO₂/Al₂O₃/HfO₂/SiO₂/Si) structure were investigated. The tunnel barrier structures for nonvolatile memory (NVM) application were designed by using the quantum-mechanical tunnel model (QM) and then the CTF memory devices were fabricated by stacking various dielectric materials for tunnel barrier, charge trap layer and blocking layer. As a result, a faster P/E speed and a longer data retention time were obtained from the MAHAHOS memory device. Especially, the program speed was enhanced by 10⁴ times from 100 ms to 10 us, and the erase speed was enhanced by 10² times from 1 s to 10 ms. Also, the MAHAHOS device showed an improved retention characteristic compared with the MAHOS device. In addition, it is found that a high work function gate electrode (Pt) contributes to a significant reduction of data erasing time and an improved data retention characteristic of MAHAHOS memory device.