Data retention characteristics of nitride-based charge trap memory devices with high-k dielectrics and high-work-function metal gates for multi-gigabit flash memory

The data retention characteristics of nitride-based charge trap memories using metal-oxide-nitride-oxide-silicon (MONOS) structures employing high-k dielectrics and high-work-function metal gates have been investigated. The fabricated MONOS devices with structures of TaN/Al2O3/Si3N4/SiO2/p-Si show fast program/erase characteristics with a large memory window of greater than 6 V at program and erase voltages of +/- 18 V. From a bake retention test at high temperatures (200, 225, 250, and 275 degrees C), it is expected to take more than 40 years to lose less than 0.5 V charge loss at 85 degrees C. In this paper, we present an optimized cell structure for both improved data retention and erase speed, as well as a systematic study on the charge decay process in MONOS-type flash memory for high-density device applications.