Performance improvement of metal-Al2O3-HfO2-oxide-silicon memory devices with band-engineered Hf-aluminate/SiO2 tunnel barriers

Physical properties of Hf-aluminate (HA) films with various compositions, deposited by atomic layer deposition, were investigated in terms of microstructure, band-gap, and band-offset with respect to Si. Charge trap flash (CTF) memory devices based on HA/SiO2 stacks as tunnel barriers were also fabricated and characterized. Modulation of HA film composition produced controlled changes of the film's band-gap and band-offset. Additionally, the tunneling efficiency of the HA/SiO2 tunnel barrier stacks was observed to be higher than that for a single SiO2 tunnel barrier, in particular at high voltage bias. The band-engineered CTF memory devices with HA/SiO2 tunnel barriers showed improved program/erase speed compared with those with single SiO2 tunnel barrier. The Al-rich HA/SiO2 tunnel barriers showed a longer charge retention time with superior endurance characteristics; in contrast, the Hf-rich HA/SiO2 tunnel barrier showed degraded charge retention because of current leakage through crystallized regions in the film. (C) 2013 American Vacuum Society.