Characterization of BE-SONOS flash memory using rare-earth materials in tunnel barrier with improved memory dynamics

Abstract

In this paper, we have investigated the effect of rare-earth materials in tunnel dielectric to improve the trade-off between erase speed and retention. Here, rare-earth materials have low valence band offset with high permittivity to enhance both erase speed and retention in bandgap engineered silicon-oxide-nitride-oxide-silicon (BE-SONOS). In addition, we observed higher program speed due to lower conduction band offset as compared to SiO2. Silicate of scandate of rare earth element, GdScSiO (Gd=Gadolinium), is investigated as SiN replacement in tunnel dielectric (SiO2/SiN/SiO2) of BE-SONOS. Further, rare earth aluminates, GdAlO and LuAlO (Lu=Lutetium), are used to replace the SiO2 layer in tunnel oxide. Also, gate length is scaled down and we have observed the effect of aforementioned materials in tunnel barrier, however, for the same effective oxide thickness (EOT). We found that the scaling down of gate length has negligible impact on the reliability of the devices. As a consequence, various investigated tunnel oxide stacks possess good memory characteristics with a negligible charge loss (at 25 °C) after a period of ten years and a considerable charge loss at an elevated temperature of 150 °C.