Nonvolatile Memory with Multi-Stack Nanocrystals as Floating Gates

Nonvolatile memory technologies are focusing on devices with longer retention, faster read and write, higher bit density, improved endurance, and low-voltage program/erase characteristics. Nanocrystal (NC) memories are promising for realizing high-density nonvolatile storage with the inherent advantage of low-voltage operation [1]. Recently carbon molecules in the form of fullerenes (C60), known as “bucky balls,” also have been incorporated in non-volatile memory devices [2] with its advantages of mono-disperse nature and molecular size. In this project, various memory structures with self-assembled multi-stacked gold, platinum, and C60 nanocrystals as floating gates have been fabricated and characterized. In two-layer nanocrystal structures, the C60 bottom layer acts as an additional barrier to prevent charge back-tunneling from the upper layer, improving retention time without a commensurate penalty in program time. The upper nanocrystal layer functions as additional charge storage to provide sufficient memory window.