Metal nanocrystal/nitride heterogeneous-stack floating gate memory

Nonvolatile memories with heterogeneous-stack floating gate of metal nanocrystals and silicon nitride (Si3N4) have been fabricated and characterized. The heterogeneous gate stacks showed superior characteristics in retention and low voltage write/erase over single metal nanocrystal memories and/or nitride memories (i.e., MONOS or SONOS). The metal nanocrystals in the stack made low voltage operation possible by the direct tunneling programming, while the nitride layer as an additional charge storage trap layer enabled longer retention time. By making the double stack of Si3N4-Au-Si3N4-Au, we could enhance the memory characteristics even further