Multilevel Nonvolatile Small-Molecule Memory Cell Embedded with Ni Nanocrystals Surrounded by a NiO Tunneling Barrier

Four-level nonvolatile small-molecule 4F2 memory cells were developed with a sandwiched device structure consisting of an upper Al electrode, upper small-molecule layer (Alq3, aluminum tris(8-hydroxyquinoline)), Ni nanocrystals surrounded by NiO tunneling barrier, lower small-molecule layer, and bottom Al electrode. In particular, an in situ O2-plasma oxidation process following Ni evaporation was developed to produce uniformly stable 10 nm Ni nanocrystals surrounded by a NiO tunneling barrier embedded in the small-molecule layer. They presented a memory margin (Ion/Ioff ratio) of ≈1 × 103, a retention time of more than 105 s, an endurance of more than 5 × 102 erase-and-program cycles, and multilevel cell (MLC) operation, being a terabit nonvolatile memory-cell. A vertically double-stacked 4F2 multilevel nonvolatile memory cell was also developed, showing a memory margin of ≈1 × 103 in both the top and bottom memory cells and eight-level cell operation.