Sung-Ho Seo

Multilevel nonvolatile small-molecule memory cell embedded with Ni nanocrystals surrounded by a NiO tunneling barrier.

Four-level nonvolatile small-molecule 4F(2) memory cells were developed with a sandwiched device structure consisting of an upper Al electrode, upper small-molecule layer (Alq(3), aluminum tris(8-hydroxyquinoline)), Ni nanocrystals surrounded by NiO tunneling barrier, lower small-molecule layer, and bottom Al electrode. In particular, an in situ O(2)-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 (I(on)/I(off) ratio) of approximately 1 x 10(3), a retention time of more than 10(5) s, an endurance of more than 5 x 10(2) erase-and-program cycles, and multilevel cell (MLC) operation, being a terabit nonvolatile memory-cell. A vertically double-stacked 4F(2) multilevel nonvolatile memory cell was also developed, showing a memory margin of approximately 1 x 10(3) in both the top and bottom memory cells and eight-level cell operation.

Small Molecular Organic Nonvolatile Memory Cells Fabricated with in Situ O 2 Plasma Oxidation

We developed small molecular organic nonvolatile 4F² memory cells using metal layer evaporation followed by O₂ plasma oxidation. Our memory cells sandwich an upper α-NPD layer, Al nanocrystals surrounded by Al₂O₃, and a bottom α-NPD layer between top and bottom electrodes. Their nonvolatile memory characteristics are excellent: the V th , V p (program), V e (erase), memory margin (I on /I off ), data retention time, and erase and program endurance were 2.6V, 5.3V; 8.5V, ?1.5×10², 1×10 5 s, and 1×10³ cycles, respectively. They also demonstrated symmetrical current versus voltage characteristics and a reversible erase and program process, indicating potential for terabit-level nonvolatile memory.