Dependence on Organic Thickness of Electrical Characteristics Behavior in Low Molecular Organic Novolatile memory

Abstract

AbstractRecently, organic nonvolatile memory of nonvolatile memories have attracted attention because application as next generation memory devices. In effort for realizing low-molecular organic nonvolatile memory, the dependence of organic thickness on electrical characteristic behavior in low-molecular organic nonvolatile memory was investigated. We developed an low-molecular organic nonvolatile memory fabricated with the device structure of Al/Alq3 (Aluminum tris(8-hydroxyquinoline))/Ni nanocrystals/Alq3/Al. Four different organic thicknesses, i.e., 30, 40, 50, and 100 nm, with fixing middle layer thickness were deposited by using a high vacuum thermal deposition method. The reason we chose Ni for middle metal layer is that Ni has smaller grain boundary which is benefit for scaling down and larger work function (∼5.15 eV) that can make a deep quantum well in energy band diagram, compared with those of Al. We confirmed that, as an organic thickness increases, a current level linearly decreases by an order of magnitude in a log-scale except for the 100 nm sample case. That is, Ion of 30-nm-thick sample was about 1 mA and 50-nm-thick sample was about 10 ¥ìA. The reason why the decrease in the current with increasing an organic thickness can be attributed to that electron transfer occurs less frequently because of the decrease in the hopping frequency. In addition, a 100-nm-thick sample was not shown the electrical characteristic of low-molecular organic nonvolatile memory. Meanwhile, the switching characteristics of our device showed that Vth of 2V, Vp(program) of 4V, Ve(erase) of 7V, and Ion (after programming)/Ioff (after erasing) of ~6x103. In addition, the interesting behavior of those characteristics is that the switching voltages (e.g; Vth, Vp, Ve Ion/Ioff) were not much changed with a varying an organic thickness. Therefore, we can conclude that an organic thickness does not affect significantly to the switching characteristics but current level. In addition, it was confirmed that a 30-nm-thick organic thickness was the best process condition in realizing low-molecular organic nonvolatile memory fabrication process.