Dependence on Organic Thickness of Electrical Characteristics Behavior in Low Molecular Organic Novolatile memory
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1071-F05-11
Dependence on Organic Thickness of Electrical Characteristics Behavior in Low Molecular Organic Novolatile memory Yool Guk Kim1, Sung Ho Seo1, Gun Sub Lee1, Jea Gun Park1, and Jin Kyu Kim2 1
Department of Electrical & Computer Engineering, Hanyang University, Nano SOI Process Laboratory, Room #101, HIT, Hanyang University 17 Haengdang-dong, Seoungdong-gu, Seoul, 133-791, Korea, Republic of 2
Electron Microscopy Team, Korea Basic Science Institute, 113 Gwahangno (52 Eoeun-dong), Yusung-gu, Deajeon, 305-333, Korea, Republic of
ABSTRACT We developed the devices to investigate the dependence on the organic thickness of electrical characteristics in small molecular organic nonvolatile memory. We developed four different thicknesses of organic layers, i.e., 30, 40, 50, and 100 nm, with a fixed middle layer thickness, were deposited using a high vacuum thermal evaporation. We confirmed that, as the organic layer thickness increases, the current level linearly decreases by an order of magnitude in a log-scale except for the 100-nm sample. The reason for this is that electron transfer occurs less frequently because of the decrease in the hopping frequency. Meanwhile, the switching characteristics did not much change. Therefore, we can conclude that the thickness of the organic layer does not significantly affect the switching characteristics except current level. In addition, it was confirmed that a 30-nm-thick organic layer was the best process condition for fabricating low-molecular organic nonvolatile memory. INTRODUCTION It has recently been reported that small molecular organic devices fabricated with a sandwich structure consisting of a top metal layer, small-molecular organic layer, middle metal layer, conductive organic layer, and a bottom metal layer demonstrated nonvolatile memory behaviors such as Ion (reading after programming)/Ioff (reading after erasing) of greater than 1x101 and response times of ~10 ns. The organic conductive layers of these devices are 2-amino4, 5-imidazoledicarbonitrile (AIDCN), Aluminum tris (8-hydroxyquinoline) (Alq3), and N,N’bis(1-naphthyl)-1, 1’biphenyl4-4’’diamine ( α-NPD ) .[1~6] These small molecular organic nonvolatile memories require Al nanocrystals. However, we fabricated small molecular nonvolatile memories with Ni nanocrystals. The reason we chose Ni is that has a smaller grain
boundary and a larger work function (~5.15 eV) that can make a deep quantum well in the energy band diagram. As a result, the memories showed a very large memory margin (Ion (reading after programming)/Ioff (reading after erasing) ratio) and were more reproducible. EXPERIMENTAL DETAILS We developed a small molecular organic nonvolatile memory with the device structure of a bottom Al electrode, conductive organic layer (Alq3), Ni nanocrystals surrounded by NiO, upper conductive organic layer (Alq3) , a n d a t op Al electrode. Four different organic thicknesses, i.e., 30, 40, 50, and 100 nm, with a fixed middle layer thickness were deposited by using a high vacuum thermal evaporation, a
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