Small Molecular Organic Nonvolatile Memory Fabricated with Ni Nanocrystals Embedded in Alq 3
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1071-F05-12
Small Molecular Organic Nonvolatile Memory Fabricated with Ni Nanocrystals Embedded in Alq3 YoungHwan Oh1, WooSik Nam1, GonSub Lee1, JeaGun Park1, and YongBok Lee2 1 Department of Electrical & Computer Engineering, Hanyang university, Tera-bit Nonvolatile Memory Development Center, room #101, HIT, 17 Haengdang-dong, Seongdong-gu, Seoul, 133-791, Korea, Republic of 2 Electron Microscopy Team, Korea Basic Science Institute, Deajeon, 305-333, Korea, Republic of ABSTRACT Recently, organic nonvolatile memory has attracted much interest as a candidate device for next generation nonvolatile memory because of its simple process, small device area, and high speed. To investigate electrical characteristics of small molecular organic nonvolatile memory with Ni as a middle metal layer, we developed a small molecular organic nonvolatile memory with the device structure of Aluminum tris (8-hydroxyquinolate) (Al/Alq3), Ni nanocrystals, and Alq3/Al. A high vacuum thermal deposition method was used for the device fabrication. It is critical that the fabrication process condition for Ni nanocrystals be optimized, thickness, 0.1 /sec-evaporation rate, and in-situ plasma oxidation for including ~100 effective oxidation. The reasons we chose Ni for the middle metal layer are that Ni has a smaller grain boundary, which is beneficial for scaling down and has a larger work function (~5.15 eV) that can make a deep quantum well in an energy band diagram, compared with that of Al. Our device showed an electrical nonvolatile memory behavior including Vth of ~2 V, Vw (write) of ~3.5 V, negative differential region (NDR) of 3.5~7 V, Ve (erase) of 8 V, and symmetrical electrical behavior at reverse bias. In addition, an interesting behavior of electrical properties was that, although retention and endurance characteristics were similar to the Al device, the Ion/Ioff ratio was greater than 104 at Vr (read) of 1 V. This value of the Ni device was higher than 102 compared to that of the Al device. Also, small molecular organic nonvolatile memory with a Ni middle layer with α-NPD at same fabrication condition showed more unstable characteristics than Alq3. We can speculate that there is a relationship in fabrication condition between the middle metal material and the organic material. Finally, we conclude that our device with a Ni nanocrystals middle layer is more reliable and useful for small molecular organic nonvolatile memory.
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INTRODUCTION Next generation nonvolatile memory is studied actively in many industrial and academic labs. Yang et al. (UCLA) reported on a high performance organic bistable device cell of a sandwich structure, which had Al nanocrystals embedded in a small molecular organic material 2-amino-4, 5-imidazoledicarbonitrile (AIDCN) between Al electrodes [1-3]. They fabricated Al nanocrystals by using a very low evaporation rate. Scott et al. (IBM) also reported on a device by using small molecular organic Alq3 (Aluminum tris (8-hydroxyquinoline)), which had the same structure of the UCLA’s group [4]. However,
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