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Mechanism Analysis of Nonvolatile Graphene Oxide Based Reram with Laterally Structured Device

Tuesday, 7 October 2014
Expo Center, 1st Floor, Center and Right Foyers (Moon Palace Resort)
Y. Park, J. Ko (Seoul National University), J. A. Lim (Future Convergence Research Division, Korea Institute of Science and Technology, Seoul 136791, Republic of Korea), S. Cho, J. Yoo (Seoul National University), and Y. S. Kim (Seoul National University, The Graduate School of Convergence Science and Technology, Program in Nano Science and Technology)
There has been an increase in demand for novel nonvolatile-memory technology for low-power, high speed and high scalability because of development of digital technology. With this background, various types of memory are now enthusiastically developed to overcome the limitations of traditional Si-based memory which is difficulty to miniaturize the device and to advance high performance. Resistive random access memory (ReRAM) is a good candidate for next generation devices due to its high speed, low voltage consumption and high scalability. Recently flexible electronic devices such as wearable electronics and optoelectronics have attracted interest, so flexible ReRAM devices are also required. Metal oxide thin film based memory in ReRAM have hitherto been studied mainly as next generation nonvolatile memory devices and have shown good properties such as retention, endurance, and programming characteristics. However, ReRAM based on metal oxide thin film has limitations of fabrication process for flexible device due to their material properties. ReRAM using graphene oxide (GO) is the most promising candidate for the flexible device due to graphene oxide’s great electrical and mechanical properties. Graphene oxide ReRAM can be fabricated at room temperature on flexible substrates where metal oxides cannot be.

Despite of its excellent properties, the resistive switching mechanisms remain unclear. It is generally assumed that filamentary theory and oxygen migration theory are the major mechanisms of resistive switching phenomena. In this work, we demonstrate the resistive switching mechanisms of ReRAM with laterally structured devices, which have two-terminal electrodes in the same plane. The laterally structured graphene oxide ReRAM devices are fabricated by simple spin-coating method on silicon dioxide substrates. The aluminum (Al) electrodes are deposited on spin-coated grapheme oxide layer by thermal evaporation as shown in Figure 1a. These Al/GO/Al lateral devices show memory properties similar to vertical structure as shown in Figure 1b. Conventional memory devices with vertical structure consist of a MIM (metal / insulator / metal) stack are hard to demonstrate the switching properties because the conducting paths are formed inside of the active layer, graphene oxide. In case of lateral structure device, conducting paths are formed on the surface of the active layer, where it’s easily observed the conducting paths directly using TEM or XPS analysis. Graphene oxide sheets have chemically reactive oxygen functional groups such as carboxyl, epoxy and hydrogen groups decorating the edges and the basal plane. It is assumed that these oxygen functional groups acting as the electron trap site influence the performance of the device. With functional group modification which can change the properties of graphene oxide, we can infer the role of oxygen functional groups in switching mechanisms.

So, we can demonstrate the mechanism of ReRAM more clearly by lateral memory device.