Research Advisor: Prof. Yoshio Nishi
As NAND Flash memory technology is facing challenging issues such as electronic coupling between adjacent cells or high coupling of the control gate with floating gate in scaling down to and beyond 16nm technology node, investigations of new functional devices or materials has been attempted for next-generation memory technology to continue development of memory technology beyond 16 technology generation. One of new emerging non-volatile memories is resistance change random access memory(ReRAM) satisfying the requirements to replace NAND Flash; low cost, simple structure, promising 8nm technology node, low power dissipation, high endurance, possible integration in crossbar arrays in 3D.
In ReRAM, understanding the switching mechanism was very complicated because there have been many different switching phenomena in circumstances under ultimate electrical stress. One of them, oxidation/reduction of transition metals is generally accepted for unipolar switching. In this switching phenomenon, both thermal and chemical processes are correlated with the effect of electric field. To suggest clearer understanding of switching mechanism for unipolar switching, defect states in NiO are investigated, which are closely related conductivity in the transition metal-based resistive materials. Setting up feasible "ON" and "OFF" states in atomic scale gave an insight into atomic structure of conductive filament, role of oxygen (or oxygen vacancies) and its migration. With the understandings from first principle simulations, physically quantitative model about reset/retention and filament formation could be suggested. In addition to that, obtained experimental results like reduction of reset current and long retention time of RON due to inserted interfacial layer could be explained based on the quantitative model.
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