Peter Clenott

As NAND Flash memory technology is facing challenging issues such as electronic coupling between adjacent cells and high coupling of the control gate with floating gate in scaling down to and beyond 16nm technology node, new functional devices or materials has been explored to continue consecutive development of memory technology beyond 16nm technology node. One of the new emerging non-volatile memories is resistance change random access memory(ReRAM) possibly meeting the requirements to replace NAND Flash; i.e., low cost, simple structure, promising 8nm technology node, low power dissipation, high endurance, possible integration in crossbar arrays in 3D on top of silicon base CMOS ICs. In ReRAM, understanding the switching mechanism was very complicated because there have been many different phenomena co-existing under circumstances when ultimate electrical stress is applied. One of them, oxidation/reduction of transition metals is generally accepted to results in the unipolar switching. In this switching mode, both thermal and chemical processes are associated with the effect of electric field. For clearer understanding of mechanism of the unipolar switching, defect states in NiO are investigated, which is closely related to electrical conductivity of the transition metal-based resistive switching materials. Study on 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 these first principle modeling results, a quantitative model for reset/retention and filament formation was proposed. Experimental results for reduction of reset current and long retention time of RON by inserting interfacial layer between a metal electrode and resistive switching material can be explained based on the quantitative model.