Correlation between Filament Distribution and Resistive Switching Property in Binary-Transition-Metal-Oxide Based Resist
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Correlation between Filament Distribution and Resistive Switching Property in Binary-Transition-Metal-Oxide Based Resistive Random Access Memory. H. Tanaka1, K. Kinoshita1,2, M. Yoshihara1, and S. Kishida1,2 Department of Information and Electronics, Graduate School of Engineering, Tottori University, 4-101 Koyama-Minami, Tottori 680-8552, Japan. 2 Tottori Univ. Electronic Display Research Center, 522-2 Koyama-Kita, Tottori 680-0941, Japan.
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ABSTRACT Large variation in basic memory properties is a serious issue that hinders the practical use of ReRAM. This study revealed that one of the main factors causing variation is the presence of multiple filaments which have distinct set voltages in each memory cell. An operating filament switches to another filament having the smallest set voltage at each instant of switching. We propose a resistive switching model that takes the presence of multiple filaments into consideration. A Monte Carlo simulation based on the resistive switching model reproduces the set voltage distribution. Improvement of accuracy of the simulation can be also expected considering the fact that Vset increases at a certain probability at each instant of set switching. INTRODUCTION Although resistive random access memory (ReRAM) has several advantages as a nextgeneration substitute for flash memory, such as non-volatility, simple structure, and high speed operation [1], large variations in basic memory properties [2-8] must be addressed before ReRAM can be put into practical use. The presence of multiple filaments is considered to be one of the possible origins of large variation of switching voltage [5-8]. Since a method for controlling Nfila has not yet been established, it is difficult to elucidate the dependence of basic memory properties on the number (No.) of filaments, Nfila. In fact, although it has been reported that resistance in the low-resistance state (LRS; RLRS) can be controlled by limiting the current flowing through a ReRAM element at the moment of occurrence of set switching [3, 9], the origin of a change in RLRS is not clear, where the set is switching from a high-resistance state (HRS; RHRS) to LRS. Therefore, the most important factor affecting RLRS is unclear; at least three possible factors, the change in Nfila, the diameter of a filament, and resistivity of a filament. In this context, Yoda et al., [10] reported that filaments are formed on the etched surface of a NiO film without a forming process in Pt/NiO/Pt structures due to the reduction effect of dry etching [11-13]. Here, the forming process is a phenomenon similar to the soft dielectric breakdown. Nfila is proportional to the length of the perimeter of elements (4L), Nfila ∝ L, if all elements are etched under the same conditions as shown in Fig. 1(a). That is, switching properties are expected to be dependent on L in the etched elements. In this paper, we investigated dependences of resistance in an initial resistance state (IRS; RIRS), RHRS and Vset-distribution on the perimeter of Pt/NiO/Pt structures that was for
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