The Influence of Water Absorbed in Grain Boundary of a Polycrystalline NiO Layer on the Memory Characteristics of Pt/NiO
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The Influence of Water Absorbed in Grain Boundary of a Polycrystalline NiO Layer on the Memory Characteristics of Pt/NiO/Pt Resistive Random Access Memory (ReRAM) Ryosuke Ogata1, Masataka Yoshihara1, Naohiro Murayama1, Satoru Kishida1,2 and Kentaro Kinoshita1,2 1 Tottori University, Tottori 680-8550 2 Tottori University Electronic Display Research Center, Tottori, 680-8550 ABSTRACT We focused on the presence of water absorbed in the grain boundary of a polycrystalline transition metal oxide (TMO) film in an EL/poly-TMO/EL structure. The effect of supplying water to resistive random access memories (ReRAMs) of Pt/NiO/Pt structure on switching voltages and data retention characteristics was investigated. As a result, switching voltages were decreased by supplying water and reset switching was confirmed to be strongly induced by supplying water even at room temperature without applying voltage. These results suggest that water enhances resistive switching effect by providing reducing species and oxidizing species respectively such as H+ and OH-. INTRODUCTION Resistive Random Access Memory (ReRAM) is expected as a substitute for Flash memory, which is facing a miniaturization limit,1) due to advantages such as non-volatility, high density,2,3) high speed switching,4,5) and low power consumption (low switching voltages6) and low current7,8)). ReRAM takes a simple sandwich structure of top-EL/TMO/bottom-EL and utilizes a change in the resistance caused by applying a bias voltage between the top- and bottom-ELs, where EL and TMO are electrode and transition metal oxide, respectively. The resistance switching effect is generated after a forming process, which is similar to a dielectric breakdown.9,10) Then, the resistance switching from a low resistance state (LRS) to a high resistance state (HRS), which is called reset, and vice versa, which is called set, can be repeated alternately by applying a voltage. The magnitude relation of Vform > Vset > Vreset is generally satisfied for switching voltages of unipolar-type ReRAM, where Vform, Vset, and Vreset represent voltages required to cause forming, set, and reset switching respectively. In particular, reducing Vform is important, since Vform gives the maximum value of switching voltages. Assuming that the current path of ReRAM, called filament, consists of oxygen vacancies and that the resistive switching occurs by the formation and recovery of the oxygen vacancies,11,12) the presence of an oxygen reservoir, which receives (provides) oxygen from (to) the filament for set (reset) switching to occur, is necessary. Goux et al. reported that the yield of effective reset switching decreased in vacuum than in air when the thickness of the Pt top-EL was thin.13) They attributed this result to the depletion of movable oxygen species due to the release of oxygen from the inside of the ReRAM element to the environment. Goux et al. also reported that reset switching took place only when catalytic metals such as Pt and Ni are used as anode.14) Based on this result, they pointed out a po
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