Simulation Study on Reproducing Resistive Switching Effect by Soret and Fick Diffusion in Resistive Random Access Memory
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Simulation Study on Reproducing Resistive Switching Effect by Soret and Fick Diffusion in Resistive Random Access Memory Kentaro Kinoshita,1, 2 Ryosuke Koishi,1 Takumi Moriyama,1, 2 Kouki Kawano,1 Hidetoshi Miyashita,1, 2 Sang-Seok Lee,1, 2 and Satoru Kishida1, 2 1 Department of Information and Electronics, Graduate School of Engineering, Tottori University, 4-101 Koyama-Minami, Tottori 680-8552, Japan. 2 Tottori Integrated Frontier Research Center, 4-101 Koyama-Minami, Tottori 680-8552, Japan. ABSTRACT It is widely received that resistive switching in electrode (EL)/metal oxide (MO)/EL cell is caused by formation and rupture of a conductive filament (CF) consisting of oxygen vacancies, VO's. However, driving forces that migrate VO's are not elucidated yet. Considering an experimental fact that good data endurance more than 106 cycles is often observed, an isotropic driving force that gathers oxygen vacancies and form a CF for set switching is required instead of an electric field drift that is widely received as the driving force of set switching. In this paper, we reexamined driving forces and succeeded in reproducing pulse response data for wide rise time, trise, range by simulating VO migration assuming Fick and Soret diffusion, without including the electric-field drift. Therefore, it was suggested that controlling T distribution considering the waveforms of write/erase pulses and the thermodynamic parameters of ELs as well as MO is crucial for the optimization of switching speed of ReRAM. INTRODUCTION A filament model, in which a conductive filament (CF) consisting of oxygen vacancies (VO’s) is formed in the metal oxide (MO) film of an EL/MO/EL structure by a forming process and the resistive switching effect is caused by generation and repair of oxygen vacancies, is widely accepted, where EL and MO represent an electrode and a metal oxide, respectively.1) Even when metal deficient MOs such as NiO2,3) and CoO4), which have p-type semiconducting property, were used as the MO layer, it was often reported that the filament model based on the diffusion of VO’s was applicable. However, driving forces of VO migration that cause reset, which is switching from a low resistance state (LRS) to a high resistance state (HRS), and set, which is switching from LRS to HRS, are still unclear. Koh et al. reported that the oxygen reservoir of a Pt/NiO/Pt structure is the NiO film itself surrounding the CF.5) Therefore, to explain high cycling endurance of unipolar-type resistive random access memory (ReRAM), a driving force that is different from an electric field drift that is perpendicular to the EL interface is required to cause set switching. One of the candidates for this driving force is the Soret diffusion, which works in the direction of the temperature, T, gradient.6) In this paper, we examined Soret diffusion as a driving force instead of electric field drift of VO's. We succeeded in reproducing pulse response data for wide rise time, trise, range by simulating VO migration assuming Fick and Soret diffusion as driving
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