Understanding the Role of Process Parameters on the Characteristics of Transition Metal Oxide RRAM/Memristor Devices
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Understanding the Role of Process Parameters on the Characteristics of Transition Metal Oxide RRAM/Memristor Devices Branden Long, Yibo Li, and Rashmi Jha Department of Electrical Engineering and Computer Science University of Toledo, Toledo, Ohio 43606, U.S.A. ABSTRACT In this report, we studied the role of the oxygen concentration in TiOx layer of Ni/TiOx/TiO2/Ni stack based 2-terminal resistive random access memory (RRAM) devices. The sample with oxygen deficient TiOx layer showed Schottky diode type J-V characteristics in the as-fabricated state while the sample with higher oxygen content in TiOx demonstrated MIM or back-to-back connected diode behavior. The Capacitance-Voltage (C-V) profiling was performed and doping density vs. depletion width characteristic was obtained. The conductance technique was implemented to study the interface state density. The RRAM type switching behavior of these samples was studied. The sample with high oxygen in TiOx showed filament based switching after electroforming while the sample with low oxygen in TiOx showed switching governed by the charge trapping. INTRODUCTION Transition metal oxide (MOx) based 2-terminal (2-T) resistive random access memory (RRAM) /memristor devices hold tremendous potential for enabling massively dense nonvolatile memory elements on chip [1,2]. In spite of recent research progress in this area, there are several unanswered questions of fundamental nature that need to be addressed. For example, the resistive switching mechanism has been predominantly explained by two broadly accepted theories: (i) formation of filaments in MOx, and (ii) movement of oxygen vacancies (Vo2+) in MOx [1,2]. However, the role played by the process parameters such as the oxygen concentration in the MOx in governing the switching due to either of these phenomena is largely unknown. Furthermore, our understanding on the types of defects in these devices and their impact on governing the device performance has been very limited. In this paper, we report our work towards understanding the role played by oxygen concentration in the MOx stack in governing the RRAM/memristor switching behavior. Furthermore, we have implemented admittance spectroscopy techniques to understand the doping distribution and defects in 2-T RRAM devices based on MOx. We believe that these understandings will be critical for the development of the appropriate MOx materials, process conditions, and defect passivation techniques for the successful realization of RRAM/memristor devices. EXPERIMENT Sample Fabrication We performed our studies on two sets of samples with different concentration of oxygen in the MOx stack. Figure 1 shows the schematic representation of our devices. 2-T devices consisting of Ni/TiOx/TiO2/Ni stacks were fabricated on p-Si substrate. All materials were deposited using RF magnetron sputtering. The concentration of oxygen in TiOx and its thickness
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was varied between the two samples while all the other materials in the stack remained the same. The samples were fabricated by first
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