Structural and Chemical Analysis of Nanoscale Resistive Switching Devices: Assessment on Nonlinear Properties
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Structural and Chemical Analysis of Nanoscale Resistive Switching Devices: Assessment on Nonlinear Properties Kate J. Norris1,2 , J. Joshua Yang3, Nobuhiko P. Kobayashi1,2 1 Baskin School of Engineering, University of California Santa Cruz, Santa Cruz, CA 95064 U.S.A 2 Nanostructured Energy Conversion Technology and Research (NECTAR), Advanced Studies Laboratories, Univ. of California Santa Cruz – NASA Ames Research Center, Moffett Field, CA 94035 3 Electrical and Computer Engineering, University of Massachusetts, Amherst, MA 01003 USA ABSTRACT Investigation into the phenomenon of resistive switching, a reversible change in electrical resistance by the application of a voltage bias, has given rise to the device fabrication, DC electrical testing, and cross sectional TEM/EELS characterization of nanoscale resistive switching devices. Typically, resistive switching devices are composed of a thin oxide layer between two conductive electrodes where applied bias can alter the resistance states. In a crossbar array, nonlinearity of device I-V relation is a highly desirable characteristic that helps to mitigate the sneak path current leakage issue. Negative differential resistance (NDR) switching behavior offers such nonlinearity and has been observed in TaOx nanoscale devices utilizing certain electrode materials. To investigate this phenomenon, nanodevices were fabricated by sputtering TaOx onto TiN nanovias capped Nb electrodes. Cross sectional TEM/EELS were performed to reveal the physical and chemical changes in these devices to explore possible origins of nonlinear behavior when these top electrode materials are utilized with TaOx films. Introduction Resistive Random Access Memory (RRAM) devices are two terminal electrical resistance switches that retain a state of internal resistance based on the history of applied voltage and current. The occurrence of reversible resistance switching has been widely studied in a variety of material systems for applications including nonvolatile memory, logic circuits, and neuromorphic computing 1–3. These devices can be used for computing by both storing and processing information. These cross point devices are usually used in a crossbar array for real applications4,5. Most RRAM devices including those based on TaO2 and TiO2 switching materials have a linear or slightly nonlinear ON state current-voltage relations 6–9. Consequently, when reading or writing a bit of a switch all the other switches connected to the common line are partially selected, which further results in sneak path currents 10. Therefore, for large memory array applications, nonlinearity is desired to mitigate the sneak path leakage issue, which severely limits the size of the crossbar arrays and thus the density of the memory. This can be achieved with the utilization of a nonlinear selector in series with a resistive switch at each cross point. To address this here we investigate a stack that has been designed to combine resistive switching with a built-in selector. Experiment Figure 1a depicts the schematic of
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