Probing of Ag-based Resistive Switching on the Nanoscale
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Probing of Ag-based Resistive Switching on the Nanoscale A. Geresdi, 1 A. Halbritter,1 E. Szilágyi2 and G. Mihály1 1
Department of Physics, Budapest University of Technology and Economics and Condensed Matter Research Group of the Hungarian Academy of Sciences, 1111 Budapest, Budafoki út 8., Hungary 2 KFKI Research Institute for Particle and Nuclear Physics, P.O. Box 49, H-1525 Budapest, Hungary ABSTRACT We study the switching characteristics of nanoscale junctions between a metallic tip and a silver film covered by a thin Ag2S ionic conductor layer. Resistive switching phenomena are studied on samples of various Ag2S layer thicknesses. Metallic and semiconductor behavior are distinguished by current-voltage characteristics measured at room temperature and at 4.2 K. INTRODUCTION Memristive systems based on solid state ionic conductors are good candidates for the next generation of nonvolatile computer memory elements [1-3]. Pushing the limits of device fabrication to further increase the speed and integration, electrical characterization becomes important in order to ensure the control of the device parameters. The ionic conductor Ag2S has already proven to be a promising compound for novel nanoelectronic circuits [4,5]. The operation is based on the electrochemical reaction Ag (+Ag 2 S ) + e − ⇔ Ag ( metal ) controlled by the bias voltage, i.e. metallic silver is dissolved or retracted from the Ag2S. Depending on the polarity, Ag metallic filaments are built up or destructed thus the resistance of the junction can be tuned in a reversible manner [6-8]. The Ag+ ionic migration is effectively stopped at zero bias even at room temperature resulting in a nonvolatile operation. Due to the bipolar switching of this system, memory elements based on Ag2S are often presented as a realization of the memristor, the circuit element first proposed by L. Chua [9]. EXPERIMENTAL DETAILS AND SAMPLE CHARACTERIZATION Sample preparation and characterization Ag thin films with a nominal thickness of 80 nm were vacuum evaporated onto a Si substrate. The thin Ag2S layer was grown by depositing sulfur onto the Ag surface in a clean environment. First, analytic grade sulfur powder was loaded in a quartz tube, melted and cooled back in order to ensure a homogenous source. The thin film sample was then loaded in the tube to a distance of 2 cm from the sulfur. After loading both the sulfur and the sample, the tube was evacuated to 10-5 mbar. Then the temperature was ramped up to T=60°C and the sublimation of the sulfur was performed in a static vacuum for a designated time tS. Finally, the temperature was rapidly ramped down.
The samples were characterized by He-RBS (Rutherford Backscattering Spectrometry) and ERDA (Elastic Recoil Detection Analysis). The RBS and ERDA experiments were performed using an ion beam of 1620 keV 4He+ simultaneously at a tilt, recoil and scattering angles of 80°, 20° and 165°, respectively. An ion current of typically 4-8 nA was measured by a transmission Faraday cup [10]. The concentration profiles determined f
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