Exposure Light Wavelength Effects on Charge Trapping and Detrapping of nc-MoOx Embedded ZrHfO High-k Stack
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Radial Growth Model for Conical Nanobridge in Resistive Switching Memory Devices Tong Liu, Yuhong Kang, Sarah El-Helw, Tanmay Potnis, and Marius Orlowski Bradley Department of Electrical and Computer Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, U.S.A. ABSTRACT A phenomenological model has been proposed for the radial growth of the copper or silver nanobridge in the conductive bridge random access memory devices. In this model, the growth rate of the bridge is proportional to the local ion flux based on the hopping mechanism. Due to the differences of the local electric field, the growth rate is different along a conical shape nanobridge. The model accounts for the growth rate difference by introducing a geometrical form factor. Based on the model, the top and bottom radii are predicted for truncated conical copper nanobridge. The model is validated with data obtained on Cu/TaOx/Pt resistive devices. INTRODUCTION Conductive bridge random access memory (CBRAM) has attracted considerable attention due to its potential applications for nonvolatile memory and neuromorphic computation [1]. CBRAM devices consist of a thin insulating film sandwiched between an active metal layer (anode) and an inert metal layer (cathode). Silver and copper have been used for the anode layer and the insulating layer is a solid electrolyte for the active metal ions. The details of fabrication process and electrical characterization of the Cu/TaOx/Pt devices used for this study have been reported elsewhere [2-4]. With positive voltage applied to the active metal electrode, Ag+ or Cu+ ions can dissolve into the solid electrolyte and migrate under the influence of the electric field. Initially, due to the insulating property of the electrolyte, the device is in its high-resistance state (HRS). When the metal ions are reduced on the inert metal layer, they nucleate and a metallic nanobridge begins to form. Once the nanobridge makes a connection with both electrodes, the device transitions to the low resistance state (LRS). When the voltage reaches the set voltage (VSET), the nanobridge is established and the current increases abruptly. Compliance current (ICC) is applied to prevent damage to the cell. The nanobridge can be ruptured when a negative reset voltage (VRESET) is reached, and the current collapses to a small value. Multilevel data storage capability is one of the major advantages of CBRAM. This utility is implemented by controlling the resistance of a CBRAM device via compliance current levels. The dependence of the LRS resistance on applied compliance current has been attributed to two physical mechanisms [5]: (i) at low compliance current, the electron tunneling current dominates and the I-V characteristics are determined by the tunneling gap size; (ii) at high compliance current, metallic contact forms between metal nanobridge and electrode followed by radial growth of the nanobridge. The fast radial growth can be attributed to the ion flux sustained by high electric fields. In this paper, w
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