A Simulation Model of Resistive Switching in Electrochemical Metallization Memory Cells (ECM)
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1160-H09-03
A Simulation Model of Resistive Switching in Electrochemical Metallization Memory Cells S. Menzel1,3, B. Klopstra1,3, C. Kügeler2,3, U. Böttger1,3, G. Staikov2,3 and R. Waser1,2,3 1 Institut für Werkstoffe der Elektrotechnik II, RWTH Aachen, Aachen, 52074, Germany 2 Institut für Festkörperforschung, Forschungszentrum Jülich GmbH, Jülich, 52425, Germany 3 JARA - Fundamentals of Future Information Technology
ABSTRACT In the present study a simulation model for set operation in electrochemical metallization memory cells was developed to obtain a better understanding of the physical processes involved in resistive switching. The set operation based on filamentary growth within a solid electrolyte was simulated using continuity equation to address the electric properties and a level set method to track the boundary of the filament. FEM simulations were performed using Comsol Multiphysics. The results showed good agreement to experimentally observed I/V - curves for set operation. Furthermore, it could be demonstrated that only one filament is responsible for set operation. Based on this FEM model a simplified resistor based 1D model was developed, showing good agreement to each other. As a refinement, Butler-Vollmer boundary conditions were introduced. This nonlinearity led to an exponential dependency between switching time and switching voltage, which is also observed in experiment. INTRODUCTION The Electrochemical Metallization Cell (ECM) is a promising candidate for future nonvolatile random access memory overcoming the limits of DRAM (volatile) and Flash (slow). The storage principle is based on change of cell resistance induced by electro-chemical driven growth and rupture of a copper or silver filament in an insulating matrix. This kind of switching was found in several materials such as AgGeSe, CuGeS, SiO2, WO3 and MSQ [1-4]. In the present study modeling is based on a copper (Cu) filament without loss of generality. During write (set) operation Cu is oxidized at the corresponding electrode and Cu ions are driven out of the Cu anode into the insulating matrix due to the applied field, whereas the insulating matrix serves as solid electrolyte. The Cu ions migrate towards the cathode. At the cathode electrochemical reduction occurs, and deposition of metallic Cu takes place. Fast drift paths in the solid electrolyte matrix or preferred nucleation sites (surface inhomogenities) at the boundary lead to filamentary growth. This growing Cu filament finally reaches the anode and switches the device to a low resistance state. In the present study modeling is based on a Cu filament without loss of generality. THEORY FEM Simulation Model A simulation model for set operation needs to account for the electrical properties, the Cu ion migration as well as filamentary growth. To simplify the model the dissolution of the anode is neglected, since the active volume of the anode is large compared to the volume of the filament. In addition Cu ion concentration gradients within the solid electrolyte matrix are
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