Improved Synaptic Behavior of CBRAM Using Internal voltage Divider for Neuromorphic Systems

Abstract

In this paper, we demonstrate the linear conductance-change characteristics of a conductive-bridging RAM (CBRAM) to be employed as an artificial synapse device in neuromorphic systems. The CBRAM with a bilayer electrolyte structure (Cu/Cu2-xS/WO3-x/W) exhibits analog switching behavior during the depression process due to the well-controlled dissolution of the conductive filament. To analyze the origin of this motion, we investigate the effective voltage applied to Cu2-xS and WO3-x. Our findings reveal that Cu2-xS, acting as a voltage divider, helps in suppressing the large voltage drop in WO3-x, where the formation/dissolution of filament occurs. Furthermore, due to the diode-like characteristics of Cu2-xS and the division of voltage drop between WO3-x and Cu2-xS, an optimum programming energy is applied to WO3-x during the depression process. This leads to linear conductance-change characteristics under identical pulses. However, abrupt conductance-change characteristics are observed during the potentiation process. Thus, we use only the device characteristics of the depression part for the neuromorphic system. An excellent classification accuracy is achieved due to the linear conductance-change characteristics and optimized pulse conditions.