Investigating contact resistance between WO_x and metal electrodes in ECRAMs via interface analysis

In neuromorphic computing, which overcomes the limitations of the von Neumann architecture, resistive processing units performing data processing and memory storage simultaneously have been widely researched. Among analog resistive devices, electrochemical random-access memories (ECRAMs) have drawn significant attention, which operate via ion movements to control channel conductance. Despite their promising switching characteristics, the contact resistance between Tungsten oxide (WO_x) channel and metal electrodes has not been studied yet. In this study, we fabricate transmission line model devices to investigate the contact resistance between WO_x and the metals of Tungsten (W), Molybdenum (Mo), and Nickel (Ni). Results show that W exhibits the lowest contact resistance with WO_x, followed by Ni and Mo. We confirm that W and Mo show Ohmic contacts, whereas Ni reveals a Schottky contact with a Schottky barrier height of 118 meV. Moreover, we demonstrate Mo only forms a metal oxidation layer of 9 nm at the interface between WO_x and Mo. Finally, we present the trend of contact resistivity depending on WO_x channel resistivity under different channel conductance values of the W contact. These findings provide insights into contact resistance of WO_x-based ECRAMs, suggesting that W is the most suitable contact material for achieving high performance.