Improved synaptic performances with tungsten-doped indium-tin-oxide alloy electrode for tantalum oxide-based resistive random-access memory devices

A reliable oxide-based tungsten-doped indium-tin-oxide/tantalum oxide/titanium nitride (W-ITO/TaO_x/TiN) memristor with controllable memory states and synaptic properties for neuromorphic computing is proposed herein. Cross-sectional electron energy-dispersive spectroscopy and X-ray photoelectron spectroscopy confirmed alloy W-ITO electrode formation above the TaO_x switching layer. Low operation voltage (SET voltage = + 1.2 V and RESET voltage − 1.5 V) with an ON/OFF ratio of > 10 was achieved owing to improved movement of oxygen ions and oxygen vacancies. Resistive-switching cycle-to-cycle variability was improved with a W-doped ITO electrode serving as the oxygen reservoir layer. A gradual step-wise resistance transition during the SET and RESET processes was observed depending on the applied DC step voltages. The conductivity of the synaptic device was successfully controlled by the pulse rise time with a fixed pulse amplitude. Essential synaptic characteristics, namely, spike rate-dependent plasticity, paired-pulse facilitation, and gradual potentiation–depression were implemented in W-ITO/TaO_x/TiN memristor. Emulation of synaptic function using the W-doped ITO electrode at the interface and a TaO_x-based memristor confirmed the potential for implementation as an artificial synapse. Graphical Abstract: [Figure not available: see fulltext.] Summary: Tungsten-doped indium-tin-oxide/tantalum oxide/titanium nitride memristor device increases oxygen vacancy (V_O) at the W-ITO/TaO_x interface, and thus, the d-band appears between the bandgap of W-doped ITO. A reliable synaptic weight change was controlled by varying the pulse interval and gradual conductance change monitored by sequential positive and negative pulse train applications.