Effect of SiO₂ interfacial layer on InGaZnO-based memristors for neuromorphic computing applications

To achieve progressive resistance modulation with memristors, we utilized InGaZnO (IGZO) films with a Pd top electrode to form a Schottky barrier at the interface. As oxygen vacancies (V_O) were ionized and recombined in the IGZO layer depending on the applied voltage polarity, the magnitude of the barrier was smoothly adjusted, enabling analogous modulation of current. Because a native SiO₂ layer was invariably formed on the Si bottom electrode (BE) during fabrication, we analyzed the impact of the SiO₂ layer on the memristive characteristics of the IGZO layer through a comparison between memristors with differently formed SiO₂ layers. Even when the native oxide was removed via wet etching, the subsequent IGZO sputtering induced oxidation at the Si BE interface by scavenging oxygen ions, resulting in a non-stoichiometric IGZO layer. Contrarily, when the interfacial SiO₂ was intentionally deposited using an e-beam evaporator after wet etching, physical analysis showed that the scavenging of oxygen ions from the IGZO layer was inhibited. Among the fabricated samples, the memristor with the V_O-rich non-stoichiometric IGZO layer exhibited improved state stability over time. These optimized IGZO memristors also displayed analogously tunable weight-update behavior when incorporated into neuromorphic synaptic devices, enabling artificial neural networks to achieve high pattern-recognition accuracy.