Sophisticated Conductance Control and Multiple Synapse Functions in TiO₂‐Based Multistack‐Layer Crossbar Array Memristor for High‐Performance Neuromorphic Systems

Abstract In this study, oxygen‐rich TiO_y and TiO_x layers are intentionally designed to have different oxygen compositions, functioning as an overshoot suppression layer (OSL) and oxygen reservoirs. Furthermore, by natural oxidation reactions occurring between the TiO_y/TiO_x/Al₂O₃ switching layer and the Pt/Al top electrode, an additional AlO_y layer can be induced to act as an additional OSL. The proposed annealing process accelerates the oxidation reaction of AlO_y/TiO_y OSLs, thereby enhancing the self‐compliance feature of devices. Moreover, the ultrathin AlN serves as an oxygen barrier layer (OBL) that inhibits the movement of oxygen ions at the interface between the Al₂O₃ layer and the Pt/Ti bottom electrode. The optimized devices are tested by DC sweep and pulses for neuromorphic computing systems. To realize biological synapse characteristics, several key synaptic memory plasticities are proposed. Finally, a 24 × 24 crossbar array based on the 0T‐1R structure, incorporating optimized AlO_y/TiO_y OSLs and OBL via the annealing process, is characterized. During the electroforming step, all specified target cells (marked with the letters “ESDL”) achieved self‐compliance at low current levels without experiencing hard‐breakdown failures or interference among neighboring cells. The successful array performance is demonstrated by the accurate tuning of target weights.