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This study implements a highly uniform 3D vertically stack resistive random‐access memory (VRRAM) with a four‐layer contact hole structure. The fabrication process of a four‐layer VRRAM is demonstrated, and its physical and electrical properties are thoroughly examined. X‐ray photoelectron spectroscopy and transmission electron microscopy are employed to analyze the chemical distribution and physical structure of the VRRAM device. Multilevel capability, reliable endurance (>104 cycles), and retention (104 s) are successfully obtained. Synaptic memory plasticity, such as spike time‐dependent plasticity, spike rate‐dependent plasticity, excitatory post‐synaptic current, paired‐pulse facilitation, and long‐term potentiation and depression is presented. Finally, the vector‐matrix multiplication (VMM) operation is conducted on a 4 × 12 VRRAM array, according to the low resistance state ratio. It is ascertained that the accuracy drop, which can occur due to VMM error, can be limited to a decrease of less than 0.44% point. Utilizing the high‐density, multilevel, and biological characteristics of VRRAM, it is possible to implement high‐performance neuromorphic systems that require densely integrated synaptic devices. [ABSTRACT FROM AUTHOR]

In this study, oxygen‐rich TiOy and TiOx 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 TiOy/TiOx/Al2O3 switching layer and the Pt/Al top electrode, an additional AlOy layer can be induced to act as an additional OSL. The proposed annealing process accelerates the oxidation reaction of AlOy/TiOy 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 AlOy/TiOy 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. [ABSTRACT FROM AUTHOR]