A Fully Si-Compatible Ni/Si₃ N₄ /Al₂ O₃ /p⁺ Poly-Si RRAM Device for Analog Synapse and Its System-Level Assessment toward Processing-in-Memory Applications

We propose a fully Si-compatible resistive-switching random-access memory (RRAM) device consisting of a Ni/Si₃ N₄ /Al₂ O₃ /p⁺ poly-Si structure for processing-in-memory (PIM) applications fabricated through a process integration with Si CMOS compatibility. By introduction of an ultrathin Al₂ O₃ tunneling layer between the Si₃ N₄ switching layer and p⁺ poly-Si bottom electrode, the leakage current in the high-resistance state (HRS) is suppressed, resulting in stable bipolar switching characteristics with a high on/off current ratio of approximately 10⁴, maintained for more than 10⁷ switching operations, as evidenced through durability measurements. The retention characteristics were also maintained without degradation for a considerable time (>10⁵ s). When potentiation (6.5 V, 3 μs) and depression (−3.7 V, 3 μs) pulses with the same voltage and time conditions were applied, the device exhibited stable conductance change characteristics with high linearity and symmetry, demonstrating its potential for use as an analog synaptic device through repeatable signal modulation. The average conductance changes were 1.72 and 1.60 μS for potentiation and depression, respectively, confirming balanced weighting characteristics. Furthermore, based on experimentally obtained device characteristics, we implemented a VGG-8 convolutional neural network using the NeuroSim 1.4 framework and achieved high inference accuracy (90.25%), along with low latency and high energy efficiency on the CIFAR-10 data set. Thus, the proposed device holds promise for next-generation nonvolatile memory and analog neural network computing, particularly for energy-efficient processing-in-memory architectures.