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This paper presents the fabrication and characterization of the cross-point structure 20 × 20 μm 2 RRAM with TiO x /TiO y bi-layer insulator for synaptic application in neuromorphic systems. The measured oxygen concentration of the TiO x /TiO y switching layers of the fabricated devices using X-ray photoelectron spectroscopy analysis showed that the oxygen concentration ratio between TiO x and TiO y is ~ 1.5. After electroforming at ~ 5.62 V, the on/off ratio was ~ 76 at 0.2 V with the DC sweep voltage scheme. Synaptic behaviors including long-term potentiation (LTP) and long-term depression (LTD) were performed with 50 identical pulses for the implementation of RRAM into neuromorphic systems based on convolutional neural networks. Also, linearly increased (or decreased) 25 pulses were applied to the device so that the conductance changes linearly. The resulting linear LTP and LTD characteristics were mirror-symmetric, which could maximize the accuracy. For Hebbian learning, the device also mimicked the spike-timing-dependent plasticity properties with a conductance change from − 77.79% to 96.07% using a time-division multiplexing approach.

In this study, we have investigated the resistive switching behavior of multi-stacked PVA/ GO+PVA composite/PVA insulating layer-based RRAM (resistive random-access memory) as the annealing temperature of the insulating layer was varied between 100 °C, 150 °C, and 200 °C. The fabricated RRAM device with a multi-stacked insulating layer annealed at 200 °C showed relatively good switching properties with a high on/off ratio (∼10 4 ) and low V SET (3.5±0.29 V) and V RESET (−1.81±0.10 V), which were uniformly distributed over 100 DC sweep cycles. In terms of reliability, multi-stacked insulating layer-based RRAM devices exhibited good retention (>2×10 3 s) and DC sweep endurance (>80) due to the enhanced stability of the insulating layer by good dispersion and the thermal treatment. The conduction mechanisms of the device at low resistance state (LRS) and high resistance state (HRS) were analyzed through Ohmic conduction LRS and Poole-Frenkel emission of HRS, respectively. In addition, we demonstrated the filamentary switching mechanism of resistive switching in our proposed devices.

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