Bipolar Switching and Synaptic Behaviors Observed in Titanium-Constrained Phase-Change Heterostructures

Phase-change random-access memory (PCRAM) is an emerging technology for next-generation memory owing to its high on/off ratio, simple fabrication, and excellent stability. However, its unipolar operation limits its ability to replicate the complex synaptic behaviors required for neuromorphic applications. Although unipolar PCRAM has been explored as a neuromorphic device, its performance is limited by the intricacies of peripheral circuit requirements. To achieve better bipolar operation, this study introduces a novel bipolar PCRAM structure by incorporating titanium interlayers into an SbTe-based PCRAM device. The integration of titanium as an atomic migration moderator reduces diffusion pathways, thereby stabilizing the operating voltage to approximately ±0.6 V while increasing endurance to more than 8 × 10⁴ cycles. Furthermore, various synaptic behaviors such as potentiation, depression, and spike-timing-dependent plasticity were reliably mimicked. Neural network simulations performed with experimental data from the device achieved 88% classification accuracy on the Modified National Institute of Standards and Technology dataset, highlighting the feasibility of this architecture for real-world neuromorphic applications. The proposed bipolar PCRAM structure simplifies circuit design and offers a scalable approach for efficient neuromorphic computing.