Van der Waals crystals are stepping into the spotlight as a potential game-changer in the realm of neuromorphic computing. This cutting-edge research, led by Professor Taesung Kim and his team at Sungkyunkwan University, has developed an optoelectronic synaptic device that mimics the intricate workings of human neurons and synapses at a device scale. The key innovation lies in the creation of a designable van der Waals (vdW) crystal through a single-step sulfurization process using mixed plasma, offering a structural solution to configure semiconductor materials for brain-inspired computing.
The research team's focus on the structural similarity between light-sensitive ion channels in biological membranes and layered vdW lattices is a strategic move. By applying an argon and hydrogen sulfide (Ar + H₂S) plasma sulfurization process to bulk van der Waals rhenium selenide (ReSe₂), they transformed the upper portion of the material into a nano-crystalline ReSe₂ layer, while preserving the underlying bulk single-crystalline ReSe₂ layer. This two-layered structure mimics the light-sensitive ion channels of a neuronal cell membrane and the intracellular environment, respectively, and was fabricated without additional deposition or patterning steps.
The scanning probe microscopy (SPM) technique played a crucial role in unraveling the pathways of S²⁻ (sulfur) ionic migration. The grain boundaries in the nano-crystalline ReSe₂ layer confined the sulfur ionic transport at the atomic scale, enabling deterministic control over synaptic weight updates, similar to the gating mechanism of biological ion channels. This device demonstrated key synaptic functionalities, including multi-level conductance modulation, long-term potentiation/depression (LTP/LTD), paired-pulse facilitation (PPF), and a tunable short-term to long-term memory (STM-LTM) transition.
The nano-crystalline ReSe₂ device showcased impressive retention efficiency, with a 34.7% increase in retention efficiency during learning-forgetting-relearning cycles compared to bulk ReSe₂. In system-level evaluations, the device successfully performed edge detection on natural images and achieved a 96.24% classification accuracy on the CIFAR-10 image recognition task. This development offers a materials platform for next-generation neuromorphic semiconductors and AI hardware.
Professor Taesung Kim, the corresponding author of the study, emphasizes the significance of this research, stating, 'This study demonstrates a single-step method to design the structure of van der Waals crystals for optoelectronic synaptic devices that learn and store information using light. By structurally resolving the random nature of ionic migration and interfacial issues inherent in conventional devices, this architecture can be applied to research on next-generation neuromorphic semiconductors and AI hardware.'
The research received financial support from the National Research Foundation of Korea (NRF) Leader Research Program, the Institute for Basic Science (IBS), and the Semiconductor-Track Graduate School Program funded by the Ministry of Trade, Industry and Energy (MOTIE). The study was a collaborative effort among researchers from Sungkyunkwan University (SKKU), the Center for Quantum Nanoscience at IBS, and the Korea Institute of Machinery and Materials (KIMM). The findings were published in the international journal Advanced Materials (Impact Factor: 26.8, top 1% in JCR) on June 3, 2026.
This breakthrough in van der Waals crystal technology not only showcases the potential for advanced neuromorphic computing but also opens up exciting possibilities for the future of artificial intelligence and brain-inspired hardware. As we continue to explore the intricacies of the human brain, these innovations will play a pivotal role in shaping the next generation of AI systems.
