Beom Jin Kim

Advanced monitoring of neural responses has deepened our understanding of brain functions. However, balancing sampling fidelity and spatial resolution of electrocorticography mapping remains a major challenge in neuroscience and neuroelectronics. Here we describe a flexible, two-dimensional molybdenum disulfide (MoS₂)-based active array for electrocorticography sensing that uses a dual-transistor multiplexed source follower array architecture. We grow wafer-scale trilayer MoS₂ directly on polyimide substrates for a scalable fabrication of active arrays and simultaneously scaling matrices with ultrahigh mapping resolution (up to 51 pixels mm⁻²). In vitro recordings of epileptiform activities and sinusoidal potential distributions demonstrate the high spatiotemporal resolution for full-bandwidth electrocorticography recordings using the 50 × 50 MoS₂-based active arrays, which result from the fast on-site multiplexing speeds (τ ≈ 20 ns) and the megahertz response bandwidth of the transducer. In living mice, the active arrays enable high-fidelity electrocorticography monitoring of multiscale neural processes, including auditory-evoked potentials, tonotopic maps and localized multiunit activities at high frequency. Overall, these results suggest that the MoS₂-based active arrays are promising minimally invasive high-fidelity tools for spatiotemporal neuronal monitoring.

Three-dimensional (3D) hetero-integration technology is poised to revolutionize the field of electronics by stacking functional layers vertically, thereby creating novel 3D circuity architectures with high integration density and unparalleled multifunctionality. However, the conventional 3D integration technique involves complex wafer processing and intricate interlayer wiring. Here we demonstrate monolithic 3D integration of two-dimensional, material-based artificial intelligence (AI)-processing hardware with ultimate integrability and multifunctionality. A total of six layers of transistor and memristor arrays were vertically integrated into a 3D nanosystem to perform AI tasks, by peeling and stacking of AI processing layers made from bottom-up synthesized two-dimensional materials. This fully monolithic-3D-integrated AI system substantially reduces processing time, voltage drops, latency and footprint due to its densely packed AI processing layers with dense interlayer connectivity. The successful demonstration of this monolithic-3D-integrated AI system will not only provide a material-level solution for hetero-integration of electronics, but also pave the way for unprecedented multifunctional computing hardware with ultimate parallelism.

Recent advances in two-dimensional semiconductors, particularly molybdenum disulfide (MoS₂), have enabled the fabrication of flexible electronic devices with outstanding mechanical flexibility. Previous approaches typically involved the synthesis of MoS₂ on a rigid substrate at a high temperature followed by the transfer to a flexible substrate onto which the device is fabricated. A recurring drawback with this methodology is the fact that flexible substrates have a lower melting temperature than the MoS₂ growth process, and that the transfer process degrades the electronic properties of MoS₂. Here we report a strategy for directly synthesizing high-quality and high-crystallinity MoS₂ monolayers on polymers and ultrathin glass substrates (thickness ~30 µm) at ~150 °C using metal–organic chemical vapour deposition. By avoiding the transfer process, the MoS₂ quality is preserved. On flexible field-effect transistors, we achieve a mobility of 9.1 cm² V⁻¹ s⁻¹ and a positive threshold voltage of +5 V, which is essential for reducing device power consumption. Moreover, under bending conditions, our logic circuits exhibit stable operation while phototransistors can detect light over a wide range of wavelengths from 405 nm to 904 nm.