Vapor-Phase Additive Fabrication of Ultrathin Transparent Bioelectronic Interfaces via Initiated Chemical Vapor Deposition

Advanced biomedical devices increasingly demand functional material interfaces that combine optical transparency, electrical conductivity, mechanical flexibility, and biocompatibility. Here, we present a vapor-phase additive fabrication strategy based on initiated chemical vapor deposition (iCVD) to construct ultrathin transparent electrodes for implantable bioelectronic devices. We deposited functional molecular layer whose tertiary amine groups form coordination bonds with gold atoms. This interfacial engineering transforms the three-dimensional island growth of gold into continuous two-dimensional films, enabling functional electrodes at only 10 nm gold thickness. As a solvent-free, conformal deposition process with sub-nanometer thickness control, iCVD preserves reactive functional groups while enabling scalable, uniform coating over large areas, making it well-suited for additive device manufacturing. The resulting electrodes achieve >65% optical transmittance at 550 nm, sheet resistance of 3.5 Ω sq-1, and electrochemical impedance of 0.89 Ω·cm2, yielding a figure of merit of 237.4. Integrated onto flexible parylene substrates (<5 μm), these devices exhibit mechanical durability over 20,000 compression cycles and excellent biocompatibility. In vivo validation confirmed low-noise neural recording during simultaneous optical stimulation, demonstrating the promise of vapor-phase additive fabrication for next-generation transparent biomedical devices and neural interfaces.

Hyejeong Seong received her B.S. (2007) and Ph.D. (2016) degrees in Chemical and Biomolecular Engineering from Korea Advanced Institute of Science and Technology. She worked as a Research Associate in the Stevens Group at Imperial College London from 2017 to 2020. Currently, she is a Senior Researcher in the Brain Science Institute at Korea Institute of Science and Technology. Her accolades include a Marie Skłodowska-Curie Fellow from the European Union, and an NRF-Fellowship from Republic of Korea. Her research interests focus on microfabrication of biomaterials for cell interfacing applications and biosensors.