Micro- and Nanofabrication of Flexible Bioelectronic Interfaces

Licentiatavhandling, 2026

Flexible neural interfaces represent a promising platform for the treatment of neurological disorders, enabling the restoration of motor function and communication through targeted electrical interaction with neural tissue. These devices are typically fabricated on polymeric substrates such as polyimide (PI) or Parylene C, with thin-film metal interconnects and electrode materials like iridium oxide. Increasing channel density and spatial resolution requires miniaturization, which in turn demands advanced micro- and nanofabrication techniques. This thesis investigates fabrication strategies for high-density flexible neuroelectronic implants, with a focus on reducing feature and implant size while maintaining electrical performance and structural integrity. Electron-beam lithography (EBL) is employed to pattern sub-micrometer interconnects on polymer substrates. While EBL is well established for nanoscale patterning, its application to polymer-based systems remains underexplored; this work addresses this gap by evaluating process limitations and optimization strategies. The electrical and electrochemical implications of nanoscale features are systematically studied, including interconnect resistance, electrode behavior, and the role of conductive materials and adhesion layers. In addition, fabrication approaches for high-aspect-ratio vias and multilayer architectures are developed to enable increased channel density without significantly increasing implant volume. Finally, multilayer devices with nanoscale features are fabricated to demonstrate the feasibility of EBL on PI substrates and to assess the performance of miniaturized interconnects and electrodes in neural interfaces. Overall, this work identifies key limitations in the miniaturization of flexible bioelectronic interfaces and provides fabrication strategies to improve their scalability and manufacturability, contributing to the development of high-density, chronically implantable neural devices.