Highly conformable chip-in-foil implants for neural applications

Demands for neural interfaces around functionality, high spatial resolution, and longevity have recently increased. These requirements can be met with sophisticated silicon-based integrated circuits. Embedding miniaturized dice in flexible polymer substrates significantly improves their adaptation to the mechanical environment in the body, thus improving the systems' structural biocompatibility and ability to cover larger areas of the brain. This work addresses the main challenges in developing a hybrid chip-in-foil neural implant, assessing mechanical compliance with recipient tissue for long-term application and suitable design for implant scaling and modular chip arrangement. Finite element model studies identified design rules for die geometry, interconnect routing, and contact pad positions. A microfabrication process was developed to transfer, align, and electrically interconnect multiple dice into conformable polyimide-based substrates, enabling arbitrary die shape and size at independent target positions.

Thomas Stieglitz, Calogero Gueli, Julien Martens, Niklas Floto, Max Eickenscheid, Markus Sporer, Maurits Ortmanns