Ultrathin, Transferred Layers of Metal Silicide as Faradaic Electrical Interfaces and Biofluid Barriers for Flexible Bioelectronic Implants

Actively multiplexed, flexible electronic devices represent the most sophisticated forms of technology for high-speed, high-resolution spatiotemporal mapping of electrophysiological activity on the surfaces of the brain, heart, and other organ systems. Materials that simultaneously serve as long-lived, defect-free biofluid barriers and sensitive measurement interfaces are essential for chronically stable, high-performance operation. Recent work demonstrates that conductively coupled electrical interfaces of this type can be achieved based on the use of highly doped monocrystalline silicon electrical "via" structures embedded in insulating nanomembranes of thermally grown silica. A limitation of this approach is that dissolution of the silicon in biofluids limits the system lifetimes to 1-2 years, projected based on accelerated testing. Here, we introduce a construct that extends this time scale by more than a factor of 20 through the replacement of doped silicon with a metal silicide alloy (TiSi ₂ ). Systematic investigations and reactive diffusion modeling reveal the details associated with the materials science and biofluid stability of this TiSi ₂ /SiO ₂ interface. An integration scheme that exploits ultrathin, electronic microcomponents manipulated by the techniques of transfer printing yields high-performance active systems with excellent characteristics. The results form the foundations for flexible, biocompatible electronic implants with chronic stability and Faradaic biointerfaces, suitable for a broad range of applications in biomedical research and human healthcare.