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 (TiSi2). Systematic investigations and reactive diffusion modeling reveal the details associated with the materials science and biofluid stability of this TiSi2/SiO2 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.