Hermetically sealed coatings for neural implants
Neural implants are a promising approach towards sustainable treatment of a number of severe illnesses which cannot be healed today, such as blindness, Parkinson’s disease or the locked-in syndrome. These systems consist of very thin and flexible foils of insulating and conducting layers, which must be chronically implanted. They have to work 20 years and more in the brain. This needs a stability of hermetic sealing which cannot be provided by today’s micro technology.The project aims at finding a thin film package and a technology which provide reliable operation for 20 years in the brains liquor. The applicants propose to investigate sandwich layers from polymers and oxidic interlayers. As polymers, Parylene and Polyimide will be investigated. The interlayers will be metallic oxides, made by atomic layer deposition. Also systems with full hermetic sealing for each electric interconnect separately will be prepared and analyzed. The innovation is first the development, analysis and the improvement of a new concept for hermetically sealing neural implants. Second, innovation is a new process flow to deposit anorganic-organic barriers on flexible substrates in an isotropic and flawless way. The scientific method chosen is first to develop test procedures, next to prepare a series of samples and to analyze them. The primary test procedure will be the accelerated soak test, which means immersing the probes in hot saline and measuring them by dielectric spectroscopy. Samples with different topographies are prepared. These are coated with different barrier layers, then analyzed and evaluated. For one or several selected barrier coatings a full system will be assembled and tested.Theoretical description of the water diffusion will be made by a model based on activation energies. Since corrosion happens if liquid water is present, the condensation of the diffused water molecules at the boundary of polymer and metal oxide layers at micro cavities will also be modelled.