Development of Titanium Nitride Fractal Coatings for Cardiac and Neural Electrostimulation Electrodes

This work deals with the development of reactively sputtered fractal titanium nitride coatings for use in electrostimulation and recording electrodes. Electrical stimulation of cardiac and nerve tissues is an active area of research. This presentation will focus on the process development and characterization of porous, columnar titanium nitride coatings that exhibit high electrochemically active surface areas. Depositions were conducted in an industrial-scale sputtering system with substrate temperature varying between 25 – 130oC. Low-temperature deposition of high surface area coatings is presented. These coatings are of particular interest for stimulation electrodes where dimensional stability is a concern, for example implantable neural prostheses leads. The coating microstructure was investigated with Focused Ion Beam Microscopy. These results were used to assess the impact of substrate temperature on film porosity and grain size. The electrical performance of these coatings was analyzed with Electrical Impedance Spectroscopy (EIS) to quantify the electrochemical vs. geometrical surface area, charge injection capacity, and charge storage capacity. The stress evolution of these films was measured real-time with an in situ stress monitoring system and compared to ex situ stress measurements.