Application Stability of Ceramic and Precious Metal Electrode Coatings for Use In Implantable Stimulation Devices

Cardiac stimulation electrodes have been coated with various materials for a long time. The applied electrode coatings contribute to enable an implantable pacemaker to sense the patients ECG. This helps these devices to stimulate on demand only.

Neuromodulation devices, however, do not recognize when stimulation is needed. They operate continuously or have to be turned on by remote control.

To enable them to stimulate on demand only, the interfacial properties between the electrode and its surrounding tissue have to be adjusted similarly to the interfacial properties between implantable pacemaker electrodes and cardiac tissue. Different stimulation frequencies and voltages used in neuromodulation devices, however, challenge established cardiac electrode coating materials with regard to application performance and long term stability.

An overview about various electrode coatings for application in cardiac and neuromodulation devices will be given. During the course of this study these metallic and ceramic coatings were deposited and the influence of material, thickness and surface morphology on impedance characteristics and application stability was investigated by electrochemical impedance spectroscopy and cyclic voltametry.

While the application relevant electrochemical performance is best achieved by morphological changes resulting from process parameters or thickness, the stability of the coating depends on the coating material itself.

It has been found, that the long-term stability of electrode coatings is mainly determined by the coatings susceptibility to oxidation. In the case of ceramic coatings, such as TiN, this can result in a reduced electrical conductivity, which will negatively influence the electrochemical properties. An oxidation of thin metal coatings, such as Ir, will, in addition to affecting the electrical conductivity, generate intrinsic film stress and possibly induce cracking and delamination.

It was furthermore investigated, how alloying and covering the coating material with additional, more inert materials can reduce coating oxidation and help to maintain the application relevant electrochemical performance.