Charge-injection damage

Charge Injection Limits to Avoid Tissue and Electrode Damage... 

The demand for high-resolution stimulation in neural prosthetic devices requires the development of high performance, high density microelectrode arrays. For such arrays, the choice of electrode materials has become increasingly important. Stimulation electrodes serve as the interface between electronic devices and neural systems. Since high levels of charge injection and electric fields are applied to functional and responsive tissues and electrode materials, it is critical that damage to tissues or nerves, as well as to electrode materials, from chronic stimulation be minimized or avoided [21]. 

Corrosion is not limited to relatively reactive materials like iron. In TiN, in spite of the rather capacitive nature of the metal-electrode interface for charge injection, corrosion occurs at zero electrode potential in distilled water. However, the reaction is very slow and practically does not result in considerable damage even after long periods of time [6]. Titanyl (TiO " ") ions are produced ... 

These processes do not damage the electrodes if charge injection balance into the electrode is guaranteed. Charge balance roughly means that the total amount of charge injected into the electrode remains zero. This will be explained in detail in the next chapter. 

Fig. 6.9 Scanning electron microscope photograph of an AIROF electrode showing delamination due to cathodic voltage excursions below —0.6 V against Ag AgCl. This damage is irreversible and deteriorates the charge injection capacity of the electrode considerably. From [28], with permission 2004 IEEE...

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