Effect of film structure on the electrochemical properties of gold electrodes for neural implants

Highlights: → Tuning of gold microstructure by sputter deposition pressure. → Improved electrochemical properties of columnar gold as neural device material (interface impedance, charge injection capabilities). → Comparison of columnar gold to well-established titanium nitride shows similar properties but has a more stable deposition process. → Active surface area of sputtered columnar gold comparable to electrochemically grown overlayers. - Abstract: The development of interfaces with low impedance is a prerequisite for long-term neural devices. A broad range of new materials has been developed for this purpose. Here we show how the performance of traditional gold electrodes can be improved by controlling the deposition parameters of the gold film. The morphology of the film was tuned from granular to columnar structure as shown by scanning electron microscopy of film cross sections. Electrochemical characterisation with impedance spectroscopy, chronoamperometry and cyclic voltammetry demonstrates that the dense columnar structure of the films effectively lowers the impedance of the interface and increases charge injection properties. The samples produced are also compared to titanium nitride films, a well-established electrode material with a columnar structure.