Low-Temperature Atomic Layer Deposited Oxide on Titanium Nitride Electrodes Enables Culture and Physiological...

The performance of electrode arrays insulated by low-temperature atomic layer deposited (ALD) titanium dioxide (TiO₂) or hafnium dioxide (HfO₂) for culture of electrogenic cells and for recording of extracellular action potentials is investigated. If successful, such insulation may be considered to increase the stability of future neural implants. Here, insulation of titanium nitride electrodes of microelectrode arrays (MEAs) was performed using ALD of nanometer-sized TiO₂ or hafnium oxide at low temperatures (100-200°C). The electrode properties, impedance, and leakage current were measured and compared. Although electrode insulation using ALD oxides increased the electrode impedance, it did not prevent stable, physiological recordings of electrical activity from electrogenic cells (cardiomyocytes and neurons). The insulation quality, estimated from leakage current measurements, was less than 100 nA/cm² in a range of 3 V. Cardiomyocytes were successfully cultured and recorded after 5 days on the insulated MEAs with signal shapes similar to the recordings obtained using uncoated electrodes. Light-induced electrical activity of retinal ganglion cells was recorded using a complementary metal-oxide semiconductor-based MEA insulated with HfO₂ without driving the recording electrode into saturation. The presented results demonstrate that low-temperature ALD-deposited TiO₂ and hafnium oxide are biocompatible and biostable and enable physiological recordings. Our results indicate that nanometer-sized ALD insulation can be used to protect electrodes for long-term biological applications.