Plasma-Assisted Atomic Layer Deposition of IrO₂ for Neuroelectronics

In vitro and in vivo stimulation and recording of neuron action potential is currently achieved with microelectrode arrays, either in planar or 3D geometries, adopting different materials and strategies. IrO₂ is a conductive oxide known for its excellent biocompatibility, good adhesion on different substrates, and charge injection capabilities higher than noble metals. Atomic layer deposition (ALD) allows excellent conformal growth, which can be exploited on 3D nanoelectrode arrays. In this work, we disclose the growth of nanocrystalline rutile IrO₂ at T = 150 °C adopting a new plasma-assisted ALD (PA-ALD) process. The morphological, structural, physical, chemical, and electrochemical properties of the IrO₂ thin films are reported. To the best of our knowledge, the electrochemical characterization of the electrode/electrolyte interface in terms of charge injection capacity, charge storage capacity, and double-layer capacitance for IrO₂ grown by PA-ALD was not reported yet. IrO₂ grown on PtSi reveals a double-layer capacitance (C) above 300 µF∙cm^-2, and a charge injection capacity of 0.22 ± 0.01 mC∙cm^-2 for an electrode of 1.0 cm², confirming IrO₂ grown by PA-ALD as an excellent material for neuroelectronic applications.