Spatial Atomic Layer Deposition of IrO _x Using (EtCp)Ir(CHD) and Atmospheric O₂/N₂ Plasma

High-volume production of stable and affordable electrocatalysts is essential for the large-scale green hydrogen production using proton exchange membrane (PEM) water electrolysis. Iridium oxide (IrO _x ) is a leading catalyst for the oxygen evolution reaction (OER) due to its high activity and stability in acidic conditions, but its cost and scarcity require strategies to minimize Ir usage. One promising approach is the deposition of ultrathin IrO _x films on porous substrates using spatial atomic layer deposition (SALD), which offers precise thickness control, excellent conformality, combined with high throughput. In this work, a SALD IrO _x process using (EtCp)-Ir-(CHD) and atmospheric O₂/N₂ plasma was developed. The process exhibits saturated growth with a growth-per-cycle of 0.66 Å at 150 °C. The impurity content in the films decreases sharply with increasing temperature between 80-150 °C, while metallic Ir clusters begin to form above ∼150-180 °C. Extended plasma exposure beyond saturation further reduces impurities and leads to denser, more crystalline films. Post-deposition anneal (PDA) in O₂ atmosphere was shown to fully convert the deposited films into stoichiometric crystalline IrO₂. Moreover, the conformality was studied on lateral high-aspect-ratio test structures and shown to be sufficient for depositions inside porous transport layers in PEM cells. Finally, the oxygen radical recombination probability on IrO _x during the deposition was determined to be in the order of 10^-3.