Reactive IrO₂ sputtering in reducing/oxidizing atmospheres

An Ir metal target was reactively rf sputtered in a planar magnetron source to develop iridium oxide deposition conditions. Gas blends of hydrogen, oxygen, and argon were used to provide competitive control over the reduction/oxidation characteristics of the sputter plasma. Optical emission spectroscopy allowed direct observation of hydrogen, oxygen, and iridium atomic peaks and OH molecular bands. Each of the twelve gas flow conditions could be clearly defined as either reducing or oxidizing by plasma emission spectroscopy. A given plasma reduction/oxidation state can be maintained over a wide range of gas flow conditions by coordinated adjustment of hydrogen and oxygen flows. The electrochemical properties of the iridium oxide films change dramatically in the vicinity of the reduction/oxidation plasma transition.