The influence of substrate bias on the morphology and charge capacity of rf-sputtered iridium oxide films

Iridium oxide films deposited on Ti-alloy stimulation electrode wires by rf sputtering exhibit markedly different surface morphologies and redox capacities in response to variations in applied substrate bias potential. Films deposited with a −20 volt bias were relatively smooth and featureless whereas those sputtered with a +20 volt bias were comprised of closely packed 1 micron long platelets. Intermediate substrate biases revealed a gradual progression from the smooth surface to one sparsely populated with particles to a morphology comprised of tightly packed platelets. The electrochemical properties of the films are strongly dependent on the substrate bias employed during deposition. As the DC bias was increased from −20 volts to +20 volts the anodic and cathodic charge capacities determined by cyclic voltammetry decreased linearly from 36 to 12 mC/cm².