We have investigated the charge-injection properties of sputtered ruthenium oxide (RuOx) coatings deposited on planar microelectrode arrays. Substantial charge was found to be available for injection within -0.6/0.6 V vs Ag|AgCl potential limits for the sputtered RuOx film. The charge-injection capacity increased further upon extending the potential limits to -0.7/0.7 V vs Ag|AgCl. No oxygen reduction, an unwanted side reaction, was observed during the pulsing of sputtered RuOx microelectrodes in phosphate buffered saline solution. Additionally, the RuOx coatings were found to be electrochemically stable for up to 1-billion-cycles of constant current stimulation pulsing at 8 nC/phase in model-ISF at 37° C.