A process for sputter deposition of RuOx films with high volumetric Li capacities and good cyclability was developed, demonstrating the potential for use of RuOx films as cathodes in high-performance thin-film microbatteries. Using a stoichiometric RuO2 sputtering target, the effects of oxygen content within the Ar/O-2 plasma on the stoichiometry of thin films deposited at room temperature was investigated and correlated with electrochemical performance. The oxygen content of the films was found to increase with the O-2 to Ar ratio of the sputtering gas. RuOx thin films with x >= 1.92 delivering capacities of similar to 550 mu Ah/cm(2) mu m in the 0.75-3.6 V vs. Li/Li+ voltage range, which is much higher than that of under-stoichiometric RuOx (320 mu Ah/cm(2) mu m). The capacities obtained for RuOx films significantly exceed the capacity of LiCoO2 films (similar to 60 mu Ah/cm(2) mu m) typically used in thin-film microbatteries. Given that high capacity RuOx films can be obtained using only room temperature processing, their use in thin-film microbatteries will also allow integration with silicon-based integrated circuits. (C) 2018 Elsevier Ltd. All rights reserved.