Reactively sputtered iridium oxide (IrOx) thin films have been developed as an electrochemical modification material of microelectrodes to obtain stable and high charge storage capacity in functional electrical stimulation.The effect of the oxygen flow, ranging from 5 to 40 sccm using a mixture of Ar and O2 (1∶0.5 to 1∶4) on the microstructure and electrochemical properties of the IrOx films are characterized.The optimal sputtering conditions are identified to be 10 sccm Ar flow (partial pressure is 2.4 Pa) and 25 sccm oxygen flow (partial pressure is 1.8 Pa) at which the activated lrOx microelectrode shows the highest charge storage capacity of 36.19 mC/cm2.The iridium oxide films deposited at 4.2 Pa (O2∶Ar pressure is 3∶4) show easy-to-pattern, good mechanical and electrochemical properties and hence can be an ideal ricroelectrode modification material for electrical stimulation.The electrochemical activation process of the activated iridium oxide film (AlROF) has been investigated on a microelectrode (the geometric surface area is 7850 μm2) with sputtered iridium in physiological saline solution (0.9% NaCl).The activation process could be controlled by the activation cycles which are characterized by the current-time data, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS).After activation, the charge storage capacity of the AIROF microelectrode is 40.07 mC/cm2, which is nearly 24 times more than that of iridium microelectrode.The impedance at 1 kHz of the AIROF microelectrode is 4064 ohm, about one-tenth of that of iridium microelectrode.The double layer capacitance of the AIROF microelectrode is 1.519 μF, about 34.5 times more than that of iridium microelectrode.The relationship between the electrochemical performance of the AIROF microelectrodes and the applied activation cycles is also investigated.In the neutral electrolyte at pH 7, the Ir (Ⅳ)/lr (Ⅲ) surface redox couple exhibits increasing separation of the oxidation/reduction peaks due to the protons releasesed/consumed during the Ir (Ⅳ)/Ir (Ⅲ) redox activity.Finally, the relationship between the separation of the redox peaks and the applied activation cycles is also studied.The degradation from continuous electrical stimulation is conducted by applied two million phases biphasic, symmetric square current pulses (500 μA pulse amplitude, 1 ms pulse width).On the micrometer scale, all the tested samples remain the circular shape after degradation.After degradation from continuous electrical stimulation, the 25 sccm one shows the best structural porosity, which is more easily permeable for water and ionic species, resulting in a higher charge delivery.Hence, the 25 sccm one can be an ideal microelectrode modification material for electrical stimulation with the least degradation.