Novel thin film titanium nitride micro-electrodes with excellent charge transfer capability for cell stimulation and sensing applications

Microelectrodes with high specific charge transfer capability are an important prerequisite for high resolution stimulation, and recording of neuronal and muscular tissue. Novel thin film titanium nitride (TiN) microelectrodes were fabricated onto a microelectrode array by reactive sputtering in a nitrogen/argon atmosphere. The electrodes showed excellent charge transfer capacity of 40 mC/cm² and low ac-impedance along with high pulse stability. Scanning electron microscopy revealed a regular columnar morphology providing for a large internal surface area. With respect to their electrical and mechanical properties the TiN electrodes proved superior to electrodes produced by anodic oxidation of iridium. In this type of iridium oxide irregular cracks formed probably due to the high density ratio between metal and oxide. Furthermore, in spite of high charge capacity at very low frequencies (Q_cap) the iridium oxide electrodes exhibited poor safe charge injection limit under pulsing conditions (Q_inj )