"Safe" charge-injection waveforms for iridium oxide (AIROF) microelectrodes

Abstract

Use of anodic bias improves the charge-injection limits of activated iridium oxide (AIROF) microelectrodes. Asymmetric waveforms, in which the charge balancing anodic phase is delivered at a lower current density and longer pulse width, has been found to allow for higher values of anodic bias voltages, thus maximizing the AIROF charge-injection capacity. Limiting the voltage excursion of the AIROF below the value at which electrolysis of water occurs is essential to maintaining the long-term viability of implanted electrodes. However, maintaining the electrodes at an anodic bias state while keeping the electrode voltage within these electrochemically "safe" limits complicates the topology of the electronic driver circuitry. We present two possible driver topologies that use compliance-voltage limitation in combination with cathodic current modification.