SIROF stimulation electrode evaluation using the pulse–clamp method

Miniaturized electrodes, structures, and devices are necessary to achieve high target selectivity during stimulation in single neuron networks, while significant charge transfer is essential. A reliable test method is required to evaluate charge injection capability for neural stimulation applications that demand both a large amount of charge injection and a small electrode size. A custom made pulse-clamp circuit was employed to characterize sputtered iridium oxide film (SIROF) microelectrodes. Pulseclamp measurements with 400 μs long pulses are performed in 154 mM phosphate buffered saline (PBS) solution on planar microelectrodes smaller than 100 μm in diameter. A cell model was used to verify the circuit design with SPICE simulations. The pulse-clamp results of SIROF electrodes of different sizes show charge losses of less than 6%, even at high charge density levels.