Microfabricated Capacitive Electrodes for High Channel Count ECoG Recording.

Toward understanding brain functionality, high channel count ECoG arrays enable expanding the resolution and/or physical scope of neural recordings. For fully implanted ECoG arrays, one limiting factor to scaling channel count is the size of the front-end recording electronics, which is dominated by the coupling capacitor needed at every recording channel. This paper presents an ECoG array with coupling capacitors fabricated into the electrodes that significantly reduces the area required for recording electronics and thus enables scaling to higher channel counts. Two different fabrication procedures were explored to form 4x4 arrays of 8 pF capacitor-embedded electrodes utilizing a stack of Cu, Ta2O5, and Ti/Au on a flexible substrate. Several in vivo experiments were performed on an adult rat, and physiologically evoked activity was successfully observed for shoulder and hindlimb tapping as well as for whisker deflection.