ECoG Electrode Array with Embedded Coupling Capacitors for Area Efficient Neural Recording

ECoG electrode arrays offer great potential for high-channel-count monitoring of large scale brain activity. However, scaling ECoG recording systems to high channel count is challenging due to the large silicon area demanded by the coupling capacitors necessary for DC offset voltage rejection. This paper presents a new approach to reduce the per-channel area of recording circuits by introducing a capacitor-embedded ECoG electrode structure that implements coupling capacitors within the existing electrode area. For proof of concept, a 4×4 array of 8 pF capacitor-embedded electrodes was fabricated in a 2mm × 2mm area using a three-mask process to form a capacitor stack of Cu, Ta 2 O 5 , and Ti/Cu/ Au. In vivo experiments performed on an adult rat show that physiologically-evoked activity was accurately detected according to the placement of the electrodes for manual whisker deflection, shoulder tapping and hindlimb tapping. The capacitor-embedded ECoG electrode structure provides a new method for achieving high channel count neural recording.