A novel flex-rigid and soft-release ECoG array

This article addresses a novel fabrication process for an electrocorticogram (ECoG) electrode array. It consists of three regions: a flexible recording area, a flexible cable, and a rigid field for soldering the connectors. The flexible components can adapt to the curved shape of the cerebral cortex. Furthermore, the entire structure is a free-standing membrane, attached by removable polyimide straps to its carrier substrate. This configuration allows for a high level of control during soldering, electrode characterization and sterilization, as well as a soft release of the array off its carrier just before implantation. The array contains 128 gold electrodes, each 300 nm thick, sandwiched between two 5 μm thick polyimide films. The measuring area of the device is a regular hexagon with a side length of 7.2 mm, designed for implantation on the primary visual cortex of a Rhesus monkey. The flexible cable is 4 cm long. The rigid soldering area was designed for 4×32 OMNETICS connectors. The line resistance from an electrode site to the corresponding electrical connector pin is 540 Ω.