Novel technology for the in-plane to out-of-plane transfer of multiple interconnection lines in 3D neural probes

This paper reports a novel process to accomplish the transfer of interconnection lines from the out-of-plane direction of probe combs into the plane of a common horizontal platform in compact three-dimensional (3D) silicon-based neural probe arrays. The central process step of the system assembly takes advantage of gold electroplating of micrometer-sized contact structures to form transfer contacts between the platform and multiple probe combs. In comparison with similar approaches reported in literature, the new process accommodates larger fabrication tolerances and achieves lower contact resistances. The processing of 64-channel probes with 50-μm-thick electrode combs was carried out in a batch process with a small variation of only 8% in the electroplated layer thickness of the transfer contacts. The electrical resistance of the transfer contacts is 336±18 mΩ. Electrode impedances were found to be between 140 and 320 kΩ at 1 kHz for iridium oxide coated electrodes 35 μm in diameter.