New Wafer-Level Fabrication of Ultrathin Silicon Insertion Shuttles for Flexible Neural Implants

This paper reports a novel, cost-effective process for the fabrication of ultrathin silicon (Si) shuttles applied as insertion tools for highly flexible polyimide (PI) neural implants. The process exploits the so-called etching before grinding (EBG) process established to realize Si-based neural probes of the Michigan style. In this study, EBG is combined for the first time with a subsequent deep reactive ion etch (DRIE) process applied on the wafer-level. The innovative approach allows to realize insertion shuttles with a base thickness > 50 µm using wafer grinding and to reliably thin down the slender shuttle shanks (width ≥ 35 µm) to thicknesses as small as 15 µm using DRIE. The backgrinding liquid wax applied during wafer grinding enables the safe release of the delicate shuttle structures from their carrier wafer using isopropanol. Flexible, 15-µm-thin neural probes made from PI are precisely aligned and temporarily bonded to the custom-designed insertion shuttles applying polyethylene glycol (PEG) and reliably deployed into cortical tissue.