Flexible intracortical neural probes elicit a lower foreign body response when compared to rigid implants. However, by incorporating complementary metal-oxide-semiconductor (CMOS) circuitry, silicon-based neural probes can offer an improved scalability and more functionalities than any other currently available technology.
Objective: Our goal is the development of a novel neural probe that combines flexibility with the functionalities of active CMOS-based probes.
Methods: We interface CMOS-based probe tips of only a few millimeters in length with flexible polyimide cables, which enable the complete implantation of the tips into brain tissue. The multilayer platinum metallization of the cables is patterned using a novel combination of ion beam and plasma etching. Implantation of the flexible probes is verified in brain models using stiff insertion shuttles.
Result: We assembled neural probes from passive and active tips as short as 1.5 mm and less than 180 μm in width. Active probes feature electrode arrays with 72 recording sites and multiplexing to 16 parallel output lines. We reliably patterned cables with signal lines of 2 μm in width and 3 μm in spacing. Ion beam etching deteriorated the composition of the polyimide substrate and its resistance to around 1 kΩ. An additional plasma treatment re-established high insulation resistances and recovered the chemical composition. Probes were successfully implanted to a depth of 7 mm using insertion shuttles and withstood forces of 63 mN.
Conclusions: This study presents the methods required for the fabrication and application of a new generation of neural probes.
Significance: The synergetic approach surpasses the limitation of each individual probe technology and should be considered in future developments.