Silicon ribbon cables for chronically implantable microelectrode arrays

Describes the design, fabrication, and testing of miniature ultraflexible ribbon cables for use with micromachined silicon microprobes capable of chronic recording and/or stimulation in the central nervous system (CNS). These interconnects are of critical importance in reliably linking these microelectrodes to the external world through a percutaneous connector. The silicon cables allow the realization of multilead, multistrand shielded local interconnects that are extremely flexible and yet strong enough to withstand normal handling and surgical manipulation. Cables 5 μm thick, 1-5 cm long, and from 60 to 250 μm wide have been fabricated with up to eight leads. The series lead resistance is typically 4 kΩ/cm for polysilicon and 500 Ω/cm for tantalum with shunt capacitance values of 5-10 pF/cm and an interlead capacitance below 10 fF/cm. Soak tests in buffered saline performed under electrical and mechanical stress have been underway for over three years and show subpicoampere leakage levels. Silicon microprobes with built-in ribbon cables have remained functional for up to one gear in the guinea pig CNS, recording driven single-unit activity and maintaining impedance levels in the 1-7 M Ω range.