A 32-site neural recording probe fabricated by DRIE of SOI substrates

An all-dry silicon-etch based micromachining process for neural probes was demonstrated in the manufacture of a probe with a 32-site recording electrode array. The fork-like probe shafts were formed by double-sided deep reactive ion etching (DRIE) of a silicon-on-insulator (SOI) substrate, with the buried SiO₂ layer acting as an etch stop. The shafts typically had the dimensions 5 mm × 25 μm × 20 μm and ended in chisel-shaped tips with lateral taper angles of 4°. An array of Ir electrodes, each 100 μm², and Au conductor traces were formed on top of the shafts by e-beam evaporation. An accompanying interconnect solution based on flexible printed circuitry was designed, enabling precise and flexible positioning of the probes in neural tissue. SEM studies showed sharply defined probes and probe tips. The electrical yield and function were verified in bench-top measurements in saline. The magnitude of the electrode impedance was in the 1 MΩ range at 1 kHz, which is consistent with neurophysiological recordings.