Development of multisite microelectrodes for neuroscience

Neural probes with a 32-site electrode array have been fabricated using an all-dry Si-etch based micromachining process. 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 probe shafts typically had the dimensions of 4-15 mm (length), 25 μm (width), 20-30 μm (height) and a tip taper angle of 4°. An array of electrodes, each 100 μm, as well as Au conductor traces were formed by e-beam evaporation. Both Ir and Pt were used as electrode material and focused ion beam (FIB) studies, as well as electrical measurements, showed differences between these materials. Also a post process cleaning procedure was developed to remove process residues from the electrode surface. SEM studies showed well defined straight probe shafts with sharp probe tips. The function was verified in bench-top measurements and probes have been successfully used by neuroscientists in brain preparations. The next generation of probes, with 64-sites, have already been designed and are under way in the manufacturing process.