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 SiO 2 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 µm 2 , 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 M range at 1 kHz, which is consistent with neurophysiological recordings.

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Multisite recording represents a suitable condition to study microphysiology and network interactions in the central nervous system and, therefore, to understand brain functions. Several different materials and array configurations have been proposed for the development of new probes utilized to record brain activity from experimental animal models. We describe new multisite silicon probes that broaden the currently available application base for neuroscientists. The array arrangement of the probes recording sites was extended to increase their spatial resolution. Probes were integrated with a newly developed electronic hardware and novel software for advanced real-time processing and analysis. The new system, based on 32- and 64-electrode silicon probes, proved very valuable to record field potentials and single unit activity from the olfactory-limbic cortex of the in vitro isolated guinea-pig brain preparation and to acutely record unit activity at multiple sites from the cerebellar cortex in vivo. The potential advantages of the new system in comparison to the currently available technology are discussed.

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We used a recently described all-dry silicon etch process for SOI wafers to fabricate 64-site electrode arrays in stereotrode arrangement for acute cortical recordings. The fork-like probes are connected to preamplification units by flexible, Y-shaped interconnects. This facilitates maximal experimental flexibility for simultaneously recording from all available channels from the cortex of anaesthetised rats. Preconditioned signals are amplified by a novel modular main amp, which may be software or dial controlled. Signals are 16bit digitized, recorded, analyzed, stored and processed on a DSP-based modular data acquisition system. Digital data is processed, filtered and denoised on all up to (4*32) 128 channels based on an extremely fast wavelet transformation framework.