CMOS Neural Probe With 1600 Close-Packed Recording Sites and 32 Analog Output Channels

This paper reports on the development, characterization, and validation of neural probes serving the growing needs of neuroscience for miniaturized tools enabling simultaneous high-resolution recording of neural activity in multiple brain areas. The probes consist of a needle-shaped shaft with a crosssection of 100 × 50 μm
²
and a length of 10 or 5 mm emerging from a base with dimensions of only 0.55 × 1.8 mm
²
. The shafts carry 1600 and 800 recording sites, respectively, grouped into 50 (respectively 25) blocks of 4 × 8 electrodes with an area of 17 × 17 μm
²
each, a pitch of 20 μm, and an electrode-toelectrode spacing of 3 μm. The probes are fabricated using a commercial 0.18 μm CMOS process followed by dedicated metallization, passivation, and microfabrication steps. Neural signals are accessible through 32 analog output channels via a hierarchical digital addressing scheme implementing an advanced electronic depth control concept giving the option of multiple scanning modes and offering a switching time of 416 μs at a clock frequency of 1 MHz. All output channels are shielded against each other, whereby crosstalk between neighboring channels is measured to be -58 dB at 1 kHz. Absolute impedance values at 1 kHz of single IrOx and Pt electrodes are 230 ± 38 kQ and 2.2 ± 0.3 MQ, respectively. In vivo recordings taking advantage of the new addressing concept for high-resolution recordings from multiple brain regions were successfully performed in anesthetized rats.