A Three-Dimensional Bidirectional Interface for Neural Mapping Studies
Mary Elizabeth Merriam · Deep Blue (University of Michigan) · 2010
Advances in neuro-medicine depend critically on supporting technologies, including those associated with penetrating microelectrodes. While these have developed from single-site microwires to three-dimensional micromachined electrode systems, several important issues remain. This research focused on the array-tissue interface, on application-specific electrode design, and on neural amplifiers for use in bidirectional microelectrode system front-ends. Three new three-dimensional array structures were developed. A novel architecture, which enables two perpendicular probe sets, was coupled with open-scaffold shanks to create 3-D lattice arrays for bio-response investigations. These arrays have 15% of the shank area of constant-footprint solid counterparts. Chronic (8-week) in vivo studies have shown similar 2-D lattice probes significantly mitigated the tissue reaction and dramatically increased the number of adjacent (within 50μm) surviving neurons from 36% to 87%. An innovative design for rapidly-assembled folded 3-D arrays was created, requiring only one mask beyond the standard boron-doped process. This realizes the smallest platform structure ever reported for such a device, with zero-rise above the platform top and virtually no lateral extent past the probes. Electrode and shank pitch are both 200μm on the 64-site prototype. The implanted device stands less than 350μm above the cortex and displaces only 1.7% of the instrumented area. Recordings in guinea pig cortex verified functionality. A 160-site array for neuroscience mapping of the ventral and dorsal cochlear nucleus consisting of five-probes (3-VCN, 2-DCN) permitted high-density 3-D CN mapping and somatosensory integration studies for the first time. Multi-region stimulation (1000μm2 sites) and recording (177μm2 sites) demonstrated the efficacy of bimodal silicon arrays for investigating the biological circuits of the central nervous system and as prosthetic devices. For electrode-electrolyte interface enhancement, iridium sites were modified with carbon nanotubes (CNTs). On non-released probes, in situ growth of vertically-aligned forests was achieved, and dip-coated sites exhibited an order-of-magnitude impedance reduction. Neural signals in guinea pig cortex were recorded with released dip-coated CNT-probes. A new integrated neural recording amplifier, consuming only 46.5μW of power, was designed and fabricated in a 0.5μm CMOS process. The 0.026mm2 circuit has an in-band gain of 58.9dB with a tunable lower cutoff frequency and an upper cutoff frequency of 21.3kHz.