An ASIC for Recording and Stimulation in Stacked Microchannel Neural Interfaces

This paper presents an active microchannel neural interface (MNI) using seven stacked application specific integrated circuits (ASIC). The approach provides a solution to the present problem of interconnect density in 3-dimensional MNIs. The 4 mm2 ASIC is implemented in 0.35 μm high-voltage CMOS technology. Each ASIC is the base for seven microchannels each with three electrodes in a pseudo-tripolar arrangement. Multiplexing allows stimulating or recording from any one of 49 channels, across 7 ASICs. Connections to the ASICs are made with a 5-line parallel bus. Current controlled biphasic stimulation from 5 μA to 500 μA has been demonstrated with switching between channels and ASICs. The high-voltage technology gives a compliance of 40 V for stimulation, appropriate for the high impedances within microchannels. High frequency biphasic stimulation, up to 40 kHz is achieved, suitable for reversible high frequency nerve blocks. Recording has been demonstrated with mV level signals; common-mode inputs are differentially distorted and limit the CMRR to 40dB. The ASIC has been used in vitro in conjunction with an oversize (2 mm diameter) microchannel in phosphate buffered saline, demonstrating attenuation of interference from outside the microchannel and tripolar recording of signals from within the microchannel. By using 5-lines for 49 active microchannels the device overcomes limitations with connecting many electrodes in a 3-dimensional miniaturised nerve interface

Optimal Electrode Size for Multi-Scale Extracellular-Potential Recording From Neuronal Assemblies

Advances in microfabrication technology have enabled the production of devices containing arrays of thousands of closely spaced recording electrodes, which afford subcellular resolution of electrical signals in neurons and neuronal networks. Rationalizing the electrode size and configuration in such arrays demands consideration of application-specific requirements and inherent features of the electrodes. Tradeoffs among size, spatial density, sensitivity, noise, attenuation, and other factors are inevitable. Although recording extracellular signals from neurons with planar metal electrodes is fairly well established, the effects of the electrode characteristics on the quality and utility of recorded signals, especially for small, densely packed electrodes, have yet to be fully characterized. Here, we present a combined experimental and computational approach to elucidating how electrode size, and size-dependent parameters, such as impedance, baseline noise, and transmission characteristics, influence recorded neuronal signals. Using arrays containing platinum electrodes of different sizes, we experimentally evaluated the electrode performance in the recording of local field potentials (LFPs) and extracellular action potentials (EAPs) from the following cell preparations: acute brain slices, dissociated cell cultures, and organotypic slice cultures. Moreover, we simulated the potential spatial decay of point-current sources to investigate signal averaging using known signal sources. We demonstrated that the noise and signal attenuation depend more on the electrode impedance than on electrode size, per se, especially for electrodes <10 μm in width or diameter to achieve high-spatial-resolution readout. By minimizing electrode impedance of small electrodes (<10 μm) via surface modification, we could maximize the signal-to-noise ratio to electrically visualize the propagation of axonal EAPs and to isolate single-unit spikes. Due to the large amplitude of LFP signals, recording quality was high and nearly independent of electrode size. These findings should be of value in configuring in vitro and in vivo microelectrode arrays for extracellular recordings with high spatial resolution in various applications

Sea of Electrodes Array (SEA): Customizable 3D High-Density High-Count Neural Probe Array Technology

Accurate mapping of neural circuits and interfacing with neurons for control of brain-machine interfaces require simultaneous large-scale and high spatiotemporal resolution recordings and stimulation of neurons in multiple layers and areas of the brain. Conventional penetrating micro-electrode arrays (MEAs) are limited to a few thousand electrodes at best, with limited volumetric 3D spatial resolution. This is mainly due to the types of fabrication technologies and available designs and materials for making such probes. Based on the strengths and shortcomings of the available MEAs, we present a new fabrication technology for a new class of 3D neural electrode array that provides the characteristics of a near-ideal neural interface. This research addresses some of the limitations of previous works in terms of electrode scale, density and spatial coverage (depth and span). In order to realize a scalable 3D out-of-plane array of extremely dense, slender, and sharp needles with recording sites at each of their tips, a number of techniques are developed. These includes: 1- A custom-developed silicon DRIE process to make deep (500 µm) high aspect-ratio (20-30) thru-wafer holes with controlled sidewall slope, 2- A method of extending the thru-wafer holes depth by aligning and then fusion bonding multiple silicon substrates already having holes etched in them, 3- A process for conformal refilling of ultra-deep (~2 mm) ultra-high aspect-ratio (80-100) holes with dielectric and conductive films using LPCVD process, 4- Methods of forming recording sites using self-aligned mask-less metallization processes, and 5- A method based on wet silicon etching to dissolve away the support substrate containing the refilled holes to release the electrodes. Using these technologies, we have fabricated millimeter-long (1.2mm), narrow (10-20µm diameter), sharp (submicron tip size), high-density (400 electrodes/mm2) high-count (5000+) silicon electrode arrays. Electrodes robustness, insertion and recording functionality have been demonstrated by acute in vivo recordings in rats under anesthesia using 2×2 and 3×3 arrays, where local field potentials (LFP) have been recorded. Innovative features of this technology could be utilized to produce arrays with arbitrary 3D design to target specific brain structures to achieve 3D spatial coverage over the convoluted topography of the brain. These include: 1- Length of side-by-side electrodes can be varied from tens of microns to several millimeters independently. 2- Electrodes spacing can be modified by the designer to obtain a desirable density and distribution of the array needles. 3- Electrode cross-sectional size can be controlled to obtain extremely fine, sharp and slender needles, crucial for minimizing tissue damage and improving chronic stability of implanted probes. 4- Any desired distribution of electrodes with customizable length, diameter and pitch across the array can be obtained to realize near-ideal application-specific neural probes. Potential capabilities of this work are investigated. These include integration of optical waveguides and chemical sensors and drug delivery channels to create sophisticated multi-modal multi-channel probes for electrophysiological studies of brain at the cellular levels. Limitations of developed DRIE, bonding, and LPCVD processes and tissue volume displacement by high-density arrays are discussed and a number of solutions are proposed. These results suggest maximum electrode length of ~2.5 mm and 20 µm thick electrodes. A maximum density of ~225 electrodes/mm2 for 10 µm thick electrodes is suggested for chronic applications.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/149834/1/aminsa_1.pd