An LSI-based cooperative multi-chip neural interface device, for stimulation as well as recording, is proposed and fabricated. The proposed multi-chip device consists of small (600 μm × 600 μm in the present design) intelligent neural interface unit chips. The unit chip has nine neural stimulation/recording electrodes and an individual control circuit. It can work not only as a stand-alone unit, but also in cooperation with other unit chips. One can configure any number of the unit chips as a multi-chip neural interface device. Compared to conventional single-chip architecture, the proposed multi-chip architecture has a number of advantages including thinness, mechanical strength, flexibility, and extendibility. That makes the multi-chip neural interface device more suitable for in vivo applications than conventional single-chip devices. Packaging technology for the multi-chip device was also developed. We developed a thin, flexible packaging technique for the multi-chip neural interface device and LSI-compatible Pt/Au stacked bump electrodes. The functions of the fabricated multi-chip neural interface device were characterized and the feasibility of the device as a random-access, multi-site stimulator was demonstrated.

Flexible and extendible neural interface device based on cooperative multi-chip CMOS LSI architecture

Very fine needle-electrode arrays potentially offer both low invasiveness and high spatial resolution of electrophysiological neuronal recordings in vivo. Herein we report the penetrating and recording capabilities of silicon-growth-based three-dimensional microscale-diameter needle-electrodes arrays. The fabricated needles exhibit a circular-cone shape with a 3-μm-diameter tip and a 210-μm length. Due to the microscale diameter, our silicon needles are more flexible than other microfabricated silicon needles with larger diameters. Coating the microscale-needle-tip with platinum black results in an impedance of ~600 kΩ in saline with output/input signal amplitude ratios of more than 90% at 40 Hz-10 kHz. The needles can penetrate into the whisker barrel area of a rat's cerebral cortex, and the action potentials recorded from some neurons exhibit peak-to-peak amplitudes of ~300 μVpp. These results demonstrate the feasibility of in vivo neuronal action potential recordings with a microscale needle-electrode array fabricated using silicon growth technology.

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In vivo neuronal action potential recordings via three-dimensional microscale needle-electrode arrays

In this article, the authors report on a retinal prosthesis smart stimulator that is biocompatible and fully compatible with a standard large-scale-integration (LSI) structure and that provides high-stimulation efficiency. Our stimulator is based on multimicrochip architecture. The stimulator has been specifically developed for retinal prostheses, but it could be applied to other neuroscience and clinical neuroengineering fields

Silicon LSI-based smart stimulators for retinal prosthesis

Repeated vapor-liquid-solid (VLS) growth with Au and PH3–Si2H6 mixture gas as the growth catalyst and silicon source, respectively, was used to construct n-type silicon/n-type silicon wire arrays of various lengths Silicon wires of various lengths within an array could be grown by employing second growth over the first VLS grown wire Additionally, the junction at the interface between the first and the second wires were examined Current-voltage measurements of the wires exhibited linear behavior with a resistance of 850 Ω, confirming nonelectrical barriers at the junction, while bending tests indicated that the mechanical properties of the wire did not change

Vertically aligned silicon microwire arrays of various lengths by repeated selective vapor-liquid-solid growth of n-type silicon/n-type silicon

Three-dimensional microtubes and microprobes with MOSFET circuits are integrated for use in chemical and electrical neural interface applications with microelectronics. We propose a vapor–liquid–solid (VLS) method to realize both the microtubes and microprobes, which are 2 µm and 3.6 µm in diameter, respectively, and can be fabricated after the on-chip MOSFET processes. The on-chip NMOSFET shows electrical characteristics with a threshold voltage of 1.2 V and a subthreshold swing of 145 mV decade−1, confirming that subsequent fabrications of the tube and probe are compatible with the inclusion of the on-chip circuits. The prototype oxide tube, which has 2.7 µm inner diameter and 29 µm height, has a flow rate of 550 nl min−1 with an external pump pressure of 33.5 kPa. The impedance of the on-chip Si probe, which has 2 µm diameter and 30 µm height, measured at 1 kHz in a saline environment is 2 MΩ. Insertion into a gelatin membrane confirms that both the tube and the probe show sufficient penetration capabilities.

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Integration of out-of-plane silicon dioxide microtubes, silicon microprobes and on-chip NMOSFETs by selective vapor–liquid–solid growth

This paper reports on a fabrication technique for realizing micro-Si probe arrays with MOSFETs on the same Si substrate. Micro-Si probe arrays have been successfully fabricated on Si (111) substrates by selective vapor-liquid-solid (VLS) growth using catalytic Au dot arrays and Si/sub 2/H/sub 6/ used as the gas source for a molecular-beam-epitaxy. The Si probes can be grown at temperatures ranging from 500/spl deg/C to 700/spl deg/C. In this paper, MOSFETs were fabricated on Si (111) substrates and Au dots were placed at the drain regions of the MOSFETs in order to grow the Si probes. VLS growth at 700/spl deg/C for 2 h was carried out on these substrates. Consequently, the MOSFETs can be used in on-chip circuits for the VLS-Si probe array. The electrical characteristics of the MOSFETs were measured before and after the VLS process. After the VLS process, no changes in the MOSFET characteristics were observed due to the effects of Au-diffusion, and the results confirmed that VLS growth at a temperature of 700/spl deg/C allows fabrication of micro-Si probes without deterioration of the MOSFETs. VLS-Si probes with controlled conductance were realized. The as-grown Si probes were of high resistance, but could be changed to various conductivities by impurity diffusion.

/pdf/selective-vapor-liquid-solid-epitaxial-growth-of-micro-si-2p5e50609x.pdf

Selective vapor-liquid-solid epitaxial growth of micro-Si probe electrode arrays with on-chip MOSFETs on Si (111) substrates

This report presents a technique for multichannel electrode of penetrating Si microprobe array with on-chip integrated circuits (ICs) for use in neuroscience and biomedical engineering. Penetrating microelectrodes can be used for multipoint neural recording as well as stimulation for neurons located in the neuronal tissue. Penetrating Si probes were successfully fabricated at predetermined sites on ICs by a selective vapor-liquid-solid (VLS) Si growth. The length of the Si probe was controlled in the VLS growth, which allowed required length with same diameter of one neuron or less for in-vivo study. On-chip ICs was realized in order to site-selection for many probes. The Si probes on the circuits were spaced on 100 /spl mu/m in the array, which can provide a high-density multichannel penetrating electrode.

R. Tani

Papers

Selective vapor-liquid-solid epitaxial growth of micro-Si probe electrode arrays with on-chip MOSFETs on Si (111) substrates

Neuron size Si probe array fabricated on integrated circuits for multichannel electrode