Fast electrochemical imaging enables the dynamic study of electroactive molecule diffusion in neurotransmitter release from single cells and dopamine mapping in brain slices. In this paper, we discuss the design of an electrochemical imaging sensor using a monolithic CMOS sensor array and a multifunctional data acquisition system. Using post-CMOS fabrication, the CMOS sensor integrates 1024 on-chip electrodes on the surface and contains 1024 low-noise amplifiers to simultaneous process parallel electrochemical recordings. Each electrochemical electrode and amplifier are optimized to operate at 10.38 kHz sampling rate. To support the operation of the high-throughput CMOS device, a multifunctional data acquisition device is developed to provide the required speed and accuracy. The high analog data rate of 10.63 MHz from all 1024 amplifiers is redundantly sampled by the custom-designed data acquisition system which can process up to 73.6 MHz with up to ~400 Mbytes/s data rate to a computer using USB 3.0 interface. To contain the liquid above the electrochemical sensors and prevent electronic and wire damage, we packaged the monolithic sensor using a 3D-printed well. Using the presented device, 32 pixel × 32 pixel electrochemical imaging of dopamine diffusion is successfully demonstrated at over 10,000 frames per second, the fastest reported to date.
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1024-Electrode Hybrid Voltage/Current-Clamp Neural Interface System-on-Chip with Dynamic Incremental-SAR Acquisition
We present a neural interface system-on-chip (NISoC) with
1,024 channels of simultaneous electrical recording and stimulation
for high-resolution high-throughput electrophysiology. The
2mm 2mm NISoC in 65nm CMOS integrates a 32 32 array
of electrodes vertically coupled to analog front-ends supporting
both voltage and current clamping through a programmable interface,
ranging over 100dB in voltage and 120dB in current, with
0.82mW power per channel at 5.96mVrms input-referred voltage
noise from DC to 12.5kHz signal bandwidth. This includes onchip
acquisition with a back-end array of 32 dynamic incremental
SAR ADCs for 25Msps 11-ENOB acquisition at 2fJ/level FOM.
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- Award ID(s):
- 1728497
- NSF-PAR ID:
- 10192278
- Date Published:
- Journal Name:
- 2020 IEEE Symposium on VLSI Circuits (VLSI-Circuits)
- Page Range / eLocation ID:
- 1 to 2
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Introduction:Current brain-computer interfaces (BCIs) primarily rely on visual feedback. However, visual feedback may not be sufficient for applications such as movement restoration, where somatosensory feedback plays a crucial role. For electrocorticography (ECoG)-based BCIs, somatosensory feedback can be elicited by cortical surface electro-stimulation [1]. However, simultaneous cortical stimulation and recording is challenging due to stimulation artifacts. Depending on the orientation of stimulating electrodes, their distance to the recording site, and the stimulation intensity, these artifacts may overwhelm the neural signals of interest and saturate the recording bioamplifiers, making it impossible to recover the underlying information [2]. To understand how these factors affect artifact propagation, we performed a preliminary characterization of ECoG signals during cortical stimulation.Materials/Methods/ResultsECoG electrodes were implanted in a 39-year old epilepsy patient as shown in Fig. 1. Pairs of adjacent electrodes were stimulated as a part of language cortical mapping. For each stimulating pair, a charge-balanced biphasic square pulse train of current at 50 Hz was delivered for five seconds at 2, 4, 6, 8 and 10 mA. ECoG signals were recorded at 512 Hz. The signals were then high-pass filtered (≥1.5 Hz, zero phase), and the 5-second stimulation epochs were segmented. Within each epoch, artifact-induced peaks were detected for each electrode, except the stimulating pair, where signals were clipped due to amplifier saturation. These peaks were phase-locked across electrodes and were 20 ms apart, thus matching the pulse train frequency. The response was characterized by calculating the median peak within the 5-second epochs. Fig. 1 shows a representative response of the right temporal grid (RTG), with the stimulation channel at RTG electrodes 14 and 15. It also shows a hypothetical amplifier saturation contour of an implantable, bi-directional, ECoG-based BCI prototype [2], assuming the supply voltage of 2.2 V and a gain of 66 dB. Finally, we quantify the worstcase scenario by calculating the largest distance between the saturation contour and the midpoint of each stimulating channel.Discussion:Our results indicate that artifact propagation follows a dipole potential distribution with the extent of the saturation region (the interior of the white contour) proportional to the stimulation amplitude. In general, the artifacts propagated farthest when a 10 mA current was applied with the saturation regions extending from 17 to 32 mm away from the midpoint of the dipole. Consistent with the electric dipole model, this maximum spread happened along the direction of the dipole moment. An exception occurred at stimulation channel RTG11-16, for which an additional saturation contour emerged away from the dipole contour (not shown), extending the saturation region to 41 mm. Also, the worst-case scenario was observed at 6 mA stimulation amplitude. This departure could be a sign of a nonlinear, switch-like behavior, wherein additional conduction pathways could become engaged in response to sufficiently high stimulation.Significance:While ECoG stimulation is routinely performed in the clinical setting, quantitative studies of the resulting signals are lacking. Our preliminary study demonstrates that stimulation artifacts largely obey dipole distributions, suggesting that the dipole model could be used to predict artifact propagation. Further studies are necessary to ascertain whether these results hold across other subjects and combinations of stimulation/recording grids. Once completed, these studies will reveal practical design constraints for future implantable bi-directional ECoG-based BCIs. These include parameters such as the distances between and relative orientations of the stimulating and recording electrodes, the choice of the stimulating electrodes, the optimal placement of the reference electrode, and the maximum stimulation amplitude. These findings would also have important implications for the design of custom, low-power bioamplifiers for implantable bi-directional ECoG-based BCIs.References:[1] Hiremath, S. V., et al. "Human perception of electrical stimulation on the surface of somatosensory cortex." PloS one 12.5 (2017): e0176020.[2] Rouse, A. G., et al. "A chronic generalized bi-directional brain-machine interface." Journal of Neural Engineering 8.3 (2011): 036018more » « less
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Abstract Although tip‐enhanced tribo‐tunneling in metal/semiconductor point nanocontact is capable of producing DC with high current density, scaling up the process for power harvesting for practical applications is challenging due to the complexity of tip array fabrication and insufficient voltage output. Here, it is demonstrated that mechanical contact between a carbon aerogel and silicon (SiO2/Si) interface naturally forms multiple nanocontacts for tribo‐tunneling current generation with an open‐circuit voltage output (
V OC) reaching 2 V, and short‐circuit DC current output (I SC) of ≈15 µA. It has a theoretical current density (J *) on the order of 100 A m−2. Molecular dynamics simulation and atomistic field theory show that a strong localized electronic excitation can be induced at a dynamic carbon/SiO2sliding interface, which is in good agreement with the experimental results. The DC power output is enhanced by the intense local pressure at the presence of nanocontacts, as well as the increased sliding velocityv . To demonstrate the method for practical applications, light‐emitting diodes (LEDs) with different colors are successfully lighted by a single‐carbon aerogel monolith/SiO2sliding unit, and the DC electricity is stored in a capacitor without an additional rectification circuit. -
Abstract Carbon doped two-dimensional (2D) hexagonal boron nitride nanosheets (BNNSs) are obtained through a CO 2 —pulsed laser deposition (CO 2 —PLD) technique on silicon dioxide (SiO 2 ) or molybdenum (Mo) substrates, showing - stable hysteresis characteristics over a wide range of temperatures, which makes them a promising candidate for materials based on non-volatile memory devices. This innovative material with electronic properties of n-type characterized in the form of back-to-back Schottky diodes appears to have special features that can enhance the device performance and data retention due to its functional properties, thermal-mechanical stability, and its relation with resistive switching phenomena. It can also be used to eliminate sneak current in resistive random-access memory devices in a crossbar array. In this sense constitutes a good alternative to design two series of resistance-switching Schottky barrier models in the gold/BNNS/gold and gold/BNNS/molybdenum structures; thus, symmetrical and non-symmetrical characteristics are shown at low and high bias voltages as indicated by the electrical current-voltage (I–V) curves. On the one hand, the charge recombination caused by thermionic emission does not significantly change the rectification characteristics of the diode, only its hysteresis properties change due to the increase in external voltage in the Schottky junctions. The addition of carbon to BNNSs creates boron vacancies that exhibit partially ionic character, which also helps to enhance its electrical properties at the metal-BNNS-metal interface.more » « less
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This work presents a 4-channel, mm-scale, electro-static and piezoelectric actuator driver that uses< 1 µA total quiescent bias current and can drive actuator loads up to 120-330 V at frequencies over 1kHz. The driver achieves over 99% current efficiency and can operate untethered with an integrated photovoltaic array powered by a collimated or diffuse optical power source. The circuit is demonstrated also as a driver for an off-chip boost circuit, generating over 1.5 kV with 85% power efficiency at 45mW load. The system uses a simple 4-bit CMOS logic level interface with 100 kHz clock to actuate high voltage channels; on-chip photovoltaics also power the digital controller, and I/O bus.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/VLSICircuits18222.2020.9162837
