We present the first active silicon perforated MEA for 3D organoid interfacing, integrating CMOS electronics for lownoise, high-resolution recording, stimulation, and impedance spectroscopy (EIS) across 7 modalities. The MEA, fabricated in 130 nm CMOS technology, features a scalable 256 -island mesh with multiplexed operation, achieving low input-referred noise ($9.1 \pm 1.5 \mu \mathrm{V}_{\text {rms }}, 300 \text{Hz}-10 \text{kHz}$) and low power ($11.3 \mu \mathrm{W}$ per island). In vitro tests with cardiomyocytes demonstrate accurate recordings, network propagation mapping, and intracellular recordings via voltage stimulation. This perforated MEA offers unparalleled functionality and scalability for advancing organ-on-chip research.

To understand the neural basis of behavior, it is essential to sensitively and accurately measure neural activity at single neuron and single spike resolution. Extracellular electrophysiology delivers this, but it has biases in the neurons it detects and it imperfectly resolves their action potentials. To minimize these limitations, we developed a silicon probe with much smaller and denser recording sites than previous designs, called Neuropixels Ultra (NP Ultra). This device samples neuronal activity at ultra-high spatial density (~10 times higher than previous probes) with low noise levels, while trading off recording span. NP Ultra is effectively an implantable voltage-sensing camera that captures a planar image of a neuron's electrical field. We use a spike sorting algorithm optimized for these probes to demonstrate that the yield of visually-responsive neurons in recordings from mouse visual cortex improves up to ~3-fold. We show that NP Ultra can record from small neuronal structures including axons and dendrites. Recordings across multiple brain regions and four species revealed a subset of extracellular action potentials with unexpectedly small spatial spread and axon-like features. We share a large-scale dataset of these brain-wide recordings in mice as a resource for studies of neuronal biophysics. Finally, using ground-truth identification of three major inhibitory cortical cell types, we found that these cell types were discriminable with approximately 75% success, a significant improvement over lower-resolution recordings. NP Ultra improves spike sorting performance, detection of subcellular compartments, and cell type classification to enable more powerful dissection of neural circuit activity during behavior.

We report on the progress in multimodal high resolution integrated neural interfaces with a focus on the Neuropixels probes. Historically, the number of neurons recorded simultaneously follows a Moore's law like behavior, with numbers doubling every 6.7 years. Traditional approaches to probe fabrication have failed to meet the needs of scaling needs of neural recording. The Neuropixels platform, is a custom 130nm/55nm CMOS wafer scale process technology that enables electrode counts beyond the 1000's, enabling system level simultaneous recording of tens of thousands of neurons with single neuron spatial precision and millisecond timing resolution. This required the utilization of multilevel BEOL technology and integrating analog and digital circuitry with the electrode array, making it a standalone integrated electrophysiological micro-system. Recently, we have added a switchable two-color visible photonics module that enables cell specific stimulation and responsive electro-physiology using opto-genetics. In addition, we have added 3D-integration modules which allows die-to-wafer attachment and have extended the platform to the 55nm node to enable higher electrode and recording density. These enable the recording of 10,000 neurons in a chronic freely moving animal and 40,000 neurons in an acute headfixed set-up.

We review recent progress in neural probes for brain recording, with a focus on the Neuropixels platform. Historically the number of neurons' recorded simultaneously, follows a Moore's law like behavior, with numbers doubling every 6.7 years. Using traditional techniques of probe fabrication, continuing to scale up electrode densities is very challenging. We describe a custom CMOS process technology that enables electrode counts well beyond 1000 electrodes; with the aim to characterize large neural populations with single neuron spatial precision and millisecond timing resolution. This required integrating analog and digital circuitry with the electrode array, making it a standalone integrated electrophysiology recording system. Input referred noise and power per channel is 7.5μV and <; 50μW respectively to ensure tissue heating <; 1°C. This approach enables doubling the number of measured neurons every 12 months.

In this study, we developed and validated a single-shank silicon-based neural probe with 128 closely-packed microelectrodes suitable for high-resolution extracellular recordings. The 8-mm-long, 100-µm-wide and 50-µm-thick implantable shank of the probe fabricated using a 0.13-µm complementary metal-oxide-semiconductor (CMOS) metallization technology contains square-shaped (20 × 20 µm2), low-impedance (~ 50 kΩ at 1 kHz) recording sites made of rough and porous titanium nitride which are arranged in a 32 × 4 dense array with an inter-electrode pitch of 22.5 µm. The electrophysiological performance of the probe was tested in in vivo experiments by implanting it acutely into neocortical areas of anesthetized animals (rats, mice and cats). We recorded local field potentials, single- and multi-unit activity with superior quality from all layers of the neocortex of the three animal models, even after reusing the probe in multiple (> 10) experiments. The low-impedance electrodes monitored spiking activity with high signal-to-noise ratio; the peak-to-peak amplitude of extracellularly recorded action potentials of well-separable neurons ranged from 0.1 mV up to 1.1 mV. The high spatial sampling of neuronal activity made it possible to detect action potentials of the same neuron on multiple, adjacent recording sites, allowing a more reliable single unit isolation and the investigation of the spatiotemporal dynamics of extracellular action potential waveforms in greater detail. Moreover, the probe was developed with the specific goal to use it as a tool for the validation of electrophysiological data recorded with high-channel-count, high-density neural probes comprising integrated CMOS circuitry.

Background: The cortical slow (similar to 1 Hz) oscillation (SO), which is thought to play an active role in the consolidation of memories, is a brain rhythm characteristic of slow-wave sleep, with alternating periods of neuronal activity and silence. Although the laminar distribution of cortical activity during SO is well-studied by using linear neural probes, traditional devices have a relatively low (20-100 mu m) spatial resolution along cortical layers. New method: In this work, we demonstrate a high-density linear silicon probe fabricated to record the SO with very high spatial resolution (similar to 6 mu m), simultaneously from multiple cortical layers. Ketamine/xylazine-induced SO was acquired acutely from the neocortex of rats, followed by the examination of the high-resolution laminar structure of cortical activity. Results: The probe provided high-quality extracellular recordings, and the obtained cortical laminar profiles of the SO were in good agreement with the literature data. Furthermore, we could record the simultaneous activity of 30-50 cortical single units. Spiking activity of these neurons showed layer-specific differences. Comparison with existing methods: The developed silicon probe measures neuronal activity with at least a three-fold higher spatial resolution compared with traditional linear probes. By exploiting this feature, we could determine the site of up-state initiation with a higher precision than before. Additionally, increased spatial resolution may provide more reliable spike sorting results, as well as a higher single unit yield. Conclusions: The high spatial resolution provided by the electrodes allows to examine the fine structure of local population activity during sleep SO in greater detail.

In vivo recording of neural action-potential (AP) and local-field-potential (LFP) signals requires the use of high-resolution penetrating probes. Driven by the need for large-scale recording and minimal tissue damage, a technology roadmap has been defined for next-generation probes aiming to maximize the number of recording sites while minimizing the probe dimensions [1]. In this paper we present a 384-channel configurable active neural probe for high-density recording which implements in situ buffering under each electrode to minimize the crosstalk between adjacent metal lines along the shank and other parasitic effects inherent to traditional passive probes [2]. Up to 966 selectable, neuron-sized electrodes (12×12µm2) were densely packed along a narrow (70µm) and thin (20µm) implantable shank using integrated CMOS. With twice the number of electrodes compared to state-of-the-art neural probes [2], our design achieves the highest electrode count in a single shank reported so far.

The past decade has witnessed an explosive growth in our ability to observe and measure brain activity. Among different functional brain imaging techniques, the electrical measurement of neural activity using neural probes provides highest temporal resolution. Yet, the electrode density and the observability of currently available neural probe technologies fall short of the density of neurons in the brain by several orders of magnitude. This paper presents opportunities for neural probes to utilize advances in CMOS technology for increasing electrode density and observability of neural activity, while minimizing the tissue damage. The authors present opportunities for neural probes to adapt advanced CMOS technologies and discuss challenges in terms of maintaining the signal integrity and implementing data communication.