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Neuroelectronic interfaces with the nervous system are an essential technology in state-of-the-art neuroscience research aiming to uncover the fundamental working mechanisms of the brain. Progress towards increased spatio-temporal resolution has been tightly linked to the advance of microelectronics technology and novel materials. Translation of these technologies to neuroscience has resulted in multichannel neural probes and acquisition systems enabling the recording of brain signals using thousands of channels. This review provides an overview of state-of-the-art neuroelectronic technologies, with emphasis on recording site architectures which enable the implementation of addressable arrays for high-channel-count neural interfaces. In this field, active transduction mechanisms are gaining importance fueled by novel materials, as they facilitate the implementation of high density addressable arrays., This work has been funded by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 732032(BrainCom) and Grant Agreement No. 881603 (Graphene Flagship) and co-funded by the European Regional Development Funds (ERDF) allocated to the Programa operatiu FEDER de Catalunya 2014–2020, with the support of the Secretaria d’Universitats i Recerca of the Departament d’Empresa i Coneixement of the Generalitat de Catalunya for emerging technology clusters devoted to the valorization and transfer of research results (GraphCAT 001-P-001702). The ICN2 is supported by the Severo Ochoa Centres of Excellence program, funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706), and by the CERCA Program/Generalitat de Catalunya.

This paper presents a 1024-channel neural read-out integrated circuit (ROIC) for solution-gated GFET sensing probes in massive muECoG brain mapping. The proposed time-domain multiplexing of GFET-only arrays enables low-cost and scalable hybrid headstages. Low-power CMOS circuits are presented for the GFET analog frontend, including a CDS mechanism to improve preamplifier noise figures and 10-bit 10-kS/s A/D conversion. The 1024-channel ROIC has been fabricated in a standard 1.8-V 0.18-mum CMOS technology with 0.012 mm 2 and 36 mu W per channel. An automated methodology for the in-situ calibration of each GFET sensor is also proposed. Experimental ROIC tests are reported using a custom FPGA-based muECoG headstage with 16times 32 and 32times 32 GFET probes in saline solution and agar substrate. Compared to state-of-art neural ROICs, this work achieves the largest scalability in hybrid platforms and it allows the recording of infra-slow neural signals.

Sensor arrays used to detect electrophysiological signals from the brain are paramount in neuroscience. However, the number of sensors that can be interfaced with macroscopic data acquisition systems currently limits their bandwidth. This bottleneck originates in the fact that, typically, sensors are addressed individually, requiring a connection for each of them. Herein, we present the concept of frequency-division multiplexing (FDM) of neural signals by graphene sensors. We demonstrate the high performance of graphene transistors as mixers to perform amplitude modulation (AM) of neural signals in situ, which is used to transmit multiple signals through a shared metal line. This technology eliminates the need for switches, remarkably simplifying the technical complexity of state-of-the-art multiplexed neural probes. Besides, the scalability of FDM graphene neural probes has been thoroughly evaluated and their sensitivity demonstrated in vivo. Using this technology, we envision a new generation of high-count conformal neural probes for high bandwidth brain machine interfaces., This work has been funded by the European Union’s Horizon 2020 research and innovation programme under Grant Agreement 732032 (BrainCom), Grant Agreement 85219 and 881603 (Graphene Flagship). The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, Grant SEV-2017-0706), and by the CERCA Programme/Generalitat de Catalunya. R.G.C. and N.S. acknowledge that this work has been done in the framework of the Ph.D. in Electrical and Telecommunication Engineering at the Universitat Autonoma de Barcelona. R.G.C is supported by the International Ph.D. Programme La Caixa - Severo Ochoa (Programa Internacional de Becas “la Caixa”-Severo Ochoa). This work has made use of the Spanish ICTS Network MICRONANOFABS partially supported by MICINN and the ICTS “NANBIOSIS”, more specifically by the Micro-NanoTechnology Unit of the CIBER in Bioengineering, Biomaterials, and Nanomedicine (CIBER-BBN) at the IMB-CNM. This work is within the project 2DTecBio (FIS2017-85787-R) funded by the “Ministerio de Ciencia, Innovacion y Universidades” of Spain, the “Agencia Estatal de Investigacion (AEI)”, and the “Fondo Europeo de Desarrollo Regional (FEDER/UE)” and has received funding from Generalitat de Cataluña 2017 SGR 1426.

This paper presents a novel frequency-domain multiplexing scheme of liquid-gate GFET sensors for large-scale μECoG recording. The proposed technique allows the hybrid integration of GFET arrays and read-out ICs. In order to avoid artifacts, the proposal does not employ any switch in the GFET array and it is insensitive to the flicker noise of the CMOS frontend. A modular read-out IC architecture targeting the continuous acquisition of up to 1024 μECoG channels is introduced together with a collection of low-power CMOS circuits for the practical implementation of each building block. A test chip of the proposed system is currently being integrated in 0.18-μm 6-metal CMOS technology.

This paper proposes a compact switched-capacitor (SC) multi-bit flash quantizer for low-power high-resolution delta-sigma modulators (ΔΣMs). First, a general power model for single-loop ΔΣMs is presented to show the importance of using multi-bit quantization when facing high-resolution specifications. In this context, a SC multi-bit quantizer circuit is proposed, which exhibits low-power operation, high modularity, single comparator design and compatibility with both multi-feedforward ΔΣM architectures and other SC low-power circuit techniques, like clocked comparators and switched OpAmps. A practical 50-kHz 16-bit ΔΣM design case is also presented.

In this work a new design methodology for the low-power design of switched-capacitors delta-sigma modulators using the recently introduced switched-variable-mirror amplifiers (SVMAs) is presented. The effectiveness of the methodology is demonstrated for a third-order single-loop single-bit delta-sigma modulator employing SVMAs designed in a standard 0.18 μm CMOS technology. Results show that the proposed methodology allows for the design of state-of-the-art high-resolution ADCs while greatly boosting design cycles by removing the need for time consuming full electrical simulations.

X-ray absorption spectroscopy was used to determine the valence state in $\mathrm{L}{\mathrm{a}}_{2}\mathrm{C}{\mathrm{o}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{1+x}{\mathrm{O}}_{6}$ ($x\ensuremath{\approx}0.23$) thin films. We found that in spite of the nonstoichiometry, Co is in a divalent state while Mn ions show a mixed valence state. The relation of this finding with the magnetic properties of the films is discussed. X-ray magnetic circular dichroism measurements prove that magnetic anisotropy originates from Co spin-orbit coupling and it is strain dependent: a strong increase of the angular contribution to the magnetic moment is found when in-plane (out-of-plane) cell parameters get expanded (compressed). This behavior is reproduced by first order perturbation theory calculations.

The fabrication procedure of hollow iron oxide nanoparticles with a large surface to volume ratio by a single-step gas condensation process at ambient temperature is presented. Fe clusters formed during the sputtering process are progressively transformed into hollow cuboids with oxide shells by the Kirkendall mechanism at the expense of oxygen captured inside the deposition chamber. TEM and Raman spectroscopy techniques point to magnetite as the main component of the nanocuboids; however, the magnetic behavior exhibited by the samples suggests the presence of FeO as well. In addition, these particles showed strong stability after several months of exposure to ambient conditions, making them of potential interest in diverse technological applications. In particular, these hierarchical hollow particles turned out to be very efficient for both As(III) and As(V) absorption (326 and 190 mg/g, respectively), thus making them of strong interest for drinking water remediation., We kindly acknowledge the assistance of Guillaume Sauthier, from ICN2, for helping us with valuable X-ray photoelectron investigations. Financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Program for Centres of Excellence in R&D (SEV- 2015-0496), MAT2015-71664-R, FEDER, and funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 645658 (DAFNEOX Project) is acknowledged. N.B. thanks the Spanish MINECO for financial support through the FPI program.

Ferromagnetic insulating $\mathrm{L}{\mathrm{a}}_{2}\mathrm{CoMn}{\mathrm{O}}_{6\ensuremath{-}\ensuremath{\varepsilon}}$ (LCMO) epitaxial thin films grown on top of $\mathrm{SrTi}{\mathrm{O}}_{3}$ (001) substrates present a strong magnetic anisotropy favoring the out-of-plane (OP) orientation of the magnetization with a large anisotropy field (\ensuremath{\sim}70 kOe for film thickness of about 15 nm). Diminishing oxygen off-stoichiometry of the film enhances the anisotropy. We attribute this to the concomitant shrinkage of the OP cell parameter and to the increasing of the tensile strain of the films. Consistently, LCMO films grown on ${(\mathrm{LaAl}{\mathrm{O}}_{3})}_{0.3}{(\mathrm{S}{\mathrm{r}}_{2}\mathrm{AlTa}{\mathrm{O}}_{6})}_{0.7}$ and $\mathrm{LaAl}{\mathrm{O}}_{3}$ substrates (with a larger OP lattice parameter and compressive stress) display in-plane (IP) magnetic anisotropy. Thus, we link the strong magnetic anisotropy observed in LCMO to the film stress: tensile strain favors perpendicular anisotropy, and compressive stress favors IP anisotropy. We also report on the thickness dependence of the magnetic properties. Perpendicular anisotropy, saturation magnetization, and Curie temperature are maintained over a large range of film thickness.

We report on magnetotransport properties on La_(0.7)Sr_(0.3)MnO_(3)/MgO/Fe tunnel junctions grown epitaxially on top of (001)-oriented SrTiO_(3) substrates by sputtering. It is shown that the magnetoresistive response depends critically on the MgO/Fe interfacial properties. The appearance of an FeOX layer by the interface destroys the 1 symmetry filtering effect of the MgO/Fe system and only a small negative tunneling magnetoresistance (TMR) (∼ −3 %) is measured. However, in annealed samples a switchover from positive TMR (∼ +25% at 70 K) to negative TMR (∼ −1 %) is observed around 120 K. This change is associated with the transition from semiconducting at high T to insulating at low T taking place at the Verwey transition (TV ∼ 120 K) in Fe3O4, thus suggesting the formation of a very thin slab of magnetite at the MgO/Fe interface during annealing treatments. These results highlight the relevance of interfacial properties on the tunneling conduction process and how it can be substantially modified through appropriate interface engineering.

Under the terms of the Creative Commons Attribution (CC BY) license to their work., We report on the magnetic and structural properties of ferromagnetic-insulating La2CoMnO6-δ thin films grown on top of (001) SrTiO3 substrates by means of RF sputtering technique. Careful structural analysis, by using synchrotron X-ray diffraction, allows identifying two different crystallographic orientations that are closely related to oxygen stoichiometry and to the features (coercive fields and remanence) of the hysteresis loops. Both Curie temperature and magnetic hysteresis turn out to be dependent on the oxygen stoichiometry. In situ annealing conditions allow tailoring the oxygen content of the films, therefore controlling their microstructure and magnetic properties., We acknowledge financial support from the Spanish MEC (MAT2011-29081 and MAT2012-33207), CONSOLIDER (CSD2007-00041), and FEDER program. R.G., L.L.-M. and N.B. thank the Spanish MINECO for the financial support through the FPI program. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 312284.

This paper presents a 1024-channel ROIC for brain massive digital μECoG, which uses liquid-gate GFETs as active sensors. The proposed channel multiplexing technique at the recording array level allows strong reductions of the sensor-to-circuit connectivity, low-cost hybrid integration and low-power operation. A mixed-signal ROIC architecture and CMOS circuit solutions are introduced to compensate for GFET mismatching and for the preamplifier noise figure loss when upscaling the number of recording sites. The 1024-channel 10-bit 5-kHz 36-μ $W$ single-chip design is currently being integrated in 0.18-μm CMOS technology and post-layout simulation results are reported.