Resolving the underlying mechanisms of complex brain functions and associated disorders remains a major challenge in neuroscience, largely due to the difficulty in mapping large-scale neural network dynamics with high spatiotemporal resolution. Multimodal neural platforms that integrate optical and electrical modalities offer a promising approach that surpasses resolution limits. Over the last decade, transparent graphene microelectrodes have been proposed as highly suitable multimodal neural interfaces. However, their fabrication commonly relies on the manual transfer process of pre-grown graphene sheets which introduces reliability and scalability issues. In this study, multilayer graphene microelectrode arrays (MEAs) with electrode sizes as small as 10–50 µm in diameter, are fabricated using a transfer-free process on a transparent substrate for in vitro multimodal platforms. For the first time, the capability of transparent graphene electrodes with a diameter of just 10 µm to reliably capture extracellular spiking activity with high signal-to-noise ratios (up to ∼25 dB) is demonstrated. The recorded signal quality is found to be more limited by the electrode-tissue coupling than the MEA technology itself. Overall, this study shows the potential of transfer-free multilayer graphene MEAs to interface with neural tissue, paving the way to advancing neuroscientific research through the next-generation of multimodal neural interfaces.

Depending on the applications based on graphene, single-layer or few-layer graphene would be more beneficial. Ideally, graphene could be nucleated directly with the required thickness. However, some aspects related to graphene thickness and uniformity control still need to be solved. This work aims to better understand graphene formation using Mo thin films as a catalyst. The grown graphene films were characterized using SEM, TEM, XPS, AFM, standard Raman spectroscopy and 3D Raman surface imaging. A correlation between the catalyst thickness and the number of layers is established. All the characterization techniques show that the number of graphene layers inversely scales with the Mo catalyst thickness used for the graphene synthesis. Then, by simply adjusting the catalyst thickness, the number of graphene layers can be engineered from few-layer graphene (FLG) up to multi-layer graphene (MLG). A pinhole distribution of 1 % was detected on the films synthesized on 50 nm and 100 nm Mo thicknesses after the catalyst was etched. On the synthesized FLG (500 nm Mo), no holes were observed on the surface film after the etching process and even after a transfer onto another substrate. These results can enable the formation of FLG with a controlled thickness and good uniformity.

Low-loss deposited dielectrics are beneficial for the advancement of superconducting integrated circuits for astronomy. In the microwave band (approximately 1-10 GHz) the dielectric loss at cryogenic temperatures and low electric field strengths is dominated by two-level systems. However, the origin of the loss in the millimeter-submillimeter band (approximately 0.1-1 THz) is not understood. We measured the loss of hydrogenated-amorphous-SiC films in the 0.27-100-THz range using superconducting-microstrip resonators and Fourier-transform spectroscopy. The agreement between the loss data and a Maxwell-Helmholtz-Drude dispersion model suggests that vibrational modes above 10 THz dominate the loss in hydrogenated amorphous SiC above 200 GHz.

The unique properties of two-dimensional (2D) materials bring great promise to improve sensor performance and realise novel sensing principles. However, to enable their high-volume production, wafer-scale processes that allow integration with electronic readout circuits need to be developed. In this perspective, we review recent progress in on-chip 2D material sensors, and compare their performance to the state-of-the-art, with a focus on results achieved in the Graphene Flagship programme. We discuss transfer-based and transfer-free production flows and routes for complementary metal-oxide-semiconductor integration and prototype development. Finally, we give an outlook on the future of 2D material sensors, and sketch a roadmap towards realising their industrial and societal impact.

In this work, we report a simple, scalable, and dry fabrication technique for realizing thin-film platinum resistance temperature detectors (RTDs), utilizing spark ablation technology. Pure spark-ablated platinum nanoparticles, with an average diameter of around 2.2 nm, were directly deposited through chemical-free impaction printing onto the substrate, enabling direct sensor patterning without complex processing steps. Experimental investigations revealed that higher deposition speeds produce sparser and thermally unstable films, with 1 mm/min identified as the optimal printing rate. Additionally, it was established that the film temperature coefficient of resistance (TCR) improves with increasing layer thickness, achieving a maximum mean TCR of 2.17 × 10−3°C−1 for an 8-layer RTD. The printed Pt sensor demonstrated linear temperature-resistance characteristics while maintaining high stability and repeatability over multiple thermal cycles, spanning 25–200 °C. This study lays the groundwork for advancing practical and cost-effective printed thermal sensing technologies.

In this work, we demonstrate the use of a micro-hotplate (MHP) with graphene integrated without transfer step for NO₂ sensing. The MHP can rapidly recover the device to its initial conditions by applying a brief heat pulse. Moreover, by employing a process without graphene transfer, we prevent random polymer contamination from the transfer process. The (up to 8) graphene sensors on a single MHP show a very similar response. Finally, we demonstrate that we can extract the relative humidity from the device's response immediately after the MHP is turned off in a humid environment.

In this study, we investigated the effect of vertically aligned carbon nanofiber (VACNF) density on ethanol vapor sensing performance. VACNFs were synthesized on Si substrates using plasma-enhanced chemical vapor deposition (PECVD), where varying the acetylene flow rate resulted in different fiber densities. Morphological characterization confirmed that higher acetylene flow leads to improved alignment and denser CNF networks. Raman spectroscopy revealed reduced defect levels and increased graphitization with increasing density. Gas sensing measurements showed that moderate to high CNF densities significantly enhance sensor conductivity and ethanol sensitivity due to improved charge transport paths and increased active surface area. These results highlight the importance of CNF density optimization in designing high-performance gas sensors.

The term graphene-based gas sensors may be too broad, as there are many physicochemical differences within the graphene-based materials (GBM) used for chemiresistive gas sensors. These differences condition the sensitivity, selectivity, recovery, and ultimately the sensing performance of these devices towards air pollutants. Continuous ultraviolet irradiation aids in the desorption of gas molecules and enhances sensor performance. Under these conditions, the devices from this work can reliably monitor NO₂ and CO at room temperature, below the human-recommended exposure limits, presenting NO₂ LoD down to ∼20 ppb. By selecting GBMs with different levels of defectivity, which influence gas adsorption dynamics, and through comprehensive characterization, including D, D′, D″, 2D, and G Raman bands, graphene-based gas sensors can be tailored to meet specific sensing requirements. This study examines five different non-oxidized GBM to develop tools and gain a deeper understanding of the relationships between GBM properties and their sensing performance. This research introduces a new standard for defect assessment, moving beyond graphene's D and G Raman band intensity ratio, to facilitate the successful integration of graphene-based gas sensors into everyday applications, such as environmental monitoring and industrial safety, and potentially impacting other 2D materials, thereby reducing health risks associated with air pollution.

Silicon carbide (SiC) coated vertically aligned carbon nanotubes (VACNT) are attractive material for fabricating MEMS devices as an alternative for bulk micromachining of SiC. In order to examine the mechanical properties of SiC-CNT composites at high temperatures, we fabricated VACNT micro-pillars with different amounts of SiC coating and performed high-temperature micro-pillar compression on these samples. The indentation result shows that the coating can improve the elastic modulus up to three orders of magnitude. Samples were tested at room temperature, 300°C, 600°C, and 900°C under compressive load. No significant degradation of the mechanical properties was observed at elevated temperatures, demonstrating the harsh environment potential of this composite.

As a consequence of their high strength, small thickness, and high flexibility, ultrathin graphene membranes show great potential for pressure and sound sensing applications. This study investigates the performance of multi-layer graphene membranes for microphone applications in the presence of air-loading. Since microphones need a flatband response over the full audible bandwidth, they require a sufficiently high mechanical resonance frequency. Reducing membrane thickness facilitates meeting this bandwidth requirement, and therefore, also allows increasing compliance and sensitivity of the membranes. However, at atmospheric pressure, air-loading effects can increase the effective mass, and thus, reduce the bandwidth of graphene and other 2D material-based microphones. To assess the severity of this performance-limiting effect, we characterize the acoustic response of multi-layer graphene membranes with a thickness of 8 nm in the pressure range from 30 to 1000 mbar, in air and helium environments. A bandwidth reduction by a factor ∼ 2.8 × for membranes with a diameter of 500 μm is observed. These measurements show that air-loading effects, which are usually negligible in conventional microphones, can lead to a substantial bandwidth reduction in ultrathin graphene microphones. With analytical and finite element models, we further analyze the performance limits of graphene microphones in the presence of air-loading effects.

Suspended drums made of 2D materials hold potential for sensing applications. However, the industrialization of these applications is hindered by significant device-to-device variations presumably caused by non-uniform stress distributions induced by the fabrication process. Here, we introduce a methodology to determine the stress distribution from their mechanical resonance frequencies and corresponding mode shapes as measured by a laser Doppler vibrometer (LDV). To avoid limitations posed by the optical resolution of the LDV, we leverage a manufacturing process to create ultra-large graphene drums with diameters of up to 1000 μm. We solve the inverse problem of a Föppl–von Kármán plate model by an iterative procedure to obtain the stress distribution within the drums from the experimental data. Our results show that the generally used uniform pre-tension assumption overestimates the pre-stress value, exceeding the averaged stress obtained by more than 47%. Moreover, it is found that the reconstructed stress distributions are bi-axial, which likely originates from the transfer process. The introduced methodology allows one to estimate the tension distribution in drum resonators from their mechanical response and thereby paves the way for linking the used fabrication processes to the resulting device performance.

As the dimensions of interconnects in integrated circuits continue to shrink, an urgent need arises to understand the physical mechanism associated with electromigration. Using x-ray nanodiffraction, we analyzed the stresses in Blech-structured pure Cu lines subjected to different electromigration conditions. The results suggest that the measured residual stresses in the early stages of electromigration are related to relaxation of stresses caused by thermal expansion mismatch, while a developing current-induced stress leads to reductions in the residual stress after longer test times. These findings not only validate the feasibility of measuring stress in copper lines using nanodiffraction but also highlight the need for a further understanding, particularly through in situ electromigration experiments with x-ray nanodiffraction analysis.

The authors regret that in the above article the Fig. 3 contains an error of cross-section image of group C at 48 h on Page 4. Fig. 3 should read: This correction does not influence the method, results and conclusions of the original article. The authors would like to apologise for any inconvenience caused.

This study explores the application of a novel transfer-free method for the synthesis of multilayer Chemical Vapour Deposition (CVD) graphene directly on transparent sub-strates, specifically to create transparent Microelectrode Arrays (MEAs) for optogenetic studies. Traditional methods typically involve a graphene transfer step that can compromise the material's integrity and electrical properties. By eliminating this step, our approach simplifies the fabrication process. The developed MEAs were characterised by Raman spectroscopy, op-tical transmittance, and electrochemical impedance spectroscopy. We also assessed the stability and recording capabilities of the fabricated MEAs, alongside a comparative assessment with a commercial MEA. Turbostratic graphene grown directly on quartz and sapphire was successfully achieved. Our transfer-free MEAs exhibit promising signal detection capabilities, despite a relatively high baseline noise of ∼ 23μ V. and a significantly large impedance at 1 kHz (3.2 to 9.89 M Ω) surpassing values in other studies. The devices exhibited low stability after exposure to liquid media during the soaking and ageing tests, causing large variations in the electrochemical measurements post-exposure. This was due to the permeability of the encapsulation layer and the biodegradability of the molybdenum structures, which led to significant structural and chemical changes in the devices. While further work is required to prevent the failure mechanisms of the device, this study demonstrates the feasibility of transparent MEA fabrication by means of a transfer-free approach directly on quartz substrates.

Correction to: Microsystems & Nanoengineering https://doi.org/10.1038/s41378-024-00656-x published online 21 February 2024 After publication of this article¹, it was brought to our attention that two pressure values were not correctly copied from the submitted original work to the published version. Correction 1 (from PDF, Page 4 of 9): “These membranes show resonance frequencies above the audible range (f₀₁ > 20 kHz) at 1 × 10³ mbar by piezo-shaker actuation”. The described phrase needs to be changed reporting the right pressure value of 1 × 10⁻³ mbar. The new phrase will be: “These membranes show resonance frequencies above the audible range (f₀₁ > 20 kHz) at 1 × 10⁻³ mbar by piezo-shaker actuation”. Correction 2 (from PDF, Page 4 of 9): “Energy losses and dampening are minimized due to the low pressure of 1 × 10³ mbar”. Again, the described phrase needs to be changed reporting the right pressure value of 1 × 10⁻³ mbar. The new phrase will be: “Energy losses and dampening are minimized due to the low pressure of 1 × 10⁻³ mbar”.

The continuing drive to miniaturise electronic devices requires an understanding of how the materials in these devices behave under stress, particularly with respect to electromigration. In this study, we explore the relationship between the microstructure of copper (Cu) and electromigration by using an approach that combines in situ Scanning Electron Microscopy (SEM) with Electron Backscatter Diffraction (EBSD). This in-situ SEM-EBSD technique enables real-time observation and analysis of electromigration-induced microstructure changes. Our investigation provides detailed insights into the microstructure effect on electromigration. Specifically, samples annealed at 300 °C showed void formation after the electromigration test and higher Kernal average misorientation (KAM) values, indicating higher internal strains and an inhomogeneous microstructure. In contrast, samples annealed at 500 °C maintained lower KAM values with minimal changes in crystal orientation, highlighting a more stable and uniform electromigration-resistant microstructure. Our results demonstrate the critical role of microstructure in determining the electromigration resistance of copper interconnects. By optimizing the annealing temperature, the reliability of the copper microstructure can be significantly improved by reducing the dislocations and increasing grain size, thus extending its lifetime.

The demand for accurate temperature sensing in extreme temperatures is increasing. Traditional silicon-based integrated temperature sensors usually cannot survive above 200 °C. Many researchers have started to focus on semiconductors with a large bandgap. Among them, silicon carbide (SiC) is the most promising one. Nevertheless, most reported SiC sensors are in the form of discrete components and are not compatible with integrated electronics. In this work, we demonstrate an open 4H-SiC CMOS technology, and the fabrication steps are detailed. The temperature sensing elements in this technology, including resistors based on different implanted layers and MOSFETs, are characterized up to 600 °C. At room temperature, the resistive-based elements demonstrate large negative temperature coefficients of resistance (TCRs). With increasing temperature, the TCR starts to decrease and even becomes positive. The TCR change is due to the interplay between increasing dopant ionization rate and decreasing mobility as a function of temperature. The resistance change with temperature fits well into the Steinhart-Hart model and second-order polynomial equation. The p-type diode-connected MOSFET has a sensitivity of 4.35 mV/°C with a good linearity. The nMOS-based sensor has a maximum sensitivity of -9.24 mV/°C but a compromised linearity. The characterization of these sensing elements provides important results for potential users who will work on SiC integrated temperature sensing with this technology.

Since the performance of micro-electro-mechanical system (MEMS)-based microphones is approaching fundamental physical, design, and material limits, it has become challenging to improve them. Several works have demonstrated graphene’s suitability as a microphone diaphragm. The potential for achieving smaller, more sensitive, and scalable on-chip MEMS microphones is yet to be determined. To address large graphene sizes, graphene-polymer heterostructures have been proposed, but they compromise performance due to added polymer mass and stiffness. This work demonstrates the first wafer-scale integrated MEMS condenser microphones with diameters of 2R = 220–320 μm, thickness of 7 nm multi-layer graphene, that is suspended over a back-plate with a residual gap of 5 μm. The microphones are manufactured with MEMS compatible wafer-scale technologies without any transfer steps or polymer layers that are more prone to contaminate and wrinkle the graphene. Different designs, all electrically integrated are fabricated and characterized allowing us to study the effects of the introduction of a back-plate for capacitive read-out. The devices show high mechanical compliances C_m = 0.081–1.07 μmPa⁻¹ (10–100 × higher than the silicon reported in the state-of-the-art diaphragms) and pull-in voltages in the range of 2–9.5 V. In addition, to validate the proof of concept, we have electrically characterized the graphene microphone when subjected to sound actuation. An estimated sensitivity of S_1kHz = 24.3–321 mV Pa⁻¹ for a V_bias = 1.5 V was determined, which is 1.9–25.5 × higher than of state-of-the-art microphone devices while having a ~9 × smaller area. (Figure presented.).

Synchronized rectifiers offer promising solutions for piezoelectric energy harvesting; however, achieving the promised energy extraction performance necessitates using either a bulky inductor or multiple large capacitors, which cannot be on-chip integrated and increase the system form factor. This article introduces a fully integrated sequenced synchronized switch harvesting on capacitors (3SHC) rectifier. The input piezoelectric transducer (PT) uses microelectromechanical system technology. The cantilever is equally split into multiple strongly coupled subcantilevers, with each cantilever treated as an individual PT connected to the proposed rectifier. The 3SHC rectifier cyclically operates multiple times to synchronously flip the voltage of each cantilever sequentially. With the proposed design, all the flying capacitors only need to match the capacitance of each subcantilever; hence, they can be fully integrated on-chip. The design is fabricated using standard 0.18 μ m CMOS technology. Measurement results show that the proposed 3SHC rectifier attains an 80% voltage flip efficiency and achieves a 730% power enhancement compared to a full-bridge rectifier.

Integrated circuits based on wide bandgap semiconductors are considered an attractive option for meeting the demand for high-temperature electronics. Here, we report an analog-to-digital converter fabricated in a silicon carbide complementary metal-oxide-semiconductor technology now available through Europractice. The MOSFET component in this technology was measured up to 500 °C, and the key parameters, such as threshold voltage, field-effect mobility, and channel-length modulation parameters, were extracted. A 4-bit flash data converter, consisting of 266 transistors, is implemented with this technology and demonstrates correct operation up to 400 °C. Finally, the gate oxide quality is investigated by time-dependent dielectric breakdown measurements at 500 °C. A field-acceleration factor of 4.4 dec/(MV/cm) is obtained by applying the E model.