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.).

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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”.

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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.

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Micro-physiological systems (MPS) hold the potential for advancing drug research by emulating realistic in vitro human (patho)physiology models. These systems replicate organ microenvironments, delivering stimuli similar to those experienced by organs in vivo. Active biomechanical cues, like shear force and tensile stress, profoundly influence cell activity and can alter biochemical responses. The critical factors encompass the nature, duration, magnitude, and frequency of these cues [1]. A currently popular solution to provide biomechanical stimulation employs pneumatic actuation, which is powerful and multifunctional, but bulky, expensive, and inconvenient to use. Electroactive polymers (EAP), also known as artificial muscles, are gaining attention as a potential alternative for improved versatility [2]. Ionic polymer-metal composites (IPMCs) are a class of ionic EAPs which operate at low voltage and exhibit large displacement [3]. They are intrinsically suitable for cell culture media as their operating principle is based on electrolytes (Fig. 1A). However, IPMCs employ metallic electrodes, which eliminate the optical transparency essential in fundamental biological experiments.
In this study, we present the design, fabrication, and characterization of a selectively transparent IPMC for utilization in MPS to apply controllable mechanical stimuli to tissues. A multiphysics-based finite-element model was constructed and validated basing on literature data [4] to estimate the maximum tip displacement of IPMC cantilevers. The model was used to study several cantilever configurations to determine the best electrode patterning topology for the transparency, stiffness, and tip displacement trade-off. The optimized designs were implemented in wafer-scale cleanroom-compatible fabrication (Fig. 1B-C). The novel fabrication process involved sequential patterning of planar Au electrodes on polydimethylsiloxane (PDMS) substrates, and covalent bonding of a pair of such Au-patterned PDMS substrates to an ionomer (Nafion) through silanization (Fig 1B). Preliminary electro-mechanical characterization of the performance of the selectively transparent IPMC cantilevers (Fig. 1D) and biocompatibility tests indicate a potential for integration and use in MPS and organ-on-chip platforms.@en

Ionic FETs have enormous potential for energy conversion, sensing, and ionic circuits due to their efficient regulation of the nanochannel. Here ionic FETs based on single-crystal silicon nanopores and the rectification of the fabricated devices are studied. The electrical characterization results demonstrated that since the silicon-based nanopores have the advantage of modulating the surface charge due to their semiconductor nature and benefitting from the effective 3D gating effect on the nanochannel, the magnitude and polarity of surface charge can be modulated by the gate voltage. The rectification effect can be adjusted by applying a certain voltage and fulfilling a transition between anion selectivity and cation selectivity when the surface charge polarity is reversed. Moreover, current–voltage characteristics of the reported ionic FET can be switched between ohmic and diode-like regimes. The proposed ionic FETs supply a novel platform to study the ionic properties and have great potential to be applied in large-scale ionic circuits due to their excellent performance. Finally, simulation results prove the surface charge modulated by the gate voltage determines the magnitude and direction of rectification, which is consistent with the reported experiment result.

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Thermal noise is a major obstacle to observing quantum behavior in macroscopic systems. To mitigate its effect, quantum optomechanical experiments are typically performed in a cryogenic environment. However, this condition represents a considerable complication in the transition from fundamental research to quantum technology applications. It is therefore interesting to explore the possibility of achieving the quantum regime in room-temperature experiments. In this work we test the limits of sideband-cooling vibration modes of a SiN membrane in a cavity optomechanical experiment. We obtain an effective temperature of a few millikelvins, corresponding to a phononic occupation number of around 100. We show that further cooling is prevented by the excess classical noise of our laser source, and we outline the road toward the achievement of ground state cooling.

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Continuous monitoring of tissue microphysiology is a key enabling feature of the organ-on-chip (OoC) approach for in vitro drug screening and disease modeling. Integrated sensing units are particularly convenient for microenvironmental monitoring. However, sensitive in vitro and real-time measurements are challenging due to the inherently small size of OoC devices, the characteristics of commonly used materials, and external hardware setups required to support the sensing units. Here we propose a silicon-polymer hybrid OoC device that encompasses transparency and biocompatibility of polymers at the sensing area, and has the inherently superior electrical characteristics and ability to house active electronics of silicon. This multi-modal device includes two sensing units. The first unit consists of a floating-gate field-effect transistor (FG-FET), which is used to monitor changes in pH in the sensing area. The threshold voltage of the FG-FET is regulated by a capacitively-coupled gate and by the changes in charge concentration in close proximity to the extension of the floating gate, which functions as the sensing electrode. The second unit uses the extension of the FG as microelectrode, in order to monitor the action potential of electrically active cells. The layout of the chip and its packaging are compatible with multi-electrode array measurement setups, which are commonly used in electrophysiology labs. The multi-functional sensing is demonstrated by monitoring the growth of induced pluripotent stem cell-derived cortical neurons. Our multi-modal sensor is a milestone in combined monitoring of different, physiologically-relevant parameters on the same device for future OoC platforms.

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Human heart tissues grown as three-dimensional spheroids and consisting of different cardiac cell types derived from pluripotent stem cells (hiPSCs) recapitulate aspects of human physiology better than standard two-dimensional models in vitro. They typically consist of less than 5000 cells and are used to measure contraction kinetics although not contraction force. By contrast, engineered heart tissues (EHTs) formed around two flexible pillars, can measure contraction force but conventional EHTs often require between 0.5 and 2 million cells. This makes large-scale screening of many EHTs costly. Our goals here were (i) to create a physiologically relevant model that required fewer cells than standard EHTs making them less expensive, and (ii) to ensure that this miniaturized model retained correct functionality. We demonstrated that fully functional EHTs could be generated from physiologically relevant combinations of hiPSC-derived cardiomyocytes (70%), cardiac fibroblasts (15%) and cardiac endothelial cells (15%), using as few as 1.6 × 10⁴ cells. Our results showed that these EHTs were viable and functional up to 14 days after formation. The EHTs could be electrically paced in the frequency range between 0.6 and 3 Hz, with the optimum between 0.6 and 2 Hz. This was consistent across three downscaled EHT sizes tested. These findings suggest that miniaturized EHTs could represent a cost-effective microphysiological system for disease modelling and examining drug responses particularly in secondary screens for drug discovery.

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Ionic polymer metal composites (IPMCs) are a class of materials with a rising appeal in biological micro-electromechanical systems (bio-MEMS) due to their unique properties (low voltage output, bio-compatibility, affinity with ionic medium). While tailoring and improving actuation capabilities of IPMCs is a key motivator in almost all IPMC manufacturing reports, very little efforts have been dedicated to sensing using IPMC thinner than 100 µm. Most reports on IPMC manufacturing and utilization rely on 180 µm-thick Nafion with platinum electrodes, too stiff for bio-MEMS applications. The same fabrication process on thinner membranes does yield in very poor electrodes and performance, and needs to be studied to increase flexibility and sensitivity in the microscale range. This study demonstrates an electroless Pt deposition method for fabricating bio-MEMS-suitable 50 µm-thick IPMC samples. First, we perform a comparative study on the platinum distribution within the Nafion backbone as well as on the surface for the standard electroless deposition recipe for thin (50 µm) and thick (180 µm) Nafion. We report strong differences in platinum distribution for thick and thin IPMC that experienced the same manufacturing process. By varying chemical concentrations from the standard recipe we obtain convenient platinum distribution on thin Nafion, with platinum mainly localized in proximity of surface, as well as electrodes with lower sheet resistance. We could measure the flexural rigidity as 3.43 × 10 − 8 N·m², 46 times lower than standard 180 µm-thick IPMC. The calculated sensitivity is 0.476 ± 0.02 mV mm⁻¹ and the limit of detection for our sensor is 500 ± 20 µm. This procedure sets a milestone for manufacturing 50 µm-thick IPMC for transducers and sensors in bio-MEMS applications.

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The authors regret an error in the abstract of the published article: the text ‘‘(i) the Schottky emission mechanism at a low reverse voltage (0–1 V) before the current is fully turned on.’’ should be changed to ‘‘(i) the Schottky emission mechanism at a low reverse voltage (0 to 1 V) before the current is fully turned on.’’ This change does not affect the main conclusions of the manuscript. The authors would like to apologize for any inconvenience caused. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

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The next generation of satellites will need to tackle tomorrow's challenges for communication, navigation and observation. In order to do so, it is expected that the amount of satellites in orbit will keep increasing, form smart constellations and miniaturize individual satellites to make access to space cost effective. To enable this next generation of activities in space, it is vital to ensure the ability of these satellites to properly navigate themselves. This control starts with attitude measurement by the dedicated sensors on the satellite, commonly performed by sun position sensors. The state-of-the art is confronted by large signal distortions caused by light reflected by the Earth's albedo as well as keeping up with the satellite miniaturization trend. This work aims to address both these issues, by presenting a microfabricated albedo insensitive sun position sensor in silicon carbide with wafer-level integrated optics. The presented 10 mm×10 mm×1 mm system reaches a mean angular accuracy of 5.7° in a ±37° field-of-view and integrates an on-chip temperature sensor with a -3.9 mV K⁻¹ sensitivity in the 20 °C to 200 °C range.

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The application of single-crystal silicon (SCS) nanopore structures in single-molecule-based analytical devices is an emerging approach for the separation and analysis of nanoparticles. The key challenge is to fabricate individual SCS nanopores with precise sizes in a controllable and reproducible way. This paper introduces a fast-stop ionic current-monitored three-step wet etching (TSWE) method for the controllable fabrication of SCS nanopores. Since the nanopore size has a quantitative relationship with the corresponding ionic current, it can be regulated by controlling the ionic current. Thanks to the precise current-monitored and self-stop system, an array of nanoslits with a feature size of only 3 nm was obtained, which is the smallest size ever reported using the TSWE method. Furthermore, by selecting different current jump ratios, individual nanopores of specific sizes were controllably prepared, and the smallest deviation from the theoretical value was 1.4 nm. DNA translocation measurement results revealed that the prepared SCS nanopores possessed the excellent potential to be applied in DNA sequencing. [Figure not available: see fulltext.]

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Microphysiological systems consisting of multiple cell types of the human heart have been shown to recapitulate certain aspects of human physiology better than conventional 2D in vitro models [1]. Engineered heart tissues (EHTs) that self-organise into contractile 3D structures between two flexible pillars are particularly useful to measure contraction against a force. However, conventional EHTs typically require between 50,000 and 2,000,000 cells, which makes creating many EHTs for high throughput screening costly [2]. Here, we show that downscaling EHT size, in our case to include human-induced pluripotent stem cell-derived cardiomyocytes (70%), cardiac fibroblasts (15%) and cardiac endothelial cells (15%), is feasible using as few as 16,000 cells. Tissues of three different sizes formed as expected and consistently, with 47,000, 31,000, and 16,000 cells. Moreover, while keeping the load constant relative to the size of the tissue [3], there was no difference in the viability nor functionality up to 14 days after formation. Electrical pacing of the tissues was conducted within the range of 1 to 3 Hz and with an optimal pacing frequency of 1.4 Hz, which is consistent over the three EHT sizes. Our results indicate that downscaled EHTs might be used as a cost-effective alternative to larger EHTs in drug discovery. @en

We present a novel capacitive displacement sensor integrated in an engineered heart tissue (EHT) platform to measure tissue contractile properties in-situ. Co-planar spiral capacitors were integrated into the elastomeric substrate underneath the two micropillars of a previously developed EHT platform. The capacitor plates are displaced by the tension and compression that occurs in the substrate when the micropillars bend under contractile tissue force. For a contraction force of ~200 µN, applied in the middle of pillar length, the expected change in base capacitance is in the aF range. Readout of such low capacitance changes was achieved using a commercial low-noise high-sensitivity device. Characterization of static and dynamic sensor behavior agreed with numerical simulations, demonstrating a responsivity of 0.35 ± 0.07 fF/µN. Preliminary tests with cardiac tissues proved biocompatibility of the platform, as EHTs successfully formed and remained functional for at least 14 days@en

A repeatable method to fabricate multi-layer graphene (ML-gr) membranes of 2r = 85 - 155 μm (t < 10 nm) with a 100% yield on 100 mm wafers is demonstrated. These membranes show higher sensitivity than a commercial MEMS-Mic combined with an area reduction of 10x. The process overcomes one of the main limitations when integrating graphene diaphragms in microphones due to the absence of automatic transfer methods on non-planarized target substrates. This method aims to overcome this limitation by combining a full-dry release of Chemical Vapor Deposition (CVD) graphene by Deep Reactive Ion Etching (DRIE) and vapor HF (VHF).

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We present a novel design of elastic micropillars for tissue self-assembly in engineered heart tissue (EHT) platforms. The innovative tapered profile confines reproducibly the tissue position along the main micropillar axis, increasing the accuracy of tissue contraction force measurement. Polydimethylsiloxane-based pillars were designed and fabricated by wafer-level molding in an hourglass shape, with symmetric tapering producing a restriction for tissue movement in the middle of the pillars’ length. Confinement efficacy of the new geometry was validated by comparing the tissue performance in straight versus tapered (75° or 80° tapering angle) micropillars. While in all three cases compact tissues formed successfully, for both tapered designs the functionality assays evidenced yield increase from 15% to 100%, higher spatial tissue confinement, and correspondingly higher accuracy and smaller dispersion in measurements of tissue contraction force.@en

This paper outlines the first transfer-free multi-layer (ML-gr) graphene-based MEMS condenser microphone with a high aspect-ratio suitable for sensitive miniaturized portable microphones. This fabrication flow avoids thick polymers needed to realize suspended graphene-polymer heterostructures over air cavities, which generally limit the response by introducing higher mass and stiffness. Several devices are characterized both mechanically and electrically, showing pull-in voltages up to 9.5 V and resonance frequency limited bandwidths of up to 127 kHz. The work paves the way to realize next-generation graphene microphones with a 4.5x area reduction compared to current state-of-the-art MEMS microphones.@en

In this work, we present an Opto-Electro-Mechanical Modulator (OEMM) for RF-to-optical transduction realized via an ultra-coherent nanomembrane resonator capacitively coupled to an rf injection circuit made of a microfabricated read-out able to improve the electro-optomechanical interaction. This device configuration can be embedded in a Fabry–Perot cavity for electromagnetic cooling of the LC circuit in a dilution refrigerator exploiting the opto-electro-mechanical interaction. To this aim, an optically measured steady-state frequency shift of 380 Hz was seen with a polarization voltage of 30 V and a Q-factor of the assembled device above (Formula presented.) at room temperature. The rf-sputtered titanium nitride layer can be made superconductive to develop efficient quantum transducers.

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Engineered heart tissues (EHTs) showed great potential in recapitulating tissue organization and function of the human heart in vitro [1]. Contractile kinetics is one key hallmark of cardiac tissue function and maturation level of cardiomyocytes, and a critical readout from EHT platforms. Typically-used optical methods to track elastic micropillar displacement upon tissue contraction are laborious and in most cases not conducted in real-time. This hampers automation and precise control of the EHT microenvironment. We address these unmet needs by developing a co-planar capacitive displacement sensor for tissue contraction force measurement integrated within an EHT platform. The working principle of the displacement sensor relies on the deformation of the substrate wherein the sensors are integrated. Bending of each micropillar, caused by tissue contraction, results in local anti-symmetric out-of-plane deformation of the substrate. Two spiral capacitors are integrated below each micropillar of a previously developed EHT platform [2] to exploit the maximum substrate deformation. The capacitive sensors were fabricated using a combination of wafer-level micromachining and polymer processing. The mould for the micropillars and elliptic well was fabricated by deep reactive ion etching of a Si wafer. Another Si wafer was covered with an 80 μm-thick polydimethylsiloxane (PDMS) layer, whereupon sputtered Al was photolithographically patterned into sensor designs. De-moulded micropillars and wells were aligned and bonded to the wafer with sensors. Single 10 x 10 mm2 PDMS chips with integrated sensors were wire-bonded to custom-designed printed circuit boards. Analog Device AD7746 was selected to readout the expected aF-range change in base capacitance. Static characterization of the sensors showed good agreement between measured and FEM-simulated values of base capacitance. The dynamic behavior was tested using a nanoindentation setup by applying specific force at different positions along the micropillars length while measuring the electrical response. Responsivity of 0.35 ± 0.07 fF/μN was measured. Preliminary experiments with EHTs proved the biocompatibility of the new platform with integrated sensors, as tissues were functional and in culture for at least 14 days. @en