A micromachined capacitive accelerometer employing an electrothermal drive assembly and mechanical locking structure is presented. Such a structure is designed to move the stator electrodes after fabrication, and maintain them at the desired position, thereby reducing the sensing gap and improving the capacitor response. The post-processing assembly of the capacitor’s electrodes is driven by an electrothermal mechanism, and the assembled electrode position is maintained by a mechanical snap-locking structure. To demonstrate the effectiveness of the design concept, we fabricated a proof-of-concept device and a reference device reproducing a conventional design, using industrial silicon-on-insulator micromachining technology. The experimental results showed that the designed assembly and locking structure can achieve electrode position adjustment and maintain the assembly state stably. The device's capacitive response was characterized using a capacitance-voltage test and an electrostatic driving equivalent-acceleration analysis. The proposed accelerometer exhibits a larger capacitance variation than the corresponding reference device, thereby demonstrating enhanced capacitance sensitivity by enabling the complete removal of traditional fabrication limits on the capacitance-to-device-thickness ratio. These results open the path to high-performance, low-cost commercial silicon micro-accelerometers without modifying fabrication or testing procedures.

A Smart ElectroMagnetic Environment (SEME) is enabled by introducing smart electromagnetic (EM) skins, or metasurfaces, with the final aim of manipulating the reflection and/or transmission properties to improve the wireless interconnectivity in non-line-of-sight areas. We focus on manufacturing of passive and static smart EM skins for wavefront manipulation, to enable optically transparent and conformable solutions. The most significant technological innovation of this contribution is the creation of a metasurface by means of micro-manufactured modules on a transparent medium, which allows us to reach high-resolution standards and to work on unconventional substrates. Indeed, micro-fabrication of smart skins offers many advantages, e.g. choice of materials as in this case (i.e. transparent), miniaturization and, in turn, operation at higher frequencies. This constitutes a valuable counterpart to most literature works, which exploit “standard” technologies and substrates, such as classic PCB, severely limiting the manufacturing degrees of freedom (DoF) and material variety.

This paper describes a novel micro-electro-mechanical system (MEMS) tuning fork gyroscope (TFG) design that employs a chevron-shaped displacement mechanism to amplify the displacement generated by the Coriolis force, thereby increasing the TFG’s mechanical sensitivity. This approach was evaluated using both theoretical modeling and finite element analysis (FEA), and the results showed a high degree of agreement between the two methods. A conventional TFG having a comparable area was also designed and analyzed for comparison purposes. By introducing the displacement amplification mechanism, the proposed MEMS TFG design provides an output displacement about 2.5 times higher than the conventional design, according to the computation, without increasing the device footprint. Theoretical analysis and FEA on the TFG with amplification and a conventional TFG confirmed that the amplified displacement significantly improves the mechanical sensitivity of the gyroscope compared to conventional TFG designs.

The goal of lowering the material budget in microfluidics is often reached by fabrication of buried microchannels, typically achieved by deep reactive ion etching (DRIE) to create trenches, followed by sidewall passivation, and finally formation of hollow microchannels with isotropic etching. To avoid high temperatures, mask material or cleanroom restrictions, trench sidewalls can be passivated in the same DRIE tool with a fluorocarbon polymer layer using C4F8 as the source gas. Since the entire process is conducted within a DRIE tool, it significantly reduces fabrication time and complexity compared to conventional SiO2/Si3N4 passivation methods. Silicon microfabrication advancements often prioritize developing smaller or more precise features, while reliability and repeatability—crucial for large-scale production—are frequently overlooked. This study confirmed the development of a reliable, reproducible process for buried microchannel fabrication via polymer trench passivation, addressing key process instabilities and proposing functional solutions. Our optimized method employs a novel two-cycle approach of trench passivation by alternating the polymer deposition and anisotropic etching, enhancing uniformity and conformity of the passivation layer. This enables reliable fabrication of deep buried microchannels with a hydraulic diameter up to 40 μm at a depth of approximately 40 μm. In addition, the increased opening at the top of the trenches allows a significant reduction of time (above 20

Microneedles hold the potential for enabling shallow skin penetration applications where biomarkers are extracted from the interstitial fluid (ISF) and drugs are injected in a painless and effective manner. To this purpose, needles must have an inner channel. Channeled needles were demonstrated using custom silicon microtechnology, having several needle tip geometries. Nevertheless, all the proposed fabrication sequences are not compatible with mass production based on mature, standard microfabrication techniques. Furthermore, ISF extraction was also demonstrated with channeled needles but under poorly controlled conditions and over long periods of time, the latter being impractical for medical use. A range of factors may impede or slow ISF extraction that require controlled experiments. In this work we address the above tasks in terms of microfabrication sequence design, tip geometry design and experimental validation under controlled conditions. We report the development and fabrication of a silicon channeled microneedle array using conventional, industrial micromechanic processes. With only 2 lithography steps, a hypodermic needle tip profile is achieved. Using the fabricated microneedles, fluid extraction is experimented on chicken skin mockups. Extraction tests are carried out by inducing a controlled pressure gradient between the two ends of the microneedle channels, generated by loading the chip or by applying vacuum to the chip's backside. The extraction of more than 1 μL of fluid in 20 minutes is demonstrated with a maximum applied pressure gradient of 500 mbar. A correlation between the extraction rate efficiency and needles' density is observed, both for short and long extraction times. These results provide the first demonstration of in vitro interstitial fluid collection under controlled experimental conditions using silicon hollow microneedles fabricated with standard micro electro mechanical systems (MEMS) fabrication technology and minimal steps. Based on the obtained data, a comparison is drawn between pressure load and vacuum as drivers for ISF extraction, according to modelling and controlled experiments.

Coalescence-induced condensation droplet jumping has been extensively studied for anti-icing, condensation heat transfer, water harvesting, and self-cleaning. Another phenomenon that is gaining attention for potential enhancements is the self-ejection of individual droplets. However, the mechanism underlying this process remains elusive due to cases in which the abrupt detachment of an interface establishes an initial Laplace pressure difference. In this study, we investigate the self-ejection of individual droplets from uniformly hydrophobic microstructures with divergent geometries. We design, fabricate, and test arrays of truncated, nanostructured, and hydrophobic microcones arranged in a square pattern. High-speed microscopy reveals the dynamics of a single condensation droplet between four cones: after cycles of growth and stopped self-propulsion, the suspended droplet self-ejects without abrupt detachments. Through analytical modeling of the droplet in a conical pore as an approximation, we describe the slow isopressure growth phases and the rapid transients driven by surface energy release once a dynamic configuration is reached. Microcones with uniform wettability, in addition to being easier to fabricate, have the potential to enable the self-ejection of all nucleated droplets with a designed size, promising significant improvements in the aforementioned applications and others.

Fascinated by the purple color, water-repellent, and self-cleaning properties of Cotinus coggygria Scop. leaves, we studied their morphology, wetting, and condensation frosting. Wax nanotubules confer high contact angles, enabling coalescence-induced condensation droplet (out-of-plane) jumping, which, as known, contributes to slowing down frost. Another type of movement-this time in-plane-becomes predominant in reducing the frosting velocity ( v frost ) within a sub-cooling temperature range. Specifically, supercooled droplets slide toward the frost bridges upon contact, moving in the opposite direction to frost propagation. Between-11 and-2 degrees C, degrees C, Sliding on Frost (SoF) shifts from being rare to very frequent, reducing v frost / v bridge from approximately 4 to 1, respectively. Using high-speed microscopy, we observed that the advancing contact angle of supercooled water on ice decreases with temperature. We describe the primary role of this behavior in SoF with a model that accounts for the forces involved and explains the observed transition.

In this work, a novel, silicon-based micro-electromechanical valve that includes a submicrometric orifice and can operate at pressure gradients of 1 bar was used to enhance sampling for gas chromatograph mass spectrometers. The valve is based on a membrane-in-membrane design and operates with thermomechanical actuation. It includes a pin to enable self-cleaning. Prototypes were fabricated and preliminary testing was performed.

Field programmable gate arrays (FPGAs) have not only enhanced traditional sensing methods, such as pixel detection (CCD and CMOS), but also enabled the development of innovative approaches with significant potential for particle detection. This is particularly relevant in terahertz (THz) ray detection, where microbolometer-based focal plane arrays (FPAs) using microelectromechanical (MEMS) resonators are among the most promising solutions. Designing high-performance, high-pixel-density sensors is challenging without FPGAs, which are crucial for deterministic parallel processing, fast ADC/DAC control, and handling large data throughput. This paper presents a MEMS-resonator detector, fully managed via an FPGA, capable of controlling pixel excitation and tracking resonance-frequency shifts due to radiation using parallel digital lock-in amplifiers. The innovative FPGA architecture, based on a lock-in matrix, enhances the open-loop readout technique by a factor of 32. Measurements were performed on a frequency-multiplexed, 256-pixel sensor designed for imaging applications.

Multi-probe ultrasound methods can extend the field of view and improve the spatial resolution of images and have been proven effective in various applications. However, the need for expensive and cumbersome setups, together with the prohibitive real-time implementation, is hampering possible clinical applications. In this work, we present an ultrasound system capable of simultaneously and independently controlling, with a single scanner, up to four probes. Four 64-element Capacitive Micromachined Ultrasonic Transducer (CMUT) arrays were purposely developed and connected to a ULA-OP 256 scanner using four multi-coaxial cables attached to a single connector. High-frame-rate and phased scan modalities were implemented achieving maximum frame rates of 140 Hz and 26 Hz, respectively. As a proof of concept, the system was used to image, at the same time, different regions of interest of a healthy volunteer. The system represents a demonstrator capable of accelerating the research and the implementation of real-time multi-probe applications.

Electrostatically actuated microelectromechanical system (MEMS) switches with fixedfixed beams were fabricated.FEM modeling was used to calculate the contributions of stress in the fabricated beams from the measured values of pull-in voltage.The reported study provides useful guidelines to optimize the design of fixed-fixed beams, in order to reduce the stress contributions for the successful development of efficient and reliable electrostatically actuated MEMS devices.

The temperature of the sensing material has a large impact on the tin-oxide gas sensor performance. However, the thermal analysis of gas sensors is often overlooked or only partially included in the studies. The aim of this research was to employ numerical simulations to investigate the temperature effect on the detection of the ethanol in an ethanol/air mixture by positioning multiple electrodes on a single heated membrane. The experimental results validated the electrothermal simulation and indicated a significant temperature effect on the sensor responsivity. Indeed, the decrease in the average sensor temperature from 427 °C to 411 °C increased the sensing response by approximately 75 % during the 5 ppm ethanol mixture flow over the sensor array.

Surfaces capable of delaying the frosting passively and facilitating its removal are highly desirable in fields where ice introduces inefficiencies and risks. Coalescence jumping, enabled by highly hydrophobic surfaces, is already exploited to slow down the frosting but it is insufficient to completely eliminate the propagation by ice-bridging. We show how the self-ejection of single condensation droplets can frustrate the ice bridges of all the condensation droplets leading to a frost velocity lower than 0.5 um/s thus dropping below the current limits of passive surfaces by a factor of at least 2. Arrays of truncated microcones, covered by uniformly hydrophobic nanostructures, enable individual condensation droplets to growth and self-propel towards the top of the microstructures and to self-eject once a precise volume is reached. The independency of self-ejection on the neighbour droplets allows a precise control on the droplets' size and distance distributions and the ice-bridging frustration. The most performant microstructures tend to cones with a sharp tip on which the percentage of self-ejection is maximum. Looking towards applications, tapered microstructures allow maximising the percentage of self-ejecting drops while maintaining a certain mechanical strength. Further, it is shown that inserted pinning sites are not essential, which greatly facilitates manufacturing.

Rotary comb drives have been recently adopted to operate MEMS-Technology based micro systems. In several cases it is convenient to adopt a kinematic structure based on the four-bar linkage, where the coupler link has the guiding function for a generic tool as, for example, one jaw of a gripper. In this case the grasping function is granted by two symmetric jaws that are guided by two symmetric four-bar linkage structures. Since the ordinary kinematic pairs are not suitable for most planar fabrication methods of micro machining, compliant flexures must be used, with the consequence that some flexures must be embedded in the mechanical structure. For example, a microgripper based on two symmetric four-bar linkages needs 8 flexures. With the aim of coping with the problem of providing higher power to inflect all these flexures, this paper presents a new concept design which allows the coupler to be directly actuated by a second cooperating rotary comb drives, in addition to the fixed axis rotary comb drive (RCD) that actuates the crank link. The secondly added comb drive has also the advantage that its rotation center can be adjusted during the design stage with considerable freedom of choice in the plane, including positions that are not physically placed within the wafer. A microgripper prototype has been obtained by applying Deep Reaction Ion Etching (DRIE) on a Silicon on Insulator (SOI) wafer and then herein presented.

The powerful resource of parallelizing simple devices for realizing and enhancing complex operations comes with the drawback of multiple connections for addressing and controlling the individual elements. Here we report on a technological platform where several mechanical resonators can be individually probed and electrically actuated by using dispersive multiplexing within a single electrical channel. We demonstrate room temperature control of the individual device vibrational motion and spatially-resolved readouts. As the single elements have proven to be excellent bolometers and individual nodes for reservoir computing, our platform can be directly employed for single-channel addressing of multiple devices, with immediate applications for far-infrared cameras, spatial light modulators and recurrent neural networks operating at room temperature.

The design, analysis, fabrication, and characterization of two distinct MEMS rotational structures are provided; these structures include a classical symmetrical lancet structure and a novel symmetrical C-shaped structure provided with a tilted arm, and both are actuated by thermal actuators. Our proposed C-shaped structure implemented a curved beam mechanism to enhance the movement delivered by the thermal actuators. The geometrical parameters of our proposed device were optimized using the design of experiment (DOE) method. Furthermore, the analytical modeling based on Castigliano’s second theorem and the simulations based on the finite element method (FEM) were used to predict the behavior of the symmetrical C-shaped structure; the results were in good agreement with each other. The MEMS-based rotational structures were fabricated on silicon-on-insulator (SOI) wafers using bulk micromachining technology and deep reactive ion etching (DRIE) processes. The fabricated devices underwent experimental characterization; our results showed that our proposed MEMS rotational structure exhibited a 28% improvement in the delivered displacement compared to the symmetrical lancet structure. Furthermore, the experimental results showed good agreement with those obtained from numerical analysis. Our proposed structures have potential applications in a variety of MEMS devices, including accelerometers, gyroscopes, and resonators, due to their ability to maximize displacement and thus enhance sensitivity.

Free space optics laser communication using modulating retroreflectors (MR) is a challenging application for an active mirror, due to the high frequencies (>100 kHz) required to enable sufficient data transfer. Micro Electromechanical (MEMS) mirrors are a promising option for high-frequency applications, given the very small moving mass typical of such devices. Capacitive MEMS mirrors are presented here for free space communications, based on a novel fabrication sequence that introduces a single-layer thin film aluminum mirror structure with an underlying silicon oxide sacrificial layer. The use of aluminum instead of gold as a mirror layer diminishes the heating generated by the absorption of the sun’s radiation once the mirrors exit the earth’s atmosphere. Thanks to the novel fabrication sequence, the presented mirror devices have a full range actuation voltage of less than 40 V, and a high operational frequency with an eigenfrequency above 2 MHz. The devices were manufactured and characterized, and their main parameters were obtained from experimental data combined with finite element analysis, thus enabling future design optimization of the reported MEMS technology. By optical characterization of the far field diffraction pattern, good mirror performance was demonstrated.

In this work, a low-temperature fabrication process of thin-film encapsulation (TFE) with silicon nitride/chromium cap is proposed for large-size ( $750\times 300\,\,\mu \text{m}$ ) packaging of microelectromechanical systems (MEMS). A finite element method (FEM) model was developed to evaluate the shape of TFE as a function of the residual stress and the thickness of the sealing layer, providing useful guidelines for the fabrication process. The low temperature of 200 °C, which was used in the plasma-enhanced chemical vapor deposition (PECVD) of the silicon nitride capping layer, allowed an organic sacrificial material to be employed for the definition of the encapsulation area. Silicon nitride/chromium ( $1 \mu \text{m}$ /20 nm) bilayer was demonstrated to be successful to overcome the technological limitations that affect the creation of cap holes with size of $\sim 2 \mu \text{m}$ on high-topography substrates, as in the case of MEMS. Plasma focused ion beam (PFIB) and scanning electron microscopy (SEM) techniques were used in combination to gain deeper insight into the sealing process of cap holes. Specifically, a PFIB–SEM serial Section procedure was developed, resulting to be a powerful tool to directly observe the sealing profile above cap holes. Hence, the presented results greatly contribute to overcome the main technological/reliability issues of TFE, paving the way for the widespread application of the proposed encapsulation methodology to the most used MEMS devices, such as radio frequency (RF) switches, transducers, actuators, sensors, and resonators.

This paper addresses the assessment of the variability of CMUT arrays’ electro-mechanical and acoustic performance, as related to the tolerance of the CMUT vertical dimensions due to the microfabrication process. A 3-factors 3-levels factorial sensitivity analysis is carried out to compute the main effects and the interaction effects of the moving plate thickness, the passivation layers thickness, and the sacrificial layer thickness, on the CMUT resonance frequency, collapse voltage, and static capacitance, as well as on the transmission and reception sensitivity amplitude and bandwidth and time delay in water-coupled condition. The analysis is performed by means of FEM simulations of the CMUT static behavior and dynamic response, and the findings are compared to experimental data.