Micromachines

13 pages, 31150 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Innovative Integration of Dual Quantum Cascade Lasers on Silicon Photonics Platform

by Dongbo Wang, Harindra Kumar Kannojia, Pierre Jouy, Etienne Giraud, Kaspar Suter, Richard Maulini, David Gachet, Léo Hetier, Geert Van Steenberge and Bart Kuyken

Micromachines 2024, 15(8), 1055; https://doi.org/10.3390/mi15081055 - 22 Aug 2024

Viewed by 717

Abstract

For the first time, we demonstrate the hybrid integration of dual distributed feedback (DFB) quantum cascade lasers (QCLs) on a silicon photonics platform using an innovative 3D self-aligned flip-chip assembly process. The QCL waveguide geometry was predesigned with alignment fiducials, enabling a sub-micron [...] Read more.

For the first time, we demonstrate the hybrid integration of dual distributed feedback (DFB) quantum cascade lasers (QCLs) on a silicon photonics platform using an innovative 3D self-aligned flip-chip assembly process. The QCL waveguide geometry was predesigned with alignment fiducials, enabling a sub-micron accuracy during assembly. Laser oscillation was observed at the designed wavelength of 7.2 μm, with a threshold current of 170 mA at room temperature under pulsed mode operation. The optical output power after an on-chip beam combiner reached sub-milliwatt levels under stable continuous wave operation at 15 °C. The specific packaging design miniaturized the entire light source by a factor of 100 compared with traditional free-space dual lasers module. Divergence values of 2.88 mrad along the horizontal axis and 1.84 mrad along the vertical axis were measured after packaging. Promisingly, adhering to i-line lithography and reducing the reliance on high-end flip-chip tools significantly lowers the cost per chip. This approach opens new avenues for QCL integration on silicon photonic chips, with significant implications for portable mid-infrared spectroscopy devices. Full article

(This article belongs to the Special Issue The 15th Anniversary of Micromachines)

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14 pages, 2639 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Advanced Neural Functional Imaging in C. elegans Using Lab-on-a-Chip Technology

by Youngeun Kwon, Jihye Kim, Ye Bin Son, Sol Ah Lee, Shin Sik Choi and Yongmin Cho

Micromachines 2024, 15(8), 1027; https://doi.org/10.3390/mi15081027 - 12 Aug 2024

Viewed by 717

Abstract

The ability to perceive and adapt to environmental changes is crucial for the survival of all organisms. Neural functional imaging, particularly in model organisms, such as Caenorhabditis elegans, provides valuable insights into how animals sense and process external cues through their nervous [...] Read more.

The ability to perceive and adapt to environmental changes is crucial for the survival of all organisms. Neural functional imaging, particularly in model organisms, such as Caenorhabditis elegans, provides valuable insights into how animals sense and process external cues through their nervous systems. Because of its fully mapped neural anatomy, transparent body, and genetic tractability, C. elegans serves as an ideal model for these studies. This review focuses on advanced methods for neural functional imaging in C. elegans, highlighting calcium imaging techniques, lab-on-a-chip technologies, and their applications in the study of various sensory modalities, including chemosensation, mechanosensation, thermosensation, photosensation, and magnetosensation. We discuss the benefits of these methods in terms of precision, reproducibility, and ability to study dynamic neural processes in real time, ultimately advancing our understanding of the fundamental principles of neural activity and connectivity. Full article

(This article belongs to the Special Issue μ-TAS: A Themed Issue in Honor of Professor Andreas Manz)

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24 pages, 6506 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Micro-Opto-Electro-Mechanical Systems for High-Precision Displacement Sensing: A Review

by Chenguang Xin, Yingkun Xu, Zhongyao Zhang and Mengwei Li

Micromachines 2024, 15(8), 1011; https://doi.org/10.3390/mi15081011 - 6 Aug 2024

Viewed by 752

Abstract

High-precision displacement sensing has been widely used across both scientific research and industrial applications. The recent interests in developing micro-opto-electro-mechanical systems (MOEMS) have given rise to an excellent platform for miniaturized displacement sensors. Advancement in this field during past years is now yielding [...] Read more.

High-precision displacement sensing has been widely used across both scientific research and industrial applications. The recent interests in developing micro-opto-electro-mechanical systems (MOEMS) have given rise to an excellent platform for miniaturized displacement sensors. Advancement in this field during past years is now yielding integrated high-precision sensors which show great potential in applications ranging from photoacoustic spectroscopy to high-precision positioning and automation. In this review, we briefly summarize different techniques for high-precision displacement sensing based on MOEMS and discuss the challenges for future improvement. Full article

(This article belongs to the Special Issue Realizing Optical Control through Mechatronics Systems)

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20 pages, 2917 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Implementation of Accurate Parameter Identification for Proton Exchange Membrane Fuel Cells and Photovoltaic Cells Based on Improved Honey Badger Algorithm

by Wei-Lun Yu, Chen-Kai Wen, En-Jui Liu and Jen-Yuan Chang

Micromachines 2024, 15(8), 998; https://doi.org/10.3390/mi15080998 - 31 Jul 2024

Viewed by 593

Abstract

Predicting the system efficiency of green energy and developing forward-looking power technologies are key points to accelerating the global energy transition. This research focuses on optimizing the parameters of proton exchange membrane fuel cells (PEMFCs) and photovoltaic (PV) cells using the honey badger [...] Read more.

Predicting the system efficiency of green energy and developing forward-looking power technologies are key points to accelerating the global energy transition. This research focuses on optimizing the parameters of proton exchange membrane fuel cells (PEMFCs) and photovoltaic (PV) cells using the honey badger algorithm (HBA), a swarm intelligence algorithm, to accurately present the performance characteristics and efficiency of the systems. Although the HBA has a fast search speed, it was found that the algorithm’s search stability is relatively low. Therefore, this study also enhances the HBA’s global search capability through the rapid iterative characteristics of spiral search. This method will effectively expand the algorithm’s functional search range in a multidimensional and complex solution space. Additionally, the introduction of a sigmoid function will smoothen the algorithm’s exploration and exploitation mechanisms. To test the robustness of the proposed methodology, an extensive test was conducted using the CEC’17 benchmark functions set and real-life applications of PEMFC and PV cells. The results of the aforementioned test proved that with regard to the optimization of PEMFC and PV cell parameters, the improved HBA is significantly advantageous to the original in terms of both solving capability and speed. The results of this research study not only make definite progress in the field of bio-inspired computing but, more importantly, provide a rapid and accurate method for predicting the maximum power point for fuel cells and photovoltaic cells, offering a more efficient and intelligent solution for green energy. Full article

(This article belongs to the Special Issue The 15th Anniversary of Micromachines)

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12 pages, 4809 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Clot Accumulation in 3D Microfluidic Bifurcating Microvasculature Network

by Merav Belenkovich, Ruth Veksler, Yevgeniy Kreinin, Tirosh Mekler, Mariane Flores, Josué Sznitman, Michael Holinstat and Netanel Korin

Micromachines 2024, 15(8), 988; https://doi.org/10.3390/mi15080988 - 31 Jul 2024

Viewed by 682

Abstract

The microvasculature, which makes up the majority of the cardiovascular system, plays a crucial role in the process of thrombosis, with the pathological formation of blood clots inside blood vessels. Since blood microflow conditions significantly influence platelet activation and thrombosis, accurately mimicking the [...] Read more.

The microvasculature, which makes up the majority of the cardiovascular system, plays a crucial role in the process of thrombosis, with the pathological formation of blood clots inside blood vessels. Since blood microflow conditions significantly influence platelet activation and thrombosis, accurately mimicking the structure of bifurcating microvascular networks and emulating local physiological blood flow conditions are valuable for understanding blood clot formation. In this work, we present an in vitro model for blood clotting in microvessels, focusing on 3D bifurcations that align with Murray’s law, which guides vascular networks by maintaining a constant wall shear rate throughout. Using these models, we demonstrate that microvascular bifurcations act as sites facilitating thrombus formation compared to straight models. Additionally, by culturing endothelial cells on the luminal surfaces of the models, we show the potential of using our in vitro platforms to recapitulate the initial clotting in diseases involving endothelial dysfunction, such as Thrombotic Thrombocytopenic Purpura. Full article

(This article belongs to the Special Issue The 15th Anniversary of Micromachines)

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25 pages, 1058 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Determination of Arylcyclohexylamines in Biological Specimens: Sensors and Sample Pre-Treatment Approaches

by Rodrigo Pelixo, Mário Barroso, Eugenia Gallardo and Tiago Rosado

Micromachines 2024, 15(8), 984; https://doi.org/10.3390/mi15080984 - 30 Jul 2024

Viewed by 506

Abstract

Arylcyclohexylamine (ACH) compounds represent a predominant faction within new psychoactive substances. Due to their powerful dissociative effects, they are used in recreational contexts but also in situations of drug-facilitated sexual assault, and therefore, they are a constant target of analysis by forensic experts. [...] Read more.

Arylcyclohexylamine (ACH) compounds represent a predominant faction within new psychoactive substances. Due to their powerful dissociative effects, they are used in recreational contexts but also in situations of drug-facilitated sexual assault, and therefore, they are a constant target of analysis by forensic experts. In recent years, their consumption has been notably high, especially the use of ketamine, presenting daily challenges for laboratories in the determination of this and other ACH analogues. This review comprises the recent strategies that forensic specialists use to identify and quantify ACH compounds in the laboratory with more traditional analytical techniques and technology, and on the point-of-care testing via sensor technology. The study focuses on analogues of phencyclidine (PCP), ketamine, and eticyclidine, highlighting the consistent need for higher sensitivity in the analysis of various samples collected from real cases and simulations of possible matrices. The review also emphasises the ongoing research to develop more sensitive, quicker, and more capable sensors. Full article

(This article belongs to the Special Issue Exploration and Application of Micro-Devices/Sensors in Analytical Chemistry)

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32 pages, 7726 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Droplet Microfluidics for High-Throughput Screening and Directed Evolution of Biomolecules

by Goran T. Vladisaljević

Micromachines 2024, 15(8), 971; https://doi.org/10.3390/mi15080971 - 29 Jul 2024

Viewed by 843

Abstract

Directed evolution is a powerful technique for creating biomolecules such as proteins and nucleic acids with tailor-made properties for therapeutic and industrial applications by mimicking the natural evolution processes in the laboratory. Droplet microfluidics improved classical directed evolution by enabling time-consuming and laborious [...] Read more.

Directed evolution is a powerful technique for creating biomolecules such as proteins and nucleic acids with tailor-made properties for therapeutic and industrial applications by mimicking the natural evolution processes in the laboratory. Droplet microfluidics improved classical directed evolution by enabling time-consuming and laborious steps in this iterative process to be performed within monodispersed droplets in a highly controlled and automated manner. Droplet microfluidic chips can generate, manipulate, and sort individual droplets at kilohertz rates in a user-defined microchannel geometry, allowing new strategies for high-throughput screening and evolution of biomolecules. In this review, we discuss directed evolution studies in which droplet-based microfluidic systems were used to screen and improve the functional properties of biomolecules. We provide a systematic overview of basic on-chip fluidic operations, including reagent mixing by merging continuous fluid streams and droplet pairs, reagent addition by picoinjection, droplet generation, droplet incubation in delay lines, chambers and hydrodynamic traps, and droplet sorting techniques. Various microfluidic strategies for directed evolution using single and multiple emulsions and biomimetic materials (giant lipid vesicles, microgels, and microcapsules) are highlighted. Completely cell-free microfluidic-assisted in vitro compartmentalization methods that eliminate the need to clone DNA into cells after each round of mutagenesis are also presented. Full article

(This article belongs to the Special Issue μ-TAS: A Themed Issue in Honor of Professor Andreas Manz)

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13 pages, 4556 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Switchable Vanadium Dioxide Metasurface for Terahertz Ultra-Broadband Absorption and Reflective Polarization Conversion

by Wei Zou, Changqing Zhong, Lujun Hong, Jiangtao Lei, Yun Shen, Xiaohua Deng, Jing Chen and Tianjing Guo

Micromachines 2024, 15(8), 967; https://doi.org/10.3390/mi15080967 - 28 Jul 2024

Viewed by 701

Abstract

Based on the unique insulator-metal phase transition property of vanadium dioxide (VO₂), we propose an integrated metasurface with a switchable mechanism between ultra-broadband absorption and polarization conversion, operating in the terahertz (THz) frequency range. The designed metasurface device is constructed using [...] Read more.

Based on the unique insulator-metal phase transition property of vanadium dioxide (VO₂), we propose an integrated metasurface with a switchable mechanism between ultra-broadband absorption and polarization conversion, operating in the terahertz (THz) frequency range. The designed metasurface device is constructed using a stacked structure composed of VO₂ quadruple rings, a dielectric layer, copper stripes, VO₂ film, a dielectric layer, and a copper reflection layer. Our numerical simulations demonstrate that our proposed design, at high temperatures (above 358 K), exhibits an ultra-broadband absorption ranging from 4.95 to 18.39 THz, maintaining an absorptivity greater than 90%, and achieves a relative absorption bandwidth of up to 115%, significantly exceeding previous research records. At room temperature (298 K), leveraging VO₂’s insulating state, our proposed structure transitions into an effective polarization converter, without any alteration to its geometry. It enables efficient conversion between orthogonal linear polarizations across 3.51 to 10.26 THz, with cross-polarized reflection exceeding 90% and a polarization conversion ratio over 97%. More importantly, its relative bandwidth reaches up to 98%. These features highlight its wide-angle, extensive bandwidth, and high-efficiency advantages for both switching functionalities. Such an ultra-broadband convertible design offers potential applications in optical switching, temperature dependent optical sensors, and other tunable THz devices in various fields. Full article

(This article belongs to the Special Issue Recent Advances in Terahertz Devices and Applications)

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21 pages, 19988 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Study on Electrical and Mechanical Properties of Double-End Supported Elastic Substrate Prepared by Wet Etching Process

by Ding Song and Wenge Wu

Micromachines 2024, 15(7), 929; https://doi.org/10.3390/mi15070929 - 20 Jul 2024

Cited by 1 | Viewed by 710

Abstract

Preparing elastic substrates as a carrier for dual-end supported nickel chromium thin film strain sensors is crucial. Wet etching is a vital microfabrication process widely used in producing microelectronic components for various applications. This article combines lithography and wet etching methods to microprocess [...] Read more.

Preparing elastic substrates as a carrier for dual-end supported nickel chromium thin film strain sensors is crucial. Wet etching is a vital microfabrication process widely used in producing microelectronic components for various applications. This article combines lithography and wet etching methods to microprocess the external dimensions and rectangular grooves of 304 stainless steel substrates. The single-factor variable method was used to explore the influence mechanism of FeCl₃, HCl, HNO₃, and temperature on the etching rate, etching factor, and etching surface roughness. The optimal etching parameter combination was summarized: an FeCl₃ concentration of 350 g/L, HCl concentration of 150 mL/L, HNO₃ concentration of 100 mL/L, and temperature of 40 °C. In addition, by comparing the surface morphology, microstructure, and chemical and mechanical properties of a 304 stainless steel substrate before and after etching treatment, it can be seen that the height difference of the substrate surface before and after etching is between 160 μm and −70 μm, which is basically consistent with the initial design of 0.2 mm. The results of an XPS analysis and Raman spectroscopy analysis both indicate that the surface C content increases after etching, and the corrosion resistance of the surface after etching decreases. The nano-hardness after etching increased by 26.4% compared to before, and the ζ value decreased by 7%. The combined XPS and Raman results indicate that the changes in surface mechanical properties of 304 stainless steel substrates after etching are mainly caused by the formation of micro-nanostructures, grain boundary density, and dislocations after wet etching. Compared with the initial rectangular substrate, the strain of the I-shaped substrate after wet etching increased by 3.5–4 times. The results of this study provide the preliminary process parameters for the wet etching of a 304 stainless steel substrate of a strain measuring force sensor and have certain guiding significance for the realization of simple steps and low cost of 304 stainless steel substrate micro-nano-processing. Full article

(This article belongs to the Special Issue Micro- and Nanotechnologies: Materials, Manufacturing and Applications)

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12 pages, 3779 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Flexible Temperature Sensor Integrated at Needle Tip for In Situ Acupoint Temperature Monitoring

by Ci Song, Zheng Yu, Weiwen Feng, Ke Sun, Chuanbiao Wen, Shengyan Zhang, Shuguang Yu and Xinxin Li

Micromachines 2024, 15(7), 924; https://doi.org/10.3390/mi15070924 - 19 Jul 2024

Viewed by 2581

Abstract

Temperature can reflect vital activities, and researchers have attempted to guide Chinese medicine diagnosis and treatment by observing acupoint temperature changes. Integrating a temperature sensor at the needle tip enables in situ acupoint temperature measurement. However, the sensor needles for acupoint temperature monitoring [...] Read more.

Temperature can reflect vital activities, and researchers have attempted to guide Chinese medicine diagnosis and treatment by observing acupoint temperature changes. Integrating a temperature sensor at the needle tip enables in situ acupoint temperature measurement. However, the sensor needles for acupoint temperature monitoring designed in previous studies were fabricated by manually soldering thermistor beads and metal wires, making mass production difficult. In this work, using MEMS manufacturing technology, a flexible temperature sensor that can be integrated at the needle tip is proposed and can be mass-produced on silicon wafers. The sensor uses a Pt thermistor as the temperature-sensing element and has a slender flexible structure with dimensions of 125 μm width by 3.2 cm length. As the sensor is inserted into a hollow needle, the Pt thermistor is glued to the needle tip. In the temperature range of 30 °C to 50 °C, the fabricated temperature sensor has a sensitivity of 5.00 Ω∙°C⁻¹, a nonlinearity of ±0.39%FS, and a repeatability error of ±2.62%FS. Additionally, the sensor has been applied to in vivo acupoint temperature monitoring experiments in rats and demonstrated good performance, suggesting its promise for future research on acupoint temperature. Full article

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42 pages, 10634 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Computational Fluid–Structure Interaction in Microfluidics

by Hafiz Muhammad Musharaf, Uditha Roshan, Amith Mudugamuwa, Quang Thang Trinh, Jun Zhang and Nam-Trung Nguyen

Micromachines 2024, 15(7), 897; https://doi.org/10.3390/mi15070897 - 9 Jul 2024

Cited by 1 | Viewed by 1055

Abstract

Micro elastofluidics is a transformative branch of microfluidics, leveraging the fluid–structure interaction (FSI) at the microscale to enhance the functionality and efficiency of various microdevices. This review paper elucidates the critical role of advanced computational FSI methods in the field of micro elastofluidics. [...] Read more.

Micro elastofluidics is a transformative branch of microfluidics, leveraging the fluid–structure interaction (FSI) at the microscale to enhance the functionality and efficiency of various microdevices. This review paper elucidates the critical role of advanced computational FSI methods in the field of micro elastofluidics. By focusing on the interplay between fluid mechanics and structural responses, these computational methods facilitate the intricate design and optimisation of microdevices such as microvalves, micropumps, and micromixers, which rely on the precise control of fluidic and structural dynamics. In addition, these computational tools extend to the development of biomedical devices, enabling precise particle manipulation and enhancing therapeutic outcomes in cardiovascular applications. Furthermore, this paper addresses the current challenges in computational FSI and highlights the necessity for further development of tools to tackle complex, time-dependent models under microfluidic environments and varying conditions. Our review highlights the expanding potential of FSI in micro elastofluidics, offering a roadmap for future research and development in this promising area. Full article

(This article belongs to the Special Issue Flows in Micro- and Nano-Systems)

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19 pages, 8806 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Discussion and Demonstration of RF-MEMS Attenuators Design Concepts and Modules for Advanced Beamforming in the Beyond-5G and 6G Scenario—Part 2

by Girolamo Tagliapietra, Flavio Giacomozzi, Massimiliano Michelini, Romolo Marcelli, Giovanni Maria Sardi and Jacopo Iannacci

Micromachines 2024, 15(7), 895; https://doi.org/10.3390/mi15070895 - 9 Jul 2024

Viewed by 2911

Abstract

In this paper, different concepts of reconfigurable RF-MEMS attenuators for beamforming applications are proposed and critically assessed. Capitalizing on the previous part of this work, the 1-bit attenuation modules featuring series and shunt resistors and low-voltage membranes (7–9 V) are employed to develop [...] Read more.

In this paper, different concepts of reconfigurable RF-MEMS attenuators for beamforming applications are proposed and critically assessed. Capitalizing on the previous part of this work, the 1-bit attenuation modules featuring series and shunt resistors and low-voltage membranes (7–9 V) are employed to develop a 3-bit attenuator for fine-tuning attenuations (<−10 dB) in the 24.25–27.5 GHz range. More substantial attenuation levels are investigated using fabricated samples of coplanar waveguide (CPW) sections equipped with Pi-shaped resistors aiming at attenuations of −15, −30, and −45 dB. The remarkable electrical features of such configurations, showing flat attenuation curves and limited return losses, and the investigation of a switched-line attenuator design based on them led to the final proposed concept of a low-voltage 24-state attenuator. Such a simulated device combines the Pi-shaped resistors for substantial attenuations with the 3-bit design for fine-tuning operations, showing a maximum attenuation level of nearly −50 dB while maintaining steadily flat attenuation levels and limited return losses (<−11 dB) along the frequency band of interest. Full article

(This article belongs to the Special Issue Future of RF/Microwave Filtering and Memristive Devices in Nowadays Mobile Networks)

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8 pages, 3368 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

Inductive Paper-Based Flexible Contact Force Sensor Utilizing Natural Micro-Nanostructures of Paper: Simplicity, Economy, and Eco-Friendliness

by Haozhe Zhang, Junwen Zhu, Yujia Yang, Qiang Liu, Wei Xiong and Xing Yang

Micromachines 2024, 15(7), 890; https://doi.org/10.3390/mi15070890 - 7 Jul 2024

Viewed by 813

Abstract

Inductive contact force sensors, known for their high precision and anti-interference capabilities, hold significant potential applications in fields such as wearable and medical monitoring devices. Most of the current research on inductive contact force sensors employed novel nanomaterials as sensitive elements to enhance [...] Read more.

Inductive contact force sensors, known for their high precision and anti-interference capabilities, hold significant potential applications in fields such as wearable and medical monitoring devices. Most of the current research on inductive contact force sensors employed novel nanomaterials as sensitive elements to enhance their sensitivity and other performance characteristics. However, sensors developed through such methods typically involve complex preparation processes, high costs, and difficulty in biodegradation, which limit their further development. This article introduces a new flexible inductive contact force sensor using paper as a sensitive element. Paper inherently possesses micro- and nanostructures on its surface and interior, enabling it to sensitively convert changes in contact force into changes in displacement, making it suitable for use as the sensor’s sensitive element. Additionally, the advantages of paper also include its great flexibility, low cost, wide availability, and biodegradability. Performance testing on this flexible sensor showed good repeatability, hysteresis, sensitivity, and consistency. When used in experiments for monitoring human motion and respiration, this sensor also exhibited great detection performance. The proposed inductive paper-based flexible contact force sensor, with its simple structure, easy manufacturing process, cost-effectiveness, eco-friendliness, and good sensing performance, provides new insights into research for contact force sensors. Full article

(This article belongs to the Special Issue Flexible and Wearable Sensors, 3rd Edition)

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20 pages, 7096 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Advances in Energy Harvesting Technologies for Wearable Devices

by Minki Kang and Woon-Hong Yeo

Micromachines 2024, 15(7), 884; https://doi.org/10.3390/mi15070884 - 4 Jul 2024

Viewed by 1236

Abstract

The development of wearable electronics is revolutionizing human health monitoring, intelligent robotics, and informatics. Yet the reliance on traditional batteries limits their wearability, user comfort, and continuous use. Energy harvesting technologies offer a promising power solution by converting ambient energy from the human [...] Read more.

The development of wearable electronics is revolutionizing human health monitoring, intelligent robotics, and informatics. Yet the reliance on traditional batteries limits their wearability, user comfort, and continuous use. Energy harvesting technologies offer a promising power solution by converting ambient energy from the human body or surrounding environment into electrical power. Despite their potential, current studies often focus on individual modules under specific conditions, which limits practical applicability in diverse real-world environments. Here, this review highlights the recent progress, potential, and technological challenges in energy harvesting technology and accompanying technologies to construct a practical powering module, including power management and energy storage devices for wearable device developments. Also, this paper offers perspectives on designing next-generation wearable soft electronics that enhance quality of life and foster broader adoption in various aspects of daily life. Full article

(This article belongs to the Special Issue The 15th Anniversary of Micromachines)

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18 pages, 4805 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Piezoelectric Micromachined Microphone with High Acoustic Overload Point and with Electrically Controlled Sensitivity

by Libor Rufer, Josué Esteves, Didace Ekeom and Skandar Basrour

Micromachines 2024, 15(7), 879; https://doi.org/10.3390/mi15070879 - 3 Jul 2024

Viewed by 3382

Abstract

Currently, the most advanced micromachined microphones on the market are based on a capacitive coupling principle. Capacitive micro-electromechanical-system-based (MEMS) microphones resemble their millimetric counterparts, both in function and in performance. The most advanced MEMS microphones reached a competitive level compared to commonly used [...] Read more.

Currently, the most advanced micromachined microphones on the market are based on a capacitive coupling principle. Capacitive micro-electromechanical-system-based (MEMS) microphones resemble their millimetric counterparts, both in function and in performance. The most advanced MEMS microphones reached a competitive level compared to commonly used measuring microphones in most of the key performance parameters except the acoustic overload point (AOP). In an effort to find a solution for the measurement of high-level acoustic fields, microphones with the piezoelectric coupling principle have been proposed. These novel microphones exploit the piezoelectric effect of a thin layer of aluminum nitride, which is incorporated in their diaphragm structure. In these microphones fabricated with micromachining technology, no fixed electrode is necessary, in contrast to capacitive microphones. This specificity significantly simplifies both the design and the fabrication and opens the door for the improvement of the acoustic overload point, as well as harsh environmental applications. Several variations of piezoelectric structures together with an idea leading to electrically controlled sensitivity of MEMS piezoelectric microphones are discussed in this paper. Full article

(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)

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9 pages, 3672 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Positive Bias Temperature Instability in SiC-Based Power MOSFETs

by Vladislav Volosov, Santina Bevilacqua, Laura Anoldo, Giuseppe Tosto, Enzo Fontana, Alfio-lip Russo, Claudio Fiegna, Enrico Sangiorgi and Andrea Natale Tallarico

Micromachines 2024, 15(7), 872; https://doi.org/10.3390/mi15070872 - 30 Jun 2024

Viewed by 908

Abstract

This paper investigates the threshold voltage shift (ΔV_TH) induced by positive bias temperature instability (PBTI) in silicon carbide (SiC) power MOSFETs. By analyzing ΔV_TH under various gate stress voltages (V_Gstress) at 150 °C, distinct mechanisms are revealed: (i) [...] Read more.

This paper investigates the threshold voltage shift (ΔV_TH) induced by positive bias temperature instability (PBTI) in silicon carbide (SiC) power MOSFETs. By analyzing ΔV_TH under various gate stress voltages (V_Gstress) at 150 °C, distinct mechanisms are revealed: (i) trapping in the interface and/or border pre-existing defects and (ii) the creation of oxide defects and/or trapping in spatially deeper oxide states with an activation energy of ~80 meV. Notably, the adoption of different characterization methods highlights the distinct roles of these mechanisms. Moreover, the study demonstrates consistent behavior in permanent ΔV_TH degradation across V_Gstress levels using a power law model. Overall, these findings deepen the understanding of PBTI in SiC MOSFETs, providing insights for reliability optimization. Full article

(This article belongs to the Special Issue Research Progress of Advanced SiC Semiconductors)

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14 pages, 1807 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Batch-to-Batch Variation in Laser-Inscribed Graphene (LIG) Electrodes for Electrochemical Sensing

by Yifan Tang, Geisianny A. Moreira, Diana Vanegas, Shoumen P. A. Datta and Eric S. McLamore

Micromachines 2024, 15(7), 874; https://doi.org/10.3390/mi15070874 - 30 Jun 2024

Cited by 1 | Viewed by 1150

Abstract

Laser-inscribed graphene (LIG) is an emerging material for micro-electronic applications and is being used to develop supercapacitors, soft actuators, triboelectric generators, and sensors. The fabrication technique is simple, yet the batch-to-batch variation of LIG quality is not well documented in the literature. In [...] Read more.

Laser-inscribed graphene (LIG) is an emerging material for micro-electronic applications and is being used to develop supercapacitors, soft actuators, triboelectric generators, and sensors. The fabrication technique is simple, yet the batch-to-batch variation of LIG quality is not well documented in the literature. In this study, we conduct experiments to characterize batch-to-batch variation in the manufacturing of LIG electrodes for applications in electrochemical sensing. Numerous batches of 36 LIG electrodes were synthesized using a CO₂ laser system on polyimide film. The LIG material was characterized using goniometry, stereomicroscopy, open circuit potentiometry, and cyclic voltammetry. Hydrophobicity and electrochemical screening (cyclic voltammetry) indicate that LIG electrode batch-to-batch variation is less than 5% when using a commercial reference and counter electrode. Metallization of LIG led to a significant increase in peak current and specific capacitance (area between anodic/cathodic curve). However, batch-to-batch variation increased to approximately 30%. Two different platinum electrodeposition techniques were studied, including galvanostatic and frequency-modulated electrodeposition. The study shows that formation of metallized LIG electrodes with high specific capacitance and peak current may come at the expense of high batch variability. This design tradeoff has not been discussed in the literature and is an important consideration if scaling sensor designs for mass use is desired. This study provides important insight into the variation of LIG material properties for scalable development of LIG sensors. Additional studies are needed to understand the underlying mechanism(s) of this variability so that strategies to improve the repeatability may be developed for improving quality control. The dataset from this study is available via an open access repository. Full article

(This article belongs to the Special Issue Micro and Nanosensors: Fabrication, Applications and Performance Enhancements)

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30 pages, 3572 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Advances in Microfluidic Systems and Numerical Modeling in Biomedical Applications: A Review

by Mariana Ferreira, Violeta Carvalho, João Ribeiro, Rui A. Lima, Senhorinha Teixeira and Diana Pinho

Micromachines 2024, 15(7), 873; https://doi.org/10.3390/mi15070873 - 30 Jun 2024

Viewed by 1320

Abstract

The evolution in the biomedical engineering field boosts innovative technologies, with microfluidic systems standing out as transformative tools in disease diagnosis, treatment, and monitoring. Numerical simulation has emerged as a tool of increasing importance for better understanding and predicting fluid-flow behavior in microscale [...] Read more.

The evolution in the biomedical engineering field boosts innovative technologies, with microfluidic systems standing out as transformative tools in disease diagnosis, treatment, and monitoring. Numerical simulation has emerged as a tool of increasing importance for better understanding and predicting fluid-flow behavior in microscale devices. This review explores fabrication techniques and common materials of microfluidic devices, focusing on soft lithography and additive manufacturing. Microfluidic systems applications, including nucleic acid amplification and protein synthesis, as well as point-of-care diagnostics, DNA analysis, cell cultures, and organ-on-a-chip models (e.g., lung-, brain-, liver-, and tumor-on-a-chip), are discussed. Recent studies have applied computational tools such as ANSYS Fluent 2024 software to numerically simulate the flow behavior. Outside of the study cases, this work reports fundamental aspects of microfluidic simulations, including fluid flow, mass transport, mixing, and diffusion, and highlights the emergent field of organ-on-a-chip simulations. Additionally, it takes into account the application of geometries to improve the mixing of samples, as well as surface wettability modification. In conclusion, the present review summarizes the most relevant contributions of microfluidic systems and their numerical modeling to biomedical engineering. Full article

(This article belongs to the Special Issue Micro/Nanofluidic and Lab-on-a-Chip Devices for Biomedical Applications, 2nd Edition)

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16 pages, 7181 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Elasticity of Carrier Fluid: A Key Factor Affecting Mechanical Phenotyping in Deformability Cytometry

by Hassan Pouraria and Jessica P. Houston

Micromachines 2024, 15(7), 822; https://doi.org/10.3390/mi15070822 - 25 Jun 2024

Viewed by 1024

Abstract

Recently, microfluidics deformability cytometry has emerged as a powerful tool for high-throughput mechanical phenotyping of large populations of cells. These methods characterize cells by their mechanical fingerprints by exerting hydrodynamic forces and monitoring the resulting deformation. These devices have shown great promise for [...] Read more.

Recently, microfluidics deformability cytometry has emerged as a powerful tool for high-throughput mechanical phenotyping of large populations of cells. These methods characterize cells by their mechanical fingerprints by exerting hydrodynamic forces and monitoring the resulting deformation. These devices have shown great promise for label-free cytometry, yet there is a critical need to improve their accuracy and reconcile any discrepancies with other methods, such as atomic force microscopy. In this study, we employ computational fluid dynamics simulations and uncover how the elasticity of frequently used carrier fluids, such as methylcellulose dissolved in phosphate-buffered saline, is significantly influential to the resulting cellular deformation. We conducted CFD simulations conventionally used within the deformability cytometry field, which neglect fluid elasticity. Subsequently, we incorporated a more comprehensive model that simulates the viscoelastic nature of the carrier fluid. A comparison of the predicted stresses between these two approaches underscores the significance of the emerging elastic stresses in addition to the well-recognized viscous stresses along the channel. Furthermore, we utilize a two-phase flow model to predict the deformation of a promyelocyte (i.e., HL-60 cell type) within a hydrodynamic constriction channel. The obtained results highlight a substantial impact of the elasticity of carrier fluid on cellular deformation and raise questions about the accuracy of mechanical property estimates derived by neglecting elastic stresses. Full article

(This article belongs to the Special Issue Application of Microfluidic Technology in Bioengineering)

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22 pages, 9997 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Review of Integrated Gate Driver Circuits in Active Matrix Thin-Film Transistor Display Panels

by Min-Kyu Chang, Seoyeong Jeong, Darren Kim and Hyoungsik Nam

Micromachines 2024, 15(7), 823; https://doi.org/10.3390/mi15070823 - 25 Jun 2024

Viewed by 1063

Abstract

Many advanced technologies have been employed in high-performance active matrix displays, including liquid crystal displays, organic light-emitting diode displays, and micro-light-emitting diode displays. On the other side, there exists a strong demand for cost reduction, and it is one of the low-cost schemes [...] Read more.

Many advanced technologies have been employed in high-performance active matrix displays, including liquid crystal displays, organic light-emitting diode displays, and micro-light-emitting diode displays. On the other side, there exists a strong demand for cost reduction, and it is one of the low-cost schemes for integrating the driver circuit in a panel based on thin-film transistor technologies. This paper reviews the overall concept, operation principles, and various circuit approaches in shift registers for scanning pulse generation. In addition, it deals with the implementation of additional functionalities in gate drivers to support pixel compensation, multi-line driving, in-cell capacitive touch screen, pixel sensing, and adaptive scanning region control. Full article

(This article belongs to the Special Issue High-Reliability Semiconductor Devices and Integrated Circuits, 2nd Edition)

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18 pages, 4232 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Design and Evaluation of an Eye Mountable AutoDALK Robot for Deep Anterior Lamellar Keratoplasty

by Justin D. Opfermann, Yaning Wang, James Kaluna, Kensei Suzuki, William Gensheimer, Axel Krieger and Jin U. Kang

Micromachines 2024, 15(6), 788; https://doi.org/10.3390/mi15060788 - 15 Jun 2024

Viewed by 684

Abstract

Partial-thickness corneal transplants using a deep anterior lamellar keratoplasty (DALK) approach has demonstrated better patient outcomes than a full-thickness cornea transplant. However, despite better clinical outcomes from the DALK procedure, adoption of the technique has been limited because the accurate insertion of the [...] Read more.

Partial-thickness corneal transplants using a deep anterior lamellar keratoplasty (DALK) approach has demonstrated better patient outcomes than a full-thickness cornea transplant. However, despite better clinical outcomes from the DALK procedure, adoption of the technique has been limited because the accurate insertion of the needle into the deep stroma remains technically challenging. In this work, we present a novel hands-free eye mountable robot for automatic needle placement in the cornea, AutoDALK, that has the potential to simplify this critical step in the DALK procedure. The system integrates dual light-weight linear piezo motors, an OCT A-scan distance sensor, and a vacuum trephine-inspired design to enable the safe, consistent, and controllable insertion of a needle into the cornea for the pneumodissection of the anterior cornea from the deep posterior cornea and Descemet’s membrane. AutoDALK was designed with feedback from expert corneal surgeons and performance was evaluated by finite element analysis simulation, benchtop testing, and ex vivo experiments to demonstrate the feasibility of the system for clinical applications. The mean open-loop positional deviation was 9.39 µm, while the system repeatability and accuracy were 39.48 µm and 43.18 µm, respectively. The maximum combined thrust of the system was found to be 1.72 N, which exceeds the clinical penetration force of the cornea. In a head-to-head ex vivo comparison against an expert surgeon using a freehand approach, AutoDALK achieved more consistent needle depth, which resulted in fewer perforations of Descemet’s membrane and significantly deeper pneumodissection of the stromal tissue. The results of this study indicate that robotic needle insertion has the potential to simplify the most challenging task of the DALK procedure, enable more consistent surgical outcomes for patients, and standardize partial-thickness corneal transplants as the gold standard of care if demonstrated to be more safe and more effective than penetrating keratoplasty. Full article

(This article belongs to the Section B：Biology and Biomedicine)

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16 pages, 6488 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Magnetic-Controlled Microrobot: Real-Time Detection and Tracking through Deep Learning Approaches

by Hao Li, Xin Yi, Zhaopeng Zhang and Yuan Chen

Micromachines 2024, 15(6), 756; https://doi.org/10.3390/mi15060756 - 5 Jun 2024

Viewed by 953

Abstract

As one of the most significant research topics in robotics, microrobots hold great promise in biomedicine for applications such as targeted diagnosis, targeted drug delivery, and minimally invasive treatment. This paper proposes an enhanced YOLOv5 (You Only Look Once version 5) microrobot detection [...] Read more.

As one of the most significant research topics in robotics, microrobots hold great promise in biomedicine for applications such as targeted diagnosis, targeted drug delivery, and minimally invasive treatment. This paper proposes an enhanced YOLOv5 (You Only Look Once version 5) microrobot detection and tracking system (MDTS), incorporating a visual tracking algorithm to elevate the precision of small-target detection and tracking. The improved YOLOv5 network structure is used to take magnetic bodies with sizes of 3 mm and 1 mm and a magnetic microrobot with a length of 2 mm as the pretraining targets, and the training weight model is used to obtain the position information and motion information of the microrobot in real time. The experimental results show that the accuracy of the improved network model for magnetic bodies with a size of 3 mm is 95.81%, representing an increase of 2.1%; for magnetic bodies with a size of 1 mm, the accuracy is 91.03%, representing an increase of 1.33%; and for microrobots with a length of 2 mm, the accuracy is 91.7%, representing an increase of 1.5%. The combination of the improved YOLOv5 network model and the vision algorithm can effectively realize the real-time detection and tracking of magnetically controlled microrobots. Finally, 2D and 3D detection and tracking experiments relating to microrobots are designed to verify the robustness and effectiveness of the system, which provides strong support for the operation and control of microrobots in an in vivo environment. Full article

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16 pages, 8680 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Jet Electroforming of High-Aspect-Ratio Microcomponents by Periodically Lifting a Necked-Entrance Through-Mask

by Yasai Zhang, Pingmei Ming, Xinmin Zhang, Xinchao Li, Lunxu Li and Zheng Yang

Micromachines 2024, 15(6), 753; https://doi.org/10.3390/mi15060753 - 3 Jun 2024

Viewed by 581

Abstract

High-aspect-ratio micro- and mesoscale metallic components (HAR-MMMCs) can play some unique roles in quite a few application fields, but their cost-efficient fabrication is significantly difficult to accomplish. To address this issue, this study proposes a necked-entrance through-mask (NTM) periodically lifting electroforming technology with [...] Read more.

High-aspect-ratio micro- and mesoscale metallic components (HAR-MMMCs) can play some unique roles in quite a few application fields, but their cost-efficient fabrication is significantly difficult to accomplish. To address this issue, this study proposes a necked-entrance through-mask (NTM) periodically lifting electroforming technology with an impinging jet electrolyte supply. The effects of the size of the necked entrance of the through-mask and the jet speed of the electrolyte on electrodeposition behaviors, including the thickness distribution of the growing top surface, deposition defect formation, geometrical accuracy, and electrodeposition rate, are investigated numerically and experimentally. Ensuring an appropriate size of the necked entrance can effectively improve the uniformity of deposition thickness, while higher electrolyte flow velocities help enhance the density of the components under higher current densities, reducing the formation of deposition defects. It was shown that several precision HAR-MMMCs with an AR of 3.65 and a surface roughness (Ra) of down to 36 nm can be achieved simultaneously with a relatively high deposition rate of 3.6 μm/min and thickness variation as low as 1.4%. Due to the high current density and excellent mass transfer effects in the electroforming conditions, the successful electroforming of components with a Vickers microhardness of up to 520.5 HV was achieved. Mesoscale precision columns with circular and Y-shaped cross-sections were fabricated by using this modified through-mask movable electroforming process. The proposed NTM periodic lifting electroforming method is promisingly advantageous in fabricating precision HAR-MMMCs cost-efficiently. Full article

(This article belongs to the Special Issue Emerging Micro Manufacturing Technologies and Applications, 2nd Edition)

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20 pages, 26779 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Hybrid Printing of Conductive Traces from Bulk Metal for Digital Signals in Intelligent Devices

by Zeba Khan, Addythia Saphala, Sabrina Kartmann, Peter Koltay, Roland Zengerle, Oliver Amft and Zhe Shu

Micromachines 2024, 15(6), 750; https://doi.org/10.3390/mi15060750 - 2 Jun 2024

Cited by 1 | Viewed by 3296

Abstract

In this article, we explore multi-material additive manufacturing (MMAM) for conductive trace printing using molten metal microdroplets on polymer substrates to enhance digital signal transmission. Investigating microdroplet spread informs design rules for adjacent trace printing. We studied the effects of print distance on [...] Read more.

In this article, we explore multi-material additive manufacturing (MMAM) for conductive trace printing using molten metal microdroplets on polymer substrates to enhance digital signal transmission. Investigating microdroplet spread informs design rules for adjacent trace printing. We studied the effects of print distance on trace morphology and resolution, noting that printing distance showed almost no change in the printed trace pitch. Crosstalk interference between adjacent signal traces was analyzed across frequencies and validated both experimentally and through simulation; no crosstalk was visible for printed traces at input frequencies below 600 kHz. Moreover, we demonstrate printed trace reliability against thermal shock, whereby no discontinuation in conductive traces was observed. Our findings establish design guidelines for MMAM electronics, advancing digital signal transmission capabilities. Full article

(This article belongs to the Section D3: 3D Printing and Additive Manufacturing)

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37 pages, 21294 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Shape-Memory Polymers Based on Carbon Nanotube Composites

by Mariana Martins da Silva, Mariana Paiva Proença, José António Covas and Maria C. Paiva

Micromachines 2024, 15(6), 748; https://doi.org/10.3390/mi15060748 - 1 Jun 2024

Cited by 3 | Viewed by 1127

Abstract

For the past two decades, researchers have been exploring the potential benefits of combining shape-memory polymers (SMP) with carbon nanotubes (CNT). By incorporating CNT as reinforcement in SMP, they have aimed to enhance the mechanical properties and improve shape fixity. However, the remarkable [...] Read more.

For the past two decades, researchers have been exploring the potential benefits of combining shape-memory polymers (SMP) with carbon nanotubes (CNT). By incorporating CNT as reinforcement in SMP, they have aimed to enhance the mechanical properties and improve shape fixity. However, the remarkable intrinsic properties of CNT have also opened up new paths for actuation mechanisms, including electro- and photo-thermal responses. This opens up possibilities for developing soft actuators that could lead to technological advancements in areas such as tissue engineering and soft robotics. SMP/CNT composites offer numerous advantages, including fast actuation, remote control, performance in challenging environments, complex shape deformations, and multifunctionality. This review provides an in-depth overview of the research conducted over the past few years on the production of SMP/CNT composites with both thermoset and thermoplastic matrices, with a focus on the unique contributions of CNT to the nanocomposite’s response to external stimuli. Full article

(This article belongs to the Special Issue Feature Papers of Micromachines in 'Materials and Processing' 2024)

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9 pages, 2864 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

Terahertz Polarization Isolator Using Two-Dimensional Square Lattice Tellurium Rod Array

by Yong Wang, Yanqing Ai, Lin Gan, Jiao Zhou, Yangyang Wang, Wei Wang, Biaogang Xu, Wenlong He and Shiguo Li

Micromachines 2024, 15(6), 745; https://doi.org/10.3390/mi15060745 - 31 May 2024

Viewed by 635

Abstract

A novel terahertz polarization isolator using a two-dimensional square lattice tellurium rod array is numerically investigated at the interesting band of 0.22 THz in this short paper. The isolator is designed by inserting six hexagonal tellurium rods into a fully polarized photonic crystals [...] Read more.

A novel terahertz polarization isolator using a two-dimensional square lattice tellurium rod array is numerically investigated at the interesting band of 0.22 THz in this short paper. The isolator is designed by inserting six hexagonal tellurium rods into a fully polarized photonic crystals waveguide with high efficiency of −0.34 dB. The TE and TM photonic band gaps of the 7 × 16 tellurium photonic crystals are computed based on the plane wave expansion method, which happen to coincide at the normalized frequency domain from 0.3859(a/λ) to 0.4033(a/λ), corresponding to the frequency domain from 0.2152 to 0.2249 THz. The operating bandwidth of the tellurium photonic crystals waveguide covers 0.2146 to 0.2247 THz, calculated by the finite element method. The six hexagonal tellurium rods with smaller circumradii of 0.16a serve to isolate transverse electric waves and turn a blind eye to transverse magnetic waves. The polarization isolation function and external characteristic curves of the envisaged structure are numerically simulated, which achieves the highest isolation of −33.49 dB at the central frequency of 0.2104 THz and the maximum reflection efficiency of 98.95 percent at the frequency of 0.2141 THz. The designed isolator with a unique function and high performance provides a promising approach for implementing fully polarized THz devices for future 6G communication systems. Full article

(This article belongs to the Special Issue Recent Advances in Terahertz Devices and Applications)

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13 pages, 5896 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Novel 4H-SiC Asymmetric MOSFET with Step Trench

by Zhong Lan, Yangjie Ou, Xiarong Hu and Dong Liu

Micromachines 2024, 15(6), 724; https://doi.org/10.3390/mi15060724 - 30 May 2024

Viewed by 760

Abstract

In this article, a silicon carbide (SiC) asymmetric MOSFET with a step trench (AST-MOS) is proposed and investigated. The AST-MOS features a step trench with an extra electron current path on one side, thereby increasing the channel density of the device. A thick [...] Read more.

In this article, a silicon carbide (SiC) asymmetric MOSFET with a step trench (AST-MOS) is proposed and investigated. The AST-MOS features a step trench with an extra electron current path on one side, thereby increasing the channel density of the device. A thick oxide layer is also employed at the bottom of the step trench, which is used as a new voltage-withstanding region. Furthermore, the ratio of the gate-to-drain capacitance (C_gd) to the gate-to-source capacitance (C_gs) is significantly reduced in the AST-MOS. As a result, the AST-MOS compared with the double-trench MOSFET (DT-MOS) and deep double-trench MOSFET (DDT-MOS), is demonstrated to have an increase of 200 V and 50 V in the breakdown voltage (BV), decreases of 21.8% and 10% in the specific on-resistance (R_on,sp), a reduction of about 1 V in the induced crosstalk voltage, and lower switching loss. Additionally, the trade-off between the resistance of the JFET region (R_JFET) and the electric field in the gate oxide (E_ox) is studied for a step trench and a deep trench. The improved performances suggest that a step trench is a competitive option in advanced device design. Full article

(This article belongs to the Special Issue Microelectronic Devices: Physics, Design and Applications)

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20 pages, 2278 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Progress in Spin Logic Devices Based on Domain-Wall Motion

by Bob Bert Vermeulen, Bart Sorée, Sebastien Couet, Kristiaan Temst and Van Dai Nguyen

Micromachines 2024, 15(6), 696; https://doi.org/10.3390/mi15060696 - 24 May 2024

Viewed by 887

Abstract

Spintronics, utilizing both the charge and spin of electrons, benefits from the nonvolatility, low switching energy, and collective behavior of magnetization. These properties allow the development of magnetoresistive random access memories, with magnetic tunnel junctions (MTJs) playing a central role. Various spin logic [...] Read more.

Spintronics, utilizing both the charge and spin of electrons, benefits from the nonvolatility, low switching energy, and collective behavior of magnetization. These properties allow the development of magnetoresistive random access memories, with magnetic tunnel junctions (MTJs) playing a central role. Various spin logic concepts are also extensively explored. Among these, spin logic devices based on the motion of magnetic domain walls (DWs) enable the implementation of compact and energy-efficient logic circuits. In these devices, DW motion within a magnetic track enables spin information processing, while MTJs at the input and output serve as electrical writing and reading elements. DW logic holds promise for simplifying logic circuit complexity by performing multiple functions within a single device. Nevertheless, the demonstration of DW logic circuits with electrical writing and reading at the nanoscale is still needed to unveil their practical application potential. In this review, we discuss material advancements for high-speed DW motion, progress in DW logic devices, groundbreaking demonstrations of current-driven DW logic, and its potential for practical applications. Additionally, we discuss alternative approaches for current-free information propagation, along with challenges and prospects for the development of DW logic. Full article

(This article belongs to the Special Issue Magnetic and Spin Devices, 3rd Edition)

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52 pages, 26368 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Multi-Scale Traditional and Non-Traditional Machining of Bulk Metallic Glasses (BMGs)—Review of Challenges, Recent Advances, and Future Directions

by Muhammad P. Jahan, Aakash Niraula, Muhammad Abdun Nafi and Asma Perveen

Micromachines 2024, 15(6), 686; https://doi.org/10.3390/mi15060686 - 23 May 2024

Viewed by 3478

Abstract

Bulk metallic glasses (BMGs) are growing in popularity prominently due to their potential in micro-electromechanical systems (MEMSs) and aerospace applications. BMGs have unique mechanical properties, i.e., high strength, hardness, modulus of elasticity, and wear resistance, due to their disordered atomic structure. Due to [...] Read more.

Bulk metallic glasses (BMGs) are growing in popularity prominently due to their potential in micro-electromechanical systems (MEMSs) and aerospace applications. BMGs have unique mechanical properties, i.e., high strength, hardness, modulus of elasticity, and wear resistance, due to their disordered atomic structure. Due to their unique mechanical properties and amorphous structures, machining of BMGs remains a challenge. This paper aims to carry out a detailed literature review on various aspects of the machining of bulk metallic glasses using both conventional and non-conventional processes, including experimental approaches, modeling, statistical findings, challenges, and guidelines for machining this difficult-to-machine material. Conventional machining processes were found to be challenging for machining bulk metallic glasses due to their high hardness, brittleness, and tendency to convert their amorphous structure into a crystalline structure, especially at the machined surface and sub-surface. Although their high electrical conductivity makes them suitable for machining by non-conventional processes, they impose new challenges such as heat-affected zones and crystallization. Therefore, the successful machining of BMGs requires more in-depth analysis of cutting forces, tool wear, burr formation, surface finish, recast layers or heat-affected zones, crystallization, and mechanical property changes among different varieties of BMGs. This review paper provides guidelines emerging from in-depth analysis of previous studies, as well as offering directions for future research in the machining of BMGs. Full article

(This article belongs to the Special Issue Micro and Nano Machining Processes, 3rd Edition)

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14 pages, 4374 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Highly Sensitive Dual-Drive Microfluidic Device for Multiplexed Detection of Respiratory Virus Antigens

by Xiaohui Yang, Yixian Li, Josh Zixi Lee, Yuanmin Sun, Xin Tan, Yijie Liu, Yang Yu, Huiqiang Li and Xue Li

Micromachines 2024, 15(6), 685; https://doi.org/10.3390/mi15060685 - 23 May 2024

Viewed by 894

Abstract

Conventional microfluidic systems that rely on capillary force have a fixed structure and limited sensitivity, which cannot meet the demands of clinical applications. Herein, we propose a dual-drive microfluidic device for sensitive and flexible detection of multiple pathogenic microorganisms antigens/antibodies. The device comprises [...] Read more.

Conventional microfluidic systems that rely on capillary force have a fixed structure and limited sensitivity, which cannot meet the demands of clinical applications. Herein, we propose a dual-drive microfluidic device for sensitive and flexible detection of multiple pathogenic microorganisms antigens/antibodies. The device comprises a portable microfluidic analyzer and a dual-drive microfluidic chip. Along with capillary force, a second active driving force is provided by a removable self-driving valve in the waste chamber. The interval between these two driving forces can be adjusted to control the reaction time in the microchannel, optimizing the formation of antigen-antibody complexes and enhancing sensitivity. Moreover, the material used in the self-driving valve can be changed to adjust the active force strength needed for different tests. The device offers quantitative analysis for respiratory syncytial virus antigen and SARS-CoV-2 antigen using a 35 μL sample, delivering results within 5 min. The detection limits of the system were 1.121 ng/mL and 0.447 ng/mL for respiratory syncytial virus recombinant fusion protein and SARS-CoV-2 recombinant nucleoprotein, respectively. Although the dual-drive microfluidic device has been used for immunoassay for respiratory syncytial virus and SARS-CoV-2 in this study, it can be easily adapted to other immunoassay applications by changing the critical reagents. Full article

(This article belongs to the Section B4: Point-of-Care Devices)

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46 pages, 2330 KiB

Open AccessFeature PaperEditor’s ChoiceReview

3D-Printed MEMS in Italy

by Matilde Aronne, Valentina Bertana, Francesco Schimmenti, Ignazio Roppolo, Annalisa Chiappone, Matteo Cocuzza, Simone Luigi Marasso, Luciano Scaltrito and Sergio Ferrero

Micromachines 2024, 15(6), 678; https://doi.org/10.3390/mi15060678 - 22 May 2024

Viewed by 5591

Abstract

MEMS devices are more and more commonly used as sensors, actuators, and microfluidic devices in different fields like electronics, opto-electronics, and biomedical engineering. Traditional fabrication technologies cannot meet the growing demand for device miniaturisation and fabrication time reduction, especially when customised devices are [...] Read more.

MEMS devices are more and more commonly used as sensors, actuators, and microfluidic devices in different fields like electronics, opto-electronics, and biomedical engineering. Traditional fabrication technologies cannot meet the growing demand for device miniaturisation and fabrication time reduction, especially when customised devices are required. That is why additive manufacturing technologies are increasingly applied to MEMS. In this review, attention is focused on the Italian scenario in regard to 3D-printed MEMS, studying the techniques and materials used for their fabrication. To this aim, research has been conducted as follows: first, the commonly applied 3D-printing technologies for MEMS manufacturing have been illustrated, then some examples of 3D-printed MEMS have been reported. After that, the typical materials for these technologies have been presented, and finally, some examples of their application in MEMS fabrication have been described. In conclusion, the application of 3D-printing techniques, instead of traditional processes, is a growing trend in Italy, where some exciting and promising results have already been obtained, due to these new selected technologies and the new materials involved. Full article

(This article belongs to the Special Issue MEMS in Italy 2023)

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12 pages, 3199 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Flow-Independent Thermal Conductivity and Volumetric Heat Capacity Measurement of Pure Gases and Binary Gas Mixtures Using a Single Heated Wire

by Shirin Azadi Kenari, Remco J. Wiegerink, Remco G. P. Sanders and Joost C. Lötters

Micromachines 2024, 15(6), 671; https://doi.org/10.3390/mi15060671 - 21 May 2024

Viewed by 718

Abstract

Among the different techniques for monitoring the flow rate of various fluids, thermal flow sensors stand out for their straightforward measurement technique. However, the main drawback of these types of sensors is their dependency on the thermal properties of the medium, i.e., thermal [...] Read more.

Among the different techniques for monitoring the flow rate of various fluids, thermal flow sensors stand out for their straightforward measurement technique. However, the main drawback of these types of sensors is their dependency on the thermal properties of the medium, i.e., thermal conductivity (k), and volumetric heat capacity (

ρ c_{p}

). They require calibration whenever the fluid in the system changes. In this paper, we present a single hot wire suspended above a V-groove cavity that is used to measure k and

ρ c_{p}

through DC and AC excitation for both pure gases and binary gas mixtures, respectively. The unique characteristic of the proposed sensor is its independence of the flow velocity, which makes it possible to detect the medium properties while the fluid flows over the sensor chip. The measured error due to fluctuations in flow velocity is less than ±0.5% for all test gases except for He, where it is ±6% due to the limitations of the measurement setup. The working principle and measurement results are discussed. Full article

(This article belongs to the Special Issue Selected Papers from 5th International Conference on Microfluidic Handling Systems (MFHS2024))

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17 pages, 4190 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

From Formulation to Application: Effects of Plasticizer on the Printability of Fluoro Elastomer Compounds and Additive Manufacturing of Specialized Seals

by Mookkan Periyasamy, AA Mubasshir, Stiven Kodra, Sangeetham Chandramouli, Ronald Campbell, David O. Kazmer and Joey L. Mead

Micromachines 2024, 15(5), 622; https://doi.org/10.3390/mi15050622 - 5 May 2024

Viewed by 1108

Abstract

This work investigated material extrusion additive manufacturing (MatEx AM) of specialized fluoroelastomer (FKM) compounds for applications in rubber seals and gaskets. The influence of a commercially available perfluoropolyether (PFPE) plasticizer on the printability of a control FKM rubber compound was studied using a [...] Read more.

This work investigated material extrusion additive manufacturing (MatEx AM) of specialized fluoroelastomer (FKM) compounds for applications in rubber seals and gaskets. The influence of a commercially available perfluoropolyether (PFPE) plasticizer on the printability of a control FKM rubber compound was studied using a custom-designed ram material extruder, Additive Ram Material Extruder (ARME), for printing fully compounded thermoset elastomers. The plasticizer’s effectiveness was assessed based on its ability to address challenges such as high compound viscosity and post-print shrinkage, as well as its impact on interlayer adhesion. The addition of the PFPE plasticizer significantly reduced the FKM compound’s viscosity (by 70%) and post-print shrinkage (by 65%). While the addition of the plasticizer decreased the tensile strength of the control compound, specimens printed with the plasticized FKM retained 34% of the tensile strength of compression-molded samples, compared to only 23% for the unplasticized compound. Finally, the feasibility of seals and gaskets manufacturing using both conventional and unconventional additive manufacturing (AM) approaches was explored. A hybrid method combining AM and soft tooling for compression molding emerged as the optimal method for seal and gasket fabrication. Full article

(This article belongs to the Special Issue Advanced Additive Manufacturing Techniques: From Fundamental Research to Applications)

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12 pages, 4226 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Displacement Mapping as a Highly Flexible Surface Texturing Tool for Additively Photopolymerized Components

by Robert Bail and Dong Hyun Lee

Micromachines 2024, 15(5), 575; https://doi.org/10.3390/mi15050575 - 26 Apr 2024

Viewed by 1017

Abstract

Displacement mapping is a computer graphics technique that enables the design of components with regularly or randomly textured surfaces that can be quickly materialized on a three-dimensional (3D) printer when needed. This approach is, in principle, more flexible, faster, and more economical compared [...] Read more.

Displacement mapping is a computer graphics technique that enables the design of components with regularly or randomly textured surfaces that can be quickly materialized on a three-dimensional (3D) printer when needed. This approach is, in principle, more flexible, faster, and more economical compared to conventional texturing methods, but the accuracy of the texture depends heavily on the parameters used. The purpose of this study is to demonstrate how to produce a surface-textured part using polygonal (mesh) modeling software and a photopolymerizable resin and to develop a universal methodology to predict the dimensional accuracy of the model file log combined with a resin 3D printer. The printed components were characterized on a scanning confocal microscope. In the setup used in this study, the mesh size had to be reduced to 10% of the smallest feature size, and the textured layer had to be heavily (×4.5) overexposed to achieve the desired accuracy. As a practical application, two functional stamps with a regular (honeycomb) and a random texture, respectively, were successfully manufactured. The insights gained will be of great benefit for quickly and cost-effectively producing components with innovative patterns and textures for a variety of hobby, industrial, and biomedical applications. Full article

(This article belongs to the Special Issue Stereolithography (SLA) and Digital Light Processing (DLP) for Flexible and Sustainable Micro-manufacturing)

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12 pages, 5410 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Rational Design of a Surface Acoustic Wave Device for Wearable Body Temperature Monitoring

by Yudi Xie, Minglong Deng, Jinkai Chen, Yue Duan, Jikai Zhang, Danyu Mu, Shurong Dong, Jikui Luo, Hao Jin and Shoji Kakio

Micromachines 2024, 15(5), 555; https://doi.org/10.3390/mi15050555 - 23 Apr 2024

Viewed by 1262

Abstract

Continuous monitoring of vital signs based on advanced sensing technologies has attracted extensive attention due to the ravages of COVID-19. A maintenance-free and low-cost passive wireless sensing system based on surface acoustic wave (SAW) device can be used to continuously monitor temperature. However, [...] Read more.

Continuous monitoring of vital signs based on advanced sensing technologies has attracted extensive attention due to the ravages of COVID-19. A maintenance-free and low-cost passive wireless sensing system based on surface acoustic wave (SAW) device can be used to continuously monitor temperature. However, the current SAW-based passive sensing system is mostly designed at a low frequency around 433 MHz, which leads to the relatively large size of SAW devices and antenna, hindering their application in wearable devices. In this paper, SAW devices with a resonant frequency distributed in the 870 MHz to 960 MHz range are rationally designed and fabricated. Based on the finite-element method (FEM) and coupling-of-modes (COM) model, the device parameters, including interdigital transducer (IDT) pairs, aperture size, and reflector pairs, are systematically optimized, and the theoretical and experimental results show high consistency. Finally, SAW temperature sensors with a quality factor greater than 2200 are obtained for real-time temperature monitoring ranging from 20 to 50 °C. Benefitting from the higher operating frequency, the size of the sensing system can be reduced for human body temperature monitoring, showing its potential to be used as a wearable monitoring device in the future. Full article

(This article belongs to the Special Issue Novel Surface and Bulk Acoustic Wave Devices)

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0 pages, 1542 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Optimization of Graphical Parameter Extraction Algorithm for Chip-Level CMP Prediction Model Based on Effective Planarization Length

by Bowen Ren, Lan Chen, Rong Chen, Yan Sun and Yali Wang

Micromachines 2024, 15(4), 549; https://doi.org/10.3390/mi15040549 - 19 Apr 2024

Viewed by 924

Abstract

As a planarization technique, chemical mechanical polishing (CMP) continues to suffer from pattern effects that result in large variations in material thickness, which can influence circuit performance and yield. Therefore, tools for predicting post-CMP chip morphology based on the layout-dependent effect (LDE) have [...] Read more.

As a planarization technique, chemical mechanical polishing (CMP) continues to suffer from pattern effects that result in large variations in material thickness, which can influence circuit performance and yield. Therefore, tools for predicting post-CMP chip morphology based on the layout-dependent effect (LDE) have become increasingly critical and widely utilized for design verification and manufacturing development. In order to characterize the impact of patterns on polishing, such models often require the extraction of graphic parameters. However, existing extraction algorithms provide a limited description of the interaction effect between layout patterns. To address this problem, we calculate the average density as a density correction and innovatively use a one-dimensional line contact deformation profile as a weighting function. To verify our hypothesis, the density correction method is applied to a density step-height-based high-K metal gate-CMP prediction model. The surface prediction results before and after optimization are compared with the silicon data. The results show a reduction in mean squared error (MSE) of 40.1% and 35.2% in oxide and Al height predictions, respectively, compared with the preoptimization results, confirming that the optimization method can improve the prediction accuracy of the model. Full article

(This article belongs to the Special Issue Advances in Micro and Nano Manufacturing: Process Modeling and Applications, 3rd Edition)

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21 pages, 2154 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Biomaterials for Protein Delivery: Opportunities and Challenges to Clinical Translation

by Amogh Gorantla, Jacques T. V. E. Hall, Anneliese Troidle and Jelena M. Janjic

Micromachines 2024, 15(4), 533; https://doi.org/10.3390/mi15040533 - 15 Apr 2024

Viewed by 1483

Abstract

The development of biomaterials for protein delivery is an emerging field that spans materials science, bioengineering, and medicine. In this review, we highlight the immense potential of protein-delivering biomaterials as therapeutic options and discuss the multifaceted challenges inherent to the field. We address [...] Read more.

The development of biomaterials for protein delivery is an emerging field that spans materials science, bioengineering, and medicine. In this review, we highlight the immense potential of protein-delivering biomaterials as therapeutic options and discuss the multifaceted challenges inherent to the field. We address current advancements and approaches in protein delivery that leverage stimuli-responsive materials, harness advanced fabrication techniques like 3D printing, and integrate nanotechnologies for greater targeting and improved stability, efficacy, and tolerability profiles. We also discuss the demand for highly complex delivery systems to maintain structural integrity and functionality of the protein payload. Finally, we discuss barriers to clinical translation, such as biocompatibility, immunogenicity, achieving reliable controlled release, efficient and targeted delivery, stability issues, scalability of production, and navigating the regulatory landscape for such materials. Overall, this review summarizes insights from a survey of the current literature and sheds light on the interplay between innovation and the practical implementation of biomaterials for protein delivery. Full article

(This article belongs to the Special Issue Biomaterials, Biodevices and Tissue Engineering, Second Edition)

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18 pages, 4773 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Design and Implementation of a Four-Unit Array Piezoelectric Bionic MEMS Vector Hydrophone

by Shuzheng Shi, Xiaoyong Zhang, Zhanying Wang, Liyong Ma, Kai Kang, Yongjun Pang, Hong Ma and Jinjiang Hu

Micromachines 2024, 15(4), 524; https://doi.org/10.3390/mi15040524 - 14 Apr 2024

Cited by 1 | Viewed by 3355

Abstract

High-performance vector hydrophones have been gaining attention for underwater target-monitoring applications. Nevertheless, there exists the mutual constraint between sensitivity and bandwidth of a single hydrophone. To solve this problem, a four-unit array piezoelectric bionic MEMS vector hydrophone (FPVH) was developed in this paper, [...] Read more.

High-performance vector hydrophones have been gaining attention for underwater target-monitoring applications. Nevertheless, there exists the mutual constraint between sensitivity and bandwidth of a single hydrophone. To solve this problem, a four-unit array piezoelectric bionic MEMS vector hydrophone (FPVH) was developed in this paper, which has a cross-beam and a bionic fish-lateral-line-nerve-cell-cilia unit array structure. Simulation analysis and optimization in the design of the bionic microstructure have been performed by COMSOL 6.1 software to determine the structure dimensions and the lead zirconate titanate (PZT) thin film distribution. The FPVH was manufactured using MEMS technology and tested in a standing wave bucket. The results indicate that the FPVH has a sensitivity of up to −167.93 dB@1000 Hz (0 dB = 1 V/μPa), which is 12 dB higher than that of the one-unit piezoelectric MEMS vector hydrophone (OPVH). Additionally, the working bandwidth of the FPVH reaches 20 Hz~1200 Hz, exhibiting a good cosine curve with an 8-shape. This work paves a new way for the development of multi-unit piezoelectric vector hydrophones for underwater acoustic detectors. Full article

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11 pages, 1714 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Towards a Point-of-Care Test of CD4⁺ T Lymphocyte Concentrations for Immune Status Monitoring with Magnetic Flow Cytometry

by Moritz Leuthner, Mathias Reisbeck, Michael Helou and Oliver Hayden

Micromachines 2024, 15(4), 520; https://doi.org/10.3390/mi15040520 - 13 Apr 2024

Viewed by 4009

Abstract

For the treatment of human immunodeficiency virus (HIV)-infected patients, the regular assessment of the immune status is indispensable. The quantification of CD4⁺ T lymphocytes in blood by gold standard optical flow cytometry is not point-of-care testing (POCT) compatible. This incompatibility is due [...] Read more.

For the treatment of human immunodeficiency virus (HIV)-infected patients, the regular assessment of the immune status is indispensable. The quantification of CD4⁺ T lymphocytes in blood by gold standard optical flow cytometry is not point-of-care testing (POCT) compatible. This incompatibility is due to unavoidable pre-analytics, expensive and bulky optics with limited portability, and complex workflow integration. Here, we propose a non-optical, magnetic flow cytometry (MFC) workflow that offers effortless integration opportunities, including minimal user interaction, integrated sample preparation and up-concentration, and miniaturization. Furthermore, we demonstrate immunomagnetic CD4⁺ T lymphocyte labeling in whole blood with subsequent quantification using sheath-less MFC. Showing linearity over two log scales and being largely unimpaired by hematocrit, evidence is provided for POCT capabilities of HIV patients. Full article

(This article belongs to the Special Issue μ-TAS: A Themed Issue in Honor of Professor Andreas Manz)

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19 pages, 4518 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

3D Artificial Skin Platform for Investigating Pregnancy-Related Skin Pigmentation

by Uiechan Jeong, Sunhee Yoon, Sungjin Park, Tae-Joon Jeon and Sun Min Kim

Micromachines 2024, 15(4), 511; https://doi.org/10.3390/mi15040511 - 10 Apr 2024

Viewed by 1247

Abstract

In this study, we created a 3D Artificial Skin Platform that can be used for the treatment of pigmentation by artificially realizing the skin of pregnant women. For the stable realization of 3D artificial skin, a bilayer hydrogel composed of collagen type I [...] Read more.

In this study, we created a 3D Artificial Skin Platform that can be used for the treatment of pigmentation by artificially realizing the skin of pregnant women. For the stable realization of 3D artificial skin, a bilayer hydrogel composed of collagen type I and fibrin was designed and applied to the study to reduce the tension-induced contraction of collagen type I, the extracellular matrix (ECM) of artificial skin, by dynamic culture. Oxygen concentration and 17β-Estradiol (E2) concentration, which are highly related to melanin production, were selected as parameters of the pregnancy environment and applied to cell culture. Oxygen concentration, which is locally reduced in the first trimester (2.5–3%), and E2, which is upregulated in the third trimester, were applied to the cell culture process. We analyzed whether the 3D artificial skin implemented in the 3D Artificial Skin Platform could better represent the tendency of melanin expression in pregnant women than cells cultured under the same conditions in 2D. The expression levels of melanin and melanin-related genes in the 2D cell culture did not show a significant trend that was similar to the melanin expression trend in pregnant women. However, the 3D artificial skin platform showed a significant trend towards a 2-6-fold increase in melanin expression in response to low oxygen concentrations (2.5%) and E2 concentrations (17 ng/mL), which was similar to the trend in pregnant women in vivo. These results suggest that 3D artificial skin cultured on the Artificial Skin Platform has the potential to be used as a substitute for human pregnant skin in various research fields related to the treatment of pigmentation. Full article

(This article belongs to the Special Issue Tissue Engineering and Regenerative Medicine with Micromachines)

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17 pages, 11474 KiB

Open AccessEditor’s ChoiceArticle

Microstructure, Tensile Properties, and Fracture Toughness of an In Situ Rolling Hybrid with Wire Arc Additive Manufacturing AerMet100 Steel

by Lei Lei, Linda Ke, Yibo Xiong, Siyu Liu, Lei Du, Mengfan Chen, Meili Xiao, Yanfei Fu, Fei Yao, Fan Yang, Kun Wang and Baohui Li

Micromachines 2024, 15(4), 494; https://doi.org/10.3390/mi15040494 - 3 Apr 2024

Cited by 1 | Viewed by 1010

Abstract

As a type of ultra-high strength steel, AerMet100 steel is used in the aerospace and military industries. Due to the fact that AerMet100 steel is difficult to machine, people have been exploring the process of additive manufacturing to fabricate AerMet100 steel. In this [...] Read more.

As a type of ultra-high strength steel, AerMet100 steel is used in the aerospace and military industries. Due to the fact that AerMet100 steel is difficult to machine, people have been exploring the process of additive manufacturing to fabricate AerMet100 steel. In this study, AerMet100 steel was produced using an in situ rolling hybrid with wire arc additive manufacturing. Microstructure, tensile properties, and fracture toughness of as-deposited and heat-treated AerMet100 steel were evaluated in different directions. The results reveal that the manufacturing process leads to grain fragmentation and obvious microstructural refinement of the AerMet100 steel, and weakens the anisotropy of the mechanical properties. After heat treatment, the microstructure of the AerMet100 steel is mainly composed of lath martensite and reversed austenite. Alloy carbides are precipitated within the martensitic matrix, and a high density of dislocations is the primary strengthening mechanism. The existence of film-like austenite among the martensite matrix enhances the toughness of AerMet100 steel, which coordinates stress distribution and restrains crack propagation, resulting in an excellent balance between strength and toughness. The AerMet100 steel with in situ rolling is isotropy and achieves the following values: an average ultimate strength of 1747.7 ± 16.3 MPa, yield strength of 1615 ± 40.6 MPa, elongation of 8.3 ± 0.2% in deposition direction, and corresponding values in the building direction are 1821.3 ± 22.1 MPa, 1624 ± 84.5 MPa, and 7.6 ± 1.7%, and the K_IC value up to 70.6 MPa/m^0.5. Full article

(This article belongs to the Special Issue Laser Additive Manufacturing: Design, Materials, Processes and Applications, 2nd Edition)

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47 pages, 12921 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Progress and Challenges of Implantable Biodegradable Biosensors

by Fahmida Alam, Md Ashfaq Ahmed, Ahmed Hasnain Jalal, Ishrak Siddiquee, Rabeya Zinnat Adury, G M Mehedi Hossain and Nezih Pala

Micromachines 2024, 15(4), 475; https://doi.org/10.3390/mi15040475 - 30 Mar 2024

Cited by 3 | Viewed by 5582

Abstract

Implantable biosensors have evolved to the cutting-edge technology of personalized health care and provide promise for future directions in precision medicine. This is the reason why these devices stand to revolutionize our approach to health and disease management and offer insights into our [...] Read more.

Implantable biosensors have evolved to the cutting-edge technology of personalized health care and provide promise for future directions in precision medicine. This is the reason why these devices stand to revolutionize our approach to health and disease management and offer insights into our bodily functions in ways that have never been possible before. This review article tries to delve into the important developments, new materials, and multifarious applications of these biosensors, along with a frank discussion on the challenges that the devices will face in their clinical deployment. In addition, techniques that have been employed for the improvement of the sensitivity and specificity of the biosensors alike are focused on in this article, like new biomarkers and advanced computational and data communicational models. A significant challenge of miniaturized in situ implants is that they need to be removed after serving their purpose. Surgical expulsion provokes discomfort to patients, potentially leading to post-operative complications. Therefore, the biodegradability of implants is an alternative method for removal through natural biological processes. This includes biocompatible materials to develop sensors that remain in the body over longer periods with a much-reduced immune response and better device longevity. However, the biodegradability of implantable sensors is still in its infancy compared to conventional non-biodegradable ones. Sensor design, morphology, fabrication, power, electronics, and data transmission all play a pivotal role in developing medically approved implantable biodegradable biosensors. Advanced material science and nanotechnology extended the capacity of different research groups to implement novel courses of action to design implantable and biodegradable sensor components. But the actualization of such potential for the transformative nature of the health sector, in the first place, will have to surmount the challenges related to biofouling, managing power, guaranteeing data security, and meeting today’s rules and regulations. Solving these problems will, therefore, not only enhance the performance and reliability of implantable biodegradable biosensors but also facilitate the translation of laboratory development into clinics, serving patients worldwide in their better disease management and personalized therapeutic interventions. Full article

(This article belongs to the Special Issue Prospects and Challenges of Biosensors towards Diagnostics of the Diseases and Health Monitoring)

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14 pages, 5054 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Piezoelectric Micromachined Ultrasonic Transducers with Micro-Hole Inter-Etch and Sealing Process on (111) Silicon Wafer

by Yunhao Wang, Sheng Wu, Wenjing Wang, Tao Wu and Xinxin Li

Micromachines 2024, 15(4), 482; https://doi.org/10.3390/mi15040482 - 30 Mar 2024

Cited by 1 | Viewed by 3638

Abstract

Piezoelectric micromachined ultrasound transducers (PMUTs) have gained significant popularity in the field of ultrasound ranging and medical imaging owing to their small size, low power consumption, and affordability. The scar-free “MIS” (micro-hole inter-etch and sealing) process, a novel bulk-silicon manufacturing technique, has been [...] Read more.

Piezoelectric micromachined ultrasound transducers (PMUTs) have gained significant popularity in the field of ultrasound ranging and medical imaging owing to their small size, low power consumption, and affordability. The scar-free “MIS” (micro-hole inter-etch and sealing) process, a novel bulk-silicon manufacturing technique, has been successfully developed for the fabrication of pressure sensors, flow sensors, and accelerometers. In this study, we utilize the MIS process to fabricate cavity diaphragm structures for PMUTs, resulting in the formation of a flat cavity diaphragm structure through anisotropic etching of (111) wafers in a 70 °C tetramethylammonium hydroxide (TMAH) solution. This study investigates the corrosion characteristics of the MIS technology on (111) silicon wafers, arranges micro-pores etched on bulk silicon around the desired cavity structure in a regular pattern, and takes into consideration the distance compensation for lateral corrosion, resulting in a fully connected cavity structure closely approximating an ortho-hexagonal shape. By utilizing a sputtering process to deposit metallic molybdenum as upper and lower electrodes, as well as piezoelectric materials above the cavity structure, we have successfully fabricated aluminum nitride (AlN) piezoelectric ultrasonic transducer arrays of various sizes and structures. The final hexagonal PMUT cells of various sizes that were fabricated achieved a maximum quality factor (Q) of 251 and a displacement sensitivity of 18.49 nm/V across a range of resonant frequencies from 6.28 MHz to 11.99 MHz. This fabrication design facilitates the achievement of IC-compatible and cost-effective mass production of PMUT array devices with high resonance frequencies. Full article

(This article belongs to the Section A：Physics)

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13 pages, 5496 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Evaluation of Fluid Behaviors in a Pushbutton-Activated Microfluidic Device for User-Independent Flow Control

by Dong Hyun Han, Gihyun Lee, Untaek Oh, Yejin Choi and Je-Kyun Park

Micromachines 2024, 15(4), 465; https://doi.org/10.3390/mi15040465 - 29 Mar 2024

Viewed by 1062

Abstract

Although numerous studies have been conducted to realize ideal point-of-care testing (POCT), the development of a user-friendly and user-independent power-free microfluidic platform is still a challenge. Among various methods, the finger-actuation method shows a promising technique that provides a user-friendly and equipment-free way [...] Read more.

Although numerous studies have been conducted to realize ideal point-of-care testing (POCT), the development of a user-friendly and user-independent power-free microfluidic platform is still a challenge. Among various methods, the finger-actuation method shows a promising technique that provides a user-friendly and equipment-free way of delivering fluid in a designated manner. However, the design criteria and elaborate evaluation of the fluid behavior of a pushbutton-activated microfluidic device (PAMD) remain a critical bottleneck to be widely adopted in various applications. In this study, we have evaluated the fluid behavior of the PAMD based on various parameters, such as pressing velocity and depth assisted by a press machine. We have further developed a user-friendly and portable pressing block that reduces user variation in fluid behavior based on the evaluation. Full article

(This article belongs to the Special Issue Recent Advances of Microfluidics for Biomedical Applications)

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16 pages, 10654 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Strategies for Enhancing the Stability of Lithium Metal Anodes in Solid-State Electrolytes

by Hanbyeol Lee, Taeho Yoon and Oh B. Chae

Micromachines 2024, 15(4), 453; https://doi.org/10.3390/mi15040453 - 28 Mar 2024

Viewed by 1496

Abstract

The current commercially used anode material, graphite, has a theoretical capacity of only 372 mAh/g, leading to a relatively low energy density. Lithium (Li) metal is a promising candidate as an anode for enhancing energy density; however, challenges related to safety and performance [...] Read more.

The current commercially used anode material, graphite, has a theoretical capacity of only 372 mAh/g, leading to a relatively low energy density. Lithium (Li) metal is a promising candidate as an anode for enhancing energy density; however, challenges related to safety and performance arise due to Li’s dendritic growth, which needs to be addressed. Owing to these critical issues in Li metal batteries, all-solid-state lithium-ion batteries (ASSLIBs) have attracted considerable interest due to their superior energy density and enhanced safety features. Among the key components of ASSLIBs, solid-state electrolytes (SSEs) play a vital role in determining their overall performance. Various types of SSEs, including sulfides, oxides, and polymers, have been extensively investigated for Li metal anodes. Sulfide SSEs have demonstrated high ion conductivity; however, dendrite formation and a limited electrochemical window hinder the commercialization of ASSLIBs due to safety concerns. Conversely, oxide SSEs exhibit a wide electrochemical window, but compatibility issues with Li metal lead to interfacial resistance problems. Polymer SSEs have the advantage of flexibility; however their limited ion conductivity poses challenges for commercialization. This review aims to provide an overview of the distinctive characteristics and inherent challenges associated with each SSE type for Li metal anodes while also proposing potential pathways for future enhancements based on prior research findings. Full article

(This article belongs to the Special Issue Energy Conversion Materials/Devices and Their Applications)

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16 pages, 7312 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Ultraflexible PEDOT:PSS/IrO_x-Modified Electrodes: Applications in Behavioral Modulation and Neural Signal Recording in Mice

by Xueying Wang, Wanqi Jiang, Huiran Yang, Yifei Ye, Zhitao Zhou, Liuyang Sun, Yanyan Nie, Tiger H. Tao and Xiaoling Wei

Micromachines 2024, 15(4), 447; https://doi.org/10.3390/mi15040447 - 27 Mar 2024

Viewed by 1570

Abstract

Recent advancements in neural probe technology have become pivotal in both neuroscience research and the clinical management of neurological disorders. State-of-the-art developments have led to the advent of multichannel, high-density bidirectional neural interfaces that are adept at both recording and modulating neuronal activity [...] Read more.

Recent advancements in neural probe technology have become pivotal in both neuroscience research and the clinical management of neurological disorders. State-of-the-art developments have led to the advent of multichannel, high-density bidirectional neural interfaces that are adept at both recording and modulating neuronal activity within the central nervous system. Despite this progress, extant bidirectional probes designed for simultaneous recording and stimulation are beset with limitations, including elicitation of inflammatory responses and insufficient charge injection capacity. In this paper, we delineate the design and application of an innovative ultraflexible bidirectional neural probe engineered from polyimide. This probe is distinguished by its ability to facilitate high-resolution recordings and precise stimulation control in deep brain regions. Electrodes enhanced with a PEDOT:PSS/IrO_x composite exhibit a substantial increase in charge storage capacity, escalating from 0.14 ± 0.01 mC/cm² to an impressive 24.75 ± 0.18 mC/cm². This augmentation significantly bolsters the electrodes’ charge transfer efficacy. In tandem, we observed a notable reduction in electrode impedance, from 3.47 ± 1.77 MΩ to a mere 41.88 ± 4.04 kΩ, while the phase angle exhibited a positive shift from −72.61 ± 1.84° to −34.17 ± 0.42°. To substantiate the electrodes’ functional prowess, we conducted in vivo experiments, where the probes were surgically implanted into the bilateral motor cortex of mice. These experiments involved the synchronous recording and meticulous analysis of neural signal fluctuations during stimulation and an assessment of the probes’ proficiency in modulating directional turning behaviors in the subjects. The empirical evidence corroborates that targeted stimulation within the bilateral motor cortex of mice can modulate the intensity of neural signals in the stimulated locale, enabling the directional control of the mice’s turning behavior to the contralateral side of the stimulation site. Full article

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17 pages, 3830 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Automotive Augmented Reality Head-Up Displays

by Chen Zhou, Wen Qiao, Jianyu Hua and Linsen Chen

Micromachines 2024, 15(4), 442; https://doi.org/10.3390/mi15040442 - 26 Mar 2024

Viewed by 2626

Abstract

As the next generation of in-vehicle intelligent platforms, the augmented reality heads-up display (AR-HUD) has a huge information interaction capacity, can provide drivers with auxiliary driving information, avoid the distractions caused by the lower head during the driving process, and greatly improve driving [...] Read more.

As the next generation of in-vehicle intelligent platforms, the augmented reality heads-up display (AR-HUD) has a huge information interaction capacity, can provide drivers with auxiliary driving information, avoid the distractions caused by the lower head during the driving process, and greatly improve driving safety. However, AR-HUD systems still face great challenges in the realization of multi-plane full-color display, and they cannot truly achieve the integration of virtual information and real road conditions. To overcome these problems, many new devices and materials have been applied to AR-HUDs, and many novel systems have been developed. This study first reviews some key metrics of HUDs, investigates the structures of various picture generation units (PGUs), and finally focuses on the development status of AR-HUDs, analyzes the advantages and disadvantages of existing technologies, and points out the future research directions for AR-HUDs. Full article

(This article belongs to the Special Issue Novel 3D Display Technology towards Metaverse)

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16 pages, 6667 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Temperature Prediction Model for Flexible Electronic Devices Based on GA-BP Neural Network and Experimental Verification

by Jin Nan, Jiayun Chen, Min Li, Yuhang Li, Yinji Ma and Xuanqing Fan

Micromachines 2024, 15(4), 430; https://doi.org/10.3390/mi15040430 - 23 Mar 2024

Cited by 2 | Viewed by 1220

Abstract

The problem that the thermal safety of flexible electronic devices is difficult to evaluate in real time is addressed in this study by establishing a BP neural network (GA-BPNN) temperature prediction model based on genetic algorithm optimisation. The model uses a BP neural [...] Read more.

The problem that the thermal safety of flexible electronic devices is difficult to evaluate in real time is addressed in this study by establishing a BP neural network (GA-BPNN) temperature prediction model based on genetic algorithm optimisation. The model uses a BP neural network to fit the functional relationship between the input condition and the steady-state temperature of the equipment and uses a genetic algorithm to optimise the parameter initialisation problem of the BP neural network. To overcome the challenge of the high cost of obtaining experimental data, finite element analysis software is used to simulate the temperature results of the equipment under different working conditions. The prediction variance of the GA-BPNN model does not exceed 0.57 °C and has good robustness, as the model is trained according to the simulation data. The study conducted thermal validation experiments on the temperature prediction model for this flexible electronic device. The device reached steady state after 1200 s of operation at rated power. The error between the predicted and experimental results was less than 0.9 °C, verifying the validity of the model’s predictions. Compared with traditional thermal simulation and experimental methods, this model can quickly predict the temperature with a certain accuracy and has outstanding advantages in computational efficiency and integrated application of hardware and software. Full article

(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II)

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14 pages, 6585 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Enhancing Manufacturability of SU-8 Piezoelectric Composite Films for Microsystem Applications

by Irma Rocio Vazquez, Zeynel Guler and Nathan Jackson

Micromachines 2024, 15(3), 397; https://doi.org/10.3390/mi15030397 - 14 Mar 2024

Viewed by 1524

Abstract

Piezoelectric thin films are extensively used as sensing or actuating layers in various micro-electromechanical systems (MEMS) applications. However, most piezoelectrics are stiff ceramics, and current polymer piezoelectrics are not compatible with microfabrication due to their low Curie Temperature. Recent polymer-composite piezoelectrics have gained [...] Read more.

Piezoelectric thin films are extensively used as sensing or actuating layers in various micro-electromechanical systems (MEMS) applications. However, most piezoelectrics are stiff ceramics, and current polymer piezoelectrics are not compatible with microfabrication due to their low Curie Temperature. Recent polymer-composite piezoelectrics have gained interest but can be difficult to pattern. Photodefinable piezoelectric films could resolve these challenges by reducing the manufacturability steps by eliminating the etching process. But they typically have poor resolution and thickness properties. This study explores methods of enhancing the manufacturability of piezoelectric composite films by optimizing the process parameters and synthesis of SU-8 piezo-composite materials. Piezoelectric ceramic powders (barium titanate (BTO) and lead zirconate titanate (PZT)) were integrated into SU-8, a negative epoxy-based photoresist, to produce high-resolution composites in a non-cleanroom environment. I-line (365 nm) light was used to enhance resolution compared to broadband lithography. Two variations of SU-8 were prepared by thinning down SU-8 3050 and SU-8 3005. Different weight percentages of the piezoelectric powders were investigated: 5, 10, 15 and 20 wt.% along with varied photolithography processing parameters. The composites’ transmittance properties were characterized using UV-Vis spectroscopy and the films’ crystallinity was determined using X-ray diffraction (XRD). The 0–3 SU-8/piezo composites demonstrated resolutions < 2 μm while maintaining bulk piezoelectric coefficients d₃₃ > 5 pm V⁻¹. The films were developed with thicknesses >10 μm. Stacked layers were achieved and demonstrated significantly higher d₃₃ properties. Full article

(This article belongs to the Special Issue Smart Functional Micro/Nano Structured Surfaces)

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18 pages, 5866 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Progress in Droplet Structure Machining for Advanced Optics

by Jin-Kun Guo, W.D.N. Sandaruwan, Jinwei Li, Jinzhong Ling, Ying Yuan, Xin Liu, Qiang Li and Xiaorui Wang

Micromachines 2024, 15(3), 337; https://doi.org/10.3390/mi15030337 - 28 Feb 2024

Cited by 1 | Viewed by 1477

Abstract

The development of optical and photonic applications using soft-matter droplets holds great scientific and application importance. The machining of droplet structures is expected to drive breakthroughs in advancing frontier applications. This review highlights recent advancements in micro–nanofabrication techniques for soft-matter droplets, encompassing microfluidics, [...] Read more.

The development of optical and photonic applications using soft-matter droplets holds great scientific and application importance. The machining of droplet structures is expected to drive breakthroughs in advancing frontier applications. This review highlights recent advancements in micro–nanofabrication techniques for soft-matter droplets, encompassing microfluidics, laser injection, and microfluidic 3D printing. The principles, advantages, and weaknesses of these technologies are thoroughly discussed. The review introduces the utilization of a phase separation strategy in microfluidics to assemble complex emulsion droplets and control droplet geometries by adjusting interfacial tension. Additionally, laser injection can take full advantage of the self-assembly properties of soft matter to control the spontaneous organization of internal substructures within droplets, thus providing the possibility of high-precision customized assembly of droplets. Microfluidic 3D printing demonstrates a 3D printing-based method for machining droplet structures. Its programmable nature holds promise for developing device-level applications utilizing droplet arrays. Finally, the review presents novel applications of soft-matter droplets in optics and photonics. The integration of processing concepts from microfluidics, laser micro–nano-machining, and 3D printing into droplet processing, combined with the self-assembly properties of soft materials, may offer novel opportunities for processing and application development. Full article

(This article belongs to the Special Issue Research Progress of Ultra-Precision Micro-nano Machining)

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