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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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33 pages, 22149 KiB  
Review
MEMS Micromirror Actuation Techniques: A Comprehensive Review of Trends, Innovations, and Future Prospects
by Mansoor Ahmad, Mohamed Bahri and Mohamad Sawan
Micromachines 2024, 15(10), 1233; https://doi.org/10.3390/mi15101233 - 30 Sep 2024
Viewed by 1149
Abstract
Micromirrors have recently emerged as an essential component in optical scanning technology, attracting considerable attention from researchers. Their compact size and versatile capabilities, such as light steering, modulation, and switching, are leading them as potential alternatives to traditional bulky galvanometer scanners. The actuation [...] Read more.
Micromirrors have recently emerged as an essential component in optical scanning technology, attracting considerable attention from researchers. Their compact size and versatile capabilities, such as light steering, modulation, and switching, are leading them as potential alternatives to traditional bulky galvanometer scanners. The actuation of these mirrors is critical in determining their performance, as it contributes to factors such as response time, scanning angle, and power consumption. This article aims to provide a thorough exploration of the actuation techniques used to drive micromirrors, describing the fundamental operating principles. The four primary actuation modalities—electrostatic, electrothermal, electromagnetic, and piezoelectric—are thoroughly investigated. Each type of actuator’s operational principles, key advantages, and their limitations are discussed. Additionally, the discussion extends to hybrid micromirror designs that combine two types of actuation in a single device. A total of 208 closely related papers indexed in Web of Science were reviewed. The findings indicate ongoing advancements in the field, particularly in terms of size, controllability, and field of view, making micromirrors ideal candidates for applications in medical imaging, display projections, and optical communication. With a comprehensive overview of micromirror actuation strategies, this manuscript serves as a compelling resource for researchers and engineers aiming to utilize the appropriate type of micromirror in the field of optical scanning technology. Full article
(This article belongs to the Collection Optical MEMS: Design, Fabrication, Control, Modeling and Developments)
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12 pages, 2389 KiB  
Article
Scan-Rate-Dependent Ion Current Rectification in Bipolar Interfacial Nanopores
by Xiaoling Zhang, Yunjiao Wang, Jiahui Zheng, Chen Yang and Deqiang Wang
Micromachines 2024, 15(9), 1176; https://doi.org/10.3390/mi15091176 - 23 Sep 2024
Viewed by 808
Abstract
This study presents a theoretical investigation into the voltammetric behavior of bipolar interfacial nanopores due to the effect of potential scan rate (1–1000 V/s). Finite element method (FEM) is utilized to explore the current–voltage (I–V) properties of bipolar interfacial nanopores at different bulk [...] Read more.
This study presents a theoretical investigation into the voltammetric behavior of bipolar interfacial nanopores due to the effect of potential scan rate (1–1000 V/s). Finite element method (FEM) is utilized to explore the current–voltage (I–V) properties of bipolar interfacial nanopores at different bulk salt concentrations. The results demonstrate a strong impact of the scan rate on the I–V response of bipolar interfacial nanopores, particularly at relatively low concentrations. Hysteresis loops are observed in bipolar interfacial nanopores under specific scan rates and potential ranges and divided by a cross-point potential that remains unaffected by the scan rate employed. This indicates that the current in bipolar interfacial nanopores is not just reliant on the bias potential that is imposed but also on the previous conditions within the nanopore, exhibiting history-dependent or memory effects. This scan-rate-dependent current–voltage response is found to be significantly influenced by the length of the nanopore (membrane thickness). Thicker membranes exhibit a more pronounced scan-rate-dependent phenomenon, as the mass transfer of ionic species is slower relative to the potential scan rate. Additionally, unlike conventional bipolar nanopores, the ion current passing through bipolar interfacial nanopores is minimally affected by the membrane thickness, making it easier to detect. Full article
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20 pages, 7194 KiB  
Article
Deep Learning-Driven Prediction of Mechanical Properties of 316L Stainless Steel Metallographic by Laser Powder Bed Fusion
by Zhizhou Zhang, Paul Mativenga, Wenhua Zhang and Shi-qing Huang
Micromachines 2024, 15(9), 1167; https://doi.org/10.3390/mi15091167 - 21 Sep 2024
Viewed by 1027
Abstract
This study developed a new metallography–property relationship neural network (MPR-Net) to predict the relationship between the microstructure and mechanical properties of 316L stainless steel built by laser powder bed fusion (LPBF). The accuracy R2 of MPR-Net was 0.96 and 0.91 for tensile [...] Read more.
This study developed a new metallography–property relationship neural network (MPR-Net) to predict the relationship between the microstructure and mechanical properties of 316L stainless steel built by laser powder bed fusion (LPBF). The accuracy R2 of MPR-Net was 0.96 and 0.91 for tensile strength and Vickers hardness predictions, respectively, based on optical metallurgy images. Feature visualisation methods, such as gradient-weighted class activation mapping (Grad-CAM) and clustering, were employed to interpret the abstract features within the MPR-Net, providing insights into the molten pool morphology and grain formation mechanisms during the LPBF process. Experimental results showed that the optimal process parameters—190 W laser power and 700 mm/s scanning speed—yielded a maximum tensile strength of 762.83 MPa and a Vickers hardness of 253.07 HV0.2 with nearly full densification (99.97%). The study marks the first application of a convolutional neural network (MPR-Net) to predict the mechanical properties of 316L stainless steel samples manufactured through laser powder bed fusion (LPBF) based on metallography. It innovatively employs techniques such as gradient-weighted class activation mapping (Grad-CAM), spatial coherence testing, and clustering to provide deeper insights into the workings of the machine learning model, enhancing the interpretability of complex neural network decisions in material science. Full article
(This article belongs to the Special Issue Optical and Laser Material Processing)
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10 pages, 1639 KiB  
Article
One-Step Dry-Etching Fabrication of Tunable Two-Hierarchical Nanostructures
by Xu Ji, Bo Wang, Zhongshan Zhang, Yuan Xiang, Haifang Yang, Ruhao Pan and Junjie Li
Micromachines 2024, 15(9), 1160; https://doi.org/10.3390/mi15091160 - 17 Sep 2024
Viewed by 868
Abstract
Two-hierarchical nanostructures, characterized by two distinct configurations along the height direction, exhibit immense potential for applications in various fields due to their significantly enhanced controllable degree compared to single-order structures. However, due to the limitations imposed by planar technology, the realization of two-hierarchical [...] Read more.
Two-hierarchical nanostructures, characterized by two distinct configurations along the height direction, exhibit immense potential for applications in various fields due to their significantly enhanced controllable degree compared to single-order structures. However, due to the limitations imposed by planar technology, the realization of two-hierarchical nanostructures encounters huge challenges. In this work, we developed a one-step etching method based on inductively coupled plasma reactive ion etching for two-hierarchical nanostructures. Thanks to the shrinking effect of the Cr mask and the generation of a passivation layer during etching, the target materials experienced two different states from vertical etching to shrink etching. Consequently, the achieved two-hierarchical nanostructure configuration features a cross-section of an upper triangle and a lower rectangle, showing higher controllable degrees compared to the one-order ones. Both the mask pattern and etching parameters play crucial roles, by which two-hierarchical structures with diversiform shapes can be constructed controllably. This method for two-hierarchical nanostructures offers advantages including excellent control over structural properties, high processing efficiency, uniformity across large areas, and universality in materials. This developed strategy not only presents a simple and rapid nanofabrication platform for realizing optoelectronic devices, but also provides innovative ideas for designing the next generation of high-performance devices. Full article
(This article belongs to the Special Issue The 15th Anniversary of Micromachines)
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15 pages, 7305 KiB  
Article
Contact Hole Shrinkage: Simulation Study of Resist Flow Process and Its Application to Block Copolymers
by Sang-Kon Kim
Micromachines 2024, 15(9), 1151; https://doi.org/10.3390/mi15091151 - 13 Sep 2024
Viewed by 1067
Abstract
For vertical interconnect access (VIA) in three-dimensional (3D) structure chips, including those with high bandwidth memory (HBM), shrinking contact holes (C/Hs) using the resist flow process (RFP) represents the most promising technology for low- [...] Read more.
For vertical interconnect access (VIA) in three-dimensional (3D) structure chips, including those with high bandwidth memory (HBM), shrinking contact holes (C/Hs) using the resist flow process (RFP) represents the most promising technology for low-k1 (where CD=k1λ/NA,CD is the critical dimension, λ is wavelength, and NA is the numerical aperture). This method offers a way to reduce dimensions without additional complex process steps and is independent of optical technologies. However, most empirical models are heuristic methods and use linear regression to predict the critical dimension of the reflowed structure but do not account for intermediate shapes. In this research, the resist flow process (RFP) was modeled using the evolution method, the finite-element method, machine learning, and deep learning under various reflow conditions to imitate experimental results. Deep learning and machine learning have proven to be useful for physical optimization problems without analytical solutions, particularly for regression and classification tasks. In this application, the self-assembly of cylinder-forming block copolymers (BCPs), confined in prepatterns of the resist reflow process (RFP) to produce small contact hole (C/H) dimensions, was described using the self-consistent field theory (SCFT). This research paves the way for the shrink modeling of the enhanced resist reflow process (RFP) for random contact holes (C/Hs) and the production of smaller contact holes. Full article
(This article belongs to the Special Issue Recent Advances in Micro/Nano-Fabrication)
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13 pages, 4456 KiB  
Article
Preparation of High-Performance Transparent Al2O3 Dielectric Films via Self-Exothermic Reaction Based on Solution Method and Applications
by Xuecong Fang, Honglong Ning, Zihan Zhang, Rihui Yao, Yucheng Huang, Yonglin Yang, Weixin Cheng, Shaojie Jin, Dongxiang Luo and Junbiao Peng
Micromachines 2024, 15(9), 1140; https://doi.org/10.3390/mi15091140 - 11 Sep 2024
Viewed by 735
Abstract
As the competition intensifies in enhancing the integration and performance of integrated circuits, in accordance with the famous Moore’s Law, higher performance and smaller size requirements are imposed on the dielectric layers in electronic devices. Compared to vacuum methods, the production cost of [...] Read more.
As the competition intensifies in enhancing the integration and performance of integrated circuits, in accordance with the famous Moore’s Law, higher performance and smaller size requirements are imposed on the dielectric layers in electronic devices. Compared to vacuum methods, the production cost of preparing dielectric layers via solution methods is lower, and the preparation cycle is shorter. This paper utilizes a low-temperature self-exothermic reaction based on the solution method to prepare high-performance Al2O3 dielectric thin films that are compatible with flexible substrates. In this paper, we first established two non-self-exothermic systems: one with pure aluminum nitrate and one with pure aluminum acetylacetonate. Additionally, we set up one self-exothermic system where aluminum nitrate and aluminum acetylacetonate were mixed in a 1:1 ratio. Tests revealed that the leakage current density and dielectric constant of the self-exothermic system devices were significantly optimized compared to the two non-self-exothermic system devices, indicating that the self-exothermic reaction can effectively improve the quality of the dielectric film. This paper further established two self-exothermic systems with aluminum nitrate and aluminum acetylacetonate mixed in 2:1 and 1:2 ratios, respectively, for comparison. The results indicate that as the proportion of aluminum nitrate increases, the overall dielectric performance of the devices improves. The best overall performance occurs when aluminum nitrate and aluminum acetylacetonate are mixed in a ratio of 2:1: The film surface is smooth without cracks; the surface roughness is 0.747 ± 0.045 nm; the visible light transmittance reaches up to 98%; on the basis of this film, MIM devices were fabricated, with tested leakage current density as low as 1.08 × 10−8 A/cm2 @1 MV and a relative dielectric constant as high as 8.61 ± 0.06, demonstrating excellent electrical performance. Full article
(This article belongs to the Special Issue Thin Film Microelectronic Devices and Circuits)
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35 pages, 48192 KiB  
Review
Lab-on-Chip Systems for Cell Sorting: Main Features and Advantages of Inertial Focusing in Spiral Microchannels
by Isabella Petruzzellis, Rebeca Martínez Vázquez, Stefania Caragnano, Caterina Gaudiuso, Roberto Osellame, Antonio Ancona and Annalisa Volpe
Micromachines 2024, 15(9), 1135; https://doi.org/10.3390/mi15091135 - 6 Sep 2024
Viewed by 4311
Abstract
Inertial focusing-based Lab-on-Chip systems represent a promising technology for cell sorting in various applications, thanks to their alignment with the ASSURED criteria recommended by the World Health Organization: Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, and Delivered. Inertial focusing techniques using spiral [...] Read more.
Inertial focusing-based Lab-on-Chip systems represent a promising technology for cell sorting in various applications, thanks to their alignment with the ASSURED criteria recommended by the World Health Organization: Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, and Delivered. Inertial focusing techniques using spiral microchannels offer a rapid, portable, and easy-to-prototype solution for cell sorting. Various microfluidic devices have been investigated in the literature to understand how hydrodynamic forces influence particle focusing in spiral microchannels. This is crucial for the effective prototyping of devices that allow for high-throughput and efficient filtration of particles of different sizes. However, a clear, comprehensive, and organized overview of current research in this area is lacking. This review aims to fill this gap by offering a thorough summary of the existing literature, thereby guiding future experimentation and facilitating the selection of spiral geometries and materials for cell sorting in microchannels. To this end, we begin with a detailed theoretical introduction to the physical mechanisms underlying particle separation in spiral microfluidic channels. We also dedicate a section to the materials and prototyping techniques most commonly used for spiral microchannels, highlighting and discussing their respective advantages and disadvantages. Subsequently, we provide a critical examination of the key details of inertial focusing across various cross-sections (rectangular, trapezoidal, triangular, hybrid) in spiral devices as reported in the literature. Full article
(This article belongs to the Special Issue Bioinspired Interface and Fluid Manipulation: From Fundamentals to Applications)
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14 pages, 7528 KiB  
Article
Fine-Tuning of Optical Resonance Wavelength of Surface-Micromachined Optical Ultrasound Transducer Arrays for Single-Wavelength Light Source Readout
by Zhiyu Yan, Cheng Fang and Jun Zou
Micromachines 2024, 15(9), 1111; https://doi.org/10.3390/mi15091111 - 31 Aug 2024
Viewed by 785
Abstract
This article reports the fine-tuning of the optical resonance wavelength (ORW) of surface-micromachined optical ultrasound transducer (SMOUT) arrays to enable ultrasound data readout with non-tunable interrogation light sources for photoacoustic computed tomography (PACT). Permanent ORW tuning is achieved by material deposition onto or [...] Read more.
This article reports the fine-tuning of the optical resonance wavelength (ORW) of surface-micromachined optical ultrasound transducer (SMOUT) arrays to enable ultrasound data readout with non-tunable interrogation light sources for photoacoustic computed tomography (PACT). Permanent ORW tuning is achieved by material deposition onto or subtraction from the top diaphragm of each element with sub-nanometer resolution. For demonstration, a SMOUT array is first fabricated, and its ORW is tuned for readout with an 808 nm laser diode (LD). Experiments are conducted to characterize the optical and acoustic performances of the elements within the center region of the SMOUT array. Two-dimensional and three-dimensional PACT (photoacoustic computed tomography) is also performed to evaluate the imaging performance of the ORW-tuned SMOUT array. The results show that the ORW tuning does not degrade the optical, acoustic, and overall imaging performances of the SMOUT elements. As a result, the fine-tuning method enables new SMOUT-based PACT systems that are low cost, compact, powerful, and even higher speed, with parallel readout capability. Full article
(This article belongs to the Special Issue Photoacoustic-Based Sensing Systems: Advances, Applications, and Innovative Measurement Strategies)
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12 pages, 5444 KiB  
Article
Electrical Properties and Reliability of AlGaN/GaN High Electron Mobility Transistor under RF Overdrive Stress at High Temperature
by Chang Liu, Yiqiang Chen, Yuhan Xie, Hongxia Liu and Zongqi Cai
Micromachines 2024, 15(9), 1100; https://doi.org/10.3390/mi15091100 - 30 Aug 2024
Viewed by 704
Abstract
We have investigated the electrical properties and reliability of AlGaN/GaN high electron mobility transistors (HEMT) under high-temperature RF overdrive stress. The experimental results show that the drain current and transconductance of the device decrease at 25 °C and 55 °C but do not [...] Read more.
We have investigated the electrical properties and reliability of AlGaN/GaN high electron mobility transistors (HEMT) under high-temperature RF overdrive stress. The experimental results show that the drain current and transconductance of the device decrease at 25 °C and 55 °C but do not change significantly at 85 °C before and after the stress. The decline rate of the saturation drain current, the degradation amplitude of transconductance, and the drift amplitude of threshold voltage decrease with the increase in temperature. The results of pulse I–V and low-frequency noise tests show that the current collapse is inhibited, and the trap density is reduced at higher temperatures. The Electroluminescence (EL) test shows that the luminescence characteristics of the device after RF overdrive stress are more scattered and weaker. We believe that the degradation at lower temperatures is mainly due to the influence of the hot electron effect (HEE), while the change in electrical properties at higher temperatures is due to the weakening of HEE and the improvement of the Schottky interface. Full article
(This article belongs to the Section D1: Semiconductor Devices)
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30 pages, 13622 KiB  
Review
Key Technologies in Developing Chip-Scale Hot Atomic Devices for Precision Quantum Metrology
by Huiyao Yu, Xuyuan Zhang, Jian Zhang, Zhendong Wu, Long Jiao, Kan Li and Wenqiang Zheng
Micromachines 2024, 15(9), 1095; https://doi.org/10.3390/mi15091095 - 29 Aug 2024
Viewed by 1253
Abstract
Chip-scale devices harnessing the interaction between hot atomic ensembles and light are pushing the boundaries of precision measurement techniques into unprecedented territory. These advancements enable the realization of super-sensitive, miniaturized sensing instruments for measuring various physical parameters. The evolution of this field is [...] Read more.
Chip-scale devices harnessing the interaction between hot atomic ensembles and light are pushing the boundaries of precision measurement techniques into unprecedented territory. These advancements enable the realization of super-sensitive, miniaturized sensing instruments for measuring various physical parameters. The evolution of this field is propelled by a suite of sophisticated components, including miniaturized single-mode lasers, microfabricated alkali atom vapor cells, compact coil systems, scaled-down heating systems, and the application of cutting-edge micro-electro-mechanical system (MEMS) technologies. This review delves into the essential technologies needed to develop chip-scale hot atomic devices for quantum metrology, providing a comparative analysis of each technology’s features. Concluding with a forward-looking perspective, this review discusses the future potential of chip-scale hot atomic devices and the critical technologies that will drive their advancement. Full article
(This article belongs to the Special Issue Emerging Quantum Optical Devices and Their Applications)
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21 pages, 3257 KiB  
Review
Democratizing Microreactor Technology for Accelerated Discoveries in Chemistry and Materials Research
by Tomomi Sato, Koji Masuda, Chikako Sano, Keiji Matsumoto, Hidetoshi Numata, Seiji Munetoh, Toshihiro Kasama and Ryo Miyake
Micromachines 2024, 15(9), 1064; https://doi.org/10.3390/mi15091064 - 23 Aug 2024
Viewed by 1098
Abstract
Microreactor technologies have emerged as versatile platforms with the potential to revolutionize chemistry and materials research, offering sustainable solutions to global challenges in environmental and health domains. This survey paper provides an in-depth review of recent advancements in microreactor technologies, focusing on their [...] Read more.
Microreactor technologies have emerged as versatile platforms with the potential to revolutionize chemistry and materials research, offering sustainable solutions to global challenges in environmental and health domains. This survey paper provides an in-depth review of recent advancements in microreactor technologies, focusing on their role in facilitating accelerated discoveries in chemistry and materials. Specifically, we examine the convergence of microfluidics with machine intelligence and automation, enabling the exploitation of the cyber-physical environment as a highly integrated experimentation platform for rapid scientific discovery and process development. We investigate the applicability and limitations of microreactor-enabled discovery accelerators in various chemistry and materials contexts. Despite their tremendous potential, the integration of machine intelligence and automation into microreactor-based experiments presents challenges in establishing fully integrated, automated, and intelligent systems. These challenges can hinder the broader adoption of microreactor technologies within the research community. To address this, we review emerging technologies that can help lower barriers and facilitate the implementation of microreactor-enabled discovery accelerators. Lastly, we provide our perspective on future research directions for democratizing microreactor technologies, with the aim of accelerating scientific discoveries and promoting widespread adoption of these transformative platforms. Full article
(This article belongs to the Section C：Chemistry)
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12 pages, 14542 KiB  
Communication
Offsetting Dense Particle Sedimentation in Microfluidic Systems
by Tochukwu Dubem Anyaduba and Jesus Rodriguez-Manzano
Micromachines 2024, 15(9), 1063; https://doi.org/10.3390/mi15091063 - 23 Aug 2024
Viewed by 3679
Abstract
Sedimentation is an undesirable phenomenon that complicates the design of microsystems that exploit dense microparticles as delivery tools, especially in biotechnological applications. It often informs the integration of continuous mixing modules, consequently impacting the system footprint, cost, and complexity. The impact of sedimentation [...] Read more.
Sedimentation is an undesirable phenomenon that complicates the design of microsystems that exploit dense microparticles as delivery tools, especially in biotechnological applications. It often informs the integration of continuous mixing modules, consequently impacting the system footprint, cost, and complexity. The impact of sedimentation is significantly worse in systems designed with the intent of particle metering or binary encapsulation in droplets. Circumventing this problem involves the unsatisfactory adoption of gel microparticles as an alternative. This paper presents two solutions—a hydrodynamic solution that changes the particle sedimentation trajectory relative to a flow-rate dependent resultant force, and induced hindered settling (i-HS), which exploits Richardson–Zaki (RZ) corrections of Stokes’ law. The hydrodynamic solution was validated using a multi-well fluidic multiplexing and particle metering manifold. Computational image analysis of multiplex metering efficiency using this method showed an average reduction in well-to-well variation in particle concentration from 45% (Q = 1 mL/min, n = 32 total wells) to 17% (Q = 10 mL/min, n = 48 total wells). By exploiting a physical property (cloud point) of surfactants in the bead suspension in vials, the i-HS achieved a 58% reduction in the sedimentation rate. This effect results from the surfactant phase change, which increases the turbidity (transient increase in particle concentration), thereby exploiting the RZ theories. Both methods can be used independently or synergistically to eliminate bead settling in microsystems or to minimize particle sedimentation Full article
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13 pages, 31150 KiB  
Article
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 1248
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  
Review
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 1027
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  
Review
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 1370
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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12 pages, 4809 KiB  
Article
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 1124
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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20 pages, 2917 KiB  
Article
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 813
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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25 pages, 1058 KiB  
Review
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 958
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  
Review
Droplet Microfluidics for High-Throughput Screening and Directed Evolution of Biomolecules
by Goran T. Vladisavljević
Micromachines 2024, 15(8), 971; https://doi.org/10.3390/mi15080971 - 29 Jul 2024
Viewed by 1779
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  
Article
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 1094
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  
Article
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 920
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  
Article
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 2889
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  
Review
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 2 | Viewed by 1827
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  
Article
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 3039
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  
Communication
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 1098
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  
Review
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
Cited by 1 | Viewed by 2382
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  
Article
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 3747
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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14 pages, 1807 KiB  
Article
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 1505
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  
Review
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 2467
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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9 pages, 3672 KiB  
Article
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 1308
Abstract
This paper investigates the threshold voltage shift (ΔVTH) induced by positive bias temperature instability (PBTI) in silicon carbide (SiC) power MOSFETs. By analyzing ΔVTH under various gate stress voltages (VGstress) at 150 °C, distinct mechanisms are revealed: (i) [...] Read more.
This paper investigates the threshold voltage shift (ΔVTH) induced by positive bias temperature instability (PBTI) in silicon carbide (SiC) power MOSFETs. By analyzing ΔVTH under various gate stress voltages (VGstress) 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 ΔVTH degradation across VGstress 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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22 pages, 9997 KiB  
Review
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
Cited by 1 | Viewed by 1605
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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16 pages, 7181 KiB  
Article
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 1208
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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18 pages, 4232 KiB  
Article
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 866
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  
Article
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
Cited by 1 | Viewed by 1380
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  
Article
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
Cited by 1 | Viewed by 787
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  
Article
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 3517
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  
Review
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 1563
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  
Communication
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 825
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  
Article
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 1031
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 (Cgd) to the gate-to-source capacitance (Cgs) 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 (Ron,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 (RJFET) and the electric field in the gate oxide (Eox) 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  
Review
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 1166
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  
Review
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 3753
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  
Article
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 1093
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  
Review
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
Cited by 3 | Viewed by 6172
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  
Article
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 889
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 (ρcp). 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 ρcp 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  
Article
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
Cited by 1 | Viewed by 1348
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  
Article
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 1272
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  
Article
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
Cited by 1 | Viewed by 1556
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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15 pages, 1542 KiB  
Article
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 1061
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  
Review
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 1965
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  
Article
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 2 | Viewed by 3602
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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