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Micromachines
Volume 15
Issue 6
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Micromachines, Volume 15, Issue 6 (June 2024) – 89 articles

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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 (registering DOI) - 3 Jun 2024
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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9 pages, 4940 KiB  
Article
High-Speed Generation of Microbubbles with Constant Cumulative Production in a Glass Capillary Microfluidic Bubble Generator
by Jian Yu, Wei Cheng, Jinchun Ni, Changwu Li, Xinggen Su, Hui Yan, Fubing Bao and Likai Hou
Micromachines 2024, 15(6), 752; https://doi.org/10.3390/mi15060752 (registering DOI) - 2 Jun 2024
Abstract
This work reports a simple bubble generator for the high-speed generation of microbubbles with constant cumulative production. To achieve this, a gas–liquid co-flowing microfluidic device with a tiny capillary orifice as small as 5 μm is fabricated to produce monodisperse microbubbles. The diameter [...] Read more.
This work reports a simple bubble generator for the high-speed generation of microbubbles with constant cumulative production. To achieve this, a gas–liquid co-flowing microfluidic device with a tiny capillary orifice as small as 5 μm is fabricated to produce monodisperse microbubbles. The diameter of the microbubbles can be adjusted precisely by tuning the input gas pressure and flow rate of the continuous liquid phase. The co-flowing structure ensures the uniformity of the generated microbubbles, and the surfactant in the liquid phase prevents coalescence of the collected microbubbles. The diameter coefficient of variation (CV) of the generated microbubbles can reach a minimum of 1.3%. Additionally, the relationship between microbubble diameter and the gas channel orifice is studied using the low Capillary number (Ca) and Weber number (We) of the liquid phase. Moreover, by maintaining a consistent gas input pressure, the CV of the cumulative microbubble volume can reach 3.6% regardless of the flow rate of the liquid phase. This method not only facilitates the generation of microbubbles with morphologic stability under variable flow conditions, but also ensures that the cumulative microbubble production over a certain period of time remains constant, which is important for the volume-dominated application of chromatographic analysis and the component analysis of natural gas. Full article
(This article belongs to the Special Issue Recent Development of Micro/Nanofluidic Devices)
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9 pages, 2751 KiB  
Article
Highly Sensitive Force Sensor Based on High-Q Asymmetric V-Shaped CaF2 Resonator
by Deyong Wang, Jiamin Rong, Jianglong Li, Hongbo Yue, Wenyao Liu, Enbo Xing, Jun Tang and Jun Liu
Micromachines 2024, 15(6), 751; https://doi.org/10.3390/mi15060751 (registering DOI) - 2 Jun 2024
Abstract
Whispering gallery mode (WGM) resonators have high-quality factors and can be used in high-sensitivity sensors due to the narrow line width that allows for the detection of small external changes. In this paper, a force-sensing system based on a high-Q asymmetric V-shaped CaF [...] Read more.
Whispering gallery mode (WGM) resonators have high-quality factors and can be used in high-sensitivity sensors due to the narrow line width that allows for the detection of small external changes. In this paper, a force-sensing system based on a high-Q asymmetric V-shaped CaF2 resonator is proposed. Based on the dispersion coupling mechanism, the deformation of the resonator is achieved by loading force, and the resonant frequency is changed to determine the measurement. By adjusting the structural parameters of the asymmetric V-shaped resonator, the deformation of the resonator under force loading is improved. The experimental results show that the sensitivity of the V-shaped tip is 18.84 V/N, which determines the force-sensing resolution of 8.49 μN. This work provides a solution for force-sensing measurements based on a WGM resonator. Full article
(This article belongs to the Special Issue Recent Advances in Sensors and Sensing System Design)
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20 pages, 26782 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 (registering DOI) - 2 Jun 2024
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)
13 pages, 5789 KiB  
Article
The Influence of Microstructure on TCR for Inkjet-Printed Resistive Temperature Detectors Fabricated Using AgNO3/Ethylene-Glycol-Based Inks
by Aziz Radwan, Yongkun Sui and Christian Zorman
Micromachines 2024, 15(6), 749; https://doi.org/10.3390/mi15060749 (registering DOI) - 2 Jun 2024
Abstract
This study investigated the influence of microstructure on the performance of Ag inkjet-printed, resistive temperature detectors (RTDs) fabricated using particle-free inks based on a silver nitrate (AgNO3) precursor and ethylene glycol as the ink solvent. Specifically, the temperature coefficient of resistance [...] Read more.
This study investigated the influence of microstructure on the performance of Ag inkjet-printed, resistive temperature detectors (RTDs) fabricated using particle-free inks based on a silver nitrate (AgNO3) precursor and ethylene glycol as the ink solvent. Specifically, the temperature coefficient of resistance (TCR) and sensitivity for sensors printed using inks that use monoethylene glycol (mono-EG), diethylene glycol (di-EG), and triethylene glycol (tri-EG) and subjected to a low-pressure argon (Ar) plasma after printing were investigated. Scanning electron microscopy (SEM) confirmed previous findings that microstructure is strongly influenced by the ink solvent, with mono-EG inks producing dense structures, while di- and tri-EG inks produce porous structures, with tri-EG inks yielding the most porous structures. RTD testing revealed that sensors printed using mono-EG ink exhibited the highest TCR (1.7 × 10−3/°C), followed by di-EG ink (8.2 × 10−4/°C) and tri-EG ink (7.2 × 10−4/°C). These findings indicate that porosity exhibits a strong negative influence on TCR. Sensitivity was not strongly influenced by microstructure but rather by the resistance of RTD. The highest sensitivity (0.84 Ω/°C) was observed for an RTD printed using mono-EG ink but not under plasma exposure conditions that yield the highest TCR. Full article
(This article belongs to the Special Issue Microstructured Sensors: From Design to Application)
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37 pages, 21313 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 (registering DOI) - 1 Jun 2024
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)
18 pages, 990 KiB  
Article
Pulsed Laser Ablation Characteristics of Light-Absorbing Mask Layer Based on Coating Thicknesses under Laser Lift-Off Patterning Process
by Daehee Hyun, Hee-Lak Lee, Yoon-Jae Moon, Jun-Young Hwang and Seung-Jae Moon
Micromachines 2024, 15(6), 747; https://doi.org/10.3390/mi15060747 (registering DOI) - 1 Jun 2024
Abstract
Thin transparent oxide layers are typically patterned for use in electronic products including semiconductors, displays, and solar cells for applications such as transparent electrodes, insulating films, and encapsulation films. Conventional patterning methods have traditionally been used in photolithography and lift-off processes. Photolithography employs [...] Read more.
Thin transparent oxide layers are typically patterned for use in electronic products including semiconductors, displays, and solar cells for applications such as transparent electrodes, insulating films, and encapsulation films. Conventional patterning methods have traditionally been used in photolithography and lift-off processes. Photolithography employs the wet development process, which has disadvantages such as potential undercut effects, swelling, chemical contamination, and high process costs. On the other hand, laser ablation, which has the advantages of high accuracy, high speed, a noncontact nature, and selective processing, can be used to pattern thin films. However, absorption in transparent oxide films is usually low. In this study, experiments were conducted to determine the ablation characteristics of mask layers. The factors affecting ablation, including beam radii, fluences, overlap ratios, and coating thicknesses, were examined; and the parameters characteristic of residue-free ablation, namely the ablation threshold, minimum fluence, and minimum ablation linewidth, were also examined. The experimental results revealed that the beam radius was an important parameter in determining the resolutions of transparent films and substrates. Full article
(This article belongs to the Special Issue Ultrafast Laser Micro- and Nanoprocessing, 2nd Edition)
18 pages, 8189 KiB  
Article
Process Development of Aluminum Electroplating from an Ionic Liquid on 150 mm Wafer Level
by Silvia Braun, Maik Wiemer and Stefan E. Schulz
Micromachines 2024, 15(6), 746; https://doi.org/10.3390/mi15060746 (registering DOI) - 1 Jun 2024
Abstract
This paper focuses on the development of electroplating on 150 mm wafer level for microsystem technology applications from 1-Ethyl-3-methylimidazolium chloride (EMImCl) with Aluminumtrichloride (AlCl3). The deposition was carried out on 150 mm wafers with Au or Al seed layers deposited by [...] Read more.
This paper focuses on the development of electroplating on 150 mm wafer level for microsystem technology applications from 1-Ethyl-3-methylimidazolium chloride (EMImCl) with Aluminumtrichloride (AlCl3). The deposition was carried out on 150 mm wafers with Au or Al seed layers deposited by physical vapor deposition (PVD). The electrodeposition was carried out using pattern plating. On the Au seed layer, bipolar pulse plating was applied. Compared to the Au seed layer, the electrodeposition on the Al seed layer was favorable, with lower current densities and pulsing frequencies. Utilizing the recurrent galvanic pulses and avoiding ionic liquid convection, inhomogeneities lower than 15% were achieved with a laboratory plating cell. One major aspect of this study was the removal of the native Al oxide prior to deposition. It was investigated on the chip and wafer levels using either current- or potential-controlled removal pulses. This process step was affected by the plasma treatment of the wafer, thus the surface free energy, prior to plating. It turned out that a higher surface free energy hindered proper oxide removal at a potential of 3 V. The theory of oxide breakdown based on electrostriction force via the electrical field was applied to discuss the findings and to derive conclusions for future plating experiments. Full article
(This article belongs to the Section D：Materials and Processing)
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9 pages, 872 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 (registering DOI) - 31 May 2024
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)
13 pages, 1252 KiB  
Article
Power Enhancement and Spot Homogenization Design for Arrayed Semiconductor Lasers
by Shunshun Zhong, Jun Xiong, Cong Xu, Fan Zhang and Ji’an Duan
Micromachines 2024, 15(6), 744; https://doi.org/10.3390/mi15060744 (registering DOI) - 31 May 2024
Abstract
Improving the spot brightness and uniformity of arrangement of the array laser is conducive to ensuring the beam quality of the fiber laser. Based on the light tracing principle, the optical model performance of two common fiber lasers was first analyzed. Then, a [...] Read more.
Improving the spot brightness and uniformity of arrangement of the array laser is conducive to ensuring the beam quality of the fiber laser. Based on the light tracing principle, the optical model performance of two common fiber lasers was first analyzed. Then, a novel rotationally polarized optical model with high power and spot uniformity was designed and optimized on the basis of the aforementioned analysis. The results of the evaluation metrics of the multi-indicator optical model show that the spot uniformity of our proposed model improved by 24.03%, the power improved by 0.55%, and the maximum light distance was shortened from 120 mm to 82.58 mm. Further, the results of the coupling tolerance analysis of the optical elements show that the total coupling efficiency was 89.04%. The coupling power and tolerance relationships did not produce degradation compared with the traditional model. Extensive comparative results show that the designed rotationally polarized optical path model can effectively improve the optical coupling efficiency and spot uniformity of arrayed semiconductor lasers. Full article
(This article belongs to the Special Issue Laser and Photoelectronics in Optical Communication)
18 pages, 5096 KiB  
Article
Bulge-Free and Homogeneous Metal Line Jet Printing with StarJet Technology
by Dániel Straubinger, Peter Koltay, Roland Zengerle, Sabrina Kartmann and Zhe Shu
Micromachines 2024, 15(6), 743; https://doi.org/10.3390/mi15060743 (registering DOI) - 31 May 2024
Abstract
The technology to jet print metal lines with precise shape fidelity on diverse substrates is gaining higher interest across multiple research fields. It finds applications in additively manufactured flexible electronics, environmentally friendly and sustainable electronics, sensor devices for medical applications, and fabricating electrodes [...] Read more.
The technology to jet print metal lines with precise shape fidelity on diverse substrates is gaining higher interest across multiple research fields. It finds applications in additively manufactured flexible electronics, environmentally friendly and sustainable electronics, sensor devices for medical applications, and fabricating electrodes for solar cells. This paper provides an experimental investigation to deepen insights into the non-contact printing of solder lines using StarJet technology, eliminating the need for surface activation, substrate heating, curing, or post-processing. Moreover, it employs bulk metal instead of conventional inks or pastes, leading to cost-effective production and enhanced conductivity. The effect of molten metal temperature, substrate temperature, standoff distance, and printing velocity was investigated on polymer foils (i.e., PET sheets). Robust printing parameters were derived to print uniform, bulge-free, bulk metal lines suitable for additive manufacturing applications. The applicability of the derived parameters was extended to 3D-printed PLA, TPU, PA-GF, and PETG substrates having a much higher surface roughness. Additionally, a high aspect ratio of approx. 16:1 wall structure has been demonstrated by printing multiple metal lines on top of each other. While challenges persist, this study contributes to advancing additively manufactured electronic devices, highlighting the capabilities of StarJet metal jet-printing technology. Full article
9 pages, 793 KiB  
Article
A Novel Small Form-Factor Handheld Optical Coherence Tomography Probe for Oral Soft Tissue Imaging
by Alok K. Kushwaha, Minqi Ji, Sneha Sethi, Lisa Jamieson, Robert A. McLaughlin and Jiawen Li
Micromachines 2024, 15(6), 742; https://doi.org/10.3390/mi15060742 (registering DOI) - 31 May 2024
Abstract
Tissue imaging is crucial in oral cancer diagnostics. Imaging techniques such as X-ray imaging, magnetic resonance imaging, optical coherence tomography (OCT) and computed tomography (CT) enable the visualization and analysis of tissues, aiding in the detection and diagnosis of cancers. A significant amount [...] Read more.
Tissue imaging is crucial in oral cancer diagnostics. Imaging techniques such as X-ray imaging, magnetic resonance imaging, optical coherence tomography (OCT) and computed tomography (CT) enable the visualization and analysis of tissues, aiding in the detection and diagnosis of cancers. A significant amount of research has been conducted on designing OCT probes for tissue imaging, but most probes are either heavy, bulky and require external mounting or are lightweight but straight. This study addresses these challenges, resulting in a curved lightweight, low-voltage and compact handheld imaging probe for oral soft tissue examination. To the best of our knowledge, this is the first curved handheld OCT probe with its shape optimized for oral applications. This probe features highly compact all-fiber optics with a diameter of 125 μm and utilizes innovative central deflection magnetic actuation for controlled beam scanning. To ensure vertical stability while scanning oral soft tissues, the fiber was secured through multiple narrow slits at the probe’s distal end. This apparatus was encased in a 3D-printed angular cylinder tube (15 mm outer diameter, 12 mm inner diameter and 160 mm in length, weighing < 20 g). An angle of 115° makes the probe easy to hold and suitable for scanning in space-limited locations. To validate the feasibility of this probe, we conducted assessments on a multi-layered imaging phantom and human tissues, visualizing microstructural features with high contrast. Full article
(This article belongs to the Special Issue Optical Coherence Tomography (OCT) Technique and Its Applications)
11 pages, 1443 KiB  
Article
Design and Fabrication of Biosensor for a Specific Microbe by Silicon-Based Interference Color System
by Muthusamy Sivakumar, Sangami Ervanan, Susithra Lakshmanan, Sathya Venkatesan, Takatoshi Kinoshita, Duraikkannu Shanthana Lakshmi and Alagarsamy Santhana Krishna Kumar
Micromachines 2024, 15(6), 741; https://doi.org/10.3390/mi15060741 (registering DOI) - 31 May 2024
Abstract
In this paper, one of the great challenges faced by silicon-based biosensors is resolved using a biomaterial multilayer. Tiny biomolecules are deposited on silicon substrates, producing devices that have the ability to act as iridescent color sensors. The color is formed by a [...] Read more.
In this paper, one of the great challenges faced by silicon-based biosensors is resolved using a biomaterial multilayer. Tiny biomolecules are deposited on silicon substrates, producing devices that have the ability to act as iridescent color sensors. The color is formed by a coating of uniform microstructures through the interference of light. The system exploits a flat, RNA-aptamer-coated silicon-based surface to which captured microbes are covalently attached. Silicon surfaces are encompassed with the layer-by-layer deposition of biomolecules, as characterized by atomic force microscopy and X-ray photoelectron spectroscopy. Furthermore, the results demonstrate an application of an RNA aptamer chip for sensing a specific bacterium. Interestingly, the detection limit for the microbe was observed to be 2 × 106 CFUmL−1 by visually observed color changes, which were confirmed further using UV-Vis reflectance spectrophotometry. In this report, a flexible method has been developed for the detection of the pathogen Sphingobium yanoikuyae, which is found in non-beverage alcohols. The optimized system is capable of detecting the specific target microbe. The simple concept of these iridescent color changes is mainly derived from the increase in thickness of the nano-ordered layers. Full article
(This article belongs to the Special Issue Nanoparticle (Bio)sensing Platform)
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23 pages, 10517 KiB  
Article
GRU-ESO Strategy for a Distributed Coil Magnetically Levitated Planar Micromotor
by Chaofan Du, Zhengfeng Ming, Yue Ming, Ding Liu, Yongzheng Li and Yuhu Zhao
Micromachines 2024, 15(6), 740; https://doi.org/10.3390/mi15060740 (registering DOI) - 31 May 2024
Abstract
Traditional magnetic levitation planar micromotors suffer from poor controllability, short travel range, low interference resistance, and low precision. To address these issues, a distributed coil magnetically levitated planar micromotor with a gated recurrent unit (GRU)-extended state observer (ESO) control strategy is proposed in [...] Read more.
Traditional magnetic levitation planar micromotors suffer from poor controllability, short travel range, low interference resistance, and low precision. To address these issues, a distributed coil magnetically levitated planar micromotor with a gated recurrent unit (GRU)-extended state observer (ESO) control strategy is proposed in this paper. First, the structural design of the distributed coil magnetically levitated planar micromotor employs a separation of levitation and displacement, reducing system coupling and increasing controllability and displacement range. Then, theoretical analysis and model establishment of the system are conducted based on the designed distributed coil magnetically levitated planar micromotor and its working principles, followed by simulation verification. Finally, based on the established system model, a GRU-ESO controller is designed. An ESO feedback control term is introduced to enhance the system’s anti-interference capability, and the GRU feedforward compensation control term is used to improve the system’s tracking control accuracy. The experimental results demonstrate the reliability of the designed distributed coil magnetic levitation planar micromotor and the effectiveness of the controller. Full article
(This article belongs to the Special Issue Magnetic Actuation for Micromachines)
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15 pages, 561 KiB  
Article
Optical Modification of a Nanoporous Alumina Structure Associated with Surface Coverage by the Ionic Liquid AliquatCl
by María Cruz López-Escalante, Valle Martínez de Yuso, Ana L. Cuevas and Juana Benavente
Micromachines 2024, 15(6), 739; https://doi.org/10.3390/mi15060739 (registering DOI) - 31 May 2024
Abstract
This manuscript analyses changes in the optical parameters of a commercial alumina nanoporous structure (AnodiscTM or AND support) due to surface coverage by the ionic liquid (IL) AliquatCl (AlqCl). XPS measurements were performed for chemical characterization of the composite AND/AlqCl and the [...] Read more.
This manuscript analyses changes in the optical parameters of a commercial alumina nanoporous structure (AnodiscTM or AND support) due to surface coverage by the ionic liquid (IL) AliquatCl (AlqCl). XPS measurements were performed for chemical characterization of the composite AND/AlqCl and the AND support, but XPS resolved angle analysis (from 15° to 75°) was carried out for the homogeneity estimation of the top surface of the ANDAlqCl sample. Optical characterization of both the composite AND/AlqCl and the AND support was performed by three non-destructive and non-invasive techniques: ellipsometry spectroscopy (SE), light transmittance/reflection, and photoluminescence. SE measurements (wavelength ranging from 250 nm to 1250 nm) allow for the determination of the refraction index of the AND/AlqCl sample, which hardly differs from that corresponding to the IL, confirming the XPS results. The presence of the IL significantly increases the light transmission of the alumina support in the visible region and reduces reflection, affecting also the maximum position of this latter curve, as well as the photoluminescence spectra. Due to these results, illuminated I–V curves for both the composite AND/AlqCl film and the AND support were also measured to estimate its possible application as a solar cell. The optical behaviour exhibited by the AND/AlqCl thin film in the visible region could be of interest for different applications. Full article
(This article belongs to the Special Issue Functional Materials and Microdevices)
18 pages, 1062 KiB  
Article
IGBT Gate Boost Drive Technology for Promoting the Overload Capacity of Traction Converter
by Yunxin Zhang, Xiaodong Dong, Linxia Wu, Xiaoyu Wang, Ming Ma, Xianjin Huang, Yong Jin and Pengze Zhu
Micromachines 2024, 15(6), 738; https://doi.org/10.3390/mi15060738 (registering DOI) - 31 May 2024
Abstract
Under certain circumstances, a high-speed railway may require constant acceleration or emergency braking, in which case the inverter may experience short-term overload conditions and the current passing through the IGBT will go beyond the rated design tolerance. Under overload conditions, the IGBT loss [...] Read more.
Under certain circumstances, a high-speed railway may require constant acceleration or emergency braking, in which case the inverter may experience short-term overload conditions and the current passing through the IGBT will go beyond the rated design tolerance. Under overload conditions, the IGBT loss will increase instantly, raising the power semiconductor device’s junction temperature in the process. This research examines the boosting-gate-voltage-driven IGBT control technology. It increases the gate drive voltage and the IGBT current capacity and decreases the conduction voltage drop of IGBT under short-term overload conditions, reducing the instantaneous loss and temperature rise undulation of IGBT. The working characteristics of IGBT devices are studied, and the influence of gate drive voltage on device loss and temperature rise fluctuations is analyzed. Based on the emergency acceleration and brake conditions of the actual train operation, the short-term overload characteristics of the inverter are analyzed. The optimization analysis of the boosting gate voltage under emergency conditions is carried out, and the IGBT drive circuit with gate voltage pumping function is designed. The effectiveness of the driving circuit is verified through PSpice simulation and actual switching characteristic test. According to the analysis of experimental data, it can be verified that increasing the gate voltage technology can reduce IGBT losses. Full article
(This article belongs to the Special Issue Insulated Gate Bipolar Transistor (IGBT) Modules)
10 pages, 2692 KiB  
Article
RGO/CuCl-Based Flexible Gas Sensor for High-Concentration Carbon Monoxide Gas Detection at Room Temperature
by Qingqing Liu, Fuzheng Zhang, Mengfei Pei and Weile Jiang
Micromachines 2024, 15(6), 737; https://doi.org/10.3390/mi15060737 (registering DOI) - 31 May 2024
Abstract
Carbon monoxide (CO) gas sensors are widely used, especially for environmental monitoring in confined spaces such as the landscape of mining cave ruins in mining parks, which is essential for ensuring the health and safety of tourists and staff. In this paper, a [...] Read more.
Carbon monoxide (CO) gas sensors are widely used, especially for environmental monitoring in confined spaces such as the landscape of mining cave ruins in mining parks, which is essential for ensuring the health and safety of tourists and staff. In this paper, a flexible CO gas sensor based on polyimide, interdigital electrodes, and reduced graphene oxide (RGO)/cuprous chloride (CuCl) composite film is designed and manufactured for reliable room temperature detection of high-concentration CO gas. The structure size of RGO/CuCl gas-sensitive film is 5 × 5 mm. The RGO with a 62.65% C-C bond is prepared by the thermal reduction method. The test results show that the sensor has a high response in the range of 400–2000 ppm CO gas concentration, and the maximum response is 1.56. The linear correlation coefficient of the sensor is 0.981, which indicates that the sensor has good output response characteristics. The response time of the sensor for 400 ppm CO gas is 332 s, which indicates that the sensor has a fast response rate. Furthermore, compared with other gases, the sensor shows higher gas selectivity for CO gas. This sensor has the characteristics of small size and easy attachment; therefore, it can be installed on the shoulder or helmet of tourists’ safety suits, providing personalized real-time warning prompts for tourists’ physical health status. Full article
8 pages, 20341 KiB  
Communication
Miniaturized Active-Frequency Selective Surfaces for Low-Power Internet of Things Devices
by Liang Zhang, Haobin Yang, Yan Wang, Shaoqing Zhang and Tongyu Ding
Micromachines 2024, 15(6), 736; https://doi.org/10.3390/mi15060736 (registering DOI) - 31 May 2024
Abstract
With the proliferation of smart devices, the Internet of Things (IoT) is rapidly expanding. This study proposes a miniaturized controllable metamaterial with low control voltage for achieving low-power and compact designs in IoT node devices. Operating at a target frequency of 2.4 GHz, [...] Read more.
With the proliferation of smart devices, the Internet of Things (IoT) is rapidly expanding. This study proposes a miniaturized controllable metamaterial with low control voltage for achieving low-power and compact designs in IoT node devices. Operating at a target frequency of 2.4 GHz, the proposed metamaterial requires only a 3.3 V control voltage and occupies approximately one-third of the wavelength in size. Experimental validation demonstrates its excellent reflective control performance, positioning it as an ideal choice for low-power IoT systems, particularly in the context of miniaturized and low-power IoT node applications. Full article
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17 pages, 4694 KiB  
Article
Particle Detection in Free-Falling Nanoliter Droplets
by Fabian Sturm, Viktoria Zieger, Peter Koltay, Daniel Frejek and Sabrina Kartmann
Micromachines 2024, 15(6), 735; https://doi.org/10.3390/mi15060735 (registering DOI) - 31 May 2024
Abstract
Sorting and dispensing distinct numbers of cellular aggregates enables the creation of three-dimensional (3D) in vitro models that replicate in vivo tissues, such as tumor tissue, with realistic metabolic properties. One method for creating these models involves utilizing Drop-on-Demand (DoD) dispensing of individual [...] Read more.
Sorting and dispensing distinct numbers of cellular aggregates enables the creation of three-dimensional (3D) in vitro models that replicate in vivo tissues, such as tumor tissue, with realistic metabolic properties. One method for creating these models involves utilizing Drop-on-Demand (DoD) dispensing of individual Multicellular Spheroids (MCSs) according to material jetting processes. In the DoD approach, a droplet dispenser ejects droplets containing these MCSs. For the reliable printing of tissue models, the exact number of dispensed MCSs must be determined. Current systems are designed to detect MCSs in the nozzle region prior to the dispensing process. However, due to surface effects, in some cases the spheroids that are detected adhere to the nozzle and are not dispensed with the droplet as expected. In contrast, detection that is carried out only after the droplet has been ejected is not affected by this issue. This work presents a system that can detect micrometer-sized synthetic or biological particles within free-falling droplets with a volume of about 30 nanoliters. Different illumination modalities and detection algorithms were tested. For a glare point projection-based approach, detection accuracies of an average of 95% were achieved for polymer particles and MCF-7 spheroids with diameters above 75 μm. For smaller particles the detection accuracy was still in the range of 70%. An approach with diffuse white light illumination demonstrated an improvement for the detection of small opaque particles. Accuracies up to 96% were achieved using this concept. This makes the two demonstrated methods suitable for improving the accuracy and quality control of particle detection in droplets for Drop-on-Demand techniques and for bioprinting. Full article
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22 pages, 14417 KiB  
Article
Electroforming of Personalized Multi-Level and Free-Form Metal Parts Utilizing Fused Deposition Modeling-Manufactured Molds
by Hazem Hamed, Sayedmohammadali Aghili, Rolf Wüthrich and Jana D. Abou-Ziki
Micromachines 2024, 15(6), 734; https://doi.org/10.3390/mi15060734 (registering DOI) - 31 May 2024
Abstract
Adapting to the growing demand for personalized, small-batch manufacturing, this study explores the development of additively manufactured molds for electroforming personalized metal parts. The approach integrates novel multi-level mold design and fabrication techniques, along with the experimental procedures for the electroforming process. This [...] Read more.
Adapting to the growing demand for personalized, small-batch manufacturing, this study explores the development of additively manufactured molds for electroforming personalized metal parts. The approach integrates novel multi-level mold design and fabrication techniques, along with the experimental procedures for the electroforming process. This work outlines design considerations and guidelines for effective electroforming in additively manufactured molds, successfully demonstrating the production of composite metal components with multi-level and free-form geometries. By emphasizing cost efficiency and part quality, particularly for limited-thickness metal components, the developed technique offers distinct advantages over existing metal additive manufacturing methods. This approach establishes itself as a flexible and durable method for metal additive manufacturing, expanding the scope of electroforming beyond traditional constraints such as thin-walled hollow structures, 2D components, and nanoscale applications. Full article
(This article belongs to the Special Issue Current Trends in Miniature Devices: Design, Fabrication, and Applications)
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12 pages, 5206 KiB  
Article
Ultrafast Detection of Arsenic Using Carbon-Fiber Microelectrodes and Fast-Scan Cyclic Voltammetry
by Noel Manring, Miriam Strini, Gene Koifman, Jonathan Xavier, Jessica L. Smeltz and Pavithra Pathirathna
Micromachines 2024, 15(6), 733; https://doi.org/10.3390/mi15060733 (registering DOI) - 31 May 2024
Abstract
Arsenic contamination poses a significant public health risk worldwide, with chronic exposure leading to various health issues. Detecting and monitoring arsenic exposure accurately remains challenging, necessitating the development of sensitive detection methods. In this study, we introduce a novel approach using fast-scan cyclic [...] Read more.
Arsenic contamination poses a significant public health risk worldwide, with chronic exposure leading to various health issues. Detecting and monitoring arsenic exposure accurately remains challenging, necessitating the development of sensitive detection methods. In this study, we introduce a novel approach using fast-scan cyclic voltammetry (FSCV) coupled with carbon-fiber microelectrodes (CFMs) for the electrochemical detection of As3+. Through an in-depth pH study using tris buffer, we optimized the electrochemical parameters for both acidic and basic media. Our sensor demonstrated high selectivity, distinguishing the As3+ signal from those of As5+ and other potential interferents under ambient conditions. We achieved a limit of detection (LOD) of 0.5 μM (37.46 ppb) and a sensitivity of 2.292 nA/μM for bare CFMs. Microscopic data confirmed the sensor’s stability at lower, physiologically relevant concentrations. Additionally, using our previously reported double-bore CFMs, we simultaneously detected As3+-Cu2+ and As3+-Cd2+ in tris buffer, enhancing the LOD of As3+ to 0.2 μM (14.98 ppb). To our knowledge, this is the first study to use CFMs for the rapid and selective detection of As3+ via FSCV. Our sensor’s ability to distinguish As3+ from As5+ in a physiologically relevant pH environment showcases its potential for future in vivo studies. Full article
(This article belongs to the Special Issue Advances in Voltammetric Sensors)
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16 pages, 3653 KiB  
Article
The Profile of Network Spontaneous Activity and Functional Organization Interplay in Hierarchically Connected Modular Neural Networks In Vitro
by Yana Pigareva, Arseniy Gladkov, Vladimir Kolpakov, Victor B. Kazantsev, Irina Mukhina and Alexey Pimashkin
Micromachines 2024, 15(6), 732; https://doi.org/10.3390/mi15060732 (registering DOI) - 31 May 2024
Abstract
Modern microtechnology methods are widely used to create neural networks on a chip with a connection architecture demonstrating properties of modularity and hierarchy similar to brain networks. Such in vitro networks serve as a valuable model for studying the interplay of functional architecture [...] Read more.
Modern microtechnology methods are widely used to create neural networks on a chip with a connection architecture demonstrating properties of modularity and hierarchy similar to brain networks. Such in vitro networks serve as a valuable model for studying the interplay of functional architecture within modules, their activity, and the effectiveness of inter-module interaction. In this study, we use a two-chamber microfluidic platform to investigate functional connectivity and global activity in hierarchically connected modular neural networks. We found that the strength of functional connections within the module and the profile of network spontaneous activity determine the effectiveness of inter-modular interaction and integration activity in the network. The direction of intermodular activity propagation configures the different densities of inhibitory synapses in the network. The developed microfluidic platform holds the potential to explore function-structure relationships and efficient information processing in two- or multilayer neural networks, in both healthy and pathological states. Full article
(This article belongs to the Section B：Biology and Biomedicine)
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16 pages, 5600 KiB  
Article
Study on Structural Design and Motion Characteristics of Magnetic Helical Soft Microrobots with Drug-Carrying Function
by Qian Gao, Tingting Lin, Ziteng Liu, Zebiao Chen, Zidong Chen, Cheng Hu and Teng Shen
Micromachines 2024, 15(6), 731; https://doi.org/10.3390/mi15060731 (registering DOI) - 31 May 2024
Abstract
Magnetic soft microrobots have a wide range of applications in targeted drug therapy, cell manipulation, and other aspects. Currently, the research on magnetic soft microrobots is still in the exploratory stage, and most of the research focuses on a single helical structure, which [...] Read more.
Magnetic soft microrobots have a wide range of applications in targeted drug therapy, cell manipulation, and other aspects. Currently, the research on magnetic soft microrobots is still in the exploratory stage, and most of the research focuses on a single helical structure, which has limited space to perform drug-carrying tasks efficiently and cannot satisfy specific medical goals in terms of propulsion speed. Therefore, balancing the motion speed and drug-carrying performance is a current challenge to overcome. In this paper, a magnetically controlled cone-helix soft microrobot structure with a drug-carrying function is proposed, its helical propulsion mechanism is deduced, a dynamical model is constructed, and the microrobot structure is prepared using femtosecond laser two-photon polymerization three-dimensional printing technology for magnetic drive control experiments. The results show that under the premise of ensuring sufficient drug-carrying space, the microrobot structure proposed in this paper can realize helical propulsion quickly and stably, and the speed of motion increases with increases in the frequency of the rotating magnetic field. The microrobot with a larger cavity diameter and a larger helical pitch exhibits faster rotary advancement speed, while the microrobot with a smaller helical height and a smaller helical cone angle outperforms other structures with the same feature sizes. The microrobot with a cone angle of 0.2 rad, a helical pitch of 100 µm, a helical height of 220 µm, and a cavity diameter of 80 µm achieves a maximum longitudinal motion speed of 390 µm/s. Full article
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21 pages, 19375 KiB  
Article
Finite Element Analysis of Plastic Deformation in Ultrasonic Vibration Superimposed Face Milling of Steel X46Cr13
by Richard Börner, Philipp Steinert, Nithin Kumar Bandaru and Andreas Schubert
Micromachines 2024, 15(6), 730; https://doi.org/10.3390/mi15060730 (registering DOI) - 30 May 2024
Abstract
Ultrasonic vibration superimposed face milling enables the generation of predefined surface microstructures by an appropriate setting of the process parameters. The geometrical reproducibility of the surface characteristics depends strongly on the plastic material deformation. Thus, the precise prediction of the emerging surface microstructures [...] Read more.
Ultrasonic vibration superimposed face milling enables the generation of predefined surface microstructures by an appropriate setting of the process parameters. The geometrical reproducibility of the surface characteristics depends strongly on the plastic material deformation. Thus, the precise prediction of the emerging surface microstructures using kinematic simulation models is limited, because they ignore the influence of material flow. Consequently, the effects of plastic as well as elastic deformation are investigated in depth by finite element analysis. Microstructured surfaces resulting from these numerical models are characterized quantitatively by areal surface parameters and compared to those from a kinematical simulation and a real machined surface. A high degree of conformity between the values of the simulated surfaces and the measured values is achieved, particularly with regard to material distribution. Deficits in predictability exist primarily due to deviations in plastic deformation. Future research can address this, either by implementing a temperature consideration or adapting specific modeling aspects like an adjusted depth of cut or experimental validated material parameters. Full article
(This article belongs to the Special Issue Micro-Manufacturing and Applications, 4th Edition: Materials and High-Precision Micromachining)
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20 pages, 14972 KiB  
Article
A Compact MIMO Antenna Based on Modal Analysis for 5G Wireless Applications
by Parveez Shariff Bhadravathi Ghouse, Deepthi Mariam John, Pallavi R. Mane, Debdeep Saha, Supreetha Balavalikar Shivarama, Sameena Pathan, Bharathi Raghavendra Bhat, Shweta Vincent and Tanweer Ali
Micromachines 2024, 15(6), 729; https://doi.org/10.3390/mi15060729 (registering DOI) - 30 May 2024
Abstract
This article presents a planar, non-angular, series-fed, dual-element dipole array MIMO antenna operating at 28 GHz with the metasurface-based isolation improvement technique. The initial design is a single-element antenna with a dual dipole array which is series-fed. These dipole elements are non-uniform in [...] Read more.
This article presents a planar, non-angular, series-fed, dual-element dipole array MIMO antenna operating at 28 GHz with the metasurface-based isolation improvement technique. The initial design is a single-element antenna with a dual dipole array which is series-fed. These dipole elements are non-uniform in shape and distance. This dipole antenna results in end-fire radiation. The dipole antenna excites the J1 mode for its operation. Further, with the view to improve channel capacity, the dipole array expands the antenna to a three-element MIMO antenna. In the MIMO antenna structure, the sum of the J1, J2, and J3 modes is excited, causing resonance at 28 GHz. This article also proposes a metasurface structure with wide stopband characteristics at 28 GHz for isolation improvement. The metasurface is composed of rectangle-shaped structures. The defected ground and metasurface structure combination suppresses the surface wave coupling among the MIMO elements. The proposed antenna results in a bandwidth ranging from 26.7 to 29.6 GHz with isolation improvement greater than 21 dB and a gain of 6.3 dBi. The antenna is validated with the diversity parameters of envelope correlation coefficient, diversity gain, and channel capacity loss. Full article
(This article belongs to the Special Issue Advanced Antenna System: Structural Analysis, Design and Application)
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13 pages, 1455 KiB  
Article
A 60 GHz Slotted Array Horn Antenna for Radar Sensing Applications in Future Global Industrial Scenarios
by Binyi Ma, Jing Li, Yu Chen, Yuheng Si, Hongyan Gao, Qiannan Wu and Mengwei Li
Micromachines 2024, 15(6), 728; https://doi.org/10.3390/mi15060728 (registering DOI) - 30 May 2024
Abstract
This paper presents the design of a 60 GHz millimeter-wave (MMW) slot array horn antenna based on the substrate-integrated waveguide (SIW) structure. The novelty of this device resides in the achievement of a broad impedance bandwidth and high gain performance by meticulously engineering [...] Read more.
This paper presents the design of a 60 GHz millimeter-wave (MMW) slot array horn antenna based on the substrate-integrated waveguide (SIW) structure. The novelty of this device resides in the achievement of a broad impedance bandwidth and high gain performance by meticulously engineering the radiation band structure and slot array. The antenna demonstrates an impressive impedance bandwidth of 14.96 GHz (24.93%), accompanied by a remarkable maximum reflection coefficient of −39.47 dB. Furthermore, the antenna boasts a gain of 10.01 dBi, showcasing its outstanding performance as a high-frequency antenna with a wide bandwidth and high gain. To validate its capabilities, we fabricated and experimentally characterized a prototype of the antenna using a probe test structure. The measurement results closely align with the simulation results, affirming the suitability of the designed antenna for radar sensing applications in future global industrial scenarios. Full article
(This article belongs to the Special Issue Recent Advances in Electromagnetic Devices)
18 pages, 3622 KiB  
Article
Responsiveness and Precision of Digital IMUs under Linear and Curvilinear Motion Conditions for Local Navigation and Positioning in Advanced Smart Mobility
by Luciano Chiominto, Emanuela Natale, Giulio D’Emilia, Sante Alessandro Grieco, Andrea Prato, Alessio Facello and Alessandro Schiavi
Micromachines 2024, 15(6), 727; https://doi.org/10.3390/mi15060727 (registering DOI) - 30 May 2024
Abstract
Abstract: Sensors based on MEMS technology, in particular Inertial Measurement Units (IMUs), when installed on vehicles, provide a real-time full estimation of vehicles’ state vector (e.g., position, velocity, yaw angle, angular rate, acceleration), which is required for the planning and control of cars’ [...] Read more.
Abstract: Sensors based on MEMS technology, in particular Inertial Measurement Units (IMUs), when installed on vehicles, provide a real-time full estimation of vehicles’ state vector (e.g., position, velocity, yaw angle, angular rate, acceleration), which is required for the planning and control of cars’ trajectories, as well as managing the in-car local navigation and positioning tasks. Moreover, data provided by the IMUs, integrated with the data of multiple inputs from other sensing systems (such as Lidar, cameras, and GPS) within the vehicle, and with the surrounding information exchanged in real time (vehicle to vehicle, vehicle to infrastructure, or vehicle to other entities), can be exploited to actualize the full implementation of “smart mobility” on a large scale. On the other hand, “smart mobility” (which is expected to improve road safety, reduce traffic congestion and environmental burden, and enhance the sustainability of mobility as a whole), to be safe and functional on a large scale, should be supported by highly accurate and trustworthy technologies based on precise and reliable sensors and systems. It is known that the accuracy and precision of data supplied by appropriately in-lab-calibrated IMUs (with respect to the primary or secondary standard in order to provide traceability to the International System of Units) allow guaranteeing high quality, reliable information managed by processing systems, since they are reproducible, repeatable, and traceable. In this work, the effective responsiveness and the related precision of digital IMUs, under sinusoidal linear and curvilinear motion conditions at 5 Hz, 10 Hz, and 20 Hz, are investigated on the basis of metrological approaches in laboratory standard conditions only. As a first step, in-lab calibrations allow one to reduce the variables of uncontrolled boundary conditions (e.g., occurring in vehicles in on-site tests) in order to identify the IMUs’ sensitivity in a stable and reproducible environment. For this purpose, a new calibration system, based on an oscillating rotating table was developed to reproduce the dynamic conditions of use in the field, and the results are compared with calibration data obtained on linear calibration benches. Full article
(This article belongs to the Special Issue MEMS Accelerometers: Design, Applications and Characterization, 2nd Edition)
26 pages, 7311 KiB  
Article
Reducing Off-State and Leakage Currents by Dielectric Permittivity-Graded Stacked Gate Oxides on Trigate FinFETs: A TCAD Study
by Alper Ülkü, Esin Uçar, Ramis Berkay Serin, Rifat Kaçar, Murat Artuç, Ebru Menşur and Ahmet Yavuz Oral
Micromachines 2024, 15(6), 726; https://doi.org/10.3390/mi15060726 (registering DOI) - 30 May 2024
Abstract
Since its invention in the 1960s, one of the most significant evolutions of metal-oxide semiconductor field effect transistors (MOSFETs) would be the 3D version that makes the semiconducting channel vertically wrapped by conformal gate electrodes, also recognized as FinFET. During recent decades, the [...] Read more.
Since its invention in the 1960s, one of the most significant evolutions of metal-oxide semiconductor field effect transistors (MOSFETs) would be the 3D version that makes the semiconducting channel vertically wrapped by conformal gate electrodes, also recognized as FinFET. During recent decades, the width of fin (Wfin) and the neighboring gate oxide width (tox) in FinFETs has shrunk from about 150 nm to a few nanometers. However, both widths seem to have been leveling off in recent years, owing to the limitation of lithography precision. Here, we show that by adapting the Penn model and Maxwell–Garnett mixing formula for a dielectric constant (κ) calculation for nanolaminate structures, FinFETs with two- and three-stage κ-graded stacked combinations of gate dielectrics with SiO2, Si3N4, Al2O3, HfO2, La2O3, and TiO2 perform better against the same structures with their single-layer dielectrics counterparts. Based on this, FinFETs simulated with κ-graded gate oxides achieved an off-state drain current (IOFF) reduced down to 6.45 × 10−15 A for the Al2O3: TiO2 combination and a gate leakage current (IG) reaching down to 2.04 × 10−11 A for the Al2O3: HfO2: La2O3 combination. While our findings push the individual dielectric laminates to the sub 1 nm limit, the effects of dielectric permittivity matching and κ-grading for gate oxides remain to have the potential to shed light on the next generation of nanoelectronics for higher integration and lower power consumption opportunities. Full article
(This article belongs to the Special Issue Multifunctional-Nanomaterials-Based Semiconductor Devices and Sensors)
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15 pages, 6089 KiB  
Article
Optical Microneedle–Lens Array for Selective Photothermolysis
by Jongho Park, Kotaro Shobayashi and Beomjoon Kim
Micromachines 2024, 15(6), 725; https://doi.org/10.3390/mi15060725 (registering DOI) - 30 May 2024
Viewed by 82
Abstract
Photothermolysis is the process that converts radiation energy into thermal energy, which results in the destruction of surrounding tissues or cells through thermal diffusion. Laser therapy that is based on photothermolysis has been a widely used treatment for various skin diseases such as [...] Read more.
Photothermolysis is the process that converts radiation energy into thermal energy, which results in the destruction of surrounding tissues or cells through thermal diffusion. Laser therapy that is based on photothermolysis has been a widely used treatment for various skin diseases such as skin cancers and port-wine stains. It offers several benefits such as non-invasiveness and selective treatment. However, the use of light, e.g., laser, for safe and effective photothermolysis becomes challenging due to the limited penetration of light into skin tissue as well as the presence of melanin, which absorbs this light. To solve the current issues, we propose an optical microneedle–lens array (OMLA) coated with gold in this work to directly deliver light to targeted skin layers without being absorbed by surrounding tissues as well as melanin, which results in the improvement of the efficiency of photothermal therapy. We developed a novel fabrication method, frame-guided micromolding, to prepare the OMLA by assembling two negative molds with simultaneous alignment. In addition, evaluations of the optical and heat transfer characteristics of the OMLA were performed. We expect our developed OMLA to play a crucial role in realizing more effective laser therapy by allowing the precise delivery of photons to the target area. Full article
(This article belongs to the Special Issue Current Trends in Microneedles: Design, Fabrication 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 (registering DOI) - 30 May 2024
Viewed by 80
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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