Micromachines

36 pages, 21470 KiB

Open AccessArticle

Development of GaN-Based, 6.6 kW, 450 V, Bi-Directional On-Board Charger with Integrated 1 kW, 12 V Auxiliary DC-DC Converter with High Power Density

by Alessandro Reali, Alessio Alemanno, Fabio Ronchi, Carlo Rossi and Corrado Florian

Micromachines 2024, 15(12), 1470; https://doi.org/10.3390/mi15121470 - 2 Dec 2024

Abstract

Automotive-grade GaN power switches have recently been made available in the market from a growing number of semiconductor suppliers. The exploitation of this technology enables the development of very efficient power converters operating at much higher switching frequencies with respect to components implemented [...] Read more.

Automotive-grade GaN power switches have recently been made available in the market from a growing number of semiconductor suppliers. The exploitation of this technology enables the development of very efficient power converters operating at much higher switching frequencies with respect to components implemented with silicon power devices. Thus, a new generation of automotive power components with an increased power density is expected to replace silicon-based products in the development of higher-performance electric and hybrid vehicles. 650 V GaN-on-silicon power switches are particularly suitable for the development of 3–7 kW on-board battery chargers (OBCs) for electric cars and motorcycles with a 400 V nominal voltage battery pack. This paper describes the design and implementation of a 6.6 kW OBC for electric vehicles using automotive-grade, 650 V, 25 mΩ, discrete GaN switches. The OBC allows bi-directional power flow, since it is composed of a bridgeless, interleaved, totem-pole PFC AC/DC active front end, followed by a dual active bridge (DAB) DC-DC converter. The OBC can operate from a single-phase 90–264 Vrms AC grid to a 200–450 V high-voltage (HV) battery and also integrates an auxiliary 1 kW DC-DC converter to connect the HV battery to the 12 V battery of the vehicle. The auxiliary DC-DC converter is a center-tapped phase-shifted full-bridge (PSFB) converter with synchronous rectification. At the low-voltage side of the auxiliary converter, 100 V GaN power switches are used. The entire OBC is liquid-cooled. The first prototype of the OBC exhibited a 96% efficiency and 2.2 kW/L power density (including the cooling system) at a 60 °C ambient temperature. Full article

(This article belongs to the Special Issue III-Nitride Materials in Electronic and Photonic Devices)

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26 pages, 14510 KiB

Open AccessArticle

Assessment of Surface Integrity in Precision Electrical Discharge Machining of HSS EN HS6-5-2C

by Ľuboslav Straka, Ján Piteľ and Ivan Čorný

Micromachines 2024, 15(12), 1469; https://doi.org/10.3390/mi15121469 - 1 Dec 2024

Abstract

The integrity of the machined surface in precision wire electrical discharge machining (WEDM) of electrically conductive materials is one of the most important quality indicators. The integrity parameters of the machined surface are primarily monitored in terms of micro and macro geometry parameters. [...] Read more.

The integrity of the machined surface in precision wire electrical discharge machining (WEDM) of electrically conductive materials is one of the most important quality indicators. The integrity parameters of the machined surface are primarily monitored in terms of micro and macro geometry parameters. This paper presents the results obtained as a part of experimental research aimed at evaluating surface crack density (SCD) when machining EN HS6-5-2C using WEDM technology. The aim was to find a combination of main technological parameters (MTP) in order to minimize the qualitative indicators SCD and Ra of the eroded surface. The results of experimental research within the framework of the evaluation of SCD and Ra indicators were processed using the Taguchi method. The integrity of the eroded surface was examined by scanning digital microscope (SDM) after application of full and multiple offset cuts with an AC Brass LP 1000 brass wire electrode. Based on the experimental measurements performed, significant facts were discovered. It was found that the largest surface integrity defects are present after the application of full cuts and the first two offset cuts. At the same time, it was found that lower values of the SCD parameter in WEDM of EN HS6-5-2C steel were recorded at thicknesses above 130.0 mm. The SCD parameter was also confronted with the Ra parameter, and it was found that they are significantly influenced by MTP. The higher value of the peak current I (19 A) and the longer duration of the discharge t_on (32 μs) result in an increase in the value of the SCD parameter from 0.005 μm·μm⁻² to 0.0256 μm·μm⁻². The resulting solutions are mathematical regression models (MRM), which allow the prediction of both monitored qualitative indicators with respect to their minimization. Full article

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

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13 pages, 1889 KiB

Open AccessArticle

Critical Design and Operating Parameters of Active Waveguide Bragg Gratings for Laser Performance

by Ángel Sanz-Felipe and Juan A. Vallés

Micromachines 2024, 15(12), 1468; https://doi.org/10.3390/mi15121468 - 30 Nov 2024

Abstract

Active waveguide Bragg gratings (AWBGs) are promising photonic structures that combine the very efficient reflective properties of a Bragg grating with the power amplification character of rare earths. This combination may lead to a potential monolithic laser under the proper conditions. However, the [...] Read more.

Active waveguide Bragg gratings (AWBGs) are promising photonic structures that combine the very efficient reflective properties of a Bragg grating with the power amplification character of rare earths. This combination may lead to a potential monolithic laser under the proper conditions. However, the photonic response of these structures highly depends on the grating design and operating parameters, so modeling its response for their laser performance is a must. In this work, a numerical method is employed to calculate the optical power propagation along an Er/Yb-codoped integrated AWBG. A complete database of the AWBG response as a function of the most relevant operational parameters is obtained. As a result, the critical values of each design and operating parameter to achieve its laser performance have been determined, which represents very useful information for further experimental design, optimization, and fabrication of these photonic structures. Full article

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

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10 pages, 9944 KiB

Open AccessArticle

Optimizing Stretchability and Electrical Stability in Bilayer-Structured Flexible Liquid Metal Composite Electrodes

by Min-Gi Kim, Kun-Woo Nam, Won-Jin Kim and Sung-Hoon Park

Micromachines 2024, 15(12), 1467; https://doi.org/10.3390/mi15121467 - 30 Nov 2024

Abstract

Gallium-based liquid metals remain in a liquid state at room temperature and exhibit excellent electrical and thermal conductivities, low viscosity, and low toxicity, making them ideal for creating highly stretchable and conductive composites suitable for flexible electronic devices. Despite these benefits, conventional single-layer [...] Read more.

Gallium-based liquid metals remain in a liquid state at room temperature and exhibit excellent electrical and thermal conductivities, low viscosity, and low toxicity, making them ideal for creating highly stretchable and conductive composites suitable for flexible electronic devices. Despite these benefits, conventional single-layer liquid metal composites face challenges, such as liquid metal leakage during deformation (e.g., stretching or bending) and limited elongation due to incomplete integration of the liquid metal within the elastomer matrix. To address these limitations, we introduced a bilayer structure into liquid metal composites, comprising a lower polydimethylsiloxane (PDMS) layer and an upper PDMS-liquid metal mixed layer. In the mixed layer, the liquid metal precipitates, forming a conductive network spanning both layers. This bilayer composite structure demonstrated significantly improved stretchability and elongation compared to pure PDMS or single-layer composites. Additionally, by adjusting the size and content of the liquid metal particles, we optimized the composite’s mechanical and electrical properties. Under optimal conditions, spherical liquid metal particles deform into elliptical shapes under tensile stress, increasing conductive pathways and reducing electrical resistance. The combined effects of the bilayer structure and particle shape deformation enhanced the composite’s stretchability and elongation, supporting its potential for flexible electronics applications. Full article

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8 pages, 448 KiB

Open AccessArticle

Quantitative Analysis of the Effect of Fluorescent Labels on DNA Strand Displacement Reaction

by Masato Toyonari, Kaori Aso and Takashi Nakakuki

Micromachines 2024, 15(12), 1466; https://doi.org/10.3390/mi15121466 - 30 Nov 2024

Abstract

DNA chemical reaction networks can perform complex information processing through careful design of reaction kinetics, which involves the reaction network structure, rate constants, and initial concentrations. The toehold-mediated strand displacement reaction (TMSDR) is a key mechanism in creating DNA circuits, offering a rational [...] Read more.

DNA chemical reaction networks can perform complex information processing through careful design of reaction kinetics, which involves the reaction network structure, rate constants, and initial concentrations. The toehold-mediated strand displacement reaction (TMSDR) is a key mechanism in creating DNA circuits, offering a rational design approach by integrating individually designed TMSDRs. Tools such as VisualDSD and NUPACK facilitate the efficient design of these systems by allowing precise tuning of reaction parameters. However, discrepancies between simulated and experimental results can occur, often due to the modification of reporter molecules. Recently, fluorophore dyes and quenchers were found to significantly impact the dynamics of irreversible TMSDRs, altering them by nearly two orders of magnitude. The impact on reaction dynamics varies with the modification site of these reporters. This study examines the mechanisms of reporter modifications affecting reversible TMSDRs, influencing transient and steady-state characteristics. This is crucial for DNA circuit design, which integrates reversible and irreversible TMSDRs. Our findings indicate that modifying fluorescent dye and quencher an appropriate distance apart (e.g., toehold length) can minimize adverse effects on the DNA reaction dynamics while ensuring effective FRET, therefore improving the accuracy of experimental verification for DNA reaction systems. Full article

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

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14 pages, 5762 KiB

Open AccessArticle

Application of Solution-Processed High-Entropy Metal Oxide Dielectric Layers with High Dielectric Constant and Wide Bandgap in Thin-Film Transistors

by Jun Liu, Xin Xiong, Han Li, Xiangchen Huang, Yajun Wang, Yifa Sheng, Zhihao Liang, Rihui Yao, Honglong Ning and Xiaoqin Wei

Micromachines 2024, 15(12), 1465; https://doi.org/10.3390/mi15121465 - 30 Nov 2024

Abstract

High-k metal oxides are gradually replacing the traditional SiO₂ dielectric layer in the new generation of electronic devices. In this paper, we report the production of five-element high entropy metal oxides (HEMOs) dielectric films by solution method and analyzed the role of [...] Read more.

High-k metal oxides are gradually replacing the traditional SiO₂ dielectric layer in the new generation of electronic devices. In this paper, we report the production of five-element high entropy metal oxides (HEMOs) dielectric films by solution method and analyzed the role of each metal oxide in the system by characterizing the film properties. On this basis, we found optimal combination of (AlGaTiYZr)O_x with the best dielectric properties, exhibiting a low leakage current of 1.2 × 10⁻⁸ A/cm² @1 MV/cm and a high dielectric constant, while the film’s visible transmittance is more than 90%. Based on the results of factor analysis, we increased the dielectric constant up to 52.74 by increasing the proportion of TiO₂ in the HEMOs and maintained a large optical bandgap (>5 eV). We prepared thin film transistors (TFTs) based on an (AlGaTiYZr)O_x dielectric layer and an InGaZnO_x (IGZO) active layer, and the devices exhibit a mobility of 18.2 cm²/Vs, a threshold voltage (V_th) of −0.203 V, and an subthreshold swing (SS) of 0.288 V/dec, along with a minimal hysteresis, which suggests a good prospect of applying HEMOs to TFTs. It can be seen that the HEMOs dielectric films prepared based on the solution method can combine the advantages of various high-k dielectrics to obtain better film properties. Moreover, HEMOs dielectric films have the advantages of simple processing, low-temperature preparation, and low cost, which are expected to be widely used as dielectric layers in new flexible, transparent, and high-performance electronic devices in the future. Full article

(This article belongs to the Special Issue Thin Film Microelectronic Devices and Circuits)

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18 pages, 2284 KiB

Open AccessCommunication

Intestinal Cells-on-Chip for Permeability Studies

by Marit Keuper-Navis, Hossein Eslami Amirabadi, Joanne Donkers, Markus Walles, Birk Poller, Bo Heming, Lisanne Pieters, Bjorn de Wagenaar, Adam Myszczyszyn, Theo Sinnige, Bart Spee, Rosalinde Masereeuw and Evita van de Steeg

Micromachines 2024, 15(12), 1464; https://doi.org/10.3390/mi15121464 - 30 Nov 2024

Abstract

Background: To accurately measure permeability of compounds in the intestine, there is a need for preclinical in vitro models that accurately represent the specificity, integrity and complexity of the human small intestinal barrier. Intestine-on-chip systems hold considerable promise as testing platforms, but several [...] Read more.

Background: To accurately measure permeability of compounds in the intestine, there is a need for preclinical in vitro models that accurately represent the specificity, integrity and complexity of the human small intestinal barrier. Intestine-on-chip systems hold considerable promise as testing platforms, but several characteristics still require optimization and further development. Methods: An established intestine-on-chip model for tissue explants was adopted for intestinal cell monolayer culture. A 3D-printed culture disc was designed to allow cell culture in static conditions and subsequent permeability studies in a dynamic environment. Membrane characteristics and standardized read-outs were investigated and compared to traditional permeability studies under static conditions. Results: By starting cultures outside the chip in conventional wells plates, the new cell disc design could support accurate cell monolayer formation for both Caco-2 and human enteroids. When transferred to the chip with laminar flow, there was accurate detection of barrier integrity (FD4 and Cascade Blue) and permeability (atenolol/antipyrine). Both flow and membrane characteristics had a significant impact on permeability outcomes. Conclusions: This novel intestinal cell-on-chip system offers large flexibility for intestinal permeability studies, although it still requires validation with more compounds to reveal its full potential. Full article

(This article belongs to the Special Issue Recent Advances in Lab-on-a-Chip and Their Biomedical Applications)

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29 pages, 10952 KiB

Open AccessReview

Resolution Enhancement Strategies in Photoacoustic Microscopy: A Comprehensive Review

by Jinying Zhang, Yifan Shi, Yexiaotong Zhang, Haoran Liu, Shihao Li and Linglu Liu

Micromachines 2024, 15(12), 1463; https://doi.org/10.3390/mi15121463 - 30 Nov 2024

Abstract

Photoacoustic imaging has emerged as a promising modality for medical imaging since its introduction. Photoacoustic microscopy (PAM), which is based on the photoacoustic effect, combines the advantages of both optical and acoustic imaging modalities. PAM facilitates high-sensitivity, high-resolution, non-contact, and non-invasive imaging by [...] Read more.

Photoacoustic imaging has emerged as a promising modality for medical imaging since its introduction. Photoacoustic microscopy (PAM), which is based on the photoacoustic effect, combines the advantages of both optical and acoustic imaging modalities. PAM facilitates high-sensitivity, high-resolution, non-contact, and non-invasive imaging by employing optical absorption as its primary contrast mechanism. The ability of PAM to specifically image parameters such as blood oxygenation and melanin content makes it a valuable addition to the suite of modern biomedical imaging techniques. This review aims to provide a comprehensive overview of the diverse technical approaches and methods employed by researchers to enhance the resolution of photoacoustic microscopy. Firstly, the fundamental principles of the photoacoustic effect and photoacoustic imaging will be presented. Subsequently, resolution enhancement methods for both acoustic-resolution photoacoustic microscopy (AR-PAM) and optical-resolution photoacoustic microscopy (OR-PAM) will be discussed independently. Finally, the aforementioned resolution enhancement methods for photoacoustic microscopy will be critically evaluated, and the current challenges and future prospects of this technology will be summarized. Full article

(This article belongs to the Special Issue Photoacoustic-Based Sensing Systems: Advances, Applications, and Innovative Measurement Strategies)

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14 pages, 4290 KiB

Open AccessArticle

A Thermal Cycler Based on Magnetic Induction Heating and Anti-Freezing Water Cooling for Rapid PCR

by Yaping Xie, Qin Jiang, Chang Chang, Xin Zhao, Haochen Yong, Xingxing Ke and Zhigang Wu

Micromachines 2024, 15(12), 1462; https://doi.org/10.3390/mi15121462 - 30 Nov 2024

Abstract

Distinguished by its exceptional sensitivity and specificity, Polymerase Chain Reaction (PCR) is a pivotal technology for pathogen detection. However, traditional PCR instruments that employ thermoelectric cooling (TEC) are often constrained by cost, efficiency, and performance variability resulting from the fluctuations in ambient temperature. [...] Read more.

Distinguished by its exceptional sensitivity and specificity, Polymerase Chain Reaction (PCR) is a pivotal technology for pathogen detection. However, traditional PCR instruments that employ thermoelectric cooling (TEC) are often constrained by cost, efficiency, and performance variability resulting from the fluctuations in ambient temperature. Here, we present a thermal cycler that utilizes electromagnetic induction heating at 50 kHz and anti-freezing water cooling with a velocity of 0.06 m/s to facilitate rapid heating and cooling of the PCR reaction chamber, significantly enhancing heat transfer efficiency. A multi-physics theoretical heat transfer model, developed using the digital twin approach, enables precise temperature control through advanced algorithms. Experimental results reveal average heating and cooling rates of 14.92 °C/s and 13.39 °C/s, respectively, significantly exceeding those of conventional methods. Compared to commercial PCR instruments, the proposed system further optimizes cost, efficiency, and practicality. Finally, PCR experiments were successfully performed using cDNA (Hepatitis B virus) at various concentrations. Full article

(This article belongs to the Special Issue Feature Papers of Micromachines in Biology and Biomedicine 2024)

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20 pages, 5658 KiB

Open AccessArticle

Microelectromechanical System Resonant Devices: A Guide for Design, Modeling and Testing

by Carolina Viola, Davide Pavesi, Lichen Weng, Giorgio Gobat, Federico Maspero and Valentina Zega

Micromachines 2024, 15(12), 1461; https://doi.org/10.3390/mi15121461 - 30 Nov 2024

Abstract

Microelectromechanical systems (MEMSs) are attracting increasing interest from the scientific community for the large variety of possible applications and for the continuous request from the market to improve performances, while keeping small dimensions and reduced costs. To be able to simulate a priori [...] Read more.

Microelectromechanical systems (MEMSs) are attracting increasing interest from the scientific community for the large variety of possible applications and for the continuous request from the market to improve performances, while keeping small dimensions and reduced costs. To be able to simulate a priori and in real time the dynamic response of resonant devices is then crucial to guide the mechanical design and to support the MEMSs industry. In this work, we propose a simplified modeling procedure able to reproduce the nonlinear dynamics of MEMS resonant devices of arbitrary geometry. We validate it through the fabrication and testing of a cantilever beam resonator functioning in the nonlinear regime and we employ it to design a ring resonator working in the linear regime. Despite the uncertainties of a fabrication process available in the university facility, we demonstrate the predictability of the model and the effectiveness of the proposed design procedure. The satisfactory agreement between numerical predictions and experimental data proves indeed the proposed a priori design tool based on reduced-order numerical models and opens the way to its practical applications in the MEMS industry. Full article

(This article belongs to the Special Issue New Advances, Methods, and Applications for Micro Inertial Sensors, 2nd Edition)

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10 pages, 3798 KiB

Open AccessArticle

750 V Breakdown in GaN Buffer on 200 mm SOI Substrates Using Reverse-Stepped Superlattice Layers

by Shuzhen You, Yilong Lei, Liang Wang, Xing Chen, Ting Zhou, Yi Wang, Junbo Wang, Tong Liu, Xiangdong Li, Shenglei Zhao, Jincheng Zhang and Yue Hao

Micromachines 2024, 15(12), 1460; https://doi.org/10.3390/mi15121460 - 30 Nov 2024

Abstract

In this work, we demonstrated the epitaxial growth of a gallium nitride (GaN) buffer structure on 200 mm SOI (silicon-on-insulator) substrates. This epitaxial layer is grown using a reversed stepped superlattice buffer (RSSL), which is composed of two superlattice (SL) layers with different [...] Read more.

In this work, we demonstrated the epitaxial growth of a gallium nitride (GaN) buffer structure on 200 mm SOI (silicon-on-insulator) substrates. This epitaxial layer is grown using a reversed stepped superlattice buffer (RSSL), which is composed of two superlattice (SL) layers with different Al component ratios stacked in reverse order. The upper layer, with a higher Al component ratio, introduces tensile stress instead of accumulative compressive stress and reduces the in situ curvature of the wafer, thereby achieving a well-controlled wafer bow ≤ ±50 µm for a 3.3 µm thick buffer. Thanks to the compliant SOI substrate, good crystal quality of the grown GaN layers was obtained, and a breakdown voltage of 750 V for a 3.3 µm thick GaN buffer was achieved. The breakdown field strength of the epitaxial GaN buffer layer on the SOI substrate is estimated to be ~2.27 MV/cm, which is higher than the breakdown field strength of the GaN-on-Si epitaxial buffer layer. This RSSL buffer also demonstrated a low buffer dispersion of less than 10%, which is good enough for the further processing of device and circuit fabrication. A D-mode GaN HEMT was fabricated on this RSSL buffer, which showed a good on/off ratio of ~10⁹ and a breakdown voltage of 450 V. Full article

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15 pages, 6126 KiB

Open AccessArticle

Investigations into Capillary Forces and Capillary Rise in a Three-Finger Microgripper and a Plate: Numerical Simulations and Experimental Validation

by Zhi Xu, Zenghua Fan, Jun Gao, Kun Zhang and Xiang Zhang

Micromachines 2024, 15(12), 1459; https://doi.org/10.3390/mi15121459 - 29 Nov 2024

Abstract

The assembly and position adjustment of micro-components have wide applications in micro-electromechanical systems, wafer packaging and biomedicine. However, current single-finger microgrippers only allow for the pickup and release of micro-components. In the present study, a three-finger capillary microgripper was developed to pick up, [...] Read more.

The assembly and position adjustment of micro-components have wide applications in micro-electromechanical systems, wafer packaging and biomedicine. However, current single-finger microgrippers only allow for the pickup and release of micro-components. In the present study, a three-finger capillary microgripper was developed to pick up, release and adjust the position of micro-components. The capillary force and the capillary rise generated by the capillary bridge were investigated by simulation and experiments. A simulation model was set up by the minimum energy method. On the established experimental platform, capillary forces were measured at different separation distances. When the volume was 0.9 μL, the maximum capillary forces gained from the capillary bridge model and experiments were 95.2 μN and 96.0 μN, respectively. A comparison of the capillary bridge models and the experimental results of the capillary forces demonstrate the reliability of the capillary bridge models. The influences of various parameters were investigated in detail by the capillary bridge model. The results demonstrate that when the side of the probe is hydrophilic, the variations in the capillary force with various factors such as separation distance and capillary bridge volume is non-monotonic, which is caused by the restriction of the probe edge. Full article

(This article belongs to the Special Issue Feature Papers of Micromachines in ‘Engineering and Technology’ 2024)

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19 pages, 5884 KiB

Open AccessArticle

Determination of the Minimum Uncut Chip Thickness of Ti-6Al-4V Titanium Alloy Based on Dead Metal Zone

by Yaohui Zheng, Wentao Huang, Yangyang Liu, Pengchao Duan and Yingxiao Wang

Micromachines 2024, 15(12), 1458; https://doi.org/10.3390/mi15121458 - 29 Nov 2024

Abstract

In Ti-6Al-4V titanium alloy micro-machining, since the uncut chip thickness (UCT) is comparable to the radius of the tool cutting edge, there exists a minimum uncut chip thickness (MUCT), and when the UCT is smaller than the MUCT, the plowing effect dominates the [...] Read more.

In Ti-6Al-4V titanium alloy micro-machining, since the uncut chip thickness (UCT) is comparable to the radius of the tool cutting edge, there exists a minimum uncut chip thickness (MUCT), and when the UCT is smaller than the MUCT, the plowing effect dominates the cutting process, which seriously affects the machined surface quality and tool life. Therefore, the reliable prediction of the MUCT is of great significance. This paper used Deform to establish an orthogonal cutting simulation model, studied the effect of the dead metal zone (DMZ) on the micro-cutting material flow, determined the DMZ range, and proposed a new method for determining the MUCT based on the DMZ. Cutting experiments were conducted to verify the accuracy of the simulation model firstly by cutting force, and then confirming the accuracy of the DMZ-based MUCT determination method through chip analysis and surface quality analysis. Finally, the effects of different cutting conditions on DMZ and MUCT were further investigated using the proposed DMZ-based MUCT determination method. The results show that the MUCT of Ti-6Al-4V titanium alloy is 4.833 μm for a tool cutting edge radius of 40μm and a cutting speed of 10 m/min. The DMZ boundary can be used as the boundary of micro-cutting plastic deformation, and the ratio of MUCT to cutting edge radius, h_p/r_n will gradually decrease with the increase in the tool cutting edge radius and the cutting speed. Full article

(This article belongs to the Section E：Engineering and Technology)

15 pages, 3702 KiB

Open AccessArticle

Impact of Conventional and Laser-Assisted Machining on the Microstructure and Mechanical Properties of Ti-Nb-Cr-V-Ni High-Entropy Alloy Fabricated with Directed Energy Deposition

by Ho-In Jeong, Osama Salem, Dong-Won Jung, Choon-Man Lee and Jeung-Hoon Lee

Micromachines 2024, 15(12), 1457; https://doi.org/10.3390/mi15121457 - 29 Nov 2024

Abstract

The high-entropy alloy (HEA) has recently attracted significant interest due to its novel alloy design concept and exceptional mechanical properties, which may exhibit either a single or multi-phase structure. Specifically, refractory high-entropy alloys (RHEA) composed of titanium, niobium, and nickel-based HEA demonstrate remarkable [...] Read more.

The high-entropy alloy (HEA) has recently attracted significant interest due to its novel alloy design concept and exceptional mechanical properties, which may exhibit either a single or multi-phase structure. Specifically, refractory high-entropy alloys (RHEA) composed of titanium, niobium, and nickel-based HEA demonstrate remarkable mechanical properties at elevated temperatures. Additive manufacturing (AM), specifically Direct Energy Deposition (DED), is efficient in fabricating high-entropy alloys (HEA) owing to its fast-cooling rates, which promote uniform microstructures and reduce defects. This study involved the fabrication of the Ti33Nb28Cr11V11Ni17 (Ti-Nb-Cr-V-Ni) RHEA utilizing DED. Additionally, the post-processing of the fabricated alloy is conducted using conventional machining (CM) and laser-assisted machining (LAM). The results indicate thermal conductivity and specific heat increased, whereas tensile strength reduced with rising temperature. Significant softening was observed above 800 °C, resulting in a considerable decrease in tensile strength. Furthermore, the LAM caused material softening and reduced the cutting force by 60.0% relative to CM. Furthermore, the chemical composition of Ti-Nb-Cr-V-Ni remained unaffected even after post-processing with CM and LAM. The research indicates that post-processing with LAM is essential for developing resilient RHEA for practical use. Full article

(This article belongs to the Special Issue Laser Micro/Nano Fabrication, Second Edition)

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25 pages, 11860 KiB

Open AccessReview

Recent Advances in Piezoelectric Compliant Devices for Ultrahigh-Precision Engineering

by Zeyi Wu, Zehao Wu, I-Ming Chen and Qingsong Xu

Micromachines 2024, 15(12), 1456; https://doi.org/10.3390/mi15121456 - 29 Nov 2024

Abstract

With advancements in small-scale research fields, precision manipulation has become crucial for interacting with small objects. As research progresses, the demand for higher precision in manipulation has led to the emergence of ultrahigh-precision engineering (UHPE), which exhibits significant potential for various applications. Traditional [...] Read more.

With advancements in small-scale research fields, precision manipulation has become crucial for interacting with small objects. As research progresses, the demand for higher precision in manipulation has led to the emergence of ultrahigh-precision engineering (UHPE), which exhibits significant potential for various applications. Traditional rigid-body manipulators suffer from issues like backlash and friction, limiting their effectiveness at smaller-scale applications. Smart materials, particularly piezoelectric materials, offer promising solutions with their rapid response and high resolution, making them ideal for creating efficient piezoelectric transducers. Meanwhile, compliant mechanisms, which use elastic deformation to transmit force and motion, eliminate inaccuracies induced by rigid-body mechanisms. Integrating piezoelectric transducers and compliant mechanisms into piezoelectric compliant devices enhances UHPE system performance. This paper reviews the recent advances in piezoelectric compliant devices. By focusing on the utilization of piezoelectric transducers and compliant mechanisms, their applications in perception, energy harvesting, and actuation have been surveyed, and future research suggestions are discussed. Full article

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14 pages, 2803 KiB

Open AccessArticle

Enhanced Drive Current in 10 nm Channel Length Gate-All-Around Field-Effect Transistor Using Ultrathin Strained Si/SiGe Channel

by Potaraju Yugender, Rudra Sankar Dhar, Swagat Nanda, Kuleen Kumar, Pandurengan Sakthivel and Arun Thirumurugan

Micromachines 2024, 15(12), 1455; https://doi.org/10.3390/mi15121455 - 29 Nov 2024

Abstract

The continuous scaling down of MOSFETs is one of the present trends in semiconductor devices to increase device performance. Nevertheless, with scaling down beyond 22 nm technology, the performance of even the newer nanodevices with multi-gate architecture declines with an increase in short [...] Read more.

The continuous scaling down of MOSFETs is one of the present trends in semiconductor devices to increase device performance. Nevertheless, with scaling down beyond 22 nm technology, the performance of even the newer nanodevices with multi-gate architecture declines with an increase in short channel effects (SCEs). Consequently, to facilitate further increases in the drain current, the use of strained silicon technology provides a better solution. Thus, the development of a novel Gate-All-Around Field-Effect Transistor (GAAFET) incorporating a strained silicon channel with a 10 nm gate length is initiated and discussed. In this device, strain is incorporated in the channel, where a strained silicon germanium layer is wedged between two strained silicon layers. The GAAFET device has four gates that surround the channel to provide improved control of the gate over the strained channel region and also reduce the short channel effects in the devices. The electrical properties, such as the on current, off current, threshold voltage (V_TH), subthreshold slope, drain-induced barrier lowering (DIBL), and I_on/I_off current ratio, of the 10 nm channel length GAAFET are compared with the 22 nm strained silicon channel GAAFET, the existing SOI FinFET device on 10 nm gate length, and IRDS 2022 specifications device. The developed 10 nm channel length GAAFET, having an ultrathin strained silicon channel, delivers enriched device performance, being augmented in contrast to the IRDS 2022 specifications device, showing improved characteristics along with amended SCEs. Full article

(This article belongs to the Section D1: Semiconductor Devices)

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24 pages, 11456 KiB

Open AccessReview

Recent Advances in Micro- and Nanorobot-Assisted Colorimetric and Fluorescence Platforms for Biosensing Applications

by Arumugam Selva Sharma and Nae Yoon Lee

Micromachines 2024, 15(12), 1454; https://doi.org/10.3390/mi15121454 - 29 Nov 2024

Abstract

Micro- and nanorobots (MNRs) have attracted significant interest owing to their promising applications in various fields, including environmental monitoring, biomedicine, and microengineering. This review explores advances in the synthetic routes used for the preparation of MNRs, focusing on both top-down and bottom-up approaches. [...] Read more.

Micro- and nanorobots (MNRs) have attracted significant interest owing to their promising applications in various fields, including environmental monitoring, biomedicine, and microengineering. This review explores advances in the synthetic routes used for the preparation of MNRs, focusing on both top-down and bottom-up approaches. Although the top-down approach dominates the field because of its versatility in design and functionality, bottom-up strategies that utilize template-assisted electrochemical deposition and bioconjugation present unique advantages in terms of biocompatibility. This review investigates the diverse propulsion mechanisms employed in MNRs, including magnetic, electric, light, and biological forces, which enable efficient navigation in various fluidic environments. The interplay between the synthesis and propulsion mechanisms of MNRs in the development of colorimetric and fluorescence detection platforms is emphasized. Additionally, we summarize the recent advancements in MNRs as sensing and biosensing platforms, particularly focusing on colorimetric and fluorescence-based detection systems. By utilizing the controlled motion of MNRs, dynamic changes in the fluorescent signals and colorimetric responses can be achieved, thereby enhancing the sensitivity and selectivity of biomolecular detection. This review highlights the transformative potential of MNRs in sensing applications and emphasizes their role in advancing diagnostic technologies through innovative motion-driven signal transduction mechanisms. Subsequently, we provide an overview of the primary challenges currently faced in MNR research, along with our perspective on the future applications of MNR-assisted colorimetric and fluorescence biosensing in chemical and biological sensing. Moreover, issues related to enhanced stability, biocompatibility, and integration with existing detection systems are discussed. Full article

(This article belongs to the Collection Women in Micromachines)

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12 pages, 10212 KiB

Open AccessArticle

Fine Control of Optical Properties of Nb₂O₅ Film by Thermal Treatment

by Xianpeng Liang, Bowen Liu, Quan Yuan, Xiaomin Lin, Shaopeng Ren, Shuaifeng Zhao, Xiaojun Yin and Shuguo Fei

Micromachines 2024, 15(12), 1453; https://doi.org/10.3390/mi15121453 - 29 Nov 2024

Abstract

Thermal treatment is a common method to improve the properties of optical thin films, but improper thermal treatment processing will result in the degradation of the optical properties of the optical thin film. The thermal stability of niobium oxide (Nb₂O₅ [...] Read more.

Thermal treatment is a common method to improve the properties of optical thin films, but improper thermal treatment processing will result in the degradation of the optical properties of the optical thin film. The thermal stability of niobium oxide (Nb₂O₅) thin films prepared by magnetron sputtering was systematically studied by analyzing the roughness and morphology of the film under different thermal treatment processes. The results show that the amorphous stability of the Nb₂O₅ thin film can be maintained up to 400 °C. Before crystallization, with an increase in annealing temperature, the surface roughness of the film has no obvious change, the refractive index decreases, and the elastic modulus and hardness increase. The residual stress was measured by a laser interferometer. The results show that the residual compressive stress is present in the film, and the residual stress decreases with an increase in thermal treatment temperature. Considering the residual stress state, phase composition, mechanical properties, and optical properties of Nb₂O₅ films at different thermal treatment temperatures, we believe that the spectral position of the optical thin film device can be finely controlled within a 1.6% wavelength, and the thermal treatment temperature of Nb₂O₅ films prepared by magnetron sputtering should not exceed 400 °C. Full article

(This article belongs to the Special Issue Advanced Optical Manufacturing Technologies and Applications)

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4 pages, 185 KiB

Open AccessEditorial

Topic Editorial on Fiber-Optic Sensors

by Muhammad A. Butt

Micromachines 2024, 15(12), 1452; https://doi.org/10.3390/mi15121452 - 29 Nov 2024

Abstract

Fiber-optic sensors are highly significant in modern technology due to their unique abilities and versatility [...] Full article

(This article belongs to the Section A：Physics)

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