Micromachines

16 pages, 1890 KiB

Open AccessArticle

Multi-Field Characterisation of Material Removal Processes in Ultrasonic Magnetorheological Chemical Compound Polishing of GaN Wafers

by Huazhuo Liang, Wenjie Chen, Youzhi Fu, Wenjie Zhou, Ling Mo, Qi Wen, Dawei Liu and Junfeng He

Micromachines 2025, 16(5), 502; https://doi.org/10.3390/mi16050502 - 25 Apr 2025

Abstract

Gallium nitride (GaN), as the core material of third-generation semiconductors, has important applications in high-temperature, high-frequency, and high-power devices, but its polishing process faces many challenges. In this work, a multifield synergistic material removal model is established to study the material removal behaviour [...] Read more.

Gallium nitride (GaN), as the core material of third-generation semiconductors, has important applications in high-temperature, high-frequency, and high-power devices, but its polishing process faces many challenges. In this work, a multifield synergistic material removal model is established to study the material removal behaviour by ultrasonic magnetorheological chemical compound polishing (UMCP) of gallium nitride wafers, and the polishing processing under different polishing solution compositions and processing conditions is used to examine the effects of the ultrasonic, chemical, and mechanical effects on the material removal rate. The results show that mechanical removal dominates during UMCP, the chemical enhancement is slightly greater than the ultrasonic action, and the synergistic interaction between the range of factors promotes better removal of the GaN materials. The percentage of mechanical removal by abrasives is about 25% to 44.63%, the mechanical removal by magnetorheological effect polishing pads is about 14.66% to 23.94%, the removal due to chemical action is about 15.52% to 23.41%, the removal due to ultrasonic action is about 11.73% to 14.66%, and the percentage of interactive removal is 6.47% to 14.36%. The abrasive composition significantly enhances the mechanical removal effect, and a higher abrasive concentration correlates to a stronger mechanical removal effect. The concentration of hydrogen peroxide has a superior effect on the chemical reaction, and too high or too low a concentration of hydrogen peroxide weakens the chemical action effect. The results of the study can provide a basis for further research on the material removal mechanism of the GaN UMCP process. Full article

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

10 pages, 1937 KiB

Open AccessArticle

Fabrication of a Spiral Microfluidic Chip for the Mass Production of Lipid Nanoparticles Using Laser Engraving

by Inseong Choi, Mincheol Cho, Minseo Song, Byeong Wook Ryu, Bo Mi Kang, Joonyeong Kim, Tae-Kyung Ryu and Sung-Wook Choi

Micromachines 2025, 16(5), 501; https://doi.org/10.3390/mi16050501 - 25 Apr 2025

Abstract

A spiral microfluidic chip (SMC) and multi-spiral microfluidic chip (MSMC) for lipid nanoparticle (LNP) production were fabricated using a CO₂ laser engraving method, using perfluoropolyether (PFPE) and poly(ethylene glycol) diacrylate as photopolymerizable base materials. The SMC includes a spiral microchannel that enables [...] Read more.

A spiral microfluidic chip (SMC) and multi-spiral microfluidic chip (MSMC) for lipid nanoparticle (LNP) production were fabricated using a CO₂ laser engraving method, using perfluoropolyether (PFPE) and poly(ethylene glycol) diacrylate as photopolymerizable base materials. The SMC includes a spiral microchannel that enables rapid fluid mixing, thereby facilitating the production of small and uniform LNPs with a size of 72.82 ± 24.14 nm and a PDI of 0.111 ± 0.011. The MSMC integrates multiple parallel SMC structures, which enables high-throughput LNP production without compromising quality and achieves a maximum production capacity of 960 mL per hour. The LNP fabrication technology using SMC and MSMC has potential applications in the pharmaceutical field due to the ease of chip fabrication, the simplicity and cost-effectiveness of the process, and the ability to produce high-quality LNPs. Full article

(This article belongs to the Special Issue Advanced Micromixing Technology)

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15 pages, 2921 KiB

Open AccessArticle

Application of Inertial Microfluidics for Isolation and Removal of Round Spermatids from a Spermatogenic Cell Sample to Assist In-Vitro Human Spermatogenesis

by Sabin Nepal, Joey Casalini, Alex Jafek and Bruce Gale

Micromachines 2025, 16(5), 500; https://doi.org/10.3390/mi16050500 - 25 Apr 2025

Abstract

In-vitro spermatogenesis holds great potential in addressing male infertility, yet one of the main challenges is separating round spermatids from other germ cells in spermatogonial stem cell cultures. STA-PUT, a method based on velocity sedimentation, has been extensively tested for this application. Though [...] Read more.

In-vitro spermatogenesis holds great potential in addressing male infertility, yet one of the main challenges is separating round spermatids from other germ cells in spermatogonial stem cell cultures. STA-PUT, a method based on velocity sedimentation, has been extensively tested for this application. Though somewhat effective, it requires bulky, expensive equipment and significant time. In contrast, the method of inertial microfluidics offers a compact, cost-effective, and faster alternative. In this study, we designed, fabricated, and tested a microfluidic spiral channel for isolating round spermatids and purifying spermatogenic cells. A commercially available spiral device close to the calculated specifications was tested for rapid prototyping, achieving 79% purity for non-spermatid cells in a single pass, with ability to achieve higher purity through repeated passes. However, the commercial device’s narrow outlets caused clogging, prompting the fabrication of a custom polydimethylsiloxane device matching the calculated specifications. This custom device demonstrated significant improvements, achieving 86% purity in a single pass compared to STA-PUT’s 38%, and that without any clogging issues. Further purification could be attained by repeated passes, as shown in earlier studies. This work underscores the efficacy of inertial microfluidics for efficient, high-purity cell separation, with the potential to revolutionize workflows in in-vitro spermatogenesis research. Full article

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

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12 pages, 1408 KiB

Open AccessArticle

Advanced MMC-Based Hydrostatic Bearings for Enhanced Linear Motion in Ultraprecision and Micromachining Applications

by Ali Khaghani, Atanas Ivanov and Mina Mortazavi

Micromachines 2025, 16(5), 499; https://doi.org/10.3390/mi16050499 - 24 Apr 2025

Abstract

This study investigates the impact of material selection on the performance of linear slideways in ultraprecision machines used for freeform surface machining. The primary objective is to address challenges related to load-bearing capacity and limited bandwidth in slow tool servo (STS) techniques. Multi-body [...] Read more.

This study investigates the impact of material selection on the performance of linear slideways in ultraprecision machines used for freeform surface machining. The primary objective is to address challenges related to load-bearing capacity and limited bandwidth in slow tool servo (STS) techniques. Multi-body dynamic (MBD) simulations are conducted to evaluate the performance of two materials, alloy steel and metal matrix composite (MMC), within the linear slideway system. Key performance parameters, including acceleration, velocity, and displacement, are analyzed to compare the two materials. The findings reveal that MMC outperforms alloy steel in acceleration, velocity, and displacement, demonstrating faster response times and greater linear displacement, which enhances the capabilities of STS-based ultraprecision machining. This study highlights the potential of utilizing lightweight materials, such as MMC, to optimize the performance and efficiency of linear slideways in precision engineering applications. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications, 5th Edition: Materials and High-Precision Micromachining)

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13 pages, 3107 KiB

Open AccessArticle

Defecation Warning Monitor Based on ScAlN Piezoelectric Ultrasonic Transducer (PMUT)

by Tao Yao, Jianwei Zong, Haoyue Zhang, Zhiyuan Hou and Liang Lou

Micromachines 2025, 16(5), 498; https://doi.org/10.3390/mi16050498 - 24 Apr 2025

Abstract

This study proposes an innovative health management solution to address the defecation care needs of the elderly population. Traditional post-defecation care methods have significant limitations, particularly imposing a considerable psychological burden on patients. By leveraging the rich physiological information contained in bowel sounds, [...] Read more.

This study proposes an innovative health management solution to address the defecation care needs of the elderly population. Traditional post-defecation care methods have significant limitations, particularly imposing a considerable psychological burden on patients. By leveraging the rich physiological information contained in bowel sounds, in this work, we designed and implemented a wearable defecation warning monitor based on scandium aluminum nitride (ScAlN) piezoelectric thin films and piezoelectric micromachined ultrasonic transducers (PMUTs). The proposed device mainly incorporates two core components: a bowel sound signal acquisition module and a real-time signal display graphical user interface (GUI) developed using the MATLAB R2023a platform. The research focuses on the systematic characterization and comparative analysis of the sound pressure sensitivity of three different signal readout structures. Experimental results demonstrate that the differential readout structure exhibits superior sensitivity. By continuously monitoring bowel sounds in healthy subjects both with and without the urge to defecate using the defecation warning monitor and a modified stethoscope, and conducting a comparative analysis of the experimental data, it is verified that the defecation warning monitor has significant advantages in clinical applications and demonstrates promising potential for defecation warning monitoring. Full article

(This article belongs to the Section A：Physics)

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15 pages, 4058 KiB

Open AccessReview

Application Prospects of a Silicon-Based MEMS Safety and Arming Device for a Micro-Explosive Train

by Wei Ren, Dongpeng Zhang, Enyi Chu, Tengjiang Hu, Anmin Yang, Hui Li, Jianhua Chen, Jiao Li and Wei Liu

Micromachines 2025, 16(5), 497; https://doi.org/10.3390/mi16050497 - 24 Apr 2025

Abstract

As the initial energetic device and driving force of weapon systems, pyrotechnics serve as the core and most sensitive explosive initiating device of weaponry. To accommodate the development requirements of various informatized and miniaturized weapons, MEMS pyrotechnics, characterized primarily by energy conversion informatization, [...] Read more.

As the initial energetic device and driving force of weapon systems, pyrotechnics serve as the core and most sensitive explosive initiating device of weaponry. To accommodate the development requirements of various informatized and miniaturized weapons, MEMS pyrotechnics, characterized primarily by energy conversion informatization, structural miniaturization, and train integration, have become a significant direction in the development of pyrotechnics technology. MEMS Safety and Arming Devices, serving as the energy transfer control mechanisms for micro-explosive trains in MEMS pyrotechnics, are one of the key technologies in the design of MEMS pyrotechnics. This study conducted a classification study of a silicon-based MEMS Safety and Arming Device from the perspective of micro-explosive train structures, analyzed the technical principles of different S&A device, explored their application progress and research status, and summarizes the trends of the micro-miniaturization, integration, and informatization of the silicon-based MEMS Safety and Arming Device, providing new ideas for the research and the design of MEMS Safety and Arming Devices. Full article

(This article belongs to the Special Issue Recent Advances in Silicon-Based MEMS Sensors and Actuators)

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12 pages, 3152 KiB

Open AccessArticle

Differential Phase Coupler Using Balun-Type Power Divider

by Chatrpol Pakasiri, Chung-Yu Chang and Sen Wang

Micromachines 2025, 16(5), 496; https://doi.org/10.3390/mi16050496 - 24 Apr 2025

Abstract

This paper presents a differential phase coupler design methodology in the IPD process. The coupler consists of a balun and two phase-shifter circuits. The compact balun was designed with lumped components and a common inductor. Each output of the balun circuit was connected [...] Read more.

This paper presents a differential phase coupler design methodology in the IPD process. The coupler consists of a balun and two phase-shifter circuits. The compact balun was designed with lumped components and a common inductor. Each output of the balun circuit was connected to a phase shifter with an opposite phase to make a desired output phase. In the design example, a three-port 90-degree hybrid coupler was implemented on the IPD process to operate at the 6 GHz WIFI frequency. The post-simulation showed that all reflection coefficients were below −19 dB, with an insertion loss of 1.76 dB and isolation of 20 dB. The core chip size was only 0.02λ₀ × 0.018λ₀. Full article

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20 pages, 25702 KiB

Open AccessArticle

Mechanism-Oriented Analysis of Core–Shell Structured CIP@SiO₂ Magnetic Abrasives for Precision-Enhanced Magnetorheological Polishing

by Chunyu Li, Shusheng Chen, Zhuoguang Zheng, Yicun Zhu, Bingsan Chen and Yongchao Xu

Micromachines 2025, 16(5), 495; https://doi.org/10.3390/mi16050495 - 24 Apr 2025

Abstract

This study addresses the critical challenge of precise control over active abrasive particles in magnetorheological polishing (MRP) through innovative core–shell particle engineering. A sol–gel synthesized CIP@SiO₂ magnetic composite abrasive with controlled SiO₂ encapsulation (20 nm shell thickness) was developed using tetraethyl [...] Read more.

This study addresses the critical challenge of precise control over active abrasive particles in magnetorheological polishing (MRP) through innovative core–shell particle engineering. A sol–gel synthesized CIP@SiO₂ magnetic composite abrasive with controlled SiO₂ encapsulation (20 nm shell thickness) was developed using tetraethyl orthosilicate (TEOS) as the silicon precursor, demonstrating significant advantages in optical-grade fused silica finishing. Systematic polishing experiments reveal that the core–shell architecture achieves a remarkable 20.16% improvement in surface quality (Ra = 1.03 nm) compared to conventional CIP/SiO₂ mixed abrasives, with notably reduced surface defects despite a modest 8–12% decrease in material removal rate. Through synergistic analysis combining elastic microcontact mechanics modeling and molecular dynamics simulations, we establish that the SiO₂ shell mediates stress distribution at tool–workpiece interfaces, effectively suppressing deep subsurface damage while maintaining nano-scale material removal efficiency. The time-dependent performance analysis further demonstrates that extended polishing durations with CIP@SiO₂ composites progressively eliminate mid-spatial frequency errors without introducing new surface artifacts. These findings provide fundamental insights into designed abrasive architectures for precision finishing applications requiring sub-nanometer surface integrity control. Full article

(This article belongs to the Special Issue Recent Advances in Micro/Nanofabrication, 2nd Edition)

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15 pages, 13926 KiB

Open AccessArticle

High-Temperature Properties of LP-DED Additive Manufactured Ferritic STS 430 Deposits on Martensitic STS 410 Base Metal

by Samsub Byun, Hyun-Ki Kang, Namhyun Kang and Seunghun Lee

Micromachines 2025, 16(5), 494; https://doi.org/10.3390/mi16050494 - 23 Apr 2025

Abstract

The aim of this work is to study the phase transformations, microstructures, and mechanical properties of ferritic stainless steel (FSS) 430 deposits on martensitic stainless steel (MSS) 410 base metal (BM) using laser powder-directed energy deposition (LP-DED) additive manufacturing. The LP-DED additive manufactured [...] Read more.

The aim of this work is to study the phase transformations, microstructures, and mechanical properties of ferritic stainless steel (FSS) 430 deposits on martensitic stainless steel (MSS) 410 base metal (BM) using laser powder-directed energy deposition (LP-DED) additive manufacturing. The LP-DED additive manufactured FSS 430 deposits on MSS 410 BM underwent post-heat treatment at 815 °C and 980 °C for 1 h, respectively. The analyses of phase transformations and microstructural evolutions of LP-DED FSS 430 on MSS 410 BM were carried out using X-ray diffraction, SEM, and EBSD. The highest strain was observed at the coarsened chromium carbide (Cr₂₃C₆) in the joint interface between AM FSS 430 and MSS 410 MB. This contributed to localized lattice distortion and mismatch in crystal structure between chromium carbide and the surrounding ferrite. Tensile strength properties at elevated temperatures were discussed to investigate the effects of the different post-heat treatments. The tensile properties of the as-built samples including tensile strength of about 550 MPa and elongation of about 20%, were the same as those of the commercial FSS 430 material. Tensile properties at 500 °C indicated a modest increase in tensile strength to 540–550 MPa. The specimens heat treated at 980 °C retained higher tensile strength than those heat treated at 815 °C. This would be attributed to the grain refinement from prior LP-DED microstructure and chromium carbide coarsening at higher heat treatment, which can increase dislocation density and yield harder mechanical behavior. Full article

(This article belongs to the Special Issue Laser Additive Manufacturing of Metallic Materials, 2nd Edition)

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5 pages, 154 KiB

Open AccessEditorial

Editorial for the Applications and Challenges for Gas Sensors

by Zhaohui Lei, Yinglin Wang and Pengfei Cheng

Micromachines 2025, 16(5), 493; https://doi.org/10.3390/mi16050493 - 23 Apr 2025

Abstract

Gas sensors, widely used in various fields, are devices used to detect the presence of a specific gas within a certain area or to continuously measure the concentration of gas components [...] Full article

(This article belongs to the Section C：Chemistry)

14 pages, 4712 KiB

Open AccessArticle

Nonlinear Hysteresis Parameter Identification of Piezoelectric Actuators Using an Improved Gray Wolf Optimizer with Logistic Chaos Initialization and a Levy Flight Variant

by Yonggang Yan, Kangqiao Duan, Jianjun Cui, Shiwei Guo, Can Cui, Yongsheng Zhou, Junjie Huang, Geng Wang, Dengpan Zhang and Fumin Zhang

Micromachines 2025, 16(5), 492; https://doi.org/10.3390/mi16050492 - 23 Apr 2025

Abstract

Piezoelectric tilt mirrors are crucial components of precision optical systems. However, the intrinsic hysteretic nonlinearity of the piezoelectric actuator severely restricts the control accuracy of these mirrors and the overall performance of the optical system. This paper proposes an improved Gray Wolf Optimization [...] Read more.

Piezoelectric tilt mirrors are crucial components of precision optical systems. However, the intrinsic hysteretic nonlinearity of the piezoelectric actuator severely restricts the control accuracy of these mirrors and the overall performance of the optical system. This paper proposes an improved Gray Wolf Optimization (GWO) algorithm for high-accuracy identification of hysteresis model parameters based on the Bouc–Wen (BW) differential equation. The proposed algorithm accurately describes the intrinsic hysteretic nonlinear behavior of piezoelectric tilt mirrors. A logistic chaotic mapping method is introduced for population initialization, while a nonlinear convergence factor and a Levy flight strategy are incorporated to enhance global search capabilities during the later stages of optimization. These modifications enable the algorithm to effectively identify BW model parameters for piezoelectric nonlinear systems. Compared to conventional Particle Swarm Optimization (PSO) and standard GWO, the improved algorithm demonstrates faster convergence, higher accuracy, and superior ergodicity, making it a promising tool for solving optimization problems, such as parameter identification in piezoelectric hysteresis systems. This work provides a robust approach for improving the precision and reliability of piezoelectric-driven optical systems. Full article

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12 pages, 2211 KiB

Open AccessArticle

Electrostatic Field Modification Enhances the Electrocatalytic Oxygen Evolution Reaction Stability of CoFe₂O₄ Catalysts

by Liwen Liang, Jiatong Miao, Xiyuan Feng, Yunlei Zhong and Wei Wang

Micromachines 2025, 16(5), 491; https://doi.org/10.3390/mi16050491 - 22 Apr 2025

Abstract

Enhancing the stability of oxygen evolution reaction (OER) catalysts is a critical challenge for realizing efficient water splitting. In this work, we introduce an innovative approach by applying an electric field during the annealing of a CoFe₂O₄/C catalyst. By [...] Read more.

Enhancing the stability of oxygen evolution reaction (OER) catalysts is a critical challenge for realizing efficient water splitting. In this work, we introduce an innovative approach by applying an electric field during the annealing of a CoFe₂O₄/C catalyst. By controlling the electric field strength (100 mV) and treatment duration (1 h), we achieved dual optimization of the catalyst’s microstructure and electronic environment, resulting in a significant improvement in catalytic stability. The experimental results demonstrate that the electric field-treated catalyst exhibits a reduced overpotential decay (only 0.8 mV) and enhanced stability (retaining 89.1% of its initial activity after 24 h) during extended OER testing. This performance significantly surpasses that of the untreated sample, which showed an overpotential decay of 1.5 mV and retained only 72.5% of its activity after 24 h. X-ray photoelectron spectroscopy (XPS) analysis confirmed that the electric field treatment promoted the formation of oxygen vacancies, substantially improved electron transfer efficiency, and optimized the local electronic environment of Co²⁺/Co³⁺ and Fe²⁺/Fe³⁺, leading to a decrease in charge transfer resistance (Rct) from 58.2 Ω to 42.9 Ω. This study not only presents a novel strategy for modulating catalyst stability via electric fields but also broadens the design concepts for OER catalytic materials by establishing a structure–activity relationship between electric field strength, microstructure, and catalytic performance, ultimately providing a theoretical foundation and experimental guidance for the development of highly efficient and stable water splitting catalysts. Full article

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11 pages, 3791 KiB

Open AccessArticle

Rapid Synthesis of Fast-Charging TiNb₂O₇ for Lithium-Ion Storage via Ultrafast Carbothermal Shock

by Xianyu Hu, Yunlei Zhong, Xiaosai Hu, Xiyuan Feng and Fengying Ye

Micromachines 2025, 16(5), 490; https://doi.org/10.3390/mi16050490 - 22 Apr 2025

Abstract

The development of fast-charging lithium-ion batteries urgently requires high-performance anode materials. In this paper, through an ultrafast carbothermal shock (CTS) strategy, titanium niobium oxide (TiNb₂O₇, TNO) with an optimized structure was successfully synthesized within 30 s. By regulating the [...] Read more.

The development of fast-charging lithium-ion batteries urgently requires high-performance anode materials. In this paper, through an ultrafast carbothermal shock (CTS) strategy, titanium niobium oxide (TiNb₂O₇, TNO) with an optimized structure was successfully synthesized within 30 s. By regulating the synthesis temperature to 1200 °C, the TNO-1200 material was obtained. Its lattice parameters (a-axis: 17.6869 Å) and unit-cell volume (796.83 Å³) were significantly expanded compared to the standard structure (a-axis: 17.51 Å, volume ~790 Å³), which widened the lithium-ion migration channels. Rietveld refinement and atomic position analysis indicated that the partial overlap of Ti/Nb atoms and the cooperative displacement of oxygen atoms induced by CTS reduced the lithium-ion diffusion energy barrier. Meanwhile, the cation disorder suppressed the polarization effect. Electrochemical tests showed that after 3000 cycles at a current density of 10 C, the specific capacity of TNO-1200 reached 125 mAh/g, with a capacity retention rate of 98%. EDS mapping confirmed the uniform distribution of elements and the absence of impurity phases. This study provides an efficient synthesis strategy and theoretical basis for the design of high-performance fast-charging battery materials through atomic-scale structural engineering. Full article

(This article belongs to the Section C：Chemistry)

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Micromachines, Volume 16, Issue 5 (May 2025) – 13 articles

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