Micromachines

14 pages, 3360 KB

Open AccessArticle

Localized Electric Field Tailoring to Balance Voltage Reliability, Current Density, and High-Frequency Performance of AlGaN/GaN HEMTs

by Yuxin Wang, Jiangwen Wang, Zilong Dong, Peiran Tian, Yuxiu Liu, Junyi Zhai and Weiguo Hu

Micromachines 2025, 16(11), 1199; https://doi.org/10.3390/mi16111199 (registering DOI) - 22 Oct 2025

Abstract

Emerging applications including advanced industrial manufacturing, cutting-edge scientific research and medical equipment demand AlGaN/GaN HEMTs possessing both high-frequency and high-voltage characteristics. However, a persistent trade-off remains between the frequency characteristics and breakdown characteristics of these devices. In this study, we employed localized electric [...] Read more.

Emerging applications including advanced industrial manufacturing, cutting-edge scientific research and medical equipment demand AlGaN/GaN HEMTs possessing both high-frequency and high-voltage characteristics. However, a persistent trade-off remains between the frequency characteristics and breakdown characteristics of these devices. In this study, we employed localized electric field tailoring (LEFT) by introducing materials with different dielectric constants to construct a non-uniform composite gate dielectric layer, aiming to balance the breakdown voltage and cut-off frequency of the device. Device models were developed using APSYS-2018 software and their reliability was experimentally validated. Research data indicates that, compared to traditional uniform high-k (typically with dielectric constants k > 10, such as HfO₂ and HfZrO) gate dielectrics, the non-uniform composite gate dielectric structure demonstrates superior transconductance, saturation current density and cut-off frequency, with minimal degradation in breakdown voltage. Specifically, relative to HfO₂ and HfZrO uniform devices, the Al₂O₃/HfO₂ and Al₂O₃/HfZrO non-uniform HEMTs achieved 20.0% and 35.2% increases in cut-off frequency, respectively. Meanwhile, breakdown voltage remained above 97% of their uniform counterparts, saturation current density and transconductance increased by approximately 5%. Therefore, this non-uniform composite gate dielectric layer structure of AlGaN/GaN HEMT with LEFT holds great potential for industrial plasma generators, magnetic resonance imaging systems and biomedical radiofrequency hyperthermia devices. Full article

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

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19 pages, 2469 KB

Open AccessArticle

Tuning Multi-Wavelength Reflection Properties of Porous Silicon Bragg Reflectors Using Silver-Nanoparticle-Assisted Electrochemical Etching

by Sheng-Yang Huang, Hsiao-Han Hsu, Amal Muhammed Musthafa, I-An Lin, Chia-Man Chou and Vincent K. S. Hsiao

Micromachines 2025, 16(11), 1198; https://doi.org/10.3390/mi16111198 (registering DOI) - 22 Oct 2025

Abstract

This study proposes an innovative silver-nanoparticle-assisted electrochemical etching method for the fabrication of porous silicon Bragg reflectors with multi-wavelength reflection characteristics. By introducing silver nanoparticles at varying concentrations (0.1–10 mg/mL) into the conventional HF–ethanol electrolyte and applying periodically modulated current densities (40/100 mA/cm [...] Read more.

This study proposes an innovative silver-nanoparticle-assisted electrochemical etching method for the fabrication of porous silicon Bragg reflectors with multi-wavelength reflection characteristics. By introducing silver nanoparticles at varying concentrations (0.1–10 mg/mL) into the conventional HF–ethanol electrolyte and applying periodically modulated current densities (40/100 mA/cm²), the transition from single-peak to multi-peak reflection spectra was successfully achieved. The results demonstrate that at a concentration of 10 mg/mL silver nanoparticles, up to four distinct reflection bands can be obtained. A systematic investigation was conducted on the influence of etching cycles (4–20 cycles) and silver nanoparticle concentration on the optical performance and microstructure. SEM analysis revealed well-defined periodic multilayer structures, while XPS analysis confirmed the presence of metallic silver on the porous silicon surface. This work provides a simple, controllable, and cost-effective approach to the development of multifunctional photonic devices, with promising applications in laser optics, solar cells, chemical sensing, and surface-enhanced Raman scattering. Full article

(This article belongs to the Special Issue Micro-Nano Photonics: From Design and Fabrication to Application)

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24 pages, 10398 KB

Open AccessArticle

An Enhanced Cooling Method for Power Modules on All-Electric Ships Based on Parameter Optimization and Special-Shaped Design of Sintered Heat Pipes

by Binyu Wang, Ting Lu, Qisheng Wu, Bobin Yao, Hongwei Zhang, Xiwei Zhou and Weiyu Liu

Micromachines 2025, 16(11), 1197; https://doi.org/10.3390/mi16111197 (registering DOI) - 22 Oct 2025

Abstract

This paper proposes an enhanced cooling method for multi-chip power modules (e.g., in MMC inverters) with uneven power loss in all-electric propulsion ships based on sintered heat pipe parameter optimization and special-shaped design. First, five key parameters of straight sintered heat pipes were [...] Read more.

This paper proposes an enhanced cooling method for multi-chip power modules (e.g., in MMC inverters) with uneven power loss in all-electric propulsion ships based on sintered heat pipe parameter optimization and special-shaped design. First, five key parameters of straight sintered heat pipes were optimized: placement directly under hotspot chips, 10 mm in diameter, quantity matching the number of hotspot chips, length equal to the heatsink side length, and direction perpendicular to heatsink fins. Then, a C-shaped heat pipe was designed using the parallel thermal resistance principle, which forms two parallel low-thermal-resistance paths and outperforms conventional U-shaped ones. Finite element simulations showed that the hotspot temperature of the conventional heatsink was 91.26 °C, while it dropped to 87.35 °C with optimized straight heat pipes and further to 80.85 °C with C-shaped ones. Experiments verified an 11.65% temperature reduction (from 86.7 °C of conventional heatsinks to 76.6 °C of C-shaped heat pipe heatsinks). This method effectively lowers hotspot temperatures, reduces device failure rates, improves the thermal reliability of power modules, and provides a generalized design methodology for heatsinks of various power electronic converters. Full article

(This article belongs to the Special Issue Latest Advancements in Semiconductor Materials, Devices, and Systems, 2nd Edition)

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18 pages, 3331 KB

Open AccessArticle

Optical Vibration Sensing Bionic Vector Hydrophone Based on Mechanically Coupled Structure

by Jinying Zhang, Jianyu Peng, Xianmei Wu, Yifan Shi, Wenpeng Xu, Yiyao Wang, Rong Zhang, Ziqi Li and Bingwen An

Micromachines 2025, 16(11), 1196; https://doi.org/10.3390/mi16111196 (registering DOI) - 22 Oct 2025

Abstract

Vector hydrophones play an extremely important role in marine exploration. How to reduce the size of vector hydrophones while improving their directional detection capability is a critical issue that needs to be addressed. The auditory organ of the fly Ormia ochracea represents a [...] Read more.

Vector hydrophones play an extremely important role in marine exploration. How to reduce the size of vector hydrophones while improving their directional detection capability is a critical issue that needs to be addressed. The auditory organ of the fly Ormia ochracea represents a prime example of achieving high-resolution directional detection within a compact size range. This paper proposes a vector hydrophone that integrates an Ormia ochracea fly-inspired mechanically coupled structure with an optical fiber vibration sensing structure, offering advantages of small size and strong electromagnetic interference immunity. The hydrophone demonstrates a good response to acoustic pulse trains and can accurately demodulate acoustic waves from 1 kHz to 10 kHz. Directional response experiments show that this hydrophone can significantly amplify the time delay differences of incoming acoustic waves. At an acoustic frequency of 9.25 kHz, the time delay amplification factor reaches approximately 50 times within the range of −90° to +90°, exhibiting good cosine directionality. Full article

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33 pages, 3868 KB

Open AccessReview

Application of Polymer Lubricants in Triboelectric Energy Harvesting: A Review

by Ali Nawaz and Hong-Joon Yoon

Micromachines 2025, 16(11), 1195; https://doi.org/10.3390/mi16111195 (registering DOI) - 22 Oct 2025

Abstract

The range of lubricant applications has broadened to include multiple sectors, aiming to optimize the operational efficiency of mechanical systems. Given their adaptable friction-reducing properties, lubricants have recently been incorporated into energy harvesting technologies such as triboelectric nanogenerators (TENGs). In such devices, lubricants [...] Read more.

The range of lubricant applications has broadened to include multiple sectors, aiming to optimize the operational efficiency of mechanical systems. Given their adaptable friction-reducing properties, lubricants have recently been incorporated into energy harvesting technologies such as triboelectric nanogenerators (TENGs). In such devices, lubricants are essential for mitigating wear, facilitating heat dissipation, eliminating contaminants, and prolonging the service life of mechanically actuated energy harvesters. Notably, emerging developments in sliding and rotational-mode TENGs leverage lubricants to improve electrical output while reducing interface degradation. However, despite significant potential, TENGs still face inherent challenges, including interface friction and energy losses from air breakdown. Recent research indicates that these drawbacks can be effectively addressed by the intentional use of polymer-based lubricants, which contribute to maintaining micro/nanostructured surfaces and minimizing air breakdown, thereby enhancing charge storage capability and increasing device robustness. This review systematically examines the categories, physicochemical attributes, and operational roles of polymeric lubricants used in TENG technology. It underscores their combined function is both primary and support materials to augment triboelectric efficiency. In addition, the article assesses how different lubricants impact device performance and durability, providing a critical analysis of their suitability based on the operational benchmarks of lubricant-embedded TENG configurations. Full article

(This article belongs to the Special Issue Research Progress in Energy Harvesters and Self-Powered Sensors)

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11 pages, 2858 KB

Open AccessArticle

Optimization Design of High-Performance Powder-Spreading Arm for Metal 3D Printers

by Guoqing Zhang, Junxin Li, Xiaoyu Zhou, Yongsheng Zhou, Juanjuan Xie and Yuchao Bai

Micromachines 2025, 16(11), 1194; https://doi.org/10.3390/mi16111194 (registering DOI) - 22 Oct 2025

Abstract

The powder-laying arm of a metal 3D printer is heavy, which can easily cause long-term damage to the powder-laying servomotor or belt, so it is necessary to design a lightweight powder-laying arm. To this end, we first use 3D modeling Rhino software to [...] Read more.

The powder-laying arm of a metal 3D printer is heavy, which can easily cause long-term damage to the powder-laying servomotor or belt, so it is necessary to design a lightweight powder-laying arm. To this end, we first use 3D modeling Rhino software to rebuild the powder-laying arm, and then, we carry out topology optimization design on the rebuilt powder-laying arm in Altair Inspire software. Finally, we use the Aurora Elva 3D printer to complete manufacturing and assembly to verify compatibility. The results show that the maximum displacement of the original powder-spreading arm is concentrated in the lower right corner at 4.319 × 10⁻⁵ mm; the maximum stress is concentrated in the middle transition part, decreasing toward the ends; the maximum stress is 3.843 × 10⁻² MPa; the stress concentration and deformation of the powder-spreading arm when spreading powder is small, which provides a large optimization space. The topology-optimized powder-spreading arm, with a 25% quality objective, maintains the integrity of the connection with the fixing hole while having a large mass reduction. The surface of the parts of the completed 3D-printed powder arm is bright, with low roughness, and there is no obvious warping and deformation or other defects; the completed 3D-printed powder-spreading arm and the assembly of the wall are closely coordinated with each other, and the location of the screw holes is appropriate, having no obvious assembly conflicts between the parts, which lays the foundation for the mass production of the powder-spreading arm of high-performance metal 3D printers. Full article

(This article belongs to the Special Issue 3D/4D Printing of Multifunctional Composites with Multifunctional Applications)

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11 pages, 2907 KB

Open AccessArticle

Electrical Characterization and Simulation of GaN-on-Si Pseudo-Vertical MOSFETs with Frequency-Dependent Gate C–V Investigation

by Valentin Ackermann, Mohammed El Amrani, Blend Mohamad, Riadh Ben Abbes, Matthew Charles, Sebastien Cavalaglio, Manuel Manrique, Julien Buckley and Bassem Salem

Micromachines 2025, 16(11), 1193; https://doi.org/10.3390/mi16111193 (registering DOI) - 22 Oct 2025

Abstract

This work presents a comprehensive study of GaN-on-Si pseudo-vertical MOSFETs focusing on single-trench and multi-trench designs. Thanks to a gate-first process flow based on an Al₂O₃/TiN MOS stack, both fabricated devices exhibit promising transistor behavior, with steady normally OFF [...] Read more.

This work presents a comprehensive study of GaN-on-Si pseudo-vertical MOSFETs focusing on single-trench and multi-trench designs. Thanks to a gate-first process flow based on an Al₂O₃/TiN MOS stack, both fabricated devices exhibit promising transistor behavior, with steady normally OFF operation, very low gate leakage current, and good switching performance. Following the extraction of a low effective channel mobility, the frequency dependence of gate-to-source C–V characteristics is studied. In addition, using TCAD Sentaurus Synopsys simulations, the impact of positive fixed charge and donor-type defects at the p-GaN/dielectric interface is investigated, together with the frequency dependency. Finally, by comparing experimental and simulated results, a mechanism is proposed linking the observed threshold voltage shift to the presence of sharp trench-bottom micro-trenching. This mechanism may further explain the origin of the additional C–V hump observed at high frequencies, which could arise from charge trapping at the p-GaN/dielectric interface or from charge inversion in the p-GaN region. Full article

(This article belongs to the Special Issue GaN-Based Materials and Devices: Research and Applications, 2nd Edition)

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21 pages, 1373 KB

Open AccessReview

Applicability Analysis of High-Voltage Transmission and Substation Equipment Based on Silicon Carbide Devices

by Huiyuan Zhang, Ming Nie, Qinxiao Dong, He Liu, Pengfei Jia, Zhiyuan Li and Yonghao Fang

Micromachines 2025, 16(11), 1192; https://doi.org/10.3390/mi16111192 (registering DOI) - 22 Oct 2025

Abstract

Power electronics is an important feature of the new power system. The high-speed development of the new power system has gradually increased the requirements for high-efficiency and high-reliability high-voltage transmission and substation equipment. Silicon carbide (SiC) devices, which have the advantages of fast [...] Read more.

Power electronics is an important feature of the new power system. The high-speed development of the new power system has gradually increased the requirements for high-efficiency and high-reliability high-voltage transmission and substation equipment. Silicon carbide (SiC) devices, which have the advantages of fast switching speed, low power loss, and high-temperature resistance, are the key core technology for the upgrading of high-voltage transmission and substation equipment. The paper begins by examining the evolution of the demand for high efficiency, compact and reliable power electronic devices for high-voltage transmission and substation systems at different stages of energy development. SiC has emerged as a key technological path to break through the physical limits of silicon-based devices, due to its outstanding material properties. Silicon-based devices encounter significant bottlenecks in high-voltage and high-frequency applications, with high switching losses and a junction temperature tolerance that is typically limited to 150 °C. In contrast, SiC devices can reduce switching losses by 60–80% and operate stably at temperatures up to 200 °C or even higher, thereby significantly enhancing system efficiency and power density. Finally, the paper provides a systematic analysis of the application of SiC devices in high-voltage transmission and substation equipment, exploring and identifying the technical bottlenecks and future research directions for SiC-based high-voltage transmission equipment. Full article

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15 pages, 3114 KB

Open AccessArticle

Impact of Extrinsic Defects in Wavelength Separation Coatings on the Process of Laser-Induced Damage

by Shichen Shen, Xinda Zhou, Yinbo Zheng, Jie Li, Tianhao Zhang, Linjie Zhao, Liqun Chai and Mingjun Chen

Micromachines 2025, 16(11), 1191; https://doi.org/10.3390/mi16111191 - 22 Oct 2025

Abstract

Wavelength separation coatings can effectively separate the fundamental frequency (1ω) and third harmonic (3ω) laser beams. However, the laser-induced damage threshold (LIDT) of the surface defect-free WS coatings for the 3ω laser is 1.68 J/cm² (obtained in the preliminary experiment), significantly lower [...] Read more.

Wavelength separation coatings can effectively separate the fundamental frequency (1ω) and third harmonic (3ω) laser beams. However, the laser-induced damage threshold (LIDT) of the surface defect-free WS coatings for the 3ω laser is 1.68 J/cm² (obtained in the preliminary experiment), significantly lower than the ideal LIDT of the fused silica substrate (80 J/cm²). This is directly correlated with extrinsic defects such as nanoscale defects and nodular defects introduced during the coating manufacturing process. Moreover, the damage in WS coatings caused by extrinsic defects is a complex physical process involving multiple physical phenomena such as material melting, vaporization, and ejection. The mechanism by which extrinsic defects interact with lasers to form damage is not yet fully elucidated. To address this, a multi-physics coupling model considering photoelectric, thermal and stress was established to simulate the incident laser propagation within coatings, the temperature distribution and thermal stress distribution of the coating material. This model systematically investigates the influence of defect location, type, and size on the laser-induced damage process. It is found that when a 10 nm-diameter defect is located at the 32nd layer of the coatings, the light intensity enhancement factor (LIEF) for 3ω laser can reach up to 5 times that for the 1ω laser. The variation in thermal stress induced by changes in defect size is jointly determined by the defect-induced modulation effect and the interference effect realized by the coating. This work theoretically reveals the mechanism of extrinsic defects in the laser damage. It provides effective guidance for establishing control standards for extrinsic defects during the optical coating process. Full article

(This article belongs to the Special Issue Advances in Digital Manufacturing and Nano Fabrication)

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Micromachines, Volume 16, Issue 11 (November 2025) – 9 articles

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