Micromachines

11 pages, 2232 KiB

Open AccessArticle

Acoustic Transmission Measurements for Extracting the Mechanical Properties of Complex 3D MEMS Transducers

by Dennis Becker, Moritz Littwin, Achim Bittner and Alfons Dehé

Micromachines 2024, 15(9), 1070; https://doi.org/10.3390/mi15091070 (registering DOI) - 24 Aug 2024

Recent publications on acoustic MEMS transducers present a new three-dimensional folded diaphragm that utilizes buried in-plane vibrating structures to increase the active area from a small chip volume. Characterization of the mechanical properties plays a key role in the development of new MEMS [...] Read more.

Recent publications on acoustic MEMS transducers present a new three-dimensional folded diaphragm that utilizes buried in-plane vibrating structures to increase the active area from a small chip volume. Characterization of the mechanical properties plays a key role in the development of new MEMS transducers, whereby established measurement methods are usually tailored to structures close to the sample surface. In order to access the lateral vibrations, extensive and destructive sample preparation is required. This work presents a new passive measurement technique that combines acoustic transmission measurements and lumped-element modelling. For diaphragms of different lengths, compliances between 0.08 × 10⁻¹⁵ and 1.04 × 10⁻¹⁵ m³/Pa are determined without using destructive or complex preparations. In particular, for lengths above 1000 µm, the results differ from numerical simulations by only 4% or less. Full article

(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)

18 pages, 3077 KiB

Open AccessArticle

Model-Based Optimization of Solid-Supported Micro-Hotplates for Microfluidic Cryofixation

by Daniel B. Thiem, Greta Szabo and Thomas P. Burg

Micromachines 2024, 15(9), 1069; https://doi.org/10.3390/mi15091069 (registering DOI) - 24 Aug 2024

Abstract

Cryofixation by ultra-rapid freezing is widely regarded as the gold standard for preserving cell structure without artefacts for electron microscopy. However, conventional cryofixation technologies are not compatible with live imaging, making it difficult to capture dynamic cellular processes at a precise time. To [...] Read more.

Cryofixation by ultra-rapid freezing is widely regarded as the gold standard for preserving cell structure without artefacts for electron microscopy. However, conventional cryofixation technologies are not compatible with live imaging, making it difficult to capture dynamic cellular processes at a precise time. To overcome this limitation, we recently introduced a new technology, called microfluidic cryofixation. The principle is based on micro-hotplates counter-cooled with liquid nitrogen. While the power is on, the sample inside a foil-embedded microchannel on top of the micro-hotplate is kept warm. When the heater is turned off, the thermal energy is drained rapidly and the sample freezes. While this principle has been demonstrated experimentally with small samples (<0.5 mm

^{2}

), there is an important trade-off between the attainable cooling rate, sample size, and heater power. Here, we elucidate these connections by theoretical modeling and by measurements. Our findings show that cooling rates of 10⁶ K s⁻¹, which are required for the vitrification of pure water, can theoretically be attained in samples up to ∼1 mm wide and

5 m

thick by using diamond substrates. If a heat sink made of silicon or copper is used, the maximum thickness for the same cooling rate is reduced to ∼3

μ

m. Importantly, cooling rates of 10⁴ K s⁻¹ to 10⁵ K s⁻¹ can theoretically be attained for samples of arbitrary area. Such rates are sufficient for many real biological samples due to the natural cryoprotective effect of the cytosol. Thus, we expect that the vitrification of millimeter-scale specimens with thicknesses in the

10 m

range should be possible using micro-hotplate-based microfluidic cryofixation technology. Full article

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

11 pages, 3782 KiB

Open AccessArticle

Development of a Novel Electrostatic-Based Bioaerosol Sampler

by Zirui Pang, Lulu Shi, Wei Liu, Wenru Liu, Xin Tian, Mingyu Wang and Jifang Tao

Micromachines 2024, 15(9), 1068; https://doi.org/10.3390/mi15091068 (registering DOI) - 24 Aug 2024

Abstract

On-site bioaerosol monitoring is essential for estimating microbial biomass and mitigating the risk of infection induced by aerosol transmission. This study introduces a novel electrostatic bioaerosol sampler, which is fabricated by the use of 3D printing, for rapid bioaerosol collection. Aerosol particles were [...] Read more.

On-site bioaerosol monitoring is essential for estimating microbial biomass and mitigating the risk of infection induced by aerosol transmission. This study introduces a novel electrostatic bioaerosol sampler, which is fabricated by the use of 3D printing, for rapid bioaerosol collection. Aerosol particles were charged and enriched in the sampler. Relationships between particle sizes and collection efficiencies under varying charging voltages were established using a charging model. The design of the sampler was optimized using commercial software, incorporating electrostatic field analysis, computational fluid dynamics (CFD), and particle trajectory simulations. To validate the sampler’s collection efficiency, polystyrene (PS) spheres in an aerosol dispenser were atomized into an aerosol. The sampler collection efficiency exceeded 90% for particles larger than 1.2 μm under an applied voltage of 4.7 kV and an airflow rate of 2 L/min. The enrichment capacity was greater than 153,000 for particles larger than 1.2 μm under an applied voltage of 4.7 kV and an airflow rate of 8 L/min. With the merits of low cost, miniaturization, and high collection efficiency, the sampler can be used to collect samples on-site and in remote areas to verify the pathogens and reduce the risk of infection through aerosol transmission. Full article

(This article belongs to the Section B4: Point-of-Care Devices)

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20 pages, 6503 KiB

Open AccessArticle

Design and Validation of a Monte Carlo Method for the Implementation of Noninvasive Wearable Devices for HbA1c Estimation Considering the Skin Effect

by Tae-Ho Kwon, Shifat Hossain, Mrinmoy Sarker Turja and Ki-Doo Kim

Micromachines 2024, 15(9), 1067; https://doi.org/10.3390/mi15091067 (registering DOI) - 24 Aug 2024

Abstract

To diagnose diabetes early or to maintain stable blood glucose levels in diabetics, blood glucose levels should be frequently checked. However, the only way to check blood glucose levels regularly is to use invasive methods, such as pricking the fingertip or using a [...] Read more.

To diagnose diabetes early or to maintain stable blood glucose levels in diabetics, blood glucose levels should be frequently checked. However, the only way to check blood glucose levels regularly is to use invasive methods, such as pricking the fingertip or using a minimally invasive patch. These invasive methods pose several problems, including being painful and potentially causing secondary infections. This study focuses on noninvasively measuring glycated hemoglobin (HbA1c) using PPG signals. In particular, the study relates to a method and a hardware design technology for removing noise that may be present in a PPG signal due to skin contact with a noninvasive HbA1c measurement device. The proposed HbA1c measurement device consists of the first sensor (PPG sensor) module including an optical barrier and the second sensor (cylindrical sensor) module for removing the skin effect. We have developed a Monte Carlo method to implement accurate, noninvasive HbA1c measurement by considering different skin properties among different subjects. Implementing this model in wearable devices will allow end users to not only monitor their glycated hemoglobin levels but also control diabetes with higher accuracy without needing any blood samples. This will be a groundbreaking advancement in modern wearable medical devices. Full article

(This article belongs to the Special Issue The 15th Anniversary of Micromachines)

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11 pages, 5108 KiB

Open AccessArticle

A Low-Power Optoelectronic Receiver IC for Short-Range LiDAR Sensors in 180 nm CMOS

by Shinhae Choi, Yeojin Chon and Sung Min Park

Micromachines 2024, 15(9), 1066; https://doi.org/10.3390/mi15091066 - 23 Aug 2024

Viewed by 178

Abstract

This paper presents a novel power-efficient topology for receivers in short-range LiDAR sensors. Conventionally, LiDAR sensors exploit complex time-to-digital converters (TDCs) for time-of-flight (ToF) distance measurements, thereby frequently leading to intricate circuit designs and persistent walk error issues. However, this work features a [...] Read more.

This paper presents a novel power-efficient topology for receivers in short-range LiDAR sensors. Conventionally, LiDAR sensors exploit complex time-to-digital converters (TDCs) for time-of-flight (ToF) distance measurements, thereby frequently leading to intricate circuit designs and persistent walk error issues. However, this work features a fully differential trans-impedance amplifier with on-chip avalanche photodiodes as optical detectors so that the need of the following post-amplifiers and output buffers can be eliminated, thus considerably reducing power consumption. Also, the combination of amplitude-to-voltage (A2V) and time-to-voltage (T2V) converters are exploited to replace the complicated TDC circuit. The A2V converter efficiently processes weak input photocurrents ranging from 1 to 50 μA_pp which corresponds to a maximum distance of 22.8 m, while the T2V converter handles relatively larger photocurrents from 40 μA_pp to 5.8 mA_pp for distances as short as 30 cm. The post-layout simulations confirm that the proposed LiDAR receiver can detect optical pulses over the range of 0.3 to 22.8 m with a low power dissipation of 10 mW from a single 1.8 V supply. This topology offers significant improvements in simplifying the receiver design and reducing the power consumption, providing a more efficient and accurate solution that is highly suitable for short-range LiDAR sensor applications. Full article

(This article belongs to the Special Issue Microelectronics and Optoelectronic Devices: From Fundamental Research to Advanced Applications)

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14 pages, 5663 KiB

Open AccessArticle

Development of Highly Sensitive and Thermostable Microelectromechanical System Pressure Sensor Based on Array-Type Aluminum–Silicon Hybrid Structures

by Min Li, Yang Xiao, Jiahong Zhang, Qingquan Liu, Xianglong Jiang and Wenhao Hua

Micromachines 2024, 15(9), 1065; https://doi.org/10.3390/mi15091065 - 23 Aug 2024

Viewed by 164

Abstract

In order to meet the better performance requirements of pressure detection, a microelectromechanical system (MEMS) piezoresistive pressure sensor utilizing an array-type aluminum–silicon hybrid structure with high sensitivity and low temperature drift is designed, fabricated, and characterized. Each element of the 3 × 3 [...] Read more.

In order to meet the better performance requirements of pressure detection, a microelectromechanical system (MEMS) piezoresistive pressure sensor utilizing an array-type aluminum–silicon hybrid structure with high sensitivity and low temperature drift is designed, fabricated, and characterized. Each element of the 3 × 3 sensor array has one stress-sensitive aluminum–silicon hybrid structure on the strain membrane for measuring pressure and another temperature-dependent structure outside the strain membrane for measuring temperature and temperature drift compensation. Finite-element numerical simulation has been adopted to verify that the array-type pressure sensor has an enhanced piezoresistive effect and high sensitivity, and then this sensor is fabricated based on the standard MEMS process. In order to further reduce the temperature drift, a thermodynamic control system whose heating feedback temperature is measured by the temperature-dependent structure is adopted to keep the working temperature of the sensor constant by using the PID algorithm. The experiment test results show that the average sensitivity of the proposed sensor after temperature compensation reaches 0.25 mV/ (V kPa) in the range of 0–370 kPa, the average nonlinear error is about 1.7%, and the thermal sensitivity drift coefficient (TCS) is reduced to 0.0152%FS/°C when the ambient temperature ranges from −20 °C to 50 °C. The research results may provide a useful reference for the development of a high-performance MEMS array-type pressure sensor. Full article

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21 pages, 3257 KiB

Open AccessReview

Democratizing Microreactor Technology for Accelerated Discoveries in Chemistry and Materials Research

by Tomomi Sato, Koji Masuda, Chikako Sano, Keiji Matsumoto, Hidetoshi Numata, Seiji Munetoh, Toshihiro Kasama and Ryo Miyake

Micromachines 2024, 15(9), 1064; https://doi.org/10.3390/mi15091064 - 23 Aug 2024

Viewed by 204

Abstract

Microreactor technologies have emerged as versatile platforms with the potential to revolutionize chemistry and materials research, offering sustainable solutions to global challenges in environmental and health domains. This survey paper provides an in-depth review of recent advancements in microreactor technologies, focusing on their [...] Read more.

Microreactor technologies have emerged as versatile platforms with the potential to revolutionize chemistry and materials research, offering sustainable solutions to global challenges in environmental and health domains. This survey paper provides an in-depth review of recent advancements in microreactor technologies, focusing on their role in facilitating accelerated discoveries in chemistry and materials. Specifically, we examine the convergence of microfluidics with machine intelligence and automation, enabling the exploitation of the cyber-physical environment as a highly integrated experimentation platform for rapid scientific discovery and process development. We investigate the applicability and limitations of microreactor-enabled discovery accelerators in various chemistry and materials contexts. Despite their tremendous potential, the integration of machine intelligence and automation into microreactor-based experiments presents challenges in establishing fully integrated, automated, and intelligent systems. These challenges can hinder the broader adoption of microreactor technologies within the research community. To address this, we review emerging technologies that can help lower barriers and facilitate the implementation of microreactor-enabled discovery accelerators. Lastly, we provide our perspective on future research directions for democratizing microreactor technologies, with the aim of accelerating scientific discoveries and promoting widespread adoption of these transformative platforms. Full article

(This article belongs to the Section C：Chemistry)

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12 pages, 14542 KiB

Open AccessCommunication

Offsetting Dense Particle Sedimentation in Microfluidic Systems

by Tochukwu Dubem Anyaduba and Jesus Rodriguez-Manzano

Micromachines 2024, 15(9), 1063; https://doi.org/10.3390/mi15091063 - 23 Aug 2024

Viewed by 180

Abstract

Sedimentation is an undesirable phenomenon that complicates the design of microsystems that exploit dense microparticles as delivery tools, especially in biotechnological applications. It often informs the integration of continuous mixing modules, consequently impacting the system footprint, cost, and complexity. The impact of sedimentation [...] Read more.

Sedimentation is an undesirable phenomenon that complicates the design of microsystems that exploit dense microparticles as delivery tools, especially in biotechnological applications. It often informs the integration of continuous mixing modules, consequently impacting the system footprint, cost, and complexity. The impact of sedimentation is significantly worse in systems designed with the intent of particle metering or binary encapsulation in droplets. Circumventing this problem involves the unsatisfactory adoption of gel microparticles as an alternative. This paper presents two solutions—a hydrodynamic solution that changes the particle sedimentation trajectory relative to a flow-rate dependent resultant force, and induced hindered settling (i-HS), which exploits Richardson–Zaki (RZ) corrections of Stokes’ law. The hydrodynamic solution was validated using a multi-well fluidic multiplexing and particle metering manifold. Computational image analysis of multiplex metering efficiency using this method showed an average reduction in well-to-well variation in particle concentration from 45% (Q = 1 mL/min, n = 32 total wells) to 17% (Q = 10 mL/min, n = 48 total wells). By exploiting a physical property (cloud point) of surfactants in the bead suspension in vials, the i-HS achieved a 58% reduction in the sedimentation rate. This effect results from the surfactant phase change, which increases the turbidity (transient increase in particle concentration), thereby exploiting the RZ theories. Both methods can be used independently or synergistically to eliminate bead settling in microsystems or to minimize particle sedimentation Full article

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13 pages, 24219 KiB

Open AccessArticle

Investigation of the Surface Characteristics of GCr15 in Electrochemical Machining

by Xuesong Liu, Guokang Su, Qingming Fan, Yongjun Zhang, Hua Chen and Chuanyun Zhang

Micromachines 2024, 15(9), 1062; https://doi.org/10.3390/mi15091062 - 23 Aug 2024

Viewed by 238

Abstract

Bearing steel (GCr15) is widely used in key parts of mechanical transmission for its excellent mechanical properties. Electrochemical machining (ECM) is a potential method for machining GCr15, as the machining process is the electrochemical dissolution of GCr15 regardless of its high hardness (>50 [...] Read more.

Bearing steel (GCr15) is widely used in key parts of mechanical transmission for its excellent mechanical properties. Electrochemical machining (ECM) is a potential method for machining GCr15, as the machining process is the electrochemical dissolution of GCr15 regardless of its high hardness (>50 HRC). In ECM, NaNO₃ solution is a popular electrolyte, as it has the ability to help in the nonlinear dissolution of many metallic alloy materials, making it useful for precision machining. However, due to high carbon content of GCr15, the electrochemical dissolution of GCr15 is unique, and there is always a black layer with high roughness on the machined surface, reducing the surface quality. In order to improve the electrochemical machining of GCr15 with a high surface quality, the surface characteristics of GCr15 in ECM were investigated. The anodic polarisation curve in the NaNO₃ electrolyte was measured and electrochemical dissolution experiments were conducted with different current densities. SEM, XRD, and XPS were employed to analyse the surface morphology and composition formed on the machined surface at different current densities. The initial results showed that there were two parts (black part and bright part) formed on the machined surface when a short circuit occurred, and the test results suggested that the black part contained a mass of Fe₃O₄ while the bright part was composed of mainly Fe and Fe₃C. Further investigation uncovered that a black flocculent layer (Fe₃O₄) always formed in a low current density (32 A/cm²) with high roughness. With the current density increased, the amount of black flocculent layer was reduced, and Fe₃C particles appeared on the machined surface. When the current density reached 81 A/cm², the entire flocculent oxide layer was removed, only some spherical Fe₃C particles were inserted on the machined surface, and the roughness was reduced from Ra7.743 μm to Ra1.783 μm. In addition, due to exposed Fe₃C particles on the machined surface, the corrosion resistance of the machined surface was significantly improved. Finally, circular arc grooves of high quality were well manufactured with current density of 81 A/cm² in NaNO₃ electrolyte. Full article

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19 pages, 10930 KiB

Open AccessReview

Recent Advances in Phthalocyanine-Based Hybrid Composites for Electrochemical Biosensors

by Keshavananda Prabhu Channabasavana Hundi Puttaningaiah and Jaehyun Hur

Micromachines 2024, 15(9), 1061; https://doi.org/10.3390/mi15091061 - 23 Aug 2024

Viewed by 228

Abstract

Biosensors are smart devices that convert biochemical responses to electrical signals. Designing biosensor devices with high sensitivity and selectivity is of great interest because of their wide range of functional operations. However, the major obstacles in the practical application of biosensors are their [...] Read more.

Biosensors are smart devices that convert biochemical responses to electrical signals. Designing biosensor devices with high sensitivity and selectivity is of great interest because of their wide range of functional operations. However, the major obstacles in the practical application of biosensors are their binding affinity toward biomolecules and the conversion and amplification of the interaction to various signals such as electrical, optical, gravimetric, and electrochemical signals. Additionally, the enhancement of sensitivity, limit of detection, time of response, reproducibility, and stability are considerable challenges when designing an efficient biosensor. In this regard, hybrid composites have high sensitivity, selectivity, thermal stability, and tunable electrical conductivities. The integration of phthalocyanines (Pcs) with conductive materials such as carbon nanomaterials or metal nanoparticles (MNPs) improves the electrochemical response, signal amplification, and stability of biosensors. This review explores recent advancements in hybrid Pcs for biomolecule detection. Herein, we discuss the synthetic strategies, material properties, working mechanisms, and integration methods for designing electrochemical biosensors. Finally, the challenges and future directions of hybrid Pc composites for biosensor applications are discussed. Full article

(This article belongs to the Special Issue Biosensors for Biomedical and Environmental Applications, Third Edition)

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10 pages, 3480 KiB

Open AccessArticle

Impact of Program–Erase Operation Intervals at Different Temperatures on 3D Charge-Trapping Triple-Level-Cell NAND Flash Memory Reliability

by Xuesong Zheng, Yifan Wu, Haitao Dong, Yizhi Liu, Pengpeng Sang, Liyi Xiao and Xuepeng Zhan

Micromachines 2024, 15(9), 1060; https://doi.org/10.3390/mi15091060 - 23 Aug 2024

Viewed by 225

Abstract

Three-dimensional charge-trapping (CT) NAND flash memory has attracted extensive attention owing to its unique merits, including huge storage capacities, large memory densities, and low bit cost. The reliability property is becoming an important factor for NAND flash memory with multi-level-cell (MLC) modes like [...] Read more.

Three-dimensional charge-trapping (CT) NAND flash memory has attracted extensive attention owing to its unique merits, including huge storage capacities, large memory densities, and low bit cost. The reliability property is becoming an important factor for NAND flash memory with multi-level-cell (MLC) modes like triple-level-cell (TLC) or quad-level-cell (QLC), which is seriously affected by the intervals between program (P) and erase (E) operations during P/E cycles. In this work, the impacts of the intervals between P&E cycling under different temperatures and P/E cycles were systematically characterized. The results are further analyzed in terms of program disturb (PD), read disturb (RD), and data retention (DR). It was found that fail bit counts (FBCs) during the high temperature (HT) PD process are much smaller than those of the room temperature (RT) PD process. Moreover, upshift error and downshift error dominate the HT PD and RT PD processes, respectively. To improve the memory reliability of 3D CT TLC NAND, different intervals between P&E operations should be adopted considering the operating temperatures. These results could provide potential insights to optimize the lifetime of NAND flash-based memory systems. Full article

(This article belongs to the Special Issue Emerging Memory Materials and Devices)

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Micromachines, Volume 15, Issue 9 (September 2024) – 11 articles

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