担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Wearable sweat-sensing devices hold significant potential for non-invasive, continuous health monitoring. However, challenges such as ensuring data accuracy, sensor reliability, and measurement stability persist. This study presents the development of a wearable system for the real-time monitoring of human sweat sodium levels, addressing these challenges through the integration of a novel microfluidic chip and a compact potentiostat. The microfluidic chip, fabricated using hydrophilic materials and designed with vertical channels, optimizes sweat flow, prevents backflow, and minimizes sample contamination. The developed wearable potentiostat, as a measurement device, precisely measures electrical currents across a wide dynamic range, from nanoamperes to milliamperes. Validation results demonstrated accurate sodium concentration measurements ranging from 10 mM to 200 mM, with a coefficient of variation below 4% and excellent agreement with laboratory instruments (intraclass correlation = 0.998). During physical exercise, the device measured a decrease in sweat sodium levels, from 101 mM to 67 mM over 30 min, reflecting typical physiological responses to sweating. These findings confirm the system’s reliability in providing continuous, real-time sweat sodium monitoring. This work advances wearable health-monitoring technologies and lays the groundwork for applications in fitness optimization and personalized hydration strategies. Future work will explore multi-biomarker integration and broader clinical trials to further validate the system’s potential.

DOI： 10.3390/s25113467

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Endotracheal intubation is frequently performed on critically ill patients or those under general anesthesia, but it carries risks of incorrect insertion into the esophagus or premature removal. To address these concerns, we propose an adaptor for tracheal intubation tube with integrated respiration monitoring functionality, enabled by a micro-electro mechanical systems (MEMS) airflow sensor packaged in a 3-D-printed housing. The adaptor shared the same dimensions as the conventional slip joint, ensuring seamless compatibility with standard intubation tubes. Basic characteristics measurement indicated a sufficient performance for human respiration monitoring. Feasibility tests using an artificial ventilator to simulate breathing demonstrated the system's effectiveness. Furthermore, proof of concept via animal experiments also demonstrated successful respiration monitoring using the proposed system. The proposed device has a potential to enhance the safety and precision of endotracheal intubation by offering real-time airflow monitoring, reducing the risk of misplacement or premature extraction.

DOI： 10.1109/JSEN.2025.3586776

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Palpation technologies in teleoperated catheterization are essential for remotely assessing tissue characteristics such as stiffness and elasticity, which are critical for identifying pathways in cardiovascular or pulmonary system, as well as to detect abnormalities such as tumors. In this letter, we present the development of a tactile sensor probe designed to support catheterization procedures. The sensor utilizes a pneumatic sensing mechanism, with its deformable tip fabricated from polydimethylsiloxane (PDMS) elastomer for biocompatibility and flexibility. Tip deformation is transmitted to a remotely located pressure sensor through a dual-fluid system using incompressible water and compressible air to relay force information. This configuration enables spatial separation between the sensing tip and the detection electronics, enhancing safety and compatibility in medical environments. Sensitivity of the system was tuned by adjusting the air gap height, and experimental results closely matched theoretical models. A reliable correlation was observed between sensor output, tip deformation, and applied normal force, confirming the sensor's capability for quantitative tactile feedback. These results demonstrate the potential of the proposed sensor for enhancing palpation in catheter-based, minimally invasive procedures.

DOI： 10.1109/LSENS.2025.3585201

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Pulmonary diseases are of the leading causes of deaths worldwide. This has motivated researchers to develop respiration monitoring devices to allow enhanced prevention and early diagnosis of the diseases. In this study, we propose a novel palm-sized real-time wireless respiration monitoring system attachable to conventional medical masks. A micro-electro mechanical systems (MEMS) calorimetric flow sensor is at the heart of the system. The sensor system is powered with coin batteries and the measurement data was transmitted through Bluetooth. The sensor package was optimized to achieve a stable output even with a short flow channel length of 34 mm, limiting the dead space. A measurement of respiration rate and tidal volume was demonstrated, which was consistent with a spirometry reference generally used for respiration measurements in hospitals.

DOI： 10.1109/Transducers61432.2025.11109997

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Thermal sensing in MEMS has great potential for developing flexible physical sensors due to the absence of resonating structures. However, achieving fast response times requires minimizing thermal mass around the sensing element. Unlike rigid MEMS sensors, flexible sensors face significant challenges in fabricating free-standing structures due to their lack of mechanical support. Traditionally, reducing thermal mass has been achieved by using thinner substrates, but this approach was limited by handling and installation difficulties. To overcome this, here we propose a laser ablation technique to selectively remove unnecessary substrate material from the backside of flexible MEMS thermal sensors. Using a pulsed UV laser, localized ablation effectively reduces thermal mass, leading to a significant improvement in response time. Experimental validation through thermal analysis and airflow sensor testing confirmed that this approach successfully suppressed time response by over 90%.

DOI： 10.1109/Transducers61432.2025.11109315

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Intravascular therapy is a minimally invasive procedure that treats vascular abnormalities and requires accurate hemodynamic assessment to ensure effective treatment. Monitoring intravascular pressure within blood vessels provides insight into flow dynamics and pathological conditions. Current devices, including pressure-sensing guidewires, rely on embedded MEMS sensors near the tip, introducing electronic components into the body, while other interventional tools, such as stents, either remain passive or measure only non-hemodynamic parameters. To address these limitations, we developed a catheter-based pressure measurement system that enables direct pressure acquisition without flow disruption or internal embedding electronics, providing a more accurate hemodynamic assessment. The system employs a Pitot tube catheter integrated with MEMS-based sensors to evaluate pressure profiles in a 3D-printed vessel model with 30Calibration of both the pressure sensor and the peristaltic pump ensured reliable data acquisition throughout the operating range. The system successfully captured the pressure distribution along the vessel, including a significant pressure drop of approximately 420 Pa across the stenotic region and partial recovery downstream. These results validate the feasibility of Pitot-based catheter probes for in situ flow evaluation and demonstrate their potential for future applications in experimental and computational hemodynamics.

DOI： 10.1109/ICA65945.2025.11252048

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

A detailed study of the sensor structure, fabrication, and technical specification is essential for process design aimed at achieving miniaturization across various applications. This article introduces a facile fabrication approach for creating a 3-D free-standing structure of micro-electro-mechanical system (MEMS) thermal flow sensors. Laser micromachining was used to pattern and separate the free-standing structure, which was then folded like origami to create a 3-D shape. The sensor operates on the principle of thermal anemometry within a constant temperature electronic circuit to detect changes in flow rate within a tube. This proposed method simplifies the fabrication process through a single-step laser fabrication, successfully producing thin nichrome sensing elements as narrow as 45.1 μm with an electrical resistance up to 6 Ω and a temperature coefficient of resistance (TCR) of 390.39 ppm/°C. Thermal analysis via infrared thermography confirms that the free-standing design effectively reduced thermal mass. We detail the sensor’s technical specifications, including time response and calibration curve, and demonstrate its sensitivity to airflow through the voltage responses. This highlights the sensor’s robust performance and its promising potential for various airflow measurement applications.

DOI： 10.1109/JSEN.2025.3559179

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This paper presents a new approach to fabricating micro-electromechanical systems (MEMS) thermal flow sensors using an integrated fiber laser micromachining process. The patterning and thinning process was achieved in a single step through the proposed digital manufacturing approach. The compact, flexible design allowed sensor mounting on practically any substrate. A free-standing structure with localized thinning minimized thermal mass, enhancing sensitivity and response speed. The proposed method eliminates the need for multi-step conventional microfabrication, offering a cost-effective and scalable solution. Airflow testing validated its potential, establishing it as a promising alternative for sensor fabrication in biomedical airflow applications.

DOI： 10.1109/Transducers61432.2025.11111450

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Thermal sensing mechanism in microelectro mechanical system (MEMS) has an inherent potential to realize various flexible physical MEMS sensors due to the absence of resonating structure. In such thermal sensors, it is crucial to limit the thermal mass around the sensing structure to speed-up the time response. The absence of rigid body presents technical challenges to fabricate free-standing sensing elements in flexible MEMS sensors. In such sensors, the thermal mass has been generally limited by the utilization of thin substrates. However, there is a limit when switching to thinner substrate becomes challenging, mainly due to handling and installation constraints. As a solution, here we propose a laser ablation process to locally remove the unnecessary substrate parts in flexible MEMS thermal sensors. The concept was validated experimentally through thermal analysis and response time measurements under operation as airflow sensors. Time response suppression of up to 50% was confirmed.

DOI： 10.1109/JSEN.2025.3529837

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Respiratory diseases, particularly chronic obstructive pulmonary disease (COPD), are a major global health concern, yet existing clinical tools fall short in accurately assessing airflow within small, lesion-affected regions of the lungs. To overcome this limitation, here we developed a novel hollow microcatheter-based actuator-sensor system capable of measuring respiration directly within the bronchioles. The system integrated a tubular airflow rate sensor, fabricated through a standard micro-electro mechanical systems (MEMS) process, into the base of a microcatheter, while the tip consisted of a hollow actuator with an outer diameter of as small as 0.8 mm. This compact design enabled accurate airflow measurement in airways as small as 0.825 mm in diameter, which corresponds to the 13^th branch of airway in healthy adults. Additionally, we systematically analyzed the relationship between airway diameter, catheter insertion depth, and airflow through the catheter to optimize measurement performance in bronchioles approximately 1 mm wide.

DOI： 10.1109/Transducers61432.2025.11111038

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

The transportation sector is a major source of global greenhouse gas emissions, contributing about a quarter of all energy-related carbon emissions. Enhancing transportation efficiency is crucial for reducing these emissions, with wall shear stress playing a key role in vehicle aerodynamics. This study presents a simple method for fabricating a flexible thermal sensor for wall shear stress detection. A thin nichrome foil was patterned using a ultraviolet (UV) laser and transferred onto various surfaces. This approach enabled the creation of a free-standing flexible microstructure. Infrared thermography confirmed localized heat dissipation, reducing thermal mass effects. Airflow tests demonstrated a response time under 20 ms, highlighting the sensor's potential for aerodynamic applications and eventually efficiency improvements in transportation systems.

DOI： 10.1109/Transducers61432.2025.11110067

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Animal experiments are essential in drug development, providing critical insights into a drug's efficacy, safety, and physiological effects before progressing to human clinical trials. In this context, we present a novel biodegradable airflow sensor designed for eco-friendly respiratory monitoring during animal studies. The sensor features a molybdenum (Mo) thin film patterned onto a flexible polyvinyl alcohol (PVA) substrate. We conducted a detailed investigation of Mo thin film deposition and achieved a temperature coefficient of resistance (TCR) of -2,063 ppm/°C through precise microstructuring. The sensor operated via Joule heating and employed constant current anemometry for airflow detection. Notably, the device fully degraded within 30 s when immersed in water, demonstrating its potential as a safe and environmentally friendly implant for temporary monitoring applications.

DOI： 10.1109/Transducers61432.2025.11109686

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Respiratory diseases such as chronic obstructive pulmonary disease (COPD) remain a leading cause of death worldwide, yet current clinical tools lack the ability to accurately quantify airflow parameters within specific lesion sites in the lungs. To address this need, we developed a balloon catheter sensor system capable of measuring respiration directly within the lung airways. A micro-electro mechanical systems (MEMS)-based thermal sensor was fabricated on a thin, flexible polyimide film and integrated into the catheter using its natural by-design buckling behavior. The balloon structure enabled airflow rate measurement independent of airway diameter, enhancing versatility. With an outer diameter of 4.0 mm, the catheter could be easily inserted into lung airways up to the 3^rd branch, which typically measures 5.6 mm in healthy adults. Real-time inhalation and exhalation airflow measurements were successfully demonstrated using an artificial ventilator model.

DOI： 10.1109/Transducers61432.2025.11110036

Scopus

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Intravenous drug administration delivers medication directly into the bloodstream, providing rapid and controlled effects, making it highly beneficial for emergencies or when immediate drug action is required. However, several risks are associated with intravenous drug administration, including infiltration and extravasation, which can lead to serious complications due to the rapid absorption of medication to the surrounding tissues. To prevent complications, here we proposed a non-contact sensor module to rapidly detect such events. The system does not interfere with the human skin, nor contaminating the flowing medication since only biocompatible materials are exposed to the liquid. The proposed sensor module was assembled as a flow channel with flow rate and pressure sensing functions. The flow rate sensing was realized using a micromachined thermal flow sensor fabricated on a thin polyimide film, while the pressure sensing was realized using a diaphragm structure and a MEMS pressure sensor. Basic characteristics of each function was evaluated and a proof of concept experiment demonstrated a rapid detection of infiltration/extravasation within a few s. Measurement of leaked fluid volume during the event was also demonstrated.

DOI： 10.1007/s10544-024-00730-1

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Currently, wearable sensors can measure vital sign frequencies, such as respiration rate, but they fall short of providing quantitative data, such as respiratory tidal volume. Meanwhile, the airflow at the mouth carries both the frequency and quantitative respiratory signals. In this study, we propose a method to calibrate a wearable piezoelectric thread sensor placed on the chest using mouth airflow for accurate quantitative respiration monitoring. Prior to human trials, we introduced an artificial ventilator as a test subject. To validate the proposed concept, we embedded a miniaturized tube airflow sensor at the ventilator’s outlet, which simulates human respiration, and attached a wearable piezoelectric thread to the piston, which moves periodically to mimic human chest movement. The integrated output readings from the wearable sensor aligned with the airflow rate measurements, demonstrating its ability to accurately monitor not only respiration rate but also quantitative metrics such as respiratory volume. Finally, tidal volume measurement was demonstrated using the wearable piezoelectric thread.

DOI： 10.3390/electronics13234577

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Present wearable sensors are able to measure the frequency of vital signs such as respiration rate and heartbeat rate, but unable to measure those quantitatively, e.g. respiratory volume and heartbeat strength. Meanwhile, airflow at mouth contains both the respiration and the heartbeat quantitative signals. In this study, we propose a calibration method for a wearable vital sensor attached on the chest using the airflow at the mouth for quantitative respiration monitoring. An artificial ventilator and an experimental animal were introduced as test benches prior to human clinical experiment. As a proof of concept, a micro-electro mechanical systems (MEMS) airflow sensor and a wearable accelerometer were implemented to both the test benches. The velocity output of the piston motion measured by the wearable sensor conformed with the airflow rate output, and the obtained results indicated that the wearable sensor can monitor not only the frequency of vital signs but also quantitative magnitudes such as the respiratory volume. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

DOI： 10.1002/tee.24045

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Respiratory diseases, including the cronic obstructive pulmonary disease (COPD) are among the leading causes of death worldwide. To date, there is no physical examination procedure that can quantify important parameters within a specific lesion area inside the lung. In this study, we propose a novel sensor probe system consisting of a basket forceps and 2 pressure sensors to simultaneously measure the expiratory airflow and the static pressure inside the pulmonary airway. A Pitot tube mechanism using 2 pressure sensors is introduced in the system for measuring both the physical quantities. Small fiber-optic pressure sensors with 0.3 mm diameter were utilized, and both the airflow rate and the static pressure characteristics were evaluated for obtaining the calibration curves. Finally, the proposed sensor system was implemented to measure both the airflow and pressure in an artificial ventilator and an experimental animal. The measurement of expired airflow and static pressure inside the airway of a rat with the diameter of 1.8 mm were demonstrated. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

DOI： 10.1002/tee.24039

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

This paper presents a facile fabrication approach for micro-electro-mechanical systems (MEMS) thermal sensors, utilizing laser ablation and origami techniques to create a 3D free-standing structure. A single-step fabrication for a micromachined metal structure was demonstrated using a fiber laser. Thin nichrome sensing structures as small as 45.1 1/4m width were fabricated, with an electrical resistance of up to 6 Ω and a TCR of 390.39 ppm/°C. Thermal analysis via infrared thermography revealed that the free-standing structure exhibits a diminished thermal mass. The voltage response for airflow demonstrates the sensing ability of the fabricated structure, showcasing its potential for airflow sensing applications.

DOI： 10.1109/SENSORS60989.2024.10785084

Scopus

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担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

Periodical tartar removal in canine is generally performed under general anesthesia to restrain its movement. A tracheal intubation tube is usually attached to the canine to allow immediate support in the case of emergency. To support such a procedure, here we propose a micro-machined flow sensor to be embedded in animal’s tracheal intubation tube for respiration monitoring. A tube thermal flow sensor based on a two-layer tube structure with a built-in film sensor was embedded inside the intubation tube where steady flow was confirmed through fluid dynamics simulation. The respiration and heartbeat monitoring using the developed device was successfully demonstrated in an animal experiment using a rat.

DOI： 10.1541/ieejsmas.144.390

Scopus

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The microelectro mechanical systems (MEMS) accelerometer has been implemented in various applications across industries. To expand its application to textiles, here, we propose a facile fabrication and packaging method for fiber-shaped flexible MEMS thermal accelerometer. The sensing structure was fabricated through a standard microfabrication process on a thin polyimide film substrate. The film was then cut into stick shape and packaged inside a flexible resin tube through a facile insertion process. A sensitivity improvement strategy by mitigating the thermal mass around the sensing structure was also introduced. Gravitational acceleration measurement using the proposed sensors was demonstrated using an inclination stage. Finally, measurement of human hand movement using the proposed sensors was demonstrated.

DOI： 10.1109/LSENS.2023.3326122

Scopus

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Respiration and heartbeat are among the important vital signs of living beings. Taking advantage of the physical attachment of the lung and heart, measurements of both can be performed simultaneously using airflow rate microsensors to measure the respiration airflow. For such airflow rate sensors, the packaging is crucial to define and encapsulate the airflow region. In this study, we propose a facile packaging technique for flexible airflow rate microsensors. The thermal calorimetric sensing structure was fabricated through a standard microfabrication technology on a thin polyimide (PI) film. The film was packaged at the center of a resin tube utilizing its buckling. We also proposed an approach to improve the time response by limiting the thermal capacity around the sensing structure through the implementation of a thin substrate for the sensing structure supported by a thicker film. The strategy successfully improved both the time response and sensitivity of the airflow rate sensor. Finally, the utilization of the sensor for simultaneous respiration and heartbeat measurement was demonstrated through an animal experiment using a small animal, namely rats.

DOI： 10.1109/JSEN.2023.3272310

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記述言語：英語   掲載種別：研究論文（学術雑誌）

In a previous study, a flexible thermal flow sensor for detecting respiratory airflow was installed inside the slip joint of an intubation tube system to support its insertion. In this study, the airflow stream distribution in the slip joint is systematically analyzed to determine the optimal placement of the airflow sensor. First, the airflow distribution in both the baby and adult tracheal intubation tubes was analyzed using finite element simulations. Backward flow was discovered near the inside surface of the slip joint during exhalation, with a stronger magnitude in the baby intubation tube in comparison with its adult counterpart. However, no backward flow was observed during inhalation. To clarify the simulated flow profile, the airflow stream inside the slip joint of the baby tracheal intubation tube during exhalation was examined experimentally. A stick-type airflow sensor was proposed and developed using MEMS technology for airflow measurements. The backward airflow was experimentally verified in the vicinity of the inside surface of the slip joint during exhalation, which was in agreement with the simulation results. Consequently, the airflow sensor is found to be optimal when placed around the radial center of the slip joint, which shows a consistent airflow profile under both inhalation and exhalation.

DOI： 10.1541/ieejsmas.143.6

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Airflow at the mouth contains both the respiration and the heartbeat signals. In this study, we propose a calibration method for a wearable vital sensor attached on the chest using the airflow at the mouth for respiration and heartbeat quantitative monitoring. An artificial ventilator and an experimental animal, namely rat, were introduced as test benches prior to human clinical experiment. As a proof of concept, a micro-electro mechanical systems (MEMS) airflow sensor and a wearable accelerometer were implemented to both the test benches. The velocity output of the piston motion measured by the wearable sensor conformed with the airflow rate output, and the obtained results indicated that the wearable sensor can monitor not only the frequency but also the respiratory volume or heartbeat strength.

Scopus

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

In this study, we propose a novel sensor probe system consisting of a basket forceps and two pressure sensors to simultaneously measure the expiratory airflow and the static pressure inside the pulmonary airway. A Pitot tube mechanism using two pressure sensors is introduced in the system for measuring both the physical quantities. Small fiber-optic pressure sensors with 0.3 mm diameter were utilized, and both the airflow rate and the static pressure characteristics were evaluated for obtaining the calibration curves. Finally, the proposed sensor system was implemented to measure both the airflow and pressure in an artificial ventilator and an experimental animal. The measurement of expired airflow and static pressure inside the airway of a rat with the diameter of 1.8 mm were demonstrated.

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）

A tube-integrated flow sensor is proposed in this study by integrating a micro-electro mechanical systems (MEMS) flow-sensing element and electrical wiring structure on the same copper on polyimide (COP) substrate. The substrate was rolled into a circular tube with the flow-sensing element installed at the center of the tube. The signal lines were simultaneously formed and connected to the Cu layer of the substrate during the fabrication of the sensing structure, thus simplifying the electrical connection process. Finally, by rolling the fabricated sensor substrate, the flow sensor device itself was transformed into a circular tube structure, which defined the airflow region. By implementing several slits on the substrate, the sensing element was successfully placed at the center of the tube where the flow velocity is maximum. Compared to the conventional sensor structure in which the sensor was placed on the inner wall surface of the tube, the sensitivity of the sensor was doubled.

DOI： 10.3390/mi14010042

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Micro-electro mechanical systems (MEMS) thermal flow sensors have been widely utilized for a wide spectrum of applications. Innovative fabrication processes using polymers have resulted in the development of their flexible alternatives which allowed mounting in a wider range of situations. To accurately measure airflow-rate using a MEMS flow sensor, the airflow region has to be defined and encapsulated. In this study, we propose a facile packaging method of flexible MEMS airflow-rate sensor. The thermal sensing structure was fabricated on a flexible polyimide film. The film was inserted into a resin tube through its taper-cut end and fixed at the center of the tube taking advantage of its buckling. Sensitivity and response speed enhancement were demonstrated by limiting the thermal loss to the substrate by introducing a sensor structure with double-layer substrate.

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Heterogeneous integration of micro-electro mechanical systems (MEMS) and complementary metal oxide semiconductor (CMOS) integrated circuits (ICs) by 3D stacking or wafer bonding is an emerging approach to advance the functionality of microdevices. Aluminum (Al) has been of interest as one of the wafer bonding materials due to its low cost and compatibility with CMOS processes. However, Al wafer bonding typically requires a high temperature of 450 (Formula presented.) C or more due to the stable native oxide which presents on the Al surface. In this study, a wafer bonding technique for heterogeneous integration using electroplated Al bonding frame is demonstrated. The bonding mechanism relies on the mechanical deformation of the electroplated Al bonding frame through a localized bonding pressure by the groove structures on the counter wafer, i.e., press marking. The native oxide on the surface was removed and a fresh Al surface at the bonding interface was released through such a large mechanical deformation. The wafer bonding was demonstrated at the bonding temperatures of 250–450 (Formula presented.) C. The influence of the bonding temperature to the quality of the bonded substrates was investigated. The bonding shear strength of 8–100 MPa was obtained, which is comparable with the other Al bonding techniques requiring high bonding temperature.

DOI： 10.3390/mi13081221

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

In establishing electrochemically deposited Al as a structural microdevice, its surface uniformity and mechanical properties such as the hardness are of great importance. In this study, an improvement of surface uniformity and mechanical hardening of the film by factors of about 100 and 4, respectively, are reported. Both were associated to the grain size effect, which is attributed to the inclusion of 2-chloronicotinyl chloride additive acting as a grain growth inhibitor in the electrochemical bath. Other important properties, such as the elastic modulus, residual stress and electrical resistivity of the deposit are also studied. This study holds a great potential to pave the way for the utilization of the electrochemically deposited Al in microsystems and related technologies.

DOI： 10.1016/j.scriptamat.2022.114599

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Aluminum has a great potential as a wafer bonding material due to its inherent compatibility with the complimentary metal oxide semiconductor (CMOS) processes. In this study, a novel wafer bonding technique for heterogeneous integration using electroplated Al bonding frame is demonstrated for the first time. The Al frames were deposited by electroplating from a chloroaluminate ionic liquid. The electroplated Al bonding frames were mechanically deformed by the groove structures on the counter wafer, i.e. press marking. Such a large mechanical deformation enabled the wafer bonding at a temperature of as low as 250°C, which is the lowest value that has ever been reported for the Al bonding. The influence of the bonding temperature to the quality of the bonded substrates were evaluated. The bonding shear strength of 8-100 MPa was obtained, which is in par with the other established techniques.

DOI： 10.1109/Transducers50396.2021.9495544

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

In this study, a micro electro mechanical system (MEMS) thermal actuator using an electrochemically deposited thick Al is reported for the first time. Due to the fine columnar shape of the grain, the electrical resistivity of the Al film was as high as 100-150 n/m, which is an order of magnitude higher than the bulk value. Such a high resistivity benefits to facilitate the Joule heating during the operation of the thermal actuator. Meanwhile, the coefficient of thermal expansion (CTE) of the electrochemically deposited Al film was experimentally evaluated to be 20-27 ppm/K, which is consistent with the previous reports. With such a large CTE, the material has a potential to enhance the working displacement and force of a thermal actuator. The suspended structure was fabricated using a tetraethyl orthosilicate (TEOS) chemical vapor deposition (CVD) SiO2 as a sacrificial layer. The tip displacement of the fabricated v-shape thermal actuator was around 10 μm at 3 V actuation voltage. The demonstration can open up a new class of MEMS thermal actuator using electroplated Al films as the structural material.

DOI： 10.1109/SSI52265.2021.9466952

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

In this paper, a degenerated in-plane and out-of-plane 2-axis resonators for roll/pitch rate integrating gyroscopes (RIGs) is reported. A dynamically balanced out-of-plane resonator is proposed to achieve small frequency mismatch between in-plane and out-of-plane modes, with high quality-factors (Q-factors). An innovative dual-mass structure was designed to reduce the torque applied to the supporting substrate in the out-of-plane mode, and thus increased the Q-factor. The concept was confirmed by both numerical simulation and the measurement of a real device. The finite element analysis (FEA) study showed the frequency mismatch as small as 6.3 Hz. Fabrication process using Au-Au thermo-compression bonding has been developed. The experimental characterization revealed that the mismatches of resonant frequencies and Q-factors were 106 Hz and 790, respectively.

DOI： 10.1109/SENSORS47087.2021.9639685

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

To practically utilize an electrochemically deposited Al film in microsystems, its material properties have to be elucidated, along with the influence of different deposition conditions. In this study, microstructure, electrical, mechanical and thermal properties of electrochemically deposited Al film from a chloroaluminate ionic liquid electrolyte are comprehensively investigated. The nanoindentation hardness and elastic modulus of the film varied between 486–908 MPa and 41–102 GPa, respectively, depending on the deposition condition. The electrical resistivity and the coefficient of thermal expansion varied between 51–160 nΩ m and 2–20 ppm/K, respectively. The results are compared to those of Al thin films deposited using other techniques. The characterized properties were found to be associated to the microstuctures of the deposits, which can be tailored by the deposition conditions. The microstructures of the deposits were comprehensively characterized by cross-sectional scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) spectroscopy. These results are useful as a design guide for the future applications of the film.

DOI： 10.1016/j.sna.2020.112384

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The sealed cavity pressure of a micro-package often becomes the determining factor of the performance of an encapsulated micro-electro mechanical system (MEMS). In this study, a sealed cavity pressure evaluation method for a micro-package using a thin diaphragm is studied comprehensively. The sealed cavity pressure is identical to the surrounding pressure when the diaphragm separating both volumes becomes flat, i.e. zero-balance method. The zero-balance method has advantages to other techniques in terms of fabrication process simplicity and pressure evaluation range. Two approaches are introduced to reduce the impact of the residual stress, which typically exists in the conventionally used silicon-on-insulator (SOI) diaphragm. The introduction of a stress compensation layer was able to reduce the impact of the residual stress of SOI-based diaphragms. However, a significant hysteresis is developed on the diaphragm, which limits the precise measurement of a sealed cavity. On the other hand the residual stress can be avoided by the usage of intentionally tensile stressed boron doped Si diaphragm, which is produced by alkaline wet etching. Using such a diaphragm, a sealed cavity pressure of several Pa can be measured with a single digit Pa accuracy.

DOI： 10.1109/JMEMS.2020.2984229

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記述言語：英語   掲載種別：研究論文（学術雑誌）

In this study, a novel fabrication method of quartz glass resonators is proposed. The resonators are mechanically supported by Au posts, which are also used as bonding material between the quartz glass device layer and the substrate. The mechanical supporting structures consist of anchor structures and sacrificial supporting structures. The anchor structures remain to support the fabricated resonators during operation while the sacrificial supporting structures are removed during the release process of the resonator. The sacrificial supporting structures were employed to mechanically support the fragile resonator structure during the whole fabrication process. The supporting structures also played a role to dissipate the generated heat during the plasma process and keep the device layer temperature low. Using the proposed method, micromachined resonators were successfully fabricated on a quartz glass substrate. The maximum process temperature was less than 400 °C, thus the method has a large potential as a mean to fabricate quartz glass microstructures on various kind of substrates including the complimentary metal-oxide semiconductor (CMOS) substrates.

DOI： 10.1016/j.sna.2020.111922

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

An in-plane and out-of-plane 2-axis resonator is required for a roll/pitch rate integrating gyroscope (RIG), which is much more challenging in design and fabrication compared with an in-plane 2-axis resonator used in a yaw RIG. In this study, we propose a dynamically balanced out-of-plane resonator to increase the out-of-plane quality factor (Q-factor). A balanced dual-mass structure is designed to reduce the torque applied to the supporting substrate, and thus increase the Q-factor of the out-of-plane mode. Design optimization for frequency matching, reducing mechanical deformation and increasing Q-factor through finite element method (FEM) simulation has been demonstrated. Manufacturing method of the device employing Au-Au thermo-compression bonding has been developed. The fabricated resonator oscillated at around 4380 Hz after remove by using an externally stacked piezoelectric actuator and laser Doppler vibrometer (LDV).

DOI： 10.1109/INERTIAL48129.2020.9090078

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