Faculty Profiles - OKA Chiemi

The Fabrication and Evaluation of a Capacitive Pressure Sensor Using Ru-Based Thin Film Metallic Glass with Structural Relaxation by Heat Treatment Open Access

Otsuka, H; Ninoseki, T; Oka, C; Hata, S; Sakurai, J

SENSORS Vol. 23 ( 23 ) 2023.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Sensors

Microelectromechanical systems (MEMS)-based capacitive pressure sensors are conventionally fabricated from diaphragms made of Si, which has a high elastic modulus that limits the control of internal stress and constrains size reduction and low-pressure measurements. Ru-based thin-film metallic glass (TFMG) exhibits a low elastic modulus, and the internal stress can be controlled by heat treatment, so it may be a suitable diaphragm material for facilitating size reduction of the sensor without performance degradation. In this study, a Ru-based TFMG was used to realize a flattened diaphragm, and structural relaxation was achieved through annealing at 310 °C for 1 h in a vacuum. The diaphragm easily deformed, even under low differential pressure, when reduced in size. A diaphragm with a diameter of 1.7 mm was then applied to successfully fabricate a capacitive pressure sensor with a sensor size of 2.4 mm2. The sensor exhibited a linearity of ±3.70% full scale and a sensitivity of 0.09 fF/Pa in the differential pressure range of 0–500 Pa.

DOI： 10.3390/s23239557

Thick film MEMS process using reverse lift-off Open Access

Takase, S; Yamada, K; Nakagawa, Y; Oka, C; Sakurai, J; Hata, S

MICROELECTRONIC ENGINEERING Vol. 281 2023.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Microelectronic Engineering

The lift-off process is a microfabrication technique that has the capability of forming thin film structures. However, several issues, such as structural shape and burr formation, arise when applying this method to the formation of thick film structures. Thick film structures formed through the lift-off process exhibit a mountainous cross-sectional shape and non-uniform film thickness due to variations in the width of the structure. These challenges make it difficult to apply the method to MEMS. While the reverse lift-off process addresses some of the structural shape problems, its initial development using metal molds makes it challenging to directly apply to MEMS without modification. Therefore, this paper proposes an adaptation to the Si process and presents a method to reduce burrs. The microfabrication characteristics are evaluated by comparing the cross-sectional shapes of thick metallic glass structures formed through both the lift-off and reverse lift-off processes. The structures formed through the reverse lift-off process exhibit a rectangular cross-sectional shape, and the film thickness remains consistent regardless of the structure's width. However, burrs persist on the backside edge of the structure, which hinders its application to MEMS. This paper confirms that pre-etching the underlying Si substrate into an inverse tapered shape effectively reduces burrs. As an illustration of the improved reverse lift-off process applied to MEMS, MEMS mirror structures are fabricated, and their resonance frequency closely aligns with the design value.

DOI： 10.1016/j.mee.2023.112081

Stress measurement based on magnetic Barkhausen noise for thin films

Omae, K; Yamazaki, T; Oka, C; Sakurai, J; Hata, S

MICROELECTRONIC ENGINEERING Vol. 279 2023.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Microelectronic Engineering

Non-destructive testing methods based on magnetic Barkhausen noise (MBN) are expected to be applied to thin films. Recently, MBN analysis using machine learning has been performed on bulk materials and used as an in-situ stress and material evaluation method. However, for thin films, it is difficult to measure due to the weak MBN signal intensity, and few examples of its use as a stress and material evaluation method have been reported. This study acquired and analyzed MBN of Fe–Co polycrystalline thin films under bending stress. After pre-processing the acquired MBNs, two representative machine learning algorithms were used to learn the relationship between MBN and stress. By quantitatively comparing the prediction accuracy of each machine learning method, the characteristics of the MBN-based stress evaluation method were discussed from two perspectives: the need for domain knowledge and its applicability to unknown data. This study provides insight into machine learning-assisted MBN analysis as a stress evaluation method for thin films. The extension of MBN-based stress evaluation methods to thin films could be applied to the non-destructive stress evaluation of micro- and nanostructures, where stress state is critical, and could improve process development efficiency.

DOI： 10.1016/j.mee.2023.112057

国際会議報告：33rd 2022 International Symposium on Micro-NanoMechatronics and Human Science (MHS2022)

岡智絵美

電気学会論文誌Ｅ（センサ・マイクロマシン部門誌） Vol. 143 ( 6 ) page： NL6_1 - NL6_1 2023.6

Parallel plate type fast atom beam source for large area irradiation

Kato Taisei, Morisaki Ryo, Yamazaki Takahiro, Oka Chiemi, Sakurai Junpei, Hata Seiichi

Proceedings of JSPE Semestrial Meeting Vol. 2023S ( 0 ) page： 720 - 721 2023.3

Unidirectional Pore Formation in Resins Using a Magnetic-Nanoparticle-Chain Template Open Access

Kobayashi, A; Sano, K; Sakurai, J; Nagano, H; Hata, S; Oka, C

IEEE MAGNETICS LETTERS Vol. 14 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Magnetics Letters

We present a novel manufacturing technique for generating unidirectional pores in ultraviolet (UV)-curable resins using self-assembled magnetic nanoparticles (MNPs) with chain-like structures.The method utilizes two templation mechanisms for pore formation: the UV-masking effect of the MNP chains and the physical presence of MNP chains themselves.Fe<inf>3</inf>O<inf>4</inf> nanoparticles and PAK-01 were used as the template and UV-curable resin,respectively.Unidirectional pores formed only when resin/MNP mixtures were cured under a strong externally applied magnetic field.Water absorption tests indicated that some of the unidirectional pores were through-hole-type pores. The pores were cylindrical with an ellipsoidal cross-section. When the UV irradiation angle (θ) was 30°, the long and short diameters of the pores were approximately 9 and 8 µm, respectively, before MNP removal, and 12 and 8 µm, respectively, after removal. After MNP removal,the ellipticity of the pores in the samples increased from 1.5 to 2.4 with the increase in θ because of the increased UV-masking effect of the MNP chains.

DOI： 10.1109/LMAG.2023.3268851

Novel measurement method of internal stress in thin films using micro spring structure Open Access

TAKASE Shun, YAMAZAKI Takahiro, OKA Chiemi, SAKURAI Junpei, HATA Seiichi

Mechanical Engineering Journal Vol. 10 ( 4 ) page： 23-00074 - 23-00074 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

As the application areas of MEMS (microelectromechanical systems) expand, more advanced functions and performance are being demanded from MEMS. To meet these demands, materials with various functionalities such as mechanical strength and shape memory, which are difficult to achieve with Si-based materials alone, are being used in MEMS. When applying new materials to MEMS, it is essential to establish micromachining techniques and control internal stresses in the same way as for Si-based thin films. In this research, a method for measuring the internal stress of thin film structures formed by microfabrication technology was developed. The thin film structure sample to be measured is in the form of a beam with fixed ends. The uniaxial strain due to internal stress is measured using a micro spring, and the internal stress is calculated. A process for fabricating a device that realizes the novel measurement method was devised and the device was fabricated. The microfabrication technique used was a reverse lift-off process, which can form thin film structures with rectangular cross-sections and uniform film thickness. Thin film metallic glass, an amorphous alloy with higher strength and lower Young's modulus than Si-based materials, was used as the new material to be measured. Using the developed measurement method, the internal stress change of the thin film was measured as a function of annealing temperature. As a result, it was confirmed that the internal stress of the thin film changed from the compressive direction to the tensile direction with increasing annealing temperature. The internal stress values measured by the novel method were compared with those measured by Stoney's equation, and the two measurement methods were close, demonstrating the usefulness of the new measurement method.

DOI： 10.1299/mej.23-00074

Effect of Structure on Driving Characteristics of the Tactile Pin Actuator for Reaction Force Variable Tactile Displays

Murase Masanori, Nambara Keita, Oka Chiemi, Hata Seiichi, Sakurai Junpei

IEEJ Transactions on Sensors and Micromachines Vol. 143 ( 8 ) page： 236 - 241 2023

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

This paper addresses the effect of structure on driving characteristics of the tactile pin actuator using Ti-Ni-Cu high formable shape memory alloy (HFSMA) for reaction force variable tactile displays. The actuator has a cross shaped 3D structure as a tactile pin that is convex at the center. When the tactile pin is pushed by a finger, it transforms and generates a reaction force against the finger. According to the superelastic effect of SMA, the reaction force can be changed by monitoring the device temperature, allowing tactile displays to present softness and hardness. We examined the driving characteristics of the actuators with different tactile pin height by simulation and measurement of actual samples. When the tactile pin height was low, the tactile pin was only deformed elasticity and reaction force was not changed with increasing device temperature. On the other hands, when the tactile pin height was large, the tactile pin was deformed with the induced martensitic transformation, and reaction force increased with increasing device temperature. In addition, the reaction force at certain temperature was increased as the tactile pin height increased, which means that this actuator can vary the range of reaction force by changing its tactile pin height.

DOI： 10.1541/ieejsmas.143.236

In-process measurement of carbon aggregate emissions in surface activated bonding

FUKUI Taisho, KATO Taisei, Oshima Kyosuke, OKA Tiemi, SAKURAI Junpei, HATA Seichi

The Proceedings of Mechanical Engineering Congress, Japan Vol. 2023 ( 0 ) page： J133p-04 2023

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

Surface activated bonding is a three-dimensional wafer stacking technology utilized in the semiconductor field. In this process wafer surfaces are activated by argon atoms irradiated from a fast atom beam source, allowing bonding to take place is at room temperature and low pressure. However, fast atom beam sources present an issue wherein carbon agglomerates, responsible for bonding defects, are discharged alongside the argon atoms. Therefore, it becomes necessary to replace the carbon electrode before these aggregates released. However, quantitatively measuring the ideal time for replacement has been challenging. To address this concern we developed and validated a quantitative in-process measurement method for monitoring discharged carbon agglomerates. This method involves illuminatinge the wafer surface, capturing dark-field images of carbon agglomerates, and performing image processing to quantify measure the amount of discharged carbon agglomerates discharged. In order to establish a reliable relationship between the size of carbon aggregates (maximum Feret diameter) and the corresponding maximum Feret diameter in the dark-field image, we conduct an investigation. The results of the measurement indicated a significant increase in the number of discharged carbon agglomerates after 150 irradiations. Moreover, the largest number of carbon agglomerates was detected in the area between 5 and 7 pixels. These results suggest that the formation of carbon agglomerates occurs through exfolitation, particularly when the irradiation is temporarily interrrupted before the 150th irradiation.

DOI： 10.1299/jsmemecj.2023.j133p-04

Simulation Estimation Of Oxide Film Removal By Fast Atom Beam

Takamatsu Yuya, Oshima Kyosuke, KATO Taisei, OKA Chiemi, SAKURAI Junpei, HATA Seiichi

The Proceedings of Mechanical Engineering Congress, Japan Vol. 2023 ( 0 ) page： J133p-06 2023

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

Fast atomic beam sources used for surface-activated bonding need to uniformly irradiate a large area. In conventional methods, the irradiation characteristics of such a fast atom beam source must be improved through trial-and-error modifications of the beam aperture arrangement, among other techniques, and by conducting silicon oxide film removal experiments and verification, all of which are inefficient. In this study, we employed the PIC-MCC and DSMC plasma simulation methods to acquire the Ar flux and incident energy distributions on the wafer surface. These distributions predict the amount of oxide film removal caused by the fast atomic beam, and based on them, we constructed a model that predicts the distribution of the amount of film removed. Subsequently, we validated of the prediction model by conducting silicon oxide film removal experiments and obtaining the distributions of the amount of film removed.

DOI： 10.1299/jsmemecj.2023.j133p-06

Prototype of a unidirectional magnetic field-applied fast atom beam source for surface-activated bonding

OSHIMA Kyosuke, Nomura Wataru, KATO Taisei, OKA Chiemi, SAKURAI Junpei, HATA Seiichi

The Proceedings of Mechanical Engineering Congress, Japan Vol. 2023 ( 0 ) page： J133p-02 2023

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

Surface-activated bonding is a wafer bonding technology where the wafer surface is activated by irradiation with a fast atom beam in a vacuum. We have demonstrated that it can improve the irradiation efficiency and reduce bonding defects caused by carbon emissions by controlling the motion of charged particles with a bidirectional magnetic field applied to the beam source. In recent years, there has been a growing need for a beam source that can irradiate a larger area. In this study, we propose a prototype of a unidirectional magnetic field-applied fast atom beam source that can be lengthened or enlarged. The proposed fast atom beam source achieved more than 1.5 times higher oxide film removal performance compared to the conventionally used fast atom beam source. In a long-term irradiation experiment, the proposed fast atom beam source emitted no carbon particles even after more than twice as many irradiations as the conventional fast atom beam source.

DOI： 10.1299/jsmemecj.2023.j133p-02

Effect of structural relaxation at bellow crystallization temperature on internal stress of Ni-Nb-Zr thin film amorphous alloys diaphragm for micro electromechanical systems sensors Open Access

Haga, F; Yamazaki, T; Oka, C; Hata, S; Hoshino, Y; Sakurai, J

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 61 ( SD ) 2022.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

In this paper, the effect of structural relaxation at temperatures below crystallization on internal stress of Ni-Nb-Zr thin film amorphous alloy (including thin film metallic glass: TFMG) diaphragms was investigated. We fabiricated the Ni-Nb-Zr diaphragm samples with four compositions. Before fabrication of diaphragm structure by etching, Ni-Nb-Zr thin films on Si substrate were annealed at a temperature below crystallization (473, 523, and 573 K) for structural relaxation. By performing bulge tests on annealed Ni-Nb-Zr diaphragms, we were able to determine their mechanical properties. As the result, Young’s modulus of all samples increased slightly with increasing annealing temperature because of the decrease of the free volumes during structural relaxation. Based on the results of internal stress, structural relaxation of all samples occurred below 473 K. Moreover, the effects of annealing temperature on internal stress differed by compositions. They were thought to be caused by the rate of structural relaxation.

DOI： 10.35848/1347-4065/ac5d12

Combinatorial search for Ti-Ni-Hf high formable shape memory alloys

Inoue, S; Yamazaki, T; Oka, C; Hata, S; Sakurai, J

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 61 ( 6 ) 2022.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

In this study, we searched for Ti-Ni-Hf high formable shape memory alloys (HFSMAs) using combinatorial methods. By adding Hf to Ti-Ni SMAs, the potential is that Ti-Ni SMAs become metallic glasses. For efficient material search, the glass transition temperature was evaluated through combinatorial measurement of electrical resistance during crystallization. From the results, we searched for Ti-Ni-Hf HFSMAs, which undergo glass transition in the amorphous state. Ni-rich Ti-Ni-Hf thin-film amorphous alloys with more than 10 at% Hf content became thin film metallic glasses, whereas Ni-poor samples did not. Further, we evaluated the effect of annealing temperature on the martensitic transformation temperature of Ti-Ni-Hf SMAs using combinatorial methods. From the results, we measured the reverse transformation start temperature A s at 368-404 K, and it varied with the annealing temperature and Hf composition.

DOI： 10.35848/1347-4065/ac6a97

Examination of Mechanical Properties and Photoelastic Properties of Gel Material for Blood Vesssel Mimics

Yamada, D; Hori, S; Abe, S; Kumeno, Y; Yamazaki, T; Oka, C; Sakurai, J; Hata, S

JOURNAL OF MEDICAL DEVICES-TRANSACTIONS OF THE ASME Vol. 15 ( 3 ) 2021.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Medical Devices Transactions of the ASME

Catheter surgery is a minimally invasive treatment in which visual information is limited to a two-dimensional image generated by an X-ray camera. This results in the possibility that stress applied by the catheter onto a blood vessel wall damages the vessel. Doctors must therefore be skillful at catheter surgery. We proposed a catheter surgery simulator that visualizes the stress applied to the blood vessel wall using photoelasticity. The manufacture of this simulator requires creating blood vessel mimics that reproduce the physical properties of blood vessel tissue using photoelasticity. This study investigated the mechanical and photoelastic properties of gel materials and selected a gel composition suitable for making blood vessel mimics. The mechanical properties of polyvinyl alcohol (PVA) hydrogel changed in the range 70–335 kPa by changing the composition ratio, and double network (DN) gel changed in the range 0.13–1.06 MPa by changing the composition ratio. These gels could be adjusted by changing the material composition to provide Young’s moduli similar to that of blood vessels. The photoelastic properties of PVA hydrogel changed in the range 1.38–2.76 109/Pa by changing the composition ratio, and DN gel changed in the range 0.012–0.029 109/Pa by changing the composition ratio.

DOI： 10.1115/1.4051516

Fabrication and Evaluation of Actuators for Reaction Force Variable Passive-type Tactile Displays

Nambara Keita, Yamazaki Takahiro, Oka Chiemi, Hata Seiichi, Sakurai Junpei

IEEJ Transactions on Sensors and Micromachines Vol. 141 ( 9 ) page： 304 - 309 2021.9

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

In this paper, we report on the fabrication and evaluation of actuator for reaction force variable passive-type tactile display using high formable Ti-Ni-Cu shape memory alloy. This actuator is driven by the superelastic effect and superior in force expression, responsiveness, and miniaturization compared to conventional tactile displays using shape memory alloys. This actuator was fabricated in a convex shape by utilizing a viscous flow of Ti-Ni-Cu metallic glass. After crystallization, the metallic glass was changed to the shape memory alloy. In this manner, we successfully acquired the desired convex cross structure with a height of 123 µm at the center of cross. Additionally, while pushing 100 µm, we successfully varied the reaction force ranged from 40 to 80 mN, necessary to deform the skin and electrical resistance linearly by controlling the temperature. From these results, we showed that the actuator of this study can be used as tactile display that can express desired hardness and softness by temperature control. We also showed the possibility that the temperature of each actuator can be controlled individually by electrical heating using the linear relationship between temperature and electrical resistance.

DOI： 10.1541/ieejsmas.141.304

Combinatorial synthesis of nanocrystalline FeSiBPCuC-Ni-(Nb,Mo) soft magnetic alloys with high corrosion resistance

Yamazaki, T; Tomita, T; Uji, K; Kuwata, H; Sano, K; Oka, C; Sakurai, J; Hata, S

JOURNAL OF NON-CRYSTALLINE SOLIDS Vol. 563 2021.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Non Crystalline Solids

Fe-based nanocrystalline FeSiBPCuC alloys (NANOMET®) with a combination of high magnetic flux density, high permeability, and low iron loss have attracted much attention for use in magnetic core devices such as small power supplies, motors, and transformers. However, further improvement of the corrosion resistance is still required because surface oxidation during the water atomization process inevitably deteriorates the magnetic properties of these alloys. Here, we use a combinatorial magnetron sputtering system to fabricate new (FeSiBPCuC)<inf>100−</inf><inf>x</inf><inf>−</inf><inf>y</inf>Ni<inf>x</inf>(Nb,Mo)<inf>y</inf> (0 ≤ x ≤ 10, 0 ≤ y ≤ 2 at%) amorphous thin films with enhanced corrosion resistance. We found that the co-presence of Ni (2–4 at%) and Mo (1–2 at%) in the FeSiBPCuC amorphous thin films promoted a further improvement of the corrosion resistance. The magnetic coercivity of (FeSiBPCuC)<inf>95.5</inf>Ni<inf>4.0</inf>Nb<inf>0.5</inf> and (FeSiBPCuC)<inf>97.0</inf>Ni<inf>2.0</inf>Mo<inf>1.0</inf> thin films was deteriorated compared with that of a FeSiBPCuC ribbon.

DOI： 10.1016/j.jnoncrysol.2021.120808

Thermo-fluid dynamic analysis in a micro-textured evaporator based on microscale infrared/visible observations for loop heat pipes Open Access

Odagiri, K; Oka, C; Kondou, C; Nagano, H

INTERNATIONAL JOURNAL OF MULTIPHASE FLOW Vol. 140 2021.7

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Multiphase Flow

This paper presents a thermo-fluid dynamic analysis in a micro-textured evaporator for loop heat pipes (LHPs) that has a super wetting surface with ethanol on the basis of an experiment and modeling. In the experiment, three kinds of stainless steel plates with various morphologies of heat transfer surfaces were tested: a normal flat plate, a sandblasted plate, and a micro-groove plate. The measured contact angles between the surfaces and ethanol were 8.2° ± 1.3°, 0°, and 0°, respectively. Evaluation of the heat transfer performance and liquid-vapor interface behavior was conducted using microscale infrared and visible observations. As a result, it was revealed that the sandblasted plate and the micro-groove plate showed 7 times and 20 times higher heat transfer coefficient under high heat flux conditions respectively, compared with the normal flat plate. Different liquid-vapor interface behaviors were found between the plate types. In the modeling, the heat transfer coefficient was predicted for each case. It was found that nucleate boiling heat transfer induced by rough surface increased the heat transfer performance in the case of the sandblasted plate. In addition, it was revealed that the thin film evaporation at the long triple-phase contact line significantly enhanced heat transfer performance in the case of the micro-groove plate. The findings indicate a new promising approach to enhance the heat transfer coefficient of LHP evaporators.

DOI： 10.1016/j.ijmultiphaseflow.2021.103623

Particle-in-cell Monte Carlo collision simulation and experimental measurement of Ar plasma in a fast atom beam source for surface-activated bonding

Ryo Morisaki, Takahiro Yamazaki, Chiemi Oka, Junpei Sakurai, Takami Hirai, Tomonori Takahashi, Hiroyuki Tsuji, Noriyasu Ohno, and Seiichi Hata

Japanese Journal of Applied Physics Vol. 60 ( SC ) page： SCCB01 2021.6

Nanoscale silica coating of porous stainless steel and its impact on water wettability

Oka, C; Odagiri, K; Nagano, H

JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH Vol. 18 ( 2 ) page： 601 - 609 2021.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Coatings Technology and Research

The water wettability of porous stainless steel specimens was enhanced via a nanoscaled silica coating for application to passive two-phase heat transfer devices. A combination of porous stainless steel and water has attracted attention in the area of the heat transfer devices. However, the water wettability of stainless steel is poor, limiting the performance of the devices. In the present study, the silica coating of the specimens was conducted via a reaction of tetraethyl orthosilicate (TEOS) after pretreatment using NaOH aq. or HCl aq. Energy-dispersive X-ray spectrometry revealed that the amount of silica deposited on the surface was dependent on the pretreatment conditions and the composition of the silica-coating solutions. Measurement of porous properties indicated that the silica coating did not affect pore diameter and gas permeability since the coating was in nanoscale. Microscale contact angles were directly evaluated using an environmental SEM. The specimens showed excellent water wettability when they were covered with numerous tiny silica bumps. When the specimen was pretreated with 2 M NaOH aq. and coated in weak alkaline TEOS solution, the contact angle of the porous stainless steel decreased from 87° to 54° after silica coating. The excellent water wettability originated from the relatively smooth surface and a sufficient coverage ratio, which resulted from the moderate strength of chemical etching of the NaOH aq. and the mild silica-coating condition in the weak alkaline solution.

DOI： 10.1007/s11998-020-00417-1