Faculty Profiles - HATA Seiichi

Other Link： https://www.sciencedirect.com/science/article/pii/S1359646223006772

Tuning magnetic properties by microstructure control of nanocrys-talline thin films for compact vibration energy harvesters Reviewed International journal

Sano Kohya, Yamazaki Takahiro, Nakamura Yuta, Ohtake Mitsuru, Oka Chiemi, Sakurai Junpei, Hata Seiichi

IEICE Electronics Express Vol. 21 ( 2 ) page： 1 - 6 2025.2

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electronics, Information and Communication Engineers

The vibration energy harvesting properties of Fe-based nanocrystalline soft magnetostrictive material (Fe-Si-B-P-Cu-C) thin films were systematically investigated. Thin films were deposited using rotational sputtering and subsequently annealed. Nanocrystallizationoccurred in the samples annealed at 100–110% of the crystallization temperature. This nanocrystallization process enhanced soft magnetic properties, however, decrease saturation magnetostriction reflecting the influence of the negative magnetostrictive α-Fe phase. The film annealed at 105% of the crystallization temperature exhibited the highest vibration power generation performance. This superior performance was attributed to the combination of enhanced soft magnetic properties, high saturation magnetic flux density, and a relatively large saturation magnetostriction.

DOI： 10.1587/elex.22.20250031

表面活性化接合用新型高速原子ビーム源 Invited Reviewed

秦　誠一

真空ジャーナル ( 191 ) page： 13 - 16 2025.1

4Dナノインプリントに向けた高成形性形状記憶合金マイクロ構造体の作製

泉光暢, 柴垣竜資, 岡智絵美, 秦誠一, 櫻井淳平

精密工学会学術講演会講演論文集 Vol. 2024A ( 0 ) page： 146 - 146 2024.8

Language：Japanese Publishing type：Part of collection (book) Publisher：公益社団法人精密工学会

高成形性形状記憶合金（HFSMA）は，非晶質状態で金属ガラスの特性を，結晶化後に形状記憶特性を示す．熱ナノインプリントによりHFSMA製繊毛構造体の加工を行い，ナノ繊毛アクチュエータの作製を検討している．本研究では，リソグラフィによりマイクロホールのSiモールドを作製し，熱ナノインプリントによってHFSMAマイクロ柱状構造体を作製した．今後は，高アスペクト比のナノ柱状（繊毛）構造体の作製を目指す．

DOI： 10.11522/pscjspe.2024a.0_146

Effect of Noise on Accuracy of Grain Size Evaluation by Magnetic Barkhausen Noise Analysis Reviewed International journal

Omae Kanna, Yamazaki Takahiro, Sano Kohya, Oka Chiemi, Sakurai Junpei, Hata Seiichi

International Journal of Automation Technology Vol. 18 ( 4 ) page： 528 - 536 2024.7

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Fuji Technology Press Ltd.

Magnetic Barkhausen noise (MBN) is a magnetic signal caused by domain wall motion and is used for non-destructive testing and evaluation of ferromagnetic materials because of its sensitivity to both mechanical and magnetic properties. Recently, machine learning models have been employed to evaluate materials based on MBN; however, the application of material evaluation to low-volume targets is challenging because of their low signal-to-noise ratio, which is due to their low vol-ume. Therefore, understanding the influence of the signal-to-noise ratio is important, particularly for low-volume objects. However, very few reports have quan-titatively assessed the influence of noise in MBN anal-ysis. In this study, we focused on noise to improve the accuracy of MBN analysis using machine learning, investigated its impact on the prediction accuracy of machine learning models, and explored methods to mit-igate its effects. A method for grain size evaluation based on MBN analysis was adopted and performed for Fe-Co alloy wires with different grain sizes. After the measurement of MBN, the relationship between the extracted features from the analysis of MBN by fast Fourier transform and grain size was learned using a gradient boosting decision tree to create a grain size evaluation model, and the coefficient of determi-nation was used to evaluate the prediction accuracy of the grain size evaluation. The machine learning model demonstrated high prediction accuracy (R2 = 0.926) across the entire grain size range. Using the model to assess the effect of signal-to-noise ratio, experiments were also conducted using MBN time-series data with artificially applied Gaussian noise. Additionally, from the insight of the distribution of predicted grain sizes, we confirmed that a noise reduction method by aver-aging the MBN prediction results can improve the prediction accuracy by reducing the effect of noise as ex-pected. This research will lead to the adoption of MBN applications, which are simple and practical methods of material evaluation, for the micro–nano discipline.

DOI： 10.20965/ijat.2024.p0528

Prototype of Parallel Plate Type Fast Atom Beam Source and its Improvement of Irradiation Characteristics Reviewed International journal

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

International Journal of Automation Technology Vol. 18 ( 4 ) page： 513 - 520 2024.7

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Fuji Technology Press Ltd.

Fast atom beam (FAB) source is used for surface activated bonding. This process is attracting attention as an essential process for next-generation semiconductor manufacturing. Traditional wafer direct bonding processes require annealing or cannot be directly bonded at room temperature. Therefore, there are restrictions on the materials that can be bonded and the combinations of materials that can be bonded. However, surface activated bonding has made it possible to directly bond dissimilar materials at room temperature. This technology is expected to be applied to the manufacturing of various MEMS and three-dimensional stacking of semiconductors. This bonding process involves bom-barding the wafer surface with fast argon atom beam in a vacuum chamber. Irradiation removes oxide layer and contaminants, exposing dangling bonds. By press-ing the wafers together, the dangling bonds are bonded together, and a strong bond is achieved. The device that generates this fast argon atom beam is FAB source. This device has been of the type that generates a saddle field electric field. However, this FAB source had a nar-row beam irradiation area and was unable to support the recent increase in wafer diameter. Therefore, it was necessary to perform irradiation using multiple FAB sources. At production sites, there is a need to develop new FAB sources that can irradiate large areas. In this study, we developed FAB source in which the beam is generated by parallel plate electrodes. We performed a comparison with the saddle field type FAB source and found that the performance was inferior in initial experiments. Next, we improved the design to oper-ate at higher voltages and increased the aperture area. Through these improvements, we have achieved performance superior to the saddle field type FAB source.

DOI： 10.20965/ijat.2024.p0513

Insights into thermally-induced disruption of magnetic-nanoparticle agglomerates Reviewed International journal Open Access

Bailin Cheng, Junpei Sakurai, Seiichi Hata, Chiemi Oka

Alexandria Engineering Journal Vol. 96 page： 72 - 81 2024.6

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal)

We investigated the temperature dependence of agglomeration systems consisting of interacting single-domain magnetic nanoparticles (MNPs). In our study, we utilized electron spin resonance (ESR) experiments to measure how temperature-induced change in agglomerate state affects the peak-to-peak width of ESR spectra (Hpp) and validated these observations through simulations. Micromagnetic simulations were conducted by combining the classical magnetic dipolar Metropolis Monte Carlo method with the semi-classical macro-spin Landau-Lifshitz-Gilbert finite element method, and the results were compared with experimental findings. Our research elucidates the behavior of thermally-induced disruption of MNP agglomerates. We discovered that the temperature at which MNPs are completely dispersed might correspond to one at which the temperature dependence of Hpp disappears.

DOI： 10.1016/j.aej.2024.03.101

Open Access

One-dimensional assemblies of magnetic iron-oxide nanoparticles Reviewed International journal

Shiojima T., Sakurai J., Hata S., Oka C.

Japanese Journal of Applied Physics Vol. 63 ( 3 ) 2024.3

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

Although high-aspect-ratio iron-oxide nanoparticles (IONPs) are known to have higher heating efficiency than spherical and cubic IONPs and focused in cancer treatment areas, their synthesis methods require high temperatures, vacuum, reduction conditions, and substantial time. In this study, we proposed and established a facile manufacturing method for one-dimensional assemblies of IONPs, expected to increase heating efficiency similar to high-aspect-ratio IONPs. We investigated how the fabrication conditions affect the length of the assemblies and found that the average length of the one-dimensional assemblies increased with the extension of magnetic-field-application time. This result demonstrates that the length could be controlled by adjusting the duration of the magnetic field application.

DOI： 10.35848/1347-4065/ad26bd

The effects of periodic textured substrate to control diffusion angle on the conversion efficiency of dye-sensitized solar cells International journal Open Access

Ryutaro Kimura, Chiemi Oka, Seiichi Hata, Junpei Sakurai

Japanese Journal of Applied Physics Vol. 63 ( 3 ) 2024.3

Authorship：Corresponding author Publishing type：Research paper (scientific journal)

We suggested improving the conversion efficiency of dye-sensitized solar cells (DSSCs) by the micro-nano periodic textures to control the diffusion angle of the incident light for certain absorbed wavelengths of the used dye. A periodic texture (Prd-Tx) was designed to enhance the light path of the wavelength of DSSCs’ dye absorption with a wide process window by optical simulation (pitch: 1400 nm, pillar diameter: 460-560 nm, pillar height: more than 500 nm). The Prd-Tx was fabricated by photolithography processes and nanoimprinting (pitch: 1400 nm, pillar diameter: 500 nm, pillar height: 1000 nm). The Prd-Tx increased the DSSCs’ conversion efficiency (η of 3.13%), surpassing our previous best result (refabricated W-Tx, η of 3.08%). It was considered that the ohmic loss was suppressed owing to the Prd-Tx enhanced electrical conductivity at the interface between the transparent electrode, F-doped tin oxide (FTO), and TiO2

DOI： 10.35848/1347-4065/ad2417

Open Access

色素増感太陽電池の変換効率への周期型回折テクスチャ基板の効果

木村龍太郎, 岡智絵美, 秦誠一, 櫻井淳平

精密工学会学術講演会講演論文集 Vol. 2024S ( 0 ) page： 713 - 714 2024.2

Authorship：Corresponding author Language：Japanese Publishing type：Part of collection (book) Publisher：公益社団法人精密工学会

本研究では，微細テクスチャの回折効果を利用してDSSCsの変換効率を向上させることを目指した．光学シミュレーションからDSSCs使用色素に適した回折テクスチャ形状を設計し，ナノインプリント等の微細加工を用いて作製した．回折テクスチャを適用したDSSCsは変換効率を向上させたが，これは回折テクスチャ上に成膜された透明電極FTOの広い表面積により，FTO/TiO2界面の導電性が向上したことに起因すると考えられた．

DOI： 10.11522/pscjspe.2024s.0_713

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

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

Sensors Vol. 23 ( 23 ) 2023.12

Authorship：Corresponding author 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

PubMed

Other Link： https://www.mdpi.com/1424-8220/23/23/9557

Thick film MEMS process using reverse lift-off Reviewed

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

Microelectronic Engineering Vol. 281 2023.9

Authorship：Last author,　Corresponding author 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

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

Other Link： https://www.sciencedirect.com/science/article/pii/S0167931723001466

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

IEEJ Transactions on Sensors and Micromachines Vol. 143 ( 8 ) page： 236 - 241 2023.8

Authorship：Corresponding author 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

Stress measurement based on magnetic Barkhausen noise for thin films Reviewed

Kanna Omae, Takahiro Yamazaki, Chiemi Oka, Junpei Sakurai, Seiichi Hata

Microelectronic Engineering Vol. 279 2023.7

Authorship：Last author,　Corresponding author 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

Web of Science

Effect of Textured Classes on Conversion Efficiency in Dye-Sensitized Solar Cells Reviewed

Other Link： https://www.sciencedirect.com/science/article/abs/pii/S0167931723001223

7) Ryutaro Kimura, Yuji Nishiyasu, Chiemi Oka, Seiichi Hata, and Junpei Sakurai

Nanomanufacturing Vol. 3 ( 3 ) page： 315 - 325 2023.6

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

Atsuki Kobayashi, Kohya Sano, Junpei Sakurai, Hosei Nagano, Seiichi Hata, Chiemi Oka

IEEE Magnetics Letters Vol. 14 2023.4

Authorship：Corresponding author 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. Fe3O4 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 theta) was 30 degrees, the long and short diameters of the pores were approximately 9 and 8 mu m, respectively, before MNP removal, and 12 and 8 mu m, 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 theta because of the increased UV-masking effect of the MNP chains.

DOI： 10.1109/LMAG.2023.3268851

Web of Science

第4回　機械材料・材料加工(技術ロードマップから見る2030年の社会) Reviewed

秦誠一, 古川英光, 中尾航, 宮下幸雄

日本機械学会誌 Vol. 126 ( 1253 ) page： 38 - 41 2023.4

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

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

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

Authorship：Last author,　Corresponding author 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

Web of Science

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 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

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 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