Faculty Profiles - OKA Chiemi

Papers - OKA Chiemi

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Combinatorial Evaluation for corrosion resistance of High Formable Shape Memory Alloys

CHIZUWA Kaname, OKA Chiemi, HATA Seiichi, SAKURAI Junpei

The Proceedings of the Materials and processing conference Vol. 2019.27 ( 0 ) page： 207 2019

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

In this study, we propose a combinatorial evaluation method for evaluating the corrosion resistance of the Ti-Ni-based high formable shape memory alloys (HFSMAs) based on anodic polarization tests. The proposed evaluation substrates compose nine samples which have different compositions. These samples are deposited on a glass substrate by carousel sputtering system and microelectromechanical processes. Further, we performed anodic polarization tests on the Ti–Ni–Zr and Ti–Ni–Cu HFSMAs samples. The polarization curves are obtained by sweeping the potential and the current density at the passive state (ips) of each composition tested is compared. In case of the Ti–Ni–Zr alloy, ips varied depending on the Zr content. When the Zr content ranged from 10 to 15 at.%, their ips were comparable with that of Ti48Ni52 used in medical devices. On the other hand, in case of the Ti-Ni-Cu alloy, their ips were similar to that of Ti48Ni52 regardless of Cu content. We obtained Ti–Ni–Zr and Ti–Ni–Cu HFSMAs having a corrosion resistance equivalent to that of Ti48Ni52. Furthermore, we conducted XPS analysis to investigate the passive film of HFSMAs. The thin surface film of Ti-Ni-Zr alloys were composed of TiO2 and ZrO2, while that of Ti-Ni-Cu alloys were composed of only TiO2. We have concluded that the formation of TiO2 enriched protective thin surface film might have been responsible for the high corrosion resistance.

DOI： 10.1299/jsmemp.2019.27.207

CiNii Research

Development of real-time photoelastic 3D stress measurement system for surgical simulator

YAMADA Daichi, HORI Simon, OKA Chiemi, SAKURAI Junpei, HATA Seiichi

The Proceedings of the Materials and processing conference Vol. 2019.27 ( 0 ) page： P01 2019

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

In recent years, minimally invasive treatment has attracted attention, and catheter surgery is one of them. On the other hand, in catheter surgery, visual information is limited to only a two-dimensional image by an X-ray camera. Therefore, there is a problem that stress is applied to the blood vessel wall and it is damaged, so doctors are required the skill of catheter surgery. In order to improve the surgeon's surgical technique, the authors have proposed a surgical simulator that realizes real-time visualization of stress by the photoelastic method. In this study, we propose a measurement system using a photoelastic method that can visualize stress in three dimensions and examine the blood vessel model shape applicable to the proposed measurement system.

DOI： 10.1299/jsmemp.2019.27.p01

CiNii Research

Improvement of conversion efficiency of dye-sensitized solar cell by textured substrates

NISHIYASU Yuji, YANG Na, OKA Chiemi, HATA Seiichi, SAKURAI Junpei

The Proceedings of the Materials and processing conference Vol. 2019.27 ( 0 ) page： P04 2019

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

In this paper, we fabricated two types of optical textured glass substrates by a polydimethylsiloxane (PDMS) nanoimprint lithography (NIL) on the front glass to enhance conversion efficiency of dye-sensitized solar cells (DSSCs). Two types of master molds for nano-texture (N-Tx) and micro-nano-double texture (D-Tx) were prepared by an aluminum anodic oxidation. Both N-Tx and D-Tx showed higher total transmittance and lower reflectance than bare glass. Finally, we fabricated DSSCs with textured glass. The used dye was red N719. The cell size was 6 mm square. As the results, the conversion efficiency of DSSCs with textured glasses increased by 26% for N-Tx (η of 3.67%) and 19% for D-Tx (η of 3.47%) compared to DSSC with flat glass (η of 2.91%).

DOI： 10.1299/jsmemp.2019.27.p04

CiNii Research

Development and evaluation of the novel FAB gun

Morisaki R., Hirai Y., Sakurai J., Mizoshiri M., Oka C., Hirai T., Takahashi T., Tsuji H., Hata S.

European Society for Precision Engineering and Nanotechnology, Conference Proceedings - 19th International Conference and Exhibition, EUSPEN 2019 page： 104 - 105 2019

Language：English Publishing type：Research paper (scientific journal) Publisher：European Society for Precision Engineering and Nanotechnology, Conference Proceedings - 19th International Conference and Exhibition, EUSPEN 2019

Argon fast atom beam (FAB) gun is used as a neutral atom beam irradiation source for surface activated bonding (SAB). Since SAB does not require any heat treatments, stress due to difference in thermal expansion coefficients does not occur, and the bonding between not only the same material but also different materials is realizable. However, the conventional FAB gun can be used for only short time because carbon abrasion powders are generated from the worn part of the inside walls of the gun due to argon ion sputtering. We developed the novel FAB gun applied magnetic fields and new position of the anodes in the gun to control the motion of the argon ions and reduce the sputtering. The design concept is that the magnetic fields guide both argon ions and electrons to the irradiation port of the gun and the argon atoms for the irradiation increased. In this study, we investigated the influence of the positions of the magnetic fields and the anodes on the plasma generation, the argon irradiation and the sputtering. With the novel FAB gun, the stable plasma is generated in the vicinity of the irradiation port, and the maximum irradiation amount is 3 times in comparison with the conventional design. Less sputtering of the inside walls of the gun was observed after the irradiation for more than thousands of minutes, while the sputtering with the conventional gun is more observed at the same condition.

Scopus

Basic research on micro processing characteristics of reverse lift-off process

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

MHS 2018 - 2018 29th International Symposium on Micro-NanoMechatronics and Human Science 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：MHS 2018 - 2018 29th International Symposium on Micro-NanoMechatronics and Human Science

In micro electromechanical systems(MEMS) technology, lift-off processes are general patterning methods for the formation of amorphous alloy thick film structures. However, thicknesses of structures fabricated in this method are not uniform and cross-sectional shapes are not flat because sputtered particles are blocked by the sidewalls of the lift-off layer. In order to solve this problem, a reverse lift-off process is proposed as a new patterning method [1]. In the reverse lift-off process, the desired structure is formed on the top of the convex pattern such as the substrate. In contrast to the lift-off process, the thickness of the structure is uniform and the cross-sectional shape is rectangular because sputtered particles are not blocked by the sidewalls. In this research, thick film structures were fabricated in reverse lift-off processes from the width of the convex pattern on the order of micrometers. And the film thickness and the cross-sectional shape of the fabricated structure are measured, and the micro processing characteristics of the reverse lift-off process, which had not yet been elucidated, were investigated. This demonstrates the usefulness of fabricating the thick film micro structures in the reverse lift-off process.

DOI： 10.1109/MHS.2018.8886962

Scopus

Fabrication of miniaturized capacitive pressure sensor using thin film metallic glass

Uejima S., Oka C., Hata S., Sakurai J.

MHS 2018 - 2018 29th International Symposium on Micro-NanoMechatronics and Human Science 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：MHS 2018 - 2018 29th International Symposium on Micro-NanoMechatronics and Human Science

In this paper, we proposed the process of the diaphragm for miniaturizing MEMS capacitive pressure sensor and controlling its sensitivity. We fabricated micro diaphragm using a Ru65Zr30Al5(at.%) thin film metallic glass (TFMG). The as-sputtered TFMG on Si substrate were annealed at 315-440°C for 5 minutes in vacuum. After annealing, micro diaphragms were fabricated by an etching Si substrate using a reactive ion etching system. Although the diaphragm without annealing had dome structure, the diaphragm annealed above 340°C formed a flat structure. The deflection of the diaphragm against applied pressure depended on the annealing temperature and decreased at higher temperatures. The pressure sensor was modeled using this diaphragms. The pressure measurement range and sensitivity were 250 Pa and 6.4×10-3 pF/Pa, respectively, for annealed at 340°C, and 1800 Pa, and 8.1 × 10-4 pF/Pa, respectively for annealed at 440°C.

DOI： 10.1109/MHS.2018.8887020

Scopus

Study of a high heat transport Loop Heat Pipe for the automobile thermal management

AONO Yoshitada, NAGANO Hosei, YAMASHITA Seiji, ISHIKIRIYAMA Mamoru, HOSHINO Yu

The Proceedings of Conference of Tokai Branch Vol. 2018.67 ( 0 ) page： 519 2018

Fabrication of micro diaphragm using thin film metallic glass

ISHIKI Ryuji, Uejima Syohei, Oka Chiemi, SAKURAI Junpei, LIN Yu-Ching, Hata Seiichi

The Proceedings of Mechanical Engineering Congress, Japan Vol. 2018 ( 0 ) page： J2220303 2018

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

A diaphragm structure is a fundamental structure in a micro machine such as MEMS. Conventionally, Si has used as a diaphragm material. However, in recent years, in order to make the diaphragm structure more sophisticated and miniaturized, high sensitivity difficult to realize by using Si is required. Therefore, in this study, we aim to create a highly precise diaphragm structure by using the thin film metallic glass which is an amorphous alloy shown glass transition as a new material which meets these demands. Pd77Cu6Si17 (at. %) and Ru65Zr30Al5 (at. %) are used for thin film metallic glass. The thin film metallic glasses are deposited on the Si substrates by sputtering. Internal stress of each film is controlled by adjusting Ar pressure during sputtering and annealing after sputtering. The internal stress of the Pd77Cu6Si17 (at. %) thin film is always tensile stress and it is minimum at an Ar pressure of 0.5 Pa, and its value is 23.6 MPa. Under this condition, we can create a highly precise diaphragm. On the contrary, the internal stress of Ru65Zr30Al5 (at. %) thin film is always compressive stress in the range of sputtering Ar pressure. So, we try to relax the internal stress of Ru65Zr30Al5 (at. %) thin film by annealing. In the proper annealing conditions, a diaphragm having the same flatness level as Pd77Cu6Si17 (at. %) is realized.

DOI： 10.1299/jsmemecj.2018.j2220303

CiNii Research

Fabrication of Miniaturized Capacitive Pressure Sensor Using Thin Film Metallic Glass

UEJIMA Shohei, OKA Chiemi, HATA Seiichi, SAKURAI Junpei

The Proceedings of Mechanical Engineering Congress, Japan Vol. 2018 ( 0 ) page： J2220304 2018

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

Further miniaturization of the diaphragm for capacitive pressure sensor requires thinner structures to deform micro diaphragm sufficiently by small differential pressure. Since stiffness of thinner structures decrease, the influence of internal stress introduced during processing cannot be ignored. In this paper, we proposed methods of controlling the internal stress for micro diaphragm using thin film metallic glasses (TFMGs). We fabricated micro diaphragms using Ru67Zr25Al8 [at.%] TFMGs. The TFMGs were fabricated by a r.f. sputtering system, and then as sputtered TFMGs had compressive internal stress. Subsequently, the as-sputtered TFMGs on Si substrate were annealed at 315-440°C for 5 minutes in vacuum. After annealing, micro diaphragms were fabricated by etching Si substrate using a reactive ion etching system. Although annealing temperatures were lower than glass transition temperature, initial internal stress was relaxed partially by the structural relaxation of the TFMGs during annealing process. While the tensile thermal stress was induced during cooling process at the interface between the substrate and TFMG. Although micro diaphragm was not induced thermal stress at interface between the substrate and TFMG, the tensile stress applied to diaphragm in the radial direction at the edge. When annealing temperatures were between 320°C and 340°C, the internal stress changed from compressive to tensile. A flat diaphragm was obtained when annealed at 330°C or higher. The pressure sensor modeled by diaphragm annealed at 340°C and the virtual electrode plate showed a linearity of 6.48 [%F.S.]. By proposed method, we succeeded the flat diaphragm and showed the method of tension control of the diaphragm.

DOI： 10.1299/jsmemecj.2018.j2220304

CiNii Research

Evaluation of the bonding methods of Ti-Ni based high formable shape memory alloys

AOYAMA Ryosuke, OKA Chiemi, HATA Seiichi, SAKURAI Junpei

The Proceedings of the Materials and processing conference Vol. 2018.26 ( 0 ) page： 901 2018

Basic research on micro processing characteristics of reverse lift-off process

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

2018 INTERNATIONAL SYMPOSIUM ON MICRO-NANOMECHATRONICS AND HUMAN SCIENCE (MHS) 2018

Fabrication of Miniaturized Capacitive Pressure Sensor using Thin Film Metallic Glass

Uejima, S; Oka, C; Hata, S; Sakurai, J

2018 INTERNATIONAL SYMPOSIUM ON MICRO-NANOMECHATRONICS AND HUMAN SCIENCE (MHS) 2018

Effect of wettability of a porous stainless steel on thermally induced liquid-vapor interface behavior

Oka C., Odagiri K., Nagano H.

SURFACE TOPOGRAPHY-METROLOGY AND PROPERTIES Vol. 5 ( 4 ) 2017.12

The role of Bgl2p in the transition to filamentous cells during biofilm formation by Candida albicans.

Chen X, Zhang R, Takada A, Iwatani S, Oka C, Kitamoto T, Kajiwara S

Mycoses Vol. 60 ( 2 ) page： 96-103 2017.2

Biodegradable and magnetic core-shell composite particle prepared by emulsion solvent diffusion method Reviewed

Chiemi Oka, Kazunori Ushimaru, Nanao Horiishi, Takeharu Tsuge, Yoshitaka Kitamoto

Japanese Journal of Applied Physics Vol. 55 page： 02BE01 2016

Heat generation of core-shell particles composed of biodegradable polymer and iron oxide Reviewed

C. Oka, K. Ushimaru, N. Horiishi, T. Tsuge, Y. Kitamoto

Journal of the Magnetics Society of Japan Vol. 40 page： 126-131 2016

Core-shell composite particles composed of biodegradable polymer particles and magnetic iron oxide nanoparticles for targeted drug delivery Reviewed

Chiemi Oka, Kazunori Ushimaru, Nanao Horiishi, Takeharu Tsuge, Yoshitaka Kitamoto

Journal of Magnetism and Magnetic Materials Vol. 381 page： 278-284 2015.1

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Papers - OKA Chiemi