Name

OHASHI, Keishi

Official Title

Senior Researcher(Professor)

Affiliation

(Research Organization for Nano & Life Innovation)

Contact Information

Mail Address

Mail Address
k-ohashi@aoni.waseda.jp

Address・Phone Number・Fax Number

Address
513 Waseda Tsurumaki-Cho, Shinjuku-ku, Tokyo, Japan
Phone Number
+81-3-5286-8341

URL

Grant-in-aids for Scientific Researcher Number
50740560

Educational background・Degree

Degree

Dr. Engineering Thesis Nagoya University Electron device/Electronic equipment

Career

1996/08-1998/05NEC Ibaraki Ltd.MR Head DivisionSenior Manager etc.
1998/05-2014/03NEC CorporationCentral Research LabsSenior Manager, Research Fellow, etc.
2014/04-2015/03Waseda UniversityInstitute of Nanoscience & NanotechnologySenior Researcher (Professor)
2015/04-Waseda UniveristyResearch Organization for Nano & Life InnovationSenior Researcher (Professor)
2004/10-2006/03RIKENFrontier Research Programs, Investigative Research Team for Long Wavelength LightTeam Leader
2006/04-2011/05Semiconductor Leading Edge Technologies, Inc.Program Manager
2019/11-EC SENSING, INC.General Manager

Academic Society Joined

Magnetics Society of Japan

Institute of Electronics Information & Communication Engineers Committee Member, Technical Committee on System NanoTechnology

The Japan Society of Applied Physics

The Electrochemical Society of Japan

Institute of Electrical and Electronics Engineers

Materials Research Society

The Electrochemical Society

International Society of Electrochemistry

OfficerCareer(Outside the campus)

1999/04-2005/03The Magnetics Society of JapanCouncilor
2001/04-2003/03Advanced Machining Technology & Development AssociationCommittee Member, Committee on Research Study for 3D Micromachining of Functional Materials
2006/08-2010/07Institute of Electronics Information & Communication EngineersVice-Chair, Technical Group on Silicon Photonics
2006/04-2012/03Semiconductor Industry Association in Japan (The JEITA Semiconductor Board)Committee Member, Arrangement Committee for INC
2008-2014The Electrochemical SocietyOrganizer, Integrated Optoelectronics
2009/04-2015/03Japan Science and Technology AgencyResearch Adviser, Creation of Nanosystems with Novel Function through Process Integration, Core Research for Evolutionary Science and Technology
2011/04-2012/03Research & Development Association for Future Electron DevicesCommittee Chairperson, Technical Planning Committee
2011/04-2014/03Japan Electronics and Information Technology Industries AssociationCommittee Member, Technical Strategy Committee for Sensing Technology
2011-2012Materials Research SocietyLead Organizer, MRS 2012 Spring, Symposium L “Group IV Photonics for Sensing and Imaging”
2016-2017The Electrochemical SocietyOrganizer, Contemporary Issues and Case Studies in Electrochemical Innovations

Award

Paper Award

2006/08Conferment Institution:Japan Society of Applied Physics

Title:Si Nano-Photodiode with a Surface Plasmon Antenna

Award Winner(Group):Tsutom Ishi, Kikuo Makita, Toshio Baba, Keishi Ohashi

Technical Award

2006/03Conferment Institution:Surface Finishing Society of Japan

Title:Development and Practical Use of the Electrodeposited CoFeNi Alloy Film for a High Density Magnetic Recording Head

Award Winner(Group):Tetsuya Osaka, Madoka Takai, Keishi Ohashi, Mikiko Saito, Yoshifumi Mizoshita, Yoshio Koshikawa

The Highest Award, Demo Day

2015/10Conferment Institution:Waseda Enhancing Development of Global Entrepreneur Program

Title:Animal Physiological Balance

Award Winner(Group):Keishi Ohashi, Mikiko Shimaoka, Yuusuke Maruyama, Kousuke Kataoka

Others Basic Information

2015/08

Recognized as a "Super EDGE Global Entrepreneur", WASEDA-EDGE Program for Development of Global Entrepreneurs, Waseda University

Research Field

Keywords

Sensing Technology

Grants-in-Aid for Scientific Research classification

Interdisciplinary science and engineering / Nano/Micro science / Nano/Microsystems

Complex systems / Biomedical engineering / Rehabilitation science/Welfare engineering

Informatics / Human informatics / Intelligent robotics

Engineering / Electrical and electronic engineering / Electron device/Electronic equipment

Cooperative Research Theme Desire

Biologicl Sensing

Institution:Cooperative research with other research organization including private (industrial) sectors

Purpose:Sponsord research

Technology Seeds

Monitoring Chemical Balance in Epidermal Barriers

Seeds Field:Nanotechnology / Materials

Chemical Health Monitor Kind to Skin

Seeds Field:Life sciences

Research interests Career

2016-2019Display device for art

Current Research Theme Keywords:Electrochromism

Cooperative Research within Japan

2014-2019Bio sensing

Current Research Theme Keywords:ISFET, sensing system

Cooperative Research within Japan

2010-2014Image Sensing using IR and Microwave

Current Research Theme Keywords:Infrared Material, Carbon Nanotube, RFID

Cooperative Research within institute

2005-2010LSI On-chip Optical Interconnect

Current Research Theme Keywords:LSI Interconnection, Photoelectric Conversion, Electrooptic Effect

Cooperative Research within Japan

2004-2006High-resolution THz-wave Imaging

Current Research Theme Keywords:Teraherz-Wave, Near-Field

Cooperative Research within Japan

2002-2010Surface-Plasmon-Resonance Devices

Current Research Theme Keywords:Surface Plasmons, Nano Ceramics

Cooperative Research within institute

1992-2002High magnetic moment material and its application to magnetic devices

Current Research Theme Keywords:Magnetic Recording, Magnetic Material

Cooperative Research within Japan

1979-1998Magnetic Thin Film Head

Current Research Theme Keywords:Micromagnetics, Electrochemistry

Cooperative Research within institute

Paper

Review of Physiological Balance Sensing in an Unobtrusive Manner

Ohashi, Keishi; Kuroiwa, Shigeki; Hideshima, Sho; Nakanishi, Takuya; Osaka, Tetsuya

Electronics and Communications in Japan 100(9) p.50 - 552017/09-2017/09

DOIScopus

Detail

ISSN:19429533

Outline:© 2017 Wiley Periodicals, Inc. The concept of unobtrusive physiological balance sensing system implementing biosensors is discussed. Biosensors connected with a data system are expected to play a significant role when we extend the sensing objects from body to mind and spirit. Here, we describe the unobtrusive monitoring system using field effect transistor–type sensors and wireless communication devices. Substances subject to the survey of our research will include small ions, immunoglobulins, and hormones.

Industrialization Trial of a Biosensor Technology

Ohashi, Keishi; Osaka, Tetsuya

ECS Transactions Peer Review Yes Invitation Yes 75(39) p.1 - 92017/01-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:A biosensing system is commercialized based on a concept of physiological balance for healthcare. The addition of low-cost biochemical sensors to the sensing system would help with scientific prescriptions based on contemporary medicine. As a candidate for a low-cost and robust chemical sensor platform, the ion-sensitive field-effect transistor (ISFET) has long been examined. After reviewing past ISFET research, our two approaches for new business trials are discussed. One approach is based on the progressiveness of technology that relies on a public finance with existing big companies. Another approach is a lean startup based on a customer development model for entrepreneurs.

Tag-antenna-based presence sensing using near-field traveling-wave reader antenna

Hattori, Wataru; Ohashi, Keishi; Fukuda, Hiroshi

2014 International Conference on the Internet of Things, IOT 2014 p.103 - 1072014/10-

DOIScopus

Detail

Outline:© 2014 IEEE. We propose tag-antenna-based sensing (TABS) for detecting objects and people using a low-cost near-field traveling-wave reader antenna. This technology is inspired by TABS, which enables the use of ordinary far-field radio-frequency identification (RFID) tags as extremely low-cost proximity presence sensor nodes. This allows the sensor nodes to be pervasively deployed in the Internet of Things (IoT); however, frequent reading errors have been a problem in applying practical usage for detecting objects and people. We introduce a low-cost near-field traveling-wave RFID reader antenna that significantly reduces reading errors. We successfully demonstrated the detection of items and human footprints by adopting this technology.

Recognized Technologies and Unrecognized Technologies

K. Ohashi

Magnetics Japan 8(6) p.288 - 2912013/12-

link

A Plastic-Based Bolometer Array Sensor Using Carbon Nanotubes for Low-cost Infrared Imaging Devices

Kaoru Narita, Ryosuke Kuribayashi, Ersin Altintas, Hiroko Someya, Kenichiro Tsuda, Keishi Ohashi, Toru Tabuchi, Shuichi Okubo, Masaharu Imazato, Shigeyuki Komatsubara

Sensors and Actuators A 195p.142 - 1472013/06-

DOI

Detail

Outline:We have developed an infrared image sensor based on bolometers on a plastic substrate that is potectially ultra low-cost due to its simple structure consisting of mainly organic materials. The bolometer includes a thermal isolator made of a very low thermal conductive polymer (parylene) and a newly developed, highly sensitive (TCR<-2%/K) carbon nanotube thin film thermister. Experiment results showed that the responsivity of our sensor was 138 V/W (at V_B = 2V) and the estimated noise equivalent temperature difference (NETD) at room temperature was 1.1 K. The row-column type 64-pixel (8 x 8) array sensor was gabricated and evaluated while the image of a heat source was focused on the sensor array by a Ge lens. Utilizing the test readout circuit based on switching modules, we obtained the images of the heat source and confirmed the basic operation of IR imaging.

Infrared Optical and Mechanical Properties of Ceramic Coatings Fabricated by Aerosol Deposition

Hiroki Tsuda, Jun Akedo, Shingo Hirose, Keishi Ohashi

Additional Conferences, Microelectronics Research Portal Peer Review Yes 2012(CICMT) p.406 - 4102012/09-

DOI

Detail

Publish Classification:Research paper (international conference proceedings)

Outline:The posibility and mechanical improvement of the infrared ceramic coatings fabricated on fluoride substrates at room temperature by aerosol deposition (AD) were investigated aiming to optical components for infrared applications and devices. The yttria coating possibility fabricated on barium fluoride substrate by the AD process was found by adjusting one of the deposition conditions The optical and mechanical properties of the fabricated ceramic coatings, which are important in practical applications, were evaluated by transmittance and hardness measurements respectively. The mechanical hardness of the fabricated yttria single coatings was increased to 4 times higher than that of the barrium fluoride substrates. Furthermore, by an additional layer on a barium fluoride substrate, the mechanical properties of the fabricated multi-coatings including an upper yttria layer were improved from that of the single yttria coating on the barium fluoride substrate, retaining the IR transmittance of the single yttria coating at the wavelength of 10 um.

Photodetection Using Surface-plasmon Enhancement

Keishi Ohashi

Journal of the Surface Science Society of Japan 33(4) p.191 - 1962012/04-

DOI

Detail

Outline:This paper describes the recent trend of the surface-plasmon technology for photo-detectors. Surface plasmons create strong near-field on a metal surface thereby reducing the size of the photodetectors. One of the merits for such small detectors is their extremely small electric capacitance. A possible effect of the small capacitance is to bring about the high efficiency of the photo detector circuit at very high frequency. Small photodiodes for on-chip optical interconnection and data communication are reviewed as an example of such applications. A near-field probe for subwavelength THz imaging is also discussed.

InGaAs Nano-Photodiode Enhanced Using Polarization-Insensitive Surface-Plasmon Antennas

Daisuke Okamoto, Junichi Fujikata, and Keishi Ohashi

Japanese Journal of Applied Physics 50(12) p.1202012011/11-

DOI

Detail

Outline:We propose InGaAs nano-photodiodes incorporated with a ring-type polarization-insensitive surface-plasmon (SP) antenna, which consists of gold concentric-ring gratings. This ring antenna induces SP resonance for any polarization of incident light and enhances light absorption in a thin InGaAs layer owing to its symmetric structure. Finite-difference time-domain simulation suggest that the carefully designed ring SP antenna can achieve a quntum efficiency of more than 70% for a wide wavelength range and a maximum efficiency of about 80% A 3 dB bandwidth of 21 GHzand an external responsivity of 0.39 A/W were experimentally demonstrated at a 1.55 um wavelength.

Introduction to the Issue on Photonics Packaging and Integration Technologies

S. M. Garcia-Blanco, M. S. Bakir, K. I. Mattheus, K. Ohashi, and F. Horst

IEEE Journal of Selected Topics in Quantum Electronics 17(3) p.495 - 4972011/05-

DOI

Detail

Outline:THE GUEST editors of the IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS (JSTQE) are pleased to introduce this issue on Photonic Packaging and Integration Technologies. The topic of this publication represents an area of increased interest in the photonics community and this publication constitutes an important milestone, putting together the latest developments in this growing field.

Using surface plasmons in electronics

Keishi Ohashi

Oyo Buturi Invitation Yes 80(2) p.146 - 1502011/02-

link

Detail

Publish Classification:Research paper (scientific journal)

Si Nano-Photodiode with Surface-Plasmon Antenna

J. Fujikata, K. Ohashi, T. Mogami

Kogaku 40(2) p.98 - 1032011/02-

link

Detail

Publish Classification:Research paper (scientific journal)

Outline:We studied the surface plasmon (SP) resonance effect on Si nano-photodiode (PD) characteristics for future optical interconnections on LSI chips. We designed an SP antenna which converts input light into SP polaritons and localizes light power on the subwavelength area, and developed a very efficient and very fast Si nano-PD which consists of the SP antenna and a small Si absorption layer. We also developed a waveguide-integrated Si nano-PD with an SP antenna for on-chip optical clock distribution. The interfacial periodic nano-scale metal-semiconductor-metal Schottky electrodes were shown to function as an SP optical antenna and also as an optical coupler between a SiON waveguide and a very thin Siabsorption layer. A very high speed response as well as enhanced photoresponsivity was achieved for a 10-m m coupling length. By using this technology, we fabricated a prototype of a large-scale-integration (LSI) on-chip optical clock system and demonstrated 5 GHz of optical clock circuit operation connected with a 4-branching H-tree structure.

Vertical-Coupling Optical Interface for On-Chip Interconnection

Hirohito Yamada, Michinao Nozawa, Masao Kinoshita, and Keishi Ohashi

Optics Express 19(2) p.698 - 7032011/01-

DOI

Detail

Outline:We present a vertical-coupling optical interface with a grating coupler for transmitting and receiving optical signals between single-mode optical fibers and microphotonic waveguides with a view to realize on-chip optical interconnection. The optical interface consisting of a simple grating structure with a reflective mirror and an optical power combiner exhibits high optical coupling efficiency and wide tolerance range for the misalignment of optical fibers. The optical interface exhibits high coupling efficiency even if the optical input is almost vertical to the chip surface.

Surface Plasmon Antenna and Si Nano Photodiode

Keishi Ohashi

O plus E 32(2) p.165 - 1682010/02-

CiNii

Discussions on the Tasks to Introduce On-chip Optical Interconnection

Keishi Ohashi, Sunao Torii, Tohru Mogami

Journal of the IEICE Peer Review Yes Invitation Yes 93(11) p.933 - 9372010/11-

link

Detail

Publish Classification:Research paper (scientific journal)

Gigahertz-Rate Optical Modulation on Mach-Zehnder PLZT Electro-Optic Modulators Formed on Silicon Substrates by Aerosol Deposition

Takanori Shimizu, Masafumi Nakada, Hiroki Tsuda, Hiroshi Miyazaki, Jun Akedo, and Keishi Ohashi

IEICE Electronics Express 6(23) p.1669 - 16752009/12-

DOI

Detail

Publish Classification:Research paper (international conference proceedings)

Outline:In this paper, we have demonstrated 10-GHz operation. Cross-sectional view of ring-resonator PLZT EO modulator structure of a PLZT EO modulator with a ring resonator formed on a silicon substrate for on-chip optical interconnects.

Lanthanum-Modified Lead Zirconate Titanate Electro-Optic Modulators Fabricated Using Aerosol Deposition for LSI Interconnects

Masafumi Nakada, Takanori Shimizu, Hiroshi Miyazaki, Hiroki Tsuda, Jun Akedo, and Keishi Ohashi

Japanese Journal of Applied Physics Peer Review Yes 48p.09KA062009/09-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:We developed lanthanum-modified lead zirconate titanate (PLZT), electro-optic modulators using aerosol deposition (AD). AD of complex oxide films on Si substrates is achievable, leading to the possible integration of these modulators into semiconductor integrated circuits. Polarization was measured in PLZT optical waveguides that were 1.8 µm in width, and ferroelectric hysteresis loops were observed. Mach–Zehnder interferometer (MZI) PLZT modulators were demonstrated with 500-µm-length electrodes, and the insertion loss of the MZI modulators changed with applied electric field. Their change in insertion loss exhibited hysteresis loops, which were comparable to their ferroelectric ones. We obtained a 2-GHz optical output signal with a relevant bias voltage.

Challenges and Prospects for Applications in the Chips (LSI Chip Optical Interconnection)

Masao Kinoshita, Keishi Ohashi

Journal of the Japan Institute of Electronics Packaging 12(5) p.452 - 4572009/08-

DOI

Detail

Publish Classification:Research paper (scientific journal)

On-Chip Optical Interconnect

Keishi Ohashi, Kenichi Nishi, Takanori Shimizu, Masafumi Nakada, Junichi Fujikata, Jun Ushida, Sunao Torii, Koichi Nose, Masayuki Mizuno, Hiroaki Yukawa, Masao Kinoshita, Nobuo Suzuki, Akiko Gomyo, Tsutomu Ishi, Daisuke Okamoto, Katsuya Furue, Toshihide Ueno, Tai Tsuchizawa, Toshifumi Watanabe, Koji Yamada, S-I Itabashi, and Jun Akedo

Proceedings of the IEEE Peer Review Yes Invitation Yes 97(7) p.1186 - 11982009/07-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:We describe a cost-effective and low-power-consumption approach for on-chip optical interconnection. This approach includes an investigation into architectures, devices, and materials. We have proposed and fabricated a bonded structure of an Si-based optical layer on a large-scale integration (LSI) chip. The fabricated optical layer contains Si nanophotodiodes for optical detectors, which are coupled with SiON waveguides using surface-plasmon antennas. Optical signals were introduced to the optical layer and distributed to the Si nanophotodiodes. The output signals from the photodiodes were sent electrically to the transimpedance-amplifier circuitries in the LSI. The signals from the photodiodes triggered of the circuitries at 5 GHz. Since electrooptical modulators consume the most power in on-chip optical interconnect systems and require a large footprint, they are critical to establish on-chip optical interconnection. Two approaches are investigated: 1) an architecture using a fewer number of modulators and 2) high electrooptical coefficient materials.

Photodetector Using Surface-Plasmon Antenna for Optical Interconnect

Keishi Ohashi and Junichi Fujikata

MRS Proceedings 1145p.1145 MM01 052009-

DOI

Detail

Publish Classification:Research paper (international conference proceedings)

Outline:We used a surface-plasmon antenna to obtain small photodetectors for LSI on-chip optical interconnection by using near-field light generated by the antenna. Such near-field devices are not constrained by the diffraction limit and they offer an approach to integrated nanoscale photonic devices. A small semiconductor structure is located near the antenna to absorb the nearfield light. This structure can be made as small as the Schottky depletion layer, so the separation between electrodes can be reduced to almost the size of the near-field region. We have demonstrated a “Si nano-photodiode” or plasmon photodiode that uses the near-field localized in a subwavelength region, which is usually relatively large in size because of the long absorption length for Si (~10 μm at a wavelength of ~800 nm). The Si nano-photodiode has a fast impulse response with a full-width at half-maximum of ~20 ps even when the bias voltage is small (~1 V or less). We demonstrated an on-chip optical interconnect chip to operate circuitry in an LSI chip by using waveguide-coupled Si nano-photodiodes.

Ultra-Small High Speed Optical Devices with Transparent Functional Thin Films

Masafumi Nakata, Keishi Ohashi

Ceramics 43(9) p.722 - 7252008/09-

CiNii

Detail

Publish Classification:Research paper (scientific journal)

LSI On-Chip Optical Interconnection with Si Nano-Photonics

J. Fujikata, K. Nishi, A. Gomyo, J. Ushida, T. Ishi, H. Yukawa, D. Okamoto, M. Nakada, T. Shimizu, M. Kinoshita, K. Nose, T. Ueno, M. Mizuno, T. Tsuchizawa, T. Watanabe, K. Yamada, S. Itabashi, and K. Ohashi

IEICE Transactions on Electronics Peer Review Yes Invitation Yes E91 C(2) p.131 - 1372008/09-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:LSI on-chip optical interconnections are discussed from the viewpoint of a comparison between optical and electrical interconnections. Based on a practical prediction of our optical device development, optical interconnects will have an advantage over electrical interconnects within a chip that has an interconnect length less than about 10mm at the hp32-22nm technology node. Fundamental optical devices and components used in interconnections have also been introduced that are small enough to be placed on top of a Si LSI and that can be fabricated using methods compatible with CMOS processes. A SiON waveguide showed a low propagation loss around 0.3dB/cm at a wavelength of 850nm, and excellent branching characteristics were achieved for MMI (multimode interference) branch structures. A Si nano-photodiode showed highly enhanced speed and efficiency with a surface plasmon antenna. By combining our Si nano-photonic devices with the advanced TIA-less optical clock distribution circuits, clock distribution above 10GHz can be achieved with a small footprint on an LSI chip.

Low-loss Silicon Oxynitride Waveguides and Branches for the 850-nm-Wavelength Region

Tai Tsuchizawa, Toshifumi Watanabe, Koji Yamada, Hiroshi Fukuda, Seiichi Itabashi, Junichi Fujikata, Akiko Gomyo, Jun Ushida, Daisuke Okamoto, Kenichi Nishi, and Keishi Ohashi

Japanese Journal of Applied Physics 47(8) p.6739 - 67432008/08-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:We developed silicon oxynitride (SiON) waveguides and branches working at around 850 nm wavelength for on-chip optical interconnection. SiON films were deposited by plasma-enhanced chemical vapor deposition (PECVD) and were very transmissive in this wavelength region. The propagation losses of fabricated waveguides were as low as 0.2–0.3 dB/cm. The branches are based on multimode interference (MMI) and exhibited excellent 3 dB characteristics. We also integrated a SiON waveguide with a Si nano-photodiode (PD) with a surface plasmon antenna. A large photocurrent of about 0.1 mA at a coupling length of only 10 µm and a high-speed response of 17 ps were demonstrated for the waveguide-integrated Si nano-PD.

Optical Properties of Pb(Zr,Ti)O3 Films Prepared by Aerosol Deposition

Hiroki Tsuda, Masafumi Nakada, Jun Akedo, and Keishi Ohashi

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control Peer Review Yes 55(5) p.97509792008/05-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:The optical properties and related band structure of ferroelectric lead zirconate titanate [PZT, Pb(Zr0.6Ti0.4)O3] films prepared on glass substrates at room temperature by aerosol deposition were investigated. The reflectance and transmittance of the PZT films were measured in the wavelength range from UV to near-infrared. The measured optical spectra were analyzed using dielectric function models that describe optical transitions in the band gap region. Optical absorption of the as-deposited PZT films was found to be larger than that of the annealed PZT films in the near-infrared wavelength range. The analyzed results indicated that post-deposition annealing increased the band gap energy of the PZT films, corresponding to a decrease in optical absorption.

Numerical Study of Near-Infrared Photodetectors with Surface-Plasmon Antenna for Optical Communication

Daisuke Okamoto, Junichi Fujikata, Kenichi Nishi, and Keishi Ohashi

Japanese Journal of Applied Physics Peer Review Yes 47(4) p.2921 - 29232008/04-

DOI

Detail

Outline:We propose an InP-based nanoscale metal–semiconductor–metal photodiode with a surface plasmon antenna composed of gold slit arrays for optical communication systems. Resonant modes of the surface plasmon antenna are numerically simulated by the finite-difference time-domain method. The calculation results suggest the advantage of the hybrid mode, which is produced by a Wood–Rayleigh anomaly mode and a vertical cavity mode. The hybrid mode enables a quantum efficiency of more than 50% when using a 250-nm-thick InGaAs absorption layer. A higher efficiency of about 95% can be achieved by combining a surface plasmon antenna with a distributed Bragg reflector consisting of 20 periods of quarter-wave InP/InGaAsP layers.

LSI Chip Optical Interconnect Technology

Keishi Ohashi, Nobuo Suzuki, Ken'ichi Nishi

The Journal of the IEICE Peer Review Yes 91(3) p.201 - 2062008/03-

link

Detail

Publish Classification:Research paper (scientific journal)

Silicon-based Optical Detrectors

Keishi Ohashi, Junichi Fujikata

Kogaku Peer Review Yes Invitation Yes 37(1) p.21 - 262008/01-

link

Detail

Publish Classification:Research paper (scientific journal)

Outline:Silicon-based photo-detectors are reviewed with emphasis on silicon photodiodes for on-chip integrated optoelectronics. A variety of device structure have been developed to obtain high-speed and high-efficiency response using silicon with relatively low optical-absorption coefficient. Optical resonators are useful for the high-speed silicon photodiodes to obtain small drift time by reducing the separation between electrodes. Surface-plasmon antenna adds other merits of small electric capacitance and efficient coupling between the waveguide and the active layer of a photodiode. These technologies make silicon photo-detectors operate at high-frequency at more than tens of GHz on a silicon chip.

Waveguide-Integrated Si Nano-Photodiode with Surface-Plasmon Antenna and Its Application to On-Chip Optical Clock Distribution

J. Fujikata, K. Nose, J. Ushida, K. Nishi, M. Kinoshita, T. Shimizu, T. Ueno, D. Okamoto, A. Gomyo, M. Mizuno, T. Tsuchizawa, T. Watanabe, K. Yamada, and K. Ohashi

Applied Physics Express 1(2) p.220012008/01-

DOI

Detail

Outline:We developed a waveguide-integrated Si nano-photodiode (PD) with a surface plasmon (SP) antenna for on-chip optical clock distribution. The interfacial periodic nano-scale metal–semiconductor–metal Schottky electrodes were shown to function as an SP optical antenna and also as an optical coupler between a SiON waveguide and a very thin Si-absorption layer. Furthermore, a very high speed response of 17 ps as well as enhanced photoresponsivity was achieved for a 10-um coupling length. By using this technology, we fabricated a prototype of a large-scale-integration (LSI) on-chip optical clock system and demonstrated 5GHz of optical clock circuit operation connected with a 4-branching H-tree structure.

A Silicon Photonics Approach for the Nanotechnology Era

K. Ohashi, K. Nishi, T. Shimizu, M. Nakada, J. Fujikata, J. Ushida, A. Gomyo, T. Ishi, K. Nose, M. Mizuno, M. Kinoshita, N. Suzuki, D. Okamoto, H. Yukawa, T. Tsuchizawa, T. Watanabe, K. Yamada, S. Itabashi, and J. Akedo

Technical Digest of IEDM 2007 - IEEE International Electron Device Meeting Peer Review Yes Invitation Yes p.787 - 7902007/12-

DOI

Detail

Publish Classification:Research paper (international conference proceedings)

Outline:Abstract: With the further scaling of feature size in the nanotechnology era, on-chip optical interconnection will be essential for meeting high-capacity data transmission needs. This paper describes a silicon photonics approach to achieving cost-effective and low-power-consumption on-chip optical interconnects, which includes the use of a small ceramic electro-optical modulator and a Si nano-photodiode coupled with a SiON/SiO2 waveguide, and discusses it in comparison with other approaches.

Silicon Photodiode Using Surface-Plasmon Resonance

Keishi Ohashi

Review of Laser Engineering 35(9) p.572 - 5762007/09-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:The concept of nano-photodiode, employing surface-plasmon antenna to create sub-wavelength size near-field, is described in relation to silicon photonics. Response time of the prototype silicon nano-photodiode was much shorter (~20 ps) than that of conventional silicon photodiodes (> 1 ns). There are two reasons for the high-speed response: short distance between electrodes (~100 nm) and small electrode area (1 square micrometer). The former is realized by lapping near-field region over depletion region (Schottky barrier) in silicon thereby eliminating time-consuming carrier diffusion process. The latter results in small electrode capacitance and thus reducing response time of the photodiode circuit. This nano-photodiode technology can be applied to other semiconductor materials such as germanium and ternary compound semiconductors.

Ultra Small Magneto-Optic Field Probe Fabricated by Aerosol Deposition

Mizuki Iwanami, Masafumi Nakada, Hiroki Tsuda, Keishi Ohashi, and Jun Akedo

IEICE Electronics Express Peer Review Yes 4(17) p.542 - 5482007/09-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:The basic performance of a newly developed microscopic magneto-optic probe is described. The probe was fabricated by directly depositing a Bi-substituted yttrium iron garnet [Bi-YIG] film onto the optical fiber edge using aerosol deposition. This fabrication process is inexpensive and simple because there are no complicated procedures such as fine lithography and etching. The film is 125-µm-wide, which is the same as the diameter of a typical single mode fiber, and approximately 10-µm-thick. The 3-dB bandwidth and spatial resolution of the probe were found to be about 3GHz and in the 10-µm order, respectively. Because the developed magneto-optic probe is very tiny and thin, it can be a powerful tool for detailed electrical characterization of densely packaged electronic circuits.

Dielectric Characteristics of PZT Films Prepared by Aerosol Deposition in Millimeter Wave Range

M. Nakada, K. Ohashi, H. Tsuda, E. Kawate and J. Akedo

Proceedings of 16th International Symposium on Application of Ferroelectrics (ISAF 2007), IEEE UFFC Peer Review Yes p.528 - 5302007/05-

DOI

Detail

Publish Classification:Research paper (international conference proceedings)

Outline:The dielectric properties of lead zirconate titanate [PZT, Pb(Zr0.3Ti0.7)O3] films, prepared by aerosol deposition (AD), were measured in the millimeter wave and THz range. Millimeter wave spectroscopy was applied for measurement in the frequency range from 45 to 80 GHz, and far-infrared Fourier transform measurements from 120 GHz to 20 THz was carried out. Spectroscopic data were analyzed with combination of Debye model with a distribution of Debye relaxation frequencies and harmonic oscillators. We clearly observed that the Debye relaxation took place below several tens GHz for annealed AD films. Combination of millimeter wave and THz spectroscopy was effective measurement technique for dielectric properties of ferroelectric materials at over millimeter wave range.

Optical Properties of Pb(Zr,Ti)O3 Films Prepared by Aerosol Deposition

H. Tsuda, M. Nakada, J. Akedo and K. Ohashi

Proceedings of 16th International Symposium on Application of Ferroelectrics (ISAF 2007), IEEE UFFC Peer Review Yes p.829 - 8302007/05-

DOI

Detail

Publish Classification:Research paper (international conference proceedings)

Outline:Optical properties of Ferroelectric lead zirconate titanate [PZT, Pb(Zr,Ti)O3] films prepared on glass substrates at room temperature by aerosol deposition (AD) were investigated. The reflectance and transmittance of PZT films were measured in the wavelength range from ultraviolet to near infrared. Optical absorption of as-deposited films was found to be larger than that of the annealed films in the near infrared wavelength range. The results analyzed using optical models with the measured spectra indicate that the band gap energy of the PZT film increases with annealing.

Optical Characteristics of a PZT Waveguide Fabricated Using Aerosol Deposition for Optical Modulators on LSI Chips

T. Shimizu, M. Nakada, H. Tsuda, J. Akedo, K. Nishi, and K. Ohashi

Proceedings of 16th International Symposium on Application of Ferroelectrics (ISAF 2007), IEEE UFFC Peer Review Yes p.831 - 8332007/05-

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Detail

Publish Classification:Research paper (international conference proceedings)

Outline:We developed a lead zirconate titanate, Pb(Zr,Ti)O3 (PZT), optical waveguide fabricated using aerosol deposition (AD). The device's optical transmission loss of about 4 dB/mm is comparable with that of AD film. The PZT optical waveguide can meet the requirements of optical modulators for low optical loss.

Ultra Small Fiber-Optic Electric Field Probe Fabricated by Aerosol Deposition

M. Iwanami, M. Nakada, H. Tsuda, K. Ohashi, and J. Akedo

Proceedings of 16th International Symposium on Application of Ferroelectrics (ISAF 2007), IEEE UFFC Peer Review Yes p.834 - 8362007/05-

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Detail

Publish Classification:Research paper (international conference proceedings)

Outline:We developed a microscopic electro-optic field probe by directly depositing a lead zirconate-titanate [PbZr0.3Ti0.7O3] film onto optical fiber edge using aerosol deposition. Its fabrication process is virtually self-aligning because there are no complicated procedures such as fine lithography and etching. The lateral size of the film pattern is 125 mum, which is the same as the diameter of a typical single mode fiber, and the thickness is approximately 5 mum. An RF electro-optic signal was successfully measured over a microstrip line. The measurable bandwidth of the probe was over 2 GHz. Because it is very tiny and thin, the developed electrooptic probe has great potential for detailed electrical characterization in the microscopic regions of high performance electronic products such as the interconnecting parts between LSI packages and printed circuit boards and spaces among different LSI chips in a package.

Si Nano-Photonics Innovate Next Generation Network Systems and LSI Technologies

Kenichi Nishi, Yutaka Urino, and Keishi Ohashi

NEC Technical Journal 2(1) p.67 - 712007/03-

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Publish Classification:Research paper(bulletin of university, research institution)

Outline:“Si nanophotonics” controls light by employing a nano-scale structural technology. Featuring state-of-the-art technologies to manufacture LSI chips, Si nanophotonics technology enables impressive miniaturization and achieves low power consumption compared to the conventional optical elements technologies. Optical signal transmission of the LSI chip has not hitherto been realized, however by adopting this Si nanophotonics technology to the elements of an LSI, NEC demonstrated the possibility to significantly improve LSI performance. With this technology NEC is proposing to create new devices to support next generation networks and LSI innovations.

Application of Electronic Devices for Aerosol Deposition Methods

Masafumi Nakada, Toshihiro Kawakami, Mizuki Iwanami, and Keishi Ohashi

NEC Technical Journal 2(1) p.76 - 802007/03-

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Publish Classification:Research paper(bulletin of university, research institution)

Outline:Oxide materials have superior functional characteristics that are attributed to their versatile structures and chemically stable characteristics. These characteristics are expected to enable their employment as the functional device materials that are required to support the ubiquitous society. The aerosol deposition method is a nanocrystalline film forming method that employs the impact solidification phenomenon of ultra fine particles. This method enables the formation of oxide films onto any type of substrate. NEC and NEC TOKIN are co-developing piezoelectric and optical device products to be used in the aerosol deposition.

Aerosol Deposition on Transparent Electro-Optic Films for Optical Modulators

Masafumi Nakada, Hiroki Tsuda, Keishi Ohashi, and Jun Akedo

IEICE Transactions on Electronics Peer Review Yes E90 C(1) p.36 - 402007/01-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:Complex thin oxide films with electro-optic (EO) properties are promising for use in advanced optical devices because of their large EO effect. We developed a method of aerosol deposition (AD) for fabricating EO films. The mechanism for AD is based on the solidification by impact of submicron particles onto a substrate. Since particles in AD films preserve their crystalline structure during the formation of film, epitaxial growth is not necessary for exhibiting the EO effect. Highly transparent Pb(Zr, Ti)O3 films, which have acceptable transmittance loss for use as optical devices, were directly deposited on glass substrates by AD. We found the Pb(Zr, Ti)O3 film by AD produced a fairly high EO coefficient (>150 pm/V), approximately 10 times larger than that of LiNbO3. A Fabry-Perot (FP) optical modulator was developed with EO films fabricated by AD. We demonstrated the modulation of optical intensity with an electrical field applied to an EO film made of ferroelectric Pb (Zr, Ti)O3.

Ultra Small Electro-Optic Field Probe Fabricated by Aerosol Deposition

Mizuki Iwanami, Masafumi Nakada, Hiroki Tsuda, Keishi Ohashi, and Jun Akedo

IEICE Electronics Express Peer Review Yes 4(2) p.26 - 322007/01-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:We developed a microscopic electro-optic field probe by directly depositing a lead zirconate-titanate [PbZr0.3Ti0.7O3] film onto the optical fiber edge using aerosol deposition. Its fabrication process is low-cost and relatively easy because there are no complicated procedures such as fine lithography and etching. The lateral size of the film is 125µm, which is the same as the diameter of a typical single mode fiber, and the thickness is approximately 5µm. An RF electro-optic signal was successfully measured over a microstrip line. The capability for detecting GHz range fields is also shown. Because it is very tiny and thin, the developed electro-optic probe has great potential for detailed electrical characterization in the microscopic regions of high performance electronic products such as the interconnecting parts between LSI packages and printed circuit boards and spaces among different LSI chips in a package.

Development of Miniturized Thin-Film Magnetic Field Probes for On-Chip Measurement

N. Ando, N. Masuda, N. Tamaki, T. Kuriyama, M. Saito, S. Saito, K. Kato, K. Ohashi, and M. Yamaguchi

Journal of the Magnetics Society of Japan Peer Review Yes 30(4) p.429 - 4342006/12-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:We developed thin-film magnetic field probes with a high spatial resolution aiming to obtain the absolute value of a high-frequency power current on an LSI chip. The spatial resolution was enhanced by miniaturizing the shielded loop coil, which is the detection part of the probe. The minimum outer size of the new coil is 50 x 22 μm. In taking measurements with the new probe over a 60-μm-wide microstrip line used as a device under test (DUT), we found that the probe output decreases by 6 dB at a distance of 40 μm. This value is less than half that of our previous probe, which was around 100 μm. In taking measurements with the new probe over 5-μm-wide microstrip lines used as a DUT, we found that the new probe achieved 10-μm-class high spatial resolution. This value is comparable to the typical width of global power lines on an LSI chip, which ranges from 10 μm to 100 μm. We estimated the configuration of the lines on an LSI chip that would enable the new probe to achieve a spatial resolution high enough to obtain the absolute value of a high-frequency power current on an LSI chip.

Silicon Nano-Photodiode with Surface Plasmon Antenna

K. Nishi, J. Fujikata, T. Ishi, K. Ohashi

OPTRONICS 25(299) p.131 - 1362006/11-

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Teraherz-Wave Near-Field Imaging with Subwavelength Resolution Using Surface-Wave-Assisted Bow-Tie Aperture

Kunihiko Ishihara, Keishi Ohashi, Tomofumi Ikari, Hiroaki Minamide, Hiroyuki Yokoyama, Jun-ichi Shikata, and Hiromasa Ito

Applied Physics Letters Peer Review Yes 89(20) p.2011202006/11-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:We demonstrate the terahertz-wave near-field imaging with subwavelength resolution using a bow-tie shaped aperture surrounded by concentric periodic structures in a metal film. A subwavelength aperture with concentric periodic grooves, which are known as a bull’s eye structure, shows extremely large enhanced transmission beyond the diffraction limit caused by the resonant excitation of surface waves. Additionally, a bow-tie aperture exhibits extraordinary field enhancement at the sharp tips of the metal, which enhances the transmission and the subwavelength spatial resolution. We introduced a bow-tie aperture to the bull’s eye structure and achieved high spatial resolution (∼λ∕17) in the near-field region. The terahertz-wave near-field image of the subwavelength metal pattern (pattern width=20μm) was obtained for the wavelength of 207μm.

Development and Practical Use of the Electrodeposited CoFeNi Alloy Film for a High Density Magnetic Recording Head

T. Osaka, M. takai, K. Ohashi, M. Saito, Y. Mizoshita, Y. Koshikawa

Journal of Surface Finishing Society of Japan 57(10) p.705 - 7112006/10-

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Development and Applications of a Si Nanophotodiode with a Surface Plasmon Antenna

Keishi Ohashi, Junichi Fujikata, Tsutomu Ishi, Daisuke Okamoto, Kikuo Makita, and Kenichi Nishi

Proceedings of SPIE Peer Review Yes 6352p.63521U 1 - 63521U 92006/09-

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Detail

Publish Classification:Research paper (international conference proceedings)

Outline:Optoelectronic and electrooptic elements are integrated on VLSI chips. The junction capacitance of a nano-photodiode is extremely low (<10aF), which permits a high load resistance to be used, resulting in higher output voltage at high frequencies. A ceramic Pb(,ZrTi)O3 film with average crystallite diameter below 20nm has a high electro-optical coefficient (>150pm/V) suitable for on-chip modulators. This paper introduces a new approach for realizing high-speed optical interconnects on silicon chips. This concept uses nano-photodiodes on silicon with extremely low parasitic capacitance (less than 10aF) enabling robust communication at very high frequencies. The results demonstrate 5GHz clocking with the promise of up to 20GHz. The authors will also discuss how the silicon nano-photodiode can be used for wavelength-division multiplexing and low-voltage electro-optic modulators for on-chip and off-chip optical communications.

Enhancement of Light Transmission with Metallic Nanostructures and Its Application to Optical Recording

J. Fujikata, T. Ishi, M. Yanagisawa, K. Ohashi

Review of Laser Engineering Invitation Yes 34(5) p.353 - 3572006/05-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:We reviewed on the enhanced photon-tunneling and the near-field enhancement effect for a metallic nanoscale aperture with a concentric surface plasmon resonance structure. About two-orders larger light transmission and an enhanced near-field were achieved by optimizing the grating structures. This enhanced near-field was applied to optical recording, and about 100-nm recorded patterns were successfully made on phase change media. This surface plasmon optics would open up the ultra-high-density recording technology.

Optical Interconnect Technologies for High-Speed VLSI Chips Using Silicon Nanophotonics

Keishi Ohashi, Junichi Fujikata, Masafumi Nakada, Tsutomu Ishi, Kenichi Nishi, Hirohito Yamada, Muneo Fukaishi, Masayuki Mizuno, Koichi Nose, Ichiro Ogura, Yutaka Urino, and Toshio Baba

Digest of Technical Papers ISSCC 2006 - IEEE International Solid-State Circuits Conference Peer Review Yes 49(23.5) p.426 - 4272006/02-

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Detail

Publish Classification:Research paper (international conference proceedings)

Outline:Optoelectronic and electrooptic elements are integrated on VLSI chips. The junction capacitance of a nano-photodiode is extremely low (<10aF), which permits a high load resistance to be used, resulting in higher output voltage at high frequencies. A ceramic Pb(,ZrTi)O3 film with average crystallite diameter below 20nm has a high electro-optical coefficient (>150pm/V) suitable for on-chip modulators. This paper introduces a new approach for realizing high-speed optical interconnects on silicon chips. This concept uses nano-photodiodes on silicon with extremely low parasitic capacitance (less than 10aF) enabling robust communication at very high frequencies. The results demonstrate 5GHz clocking with the promise of up to 20GHz. The authors will also discuss how the silicon nano-photodiode can be used for wavelength-division multiplexing and low-voltage electro-optic modulators for on-chip and off-chip optical communications.

Fabry-Perot Optical Modulator Fabricated by Aerosol Deposition

Masafumi Nakada, Keishi Ohashi, Hiroki Tsuda, and Jun Akedo

Proceedings of SPIE Peer Review Yes 6050p.6050042005/12-

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Detail

Publish Classification:Research paper (international conference proceedings)

Outline:We developed a Fabry-Perot (FP) optical modulator with electro-optic (EO) films fabricated by aerosol deposition (AD). We found the ferroelectric Pb(Zr,Ti)O3 film by AD produced a fairly high EO coefficient (>150 pm/V), approximately 10 times larger than that of LiNbO3. Since thick EO films greater than 5 μm can be deposited on a transparent electrode layer or a metallic mirror layer of the FP optical modulator by AD, the FP optical modulator can achieve low capacitance, resulting in high modulation speed. Transmittance spectra of the FP optical modulator coincided with the optical simulation spectra, which indicated that optical scattering in AD films and at the surface/boundary were very small. We demonstrated an optical intensity modulation with applied electric field to EO film of ferroelectric Pb (Zr, Ti)O3. We obtained a 4-dB modulation with 50 V for the 10-μm-thick modulator with dielectric multilayer mirror on a glass substrate.

Silicon Nano-Photodiode Using Optical Near-Field Enhanced by Surface-Plasmon Resonance

K. Ohashi, J. Fujikata, T. Ishi, K. Nishi, T. Baba

Oyo Buturi Invitation Yes 74(11) p.1453 - 14572005/11-

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Publish Classification:Research paper (scientific journal)

Excitonic Molecule in a Quantum Dot: Photoluminescence Lifetime of a Single InAs/GaAs Quantum Dot

Shunsuke Kono, Akihiko Kirihara, Akihisa Tomita, Kazuo Nakamura, Junichi Fujikata, Keishi Ohashi, Hideaki Saito, and Kenichi Nishi

Physical Review B Peer Review Yes 72p.155307 - 1553112005/10-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:Time dependence of the photoluminescence (PL) attributed to the exciton and biexciton in a single InAs∕GaAs quantum dot is investigated at 4.3K with microscopic spectroscopy. Dynamical behavior of the PL decay and the excitation intensity dependence of the exciton and biexciton PL are analyzed by rate equations assuming a cascading recombination from the biexciton to exciton state. The analysis shows that the biexciton lifetime is longer than the exciton lifetime. The estimated ratio of the biexciton lifetime to the exciton lifetime shows a molecular nature of the biexciton in the large quantum dots compared with the exciton Bohr radius.

Surface-Enhanced Raman Scattering of Silver Dendrites

M. Yanagisawa, M. Saito, T. Wada, K. Ohashi, K. Nakayama

Journal of the Surface Science Society of Japan 26(9) p.532 - 5362005/09-

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Outline:We have studied an indirect observation for surface plasmons on a variety of nano-structured surfaces by means of surface-enhanced Raman scattering (SERS). In this report, we find the ultrahigh Raman intensity image of the sputtered carbon film on silver dendrites. In order to estimate Raman enhancement on some topographic features, (A) smooth quartz substrates without silver film, (B) smooth quartz substrates with silver film of 300 nm in thickness, (C) silver protrusions of 50 nm in the tip diameter, and (D) silver dendrites were prepared. The maximum Raman intensity of G-band and D-band for the case (D) is 88,000 times larger than that on the flat glass substrates (case(A)). The relative enhancement is 5 times for the case (B) and 400 times for the case (C). In the case (D), some strong Raman scattering points, so called "hot spots" were observed at around the region of 500 nm in the dendrite structure, where the electric field intensity can be enhanced by local plasmons.

Dielectric Characteristics of Ferroelectric Films Prepared by Aerosol Deposition in THz Range

Masafumi Nakada, Keishi Ohashi, and Jun Akedo

Japanese Journal of Applied Physics Peer Review Yes 44 part 1(9B) p.6918 - 69222005/09-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:The dielectric properties of lead titanate [PbTiO3] and lanthanum-modified lead zirconate titanate [PLZT, Pb0.91La0.09(Zr0.65Ti0.35)O3] films, prepared by aerosol deposition (AD), were measured in the frequency range from 100 GHz to 10 THz and in the kHz range. THz time-domain spectroscopy was applied for measurement in the wavenumber range from 4 cm-1 to 70 cm-1, and far-infrared Fourier transform measurements from 70 cm-1 to 700 cm-1 was carried out. We observed that the dielectric constants change smoothly from kHz to THz ranges for the as-deposited PbTiO3 film, indicating that the as-deposited PbTiO3 film exhibits no dielectric dispersion due to domain wall motions. The value of the real part of the dielectric constants in the kHz range increased with annealing, suggesting the appearance of Debye relaxation by annealing. We found that the real parts of the dielectric constants of the AD-PLZT films in the kHz range were one order of magnitude smaller than those of bulk PLZT ceramics, while the dielectric responses in the THz range, which were determined by phonon modes, were comparable to those of bulk ceramic PLZT. The structure of AD-PLZT film, which consists of grains of about 20 nm in size, may affect the motion of polar nanoregions, resulting in a low dielectric response in the low frequency range.

Electro-Optic Properties of Pb(Zr1-xTix)O3 (x = 0, 0.3, 0.6) Films Prepared by Aerosol Deposition

Masafumi Nakada, Keishi Ohashi, and Jun Akedo

Japanese Journal of Applied Physics Peer Review Yes 44 part 2(34) p.L1088 - L10902005/08-

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Publish Classification:Research paper (scientific journal)

Outline:We measured annealing temperature and the Zr-to-Ti concentration ratio dependence of the electro-optic (EO) effect for highly transparent Pb(Zr1-xTix)O3 [PZT] films more than 1 µm thick, directly deposited on glass substrates by aerosol deposition (AD). X-ray diffraction patterns show that as-deposited AD films have a large strain and lattice distortions, and these affects can be attenuated by increasing annealing temperature. The dielectric constant of AD-PZT films increased with annealing temperature, which is consistent with the X-ray diffraction measurement. The EO effect was enhanced with increasing Zr concentration, and a linear EO coefficient (rc) of 102 pm/V was obtained for the PbZr0.6T0.4O3 film annealed at 600°C, whose composition is near its morphotropic phase boundary. The rc of PbZr0.6T0.4O3 films increased with annealing temperature, and the film annealed at 850°C showed an rc of 168 pm/V. The EO measurements show that AD is a highly promising film-deposition method for optical devices such as EO modulators and optical switches.

Terahertz Near-Field Imaging Using Enhanced Transmission through a Single Subwavelength Aperture

Kunihiko Ishihara, Tomofumi Ikari, Hiroaki Minamide, Jun-ichi Shikata, Keishi Ohashi, Hiroyuki Yokoyama, and Hiromasa Ito

Japanese Journal of Applied Physics Peer Review Yes 44 part 2(29) p.L929 - L9312005/07-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:We demonstrate terahertz (THz) near-field imaging using resonantly enhanced transmission of THz-wave radiation (λ~200 µm) through a bull's eye structure (a single subwavelength aperture surrounded by concentric periodic grooves in a metal plate). The bull's eye structure shows extremely large enhanced transmission, which has the advantage for a single subwavelength aperture. The spatial resolution for the bull's eye structure (with an aperture diameter d=100 µm) is evaluated in the near-field region, and a resolution of 50 µm (corresponding to λ/4) is achieved. We obtain the THz near-field images of the subwavelength metal pattern with a spatial resolution below the diffraction limit.

Strong Influence of Surface Structures on Enhanced Transmission through Subwavelength Hole Arrays

Kunihiko Ishihara and Keishi Ohashi

Japanese Journal of Applied Physics Peer Review Yes 44 part 2(30) p.L973 - L9752005/07-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:We analyzed the influence of the surface structure on enhanced transmission through subwavelength hole arrays. The hole arrays show extremely large enhanced transmission, but the transmission rapidly decreases as the hole diameter decreases. To clarify the cause of the transmission decrease, we calculated the dimple arrays and found that the diameter of the dimple strongly influences the efficiency of surface plasmon polaritons (SPPs) excitation. We show that the addition of the optimized surface structure to conventional hole arrays for the efficient SPP excitation leads to strongly enhanced transmission in much smaller diameter holes than the incident light wavelength.

Terahertz Wave Enhanced Transmission through a Single Subwavelength Aperture with Periodic Surface Structures

Kunihiko Ishihara, Gen-ichi Hatakoshi, Tomofumi Ikari, Hiroaki Minamide, Hiromasa Ito, and Keishi Ohashi

Japanese Journal of Applied Physics Peer Review Yes 44 part 2(32) p.L1005 - L10072005/07-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:We demonstrate resonantly enhanced transmission of terahertz (THz) wave radiation (λ~200 µm) through a bull's eye structure (a single subwavelength aperture surrounded by concentric periodic grooves in a metal plate). The phenomenon is caused by the resonant excitation of surface waves, which are known as surface plasmon polaritons in the optical region, generated by the concentric periodic grooves. Strongly enhanced transmission of THz-wave radiation is observed through the single subwavelength circular aperture (diameter d = 100 µm). We also show that introducing the Bragg reflector to the bull's eye structure results in the further increase of the enhanced transmission.

Electro-optic transparent films prepared by aerosol deposition method

M. Nakada, K. Ohashi

Materials Integration 18(5) p.53 - 592005/05-

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Outline:We develop functional oxide films with a large electro-optic (EO) effect for use in very small, low-power EO conversion devices. We have been applied an aerosol deposition (AD) method to form lead oxide films with a perovskite structure. [(Pb,La)(Zr,Ti)O3] films were deposited and systematically studied in terms of optical and EO properties. Transparent films, which have acceptable transmittance loss level for use as optical devices, with large EO effect were obtained. In this report, we summarize a present progress and future prospects on AD method for optical devices application.

Si Nano-Photodiode with a Surface Plasmon Antenna

Tsutomu Ishi, Junichi Fujikata, Kikuo Makita, Toshio Baba, and Keishi Ohashi

Japanese Journal of Applied Physics Peer Review Yes 44 part 2(12) p.L364 - L3662005/03-

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Publish Classification:Research paper (scientific journal)

Outline:Nano-photodiodes with a subwavelength active area using the optical near-field enhanced by surface plasmon resonance are proposed. We fabricated a Si Schottky photodiode that consists of an active area of 300 nm in diameter and a surface plasmon antenna to generate the carrier within the active area efficiently. The fabricated photodiode shows an increase of the photocurrent by several tenfold compared to that without a surface plasmon antenna. This result suggests an enhanced photogeneration of carriers in a semiconductor via surface plasmon resonance. Such a Si nano-photodiode is a potential high-speed optical signal detector because the opto-electronic conversion process occurs within a subwavelength scale.

Optical and Electro-Optical Properties of Pb(Zr,Ti)O3 and (Pb,La)(Zr,Ti)O3 Films Prepared by Aerosol Deposition Method

Masafumi Nakada, Keishi Ohashi, and Jun Akedo

Journal of Crystal Growth Peer Review Yes 275(1 2) p.e1275 - e12802005/02-

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Publish Classification:Research paper (scientific journal)

Outline:We deposited high-transparency, lanthanum-modified lead zirconate titanate [PLZT, Pb0.91La0.09(Zr0.65Ti0.35)O3] films, using an aerosol deposition method. The films showed an acceptable scattering loss level for optical devices. The transmittance of the PLZT films increased with the incident angle increase of the PLZT particle beams, because the concentration and size of the impurities, such as pores and PbO particles, decreased with the incident angle. The extinction coefficient of the highly transparent films decreased with the inverse fourth power of the wavelength, which means that the degradation of the film transmittance was due to Rayleigh scattering. This indicates that the sizes of the scattering centers in the films are at least ten times smaller than the measurement wavelength, which is consistent with the TEM observations of the sizes of the crystal grains and impurities. Lead zirconate titanate [PZT, Pb(Zr0.54Ti0.46)O3] films were also successfully deposited with a high transparency, although the PZT bulk ceramics are opaque due to optical anisotropy. Linear and quadratic electro-optical responses were observed for PZT and PLZT films, consistent with the expected bulk properties. The electro-optical coefficients were comparable to those of films deposited using conventional methods, such as the sol–gel and sputtering methods.

Large Optical Transmission through a Single Subwavelength Hole Associated with a Sharp-Apex Grating,

Tsutomu Ishi, Junichi Fujikata, and Keishi Ohashi

Japanese Journal of Applied Physics Peer Review Yes 44 part 2(4) p.L170 - L1722005/01-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:The effect of grating shapes on optical transmission in a bull's eye structure (a single subwavelength hole surrounded by a concentric grating in a metal) is discussed. Finite-difference time-domain calculations predict that a sharp-apex shape gives as high a reflective structure to the propagating surface plasmon polaritons (SPPs) as does a rectangular shape. Fabricated samples with a sharp-apex grating actually show large optical transmission (a factor of 400 greater than that of samples with a single hole) even when the number of corrugations is three. This result indicates that a sharp-apex grating acts as an effective SPP reflector to confine the energy around the hole, resulting in high optical throughput.

Surface Plasmon Enhancement Effect and Its Application to Near-Field Optical Recording

J. Fujikata, T. Ishi, H. Yokota, K. Kato, M. Yanagisawa, M. Nakada, K. Ishihara, K. Ohashi, T. Thio, and R. A. Linke

Transactions of the Magnetics Society of Japan Peer Review Yes 4(4 2) p.255 - 2592004/11-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:We studied on enhanced photon-tunneling and the near-field enhancement effect for a nano-scale aperture with a concentric surface plasmon resonance structure. About two-orders larger light transmission and an enhanced near-field were achieved by optimizing the grating structures. This enhanced near -field was applied to optical recording, and about 100 -nm recorded patterns were successfully made on phase change media. This surface plasmon optics would open up the ultra-high-density recording technology.

Miniaturized thin-film magnetic field probe with high spatial resolution for LSI chip measurement

Ando, Noriaki; Masuda, Norio; Tamaki, Naoya; Kuriyama, Toshihide; Kato, Kunio; Saito, Mikiko; Saito, Shinsaku; Ohashi, Keishi; Yamaguchi, Masahiro

IEEE International Symposium on Electromagnetic Compatibility 2p.357 - 3622004/10-2004/10

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Detail

ISSN:10774076

Outline:It is important to obtain the absolute value of current flowing through each power line on a chip of large-scale integrated (LSI) circuits by measurement because this current on an LSI chip is regarded as conductive noise. We have developed a thin-film magnetic field probe that has spatial resolution high enough to obtain the absolute value of high-frequency power current on an LSI chip. Spatial resolution was enhanced by miniaturizing the shielded loop coil, the detection part of the probe. The outer size of the new coil is 50 × 22 μm. In taking measurements with the new probe over a 60-μm-wide microstrip line used as a device under test (DUT), we obtained a 6-dB decrease point of 40 μm, which indicates the spatial resolution of the probe. This value is comparable to the typical width of power lines on an LSI chip, around 50 μm and is less than half that of our conventional probes, around 90 μm. In measurements with the new probe over an LSI chip, we obtained such a fine magnetic near-field distribution that the magnetic fields generated from the lines on the chip were separated. On-chip decoupling was also confirmed by using the new probe. The new probe enables direct verification of a circuit design for suppressing electromagnetic interference (EMI), while conventional coarse mapping of the magnetic near-field cannot be used to evaluate such conductive noise.

Electro-Optical Properties and Structures of PLZT and PT Films Prepared Using Aerosol Deposition Method

Masafumi Nakada, Keishi Ohashi, and Jun Akedo

Japanese Journal of Applied Physics Peer Review Yes 43 part 1(9B) p.6543 - 65482004/09-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:The electro-optical (EO) properties, film structures and far-infrared spectra were measured for lanthanum-modified lead zirconate titanate [PLZT, Pb0.91La0.09(Zr0.65Ti0.35)O3] and lead titanate [PT, PbTiO3] films, prepared by the aerosol deposition (AD) method. The EO response appeared for AD films annealed at over 500°C, and increased as the annealing temperature increased. Downward shifts of the diffraction peaks, compared with diffraction peak positions of the corresponding to powders, were observed for as-deposited PLZT films in X-ray diffraction patterns of θ-2θ scans. The (200) peaks shifted to higher angles with increasing X-ray incidence angle to the film surface, indicating that the peak shifts were caused by lattice distortion induced by in-plane compressive stress. The (200) peaks shifted to the powder position when annealed at 600°C, which means that the annealing can relax the residual stress. Far-infrared spectroscopy measurements of reflectivity and transmittance were carried out on the PLZT and the PT powders and films, and the IR spectra of PT films were analyzed using the classical damped harmonic oscillator models to determine the oscillation parameters. We observed LO mode degradation and the broadening of the dielectric function peaks on the AD films. The frequencies of the E (1TO) soft-phonon mode of the annealed PT films were shown to have downward shifts of over 20 cm-1, compared with those of bulk ceramics and single crystals, suggesting that the AD may have induced a microscopic lattice degradation in the PT films, which may be responsible for the small EO response.

Enhancement of Near-Field Light by Surface Plasmons

K. Ohashi, J. Fujikata, T. Ishi, K. Ishihara, M. Yanagisawa, M. Nakada, H. Yokota

Journal of Magnetics Society of Japan Peer Review Yes 28(6) p.774 - 7802004/06-

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Publish Classification:Research paper (scientific journal)

Outline:This paper discusses a technology for enhancing near-field light by controlling surface plasmons. Near-field light is effective for creating a very small heat spot, since it is localized at surface of a material. The resonance of surface plasmons at a metalsurface can control the distribution of the intensity of the nearfield. A concentric ring structure on a silver metal film was investigated as a plasmon-enhancement structure for high-density recording devices. Far-field measurements showed that the transmitted light was enhanced by a factor of 125. A hard-disk-drive-type head with a ring-type surface plasmon ebhancement structure and a hole 100 nm in diameter was fabricated. The head generated near-field light at least a hundred times as strong as that generated by a simple hole 100 nm in diameter.

Electro-Optical Properties of (Pb, La)(Zr, Ti)O3 Films Prepared by Aerosol Deposition Method

Masafumi Nakada, Keishi Ohashi, Maxim Lebedev, and Jun Akedo

Japanese Journal of Applied Physics Peer Review Yes 42 part 1(9B) p.5960 - 59622003/09-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:The electro-optical (EO) properties, film structures and far-infrared spectra were measured for lanthanum-modified lead zirconate titanate [PLZT, Pb0.91La0.09(Zr0.65Ti0.35)O3] and lead titanate [PT, PbTiO3] films, prepared by the aerosol deposition (AD) method. The EO response appeared for AD films annealed at over 500°C, and increased as the annealing temperature increased. Downward shifts of the diffraction peaks, compared with diffraction peak positions of the corresponding to powders, were observed for as-deposited PLZT films in X-ray diffraction patterns of θ-2θ scans. The (200) peaks shifted to higher angles with increasing X-ray incidence angle to the film surface, indicating that the peak shifts were caused by lattice distortion induced by in-plane compressive stress. The (200) peaks shifted to the powder position when annealed at 600°C, which means that the annealing can relax the residual stress. Far-infrared spectroscopy measurements of reflectivity and transmittance were carried out on the PLZT and the PT powders and films, and the IR spectra of PT films were analyzed using the classical damped harmonic oscillator models to determine the oscillation parameters. We observed LO mode degradation and the broadening of the dielectric function peaks on the AD films. The frequencies of the E (1TO) soft-phonon mode of the annealed PT films were shown to have downward shifts of over 20 cm-1, compared with those of bulk ceramics and single crystals, suggesting that the AD may have induced a microscopic lattice degradation in the PT films, which may be responsible for the small EO response.

Enhanced Nonlinear Optical Conversion from a Periodically Nano-Structured Metal Film

Ajay Nahata, Richard A Linke, Tsutomu Ishi, and Keishi Ohashi

Optics Letters Peer Review Yes 28(6) p.423 - 4252003/03-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:We demonstrate an ∼10^4 increase in conversion efficiency for optical second-harmonic generation (SHG) from a periodically nanostructured metal structure consisting of a single subwavelength aperture in a thin silver film surrounded by a set of concentric surface grooves. The forward-transmitted second-harmonic radiation from this structure is measured relative to that from an identical aperture with no surrounding surface periodicity. We explain the observed SHG enhancement quantitatively in terms of a measured 120× increase in the strength of the fundamental radiation in the vicinity of the aperture resulting from the periodic nanostructuring.

The Electrodeposition Conditions of CoNiFe Films, Crystal Structure, and Evaluation of Magnetic Moments

M. Saito and K. Ohashi

ECS Proceedings; Magnetic Materials, Processes, and Devices VII PV 2002-27p.241 - 2532003-

Influence of Carbon Inclusion on Properties of Electrodeposited CoNiFeMo Thin Films

Tokihiko Yokoshima, Asako Kawashima, Takuya Nakanishi, Tetsuya Osaka, Mikiko Saito, and Keishi Ohashi

ECS Proceedings; Magnetic Materials, Processes, and Devices VII PV 2002-27p.365 - 3752003-

Evaluation of the Crystal Structure, Film Properties, and Bs of Electroplated CoNiFe Films

M. Saito, N. Ishiwata, and K. Ohashi

Journal of the Electrochemical Society Peer Review Yes 149(12) p.C642 - C6472002/12-

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Detail

Publish Classification:Research paper (scientific journal)

Nano-Storage Technology and Electroplating: Large Magnetic Moment of Co-Fe-Ni

K. Ohashi

Electrochemistry Peer Review Yes Invitation Yes 70(11) p.884 - 8872002/11-

Scopus

Detail

Publish Classification:Research paper (scientific journal)

Read/Write Characteristics of Focused-Ion-Beam-Etched Heads for Perpendicular Magnetic Recording Media

S. Tsuboi, H. Matsutera, T. Ishi, N. Ishiwata, and K. Ohashi

Journal of Magnetism and Magnetic Materials Peer Review Yes 235(1 3) p.375 - 3812001/10-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:The read/write characteristics for perpendicular magnetic recording media of focused-ion-beam (FIB)-etched recording heads were investigated. It was found that the trailing edge of an FIB-etched head produces a higher gradient in the magnetic field perpendicular to the medium than a head which has not been etched. The signal-to-noise ratio of the medium increased with the FIB-etched write gap. A high-Bs and thin pole increased the magnetic field's gradient in the perpendicular direction, resulting in excellent read/write characteristics.

Read Performance of Tunneling Magneto-Resistive Heads

K. Ishihara, M. Nakada, E. Fukami, K. Nagahara, H. Honjo, and K. Ohashi

IEEE Transactions on Magnetics Peer Review Yes 37(4) p.1687 - 16902001/07-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:We discuss the read performance, including the off-track performance and noise characteristics, of TMR heads. A vortex-like sense current field in TMR heads creates insensitive zones in the free layer and affects the output voltage and effective read width. The 1/f noise in the MHz-order frequency range was observed. To achieve a low-noise TMR head for high-density recording with small junction area, a high-quality thin barrier is a key to obtaining low 1/f noise, as well as small R/spl middot/A products to reduce the shot noise.

Structural and Magnetic Properties of High Saturation Induction CoNiFe Electroplated Films

N. Ohshima, M. Saito, K. Ohashi, H. Yamamoto, and K. Mibu

IEEE Transactions on Magnetics Peer Review Yes 37(4) p.1767 - 17692001/07-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:The structure and saturation induction (Bs) of Co90-xNi10Fex (8<=x<=40) electroplated films have been studied with a view to their use as high-density write-core materials. The Bs of the films were slightly larger than those of CoNiFe powders and were increased into the 1.8 to 2.1 T range by controlling the Fe composition and the amount of bcc phase. The latter was achieved by controlling the plating conditions, i.e., the current density and bath temperature. The hyperfine field of the films was about 34 T, slightly larger than that of the powders (33 T), suggesting that their magnetic moments were slightly larger than those of equivalent bulk alloys. The Bs values were increased by increases of the amount of bcc phase relative to the equilibrium phase with increasing the magnetic moments. A band calculation showed that the bcc phase had a larger magnetization than the fcc phase although the difference between the total energies of the two phases was fairly small. This confirmed our results.

Thermal Asperity of TMR Heads for Removable Disk Drives

Keishi Ohashi, Akinobu Sato, Kunihiko Ishihara, Takao Matsubara, Tsutomu Mitsuzuka, Hisanao Tsuge, and Nobuyuki Ishiwata

IEEE Transactions on Magnetics Peer Review Yes 37(4) p.1919 - 19212001/07-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:The thermal asperity of the tunneling magnetoresistive (TMR) head was studied using Zip-type flexible media, and compared with that of the anisotropic magnetoresistive (AMR) head. The examined head had a shielded structure with the TMR element close to the air bearing surface. Nevertheless, it generated relatively small thermal asperity even when the mechanical spacing between the head and medium was less than 20 nm, at which large and frequent thermal asperity was observed when the AMR head was used. Such relatively small thermal asperity of the TMR head Is attributed mainly to the small low-temperature coefficient of the electrical resistivity of the TMR element.

High-Speed and Large Capacity Magnetic Head Technology

N. Ishiwata, H. Honjo, J. Fujikata, T. Ishi, M. Nakada, K. Ohashi

NEC Technology Journal 54(6) p.41 - 442001/06-

Detail

Publish Classification:Research paper(bulletin of university, research institution)

Outline:NEC has developed high performance magnetic head technology with ultra-small CoNiFe writer and TMR reader. Data storage systems with high data rate and large capacity are required more and more for an improvement of network society. High end HDDs are key devices for the data storage system. NEC's high performance head technology is expected to realize 40% compound growth rate of data rate and 100% compound growth rate of recording density of high end HDD in the future.

Magnetic Heads With Ultrasmall Cores for High-Speed Recording

K. Ohashi, N. Ishiwata, H. Honjo, T. Ishi, Y. Nonaka, T. Toba, S. Saito

Journal of Magnetics Society of Japan Peer Review Yes 25(6) p.1316 - 13212001/06-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:Magnetic recording heads with a high-moment Co-Ni-Fe core are examined. Saturation flux density Bs of the core is 2.0 T. Good high-frequency write performance up to 500 MHz is obtained by reducing the core length to less than 10 um. Excellent write performance of narrow (0.55 um) pole tip head is also confirmed with high coercivity of a 480 kA/m (6000 Oe) medium. Finally, simulation results for higher-density and higher-speed magnetic recording are discussed.

Low Resistance Magnetic Tunneling Junctions and Their Interface Structures

J. Fujikata, T. Ishi, S. Mori, K. Matsuda, K. Mori, H. Yokota, K. Hayashi, M. Nakada, A. Kamijo, and K. Ohashi

Journal of Applied Physics Peer Review Yes 89(11) p.7558 - 75602001/06-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:Effects of interface structure and oxidation state were studied in stacked magnetic tunnel junction (MTJ) structures with top and bottom antiferromagnetic layers to obtain optimum resistance and high tunneling magnetoresistance (TMR) ratios for read heads. The roughness of the NiFe surface and the Al coverage were significantly improved by introduction of O2 surfactant gas on the Ta-seed-layer surface, which increased TMR ratios of the MTJ with low resistance area (RA) products of less than 10 Ω μm2. Furthermore, it was found that avoidance of Ni oxidation and Co oxidation at the tunnel barrier interface is essential to obtaining high TMR ratios, and that a good Al coverage and Fe–oxide formation may enhance TMR ratios when Fe-rich magnetic materials are used. For the top-type and bottom-type structures, a TMR ratio of 12%–17% with RA products of 6–7 Ω μm2 was obtained, which provides sufficient performance for read heads.

The Effect of Preparation Conditions on The Magnetic Properties of Electroplated High-Bs CoNiFe Films

M. Saito, N. Ishiwata, and K. Ohashi

ECS Proceeding; Magnetic Materials, Processes, and Devices VI Peer Review Yes PV 2000-29p.185 - 1962001-

Detail

Publish Classification:Research paper (international conference proceedings)

Outline:We have developed a high-speed, high-density recording head by using an electroplated CoNiFe film having a saturation induction (Bs) of 2 T. The film has a bcc-fcc mixed crystallographic phase, which provides it with good soft magnetic properties. We investigated the relationship between the properties of CoNiFe films and the consitions of their electrodeposition, and we found that a low coercivity (Hc) of less than 0.16 kA/m (2 Oe) and a low magnetostriction were obtained when the bcc ratio in the films was decreased. We also found that Bs increased with an increase in the bcc/fcc phase ratio in the filoms. Electroplating at a bath temperature of less than 20 degree C and with a high current density (15 mA/cm2) was effective in increasing the bcc/fcc phase ratio in the film.

Co-Ni-Fe Write Heads with a 10-μm Yoke Length for High-Speed Recording

Y. Nonaka, H. Honjo, T. Toba, S. Saito, T. Ishi, M. Saito, N. Ishiwata, and K. Ohashi

IEEE Transactions on Magnetics Peer Review Yes 36(5) p.2514 - 25162000/09-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:We have developed a Co-Ni-Fe write head with a short yoke length for high-speed recording. By reducing the yoke length to 9.5 um, the eddy currents induced in a yoke with a relatively low resistivity (0.2 micro Ohms/m) were reduced. The head of this short yoke had good write performance for a medium with a coercivity of 400 kA/m (5000 Oe) at frequencies up to 250 MHz (the overwrite less than -30 dB, and nonlinear transition shift less than 7%.

Low-Resistance Tunnel Magnetoresistive Head

K. Ohashi, K. Hayashi, K. Nagahara, K. Ishihara, E. Fukami, J. Fujikata, S. Mori, M. Nakada, T. Mitsuzuka, K. Matsuda, H. Mori, A. Kamijo, and H. Tsuge

IEEE Transactions on Magnetics Peer Review Yes 36(5) p.2549 - 25532000/09-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:A tunnel magnetoresistive (TMR) head with a low resistance of about 30 Ohms and effective track width of 1.4 um was fabricated using an in situ natural oxidation (ISNO) technique. Its read-output was almost the same as that expected from test elements at the wafer level. We found no large difference in noise voltages between TMR head and GMR head when their resistance was about 30 Ohms. A very low-resistivity TMR element with a resistance-area product of 14 Ohms um2 and a fairly high Delta R/R of 14% was also developed using ISNO. A signal-to-noise ratio consideration suggests that such low resistance is a key to TMR heads for high recording densities.

Write Performance of Recording Heads with a High-Bs Pole for High-Hc Media

Y. Nonaka, T. Toba, S. Saito, H. Honjo, T. Ishi, N. Ishiwata, and K. Ohashi

Journal of Magnetics Society of Japan Peer Review Yes 24(4 2) p.355 - 3582000/04-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:A magnetic recording head with a Co-Ni-Fe/Ni-Fe composite write pole was designed. The saturation induction Bs of Co-Ni-Fe is 2 T. In a computer simulation of a 3D static magnetic field, a recording head with Co-Ni-Fe films on both sides of a write gap generated a longitudinal write field of 9.9 kOe at a magnetic spacing of 40 nm from the write gap. The write characteristics of the recording head with the dual high-Bs structure designed above was tested for media with high coercivities of 4.5 to 7 kOe. The overwrite performance is over 30 dB for a medium with high coercivity of 7 kOe. Straight patterns of magnetic transitions written on the medium with a coercivity of 7 kOe were observed by using a magnetic force microscope (MFM). On the other hand, bends were found in the track-edges of magnetic transitions written on a medium with a coercivity of 4.5 kOe. This indicates that the recording head generated too large a write field for the medium with a coercivity of 4.5 kOe.

Preparation of Electrodeposited High-Bs and High-ρ CoNiFe Thin Films by Mo Addition

Y. Sogawa, A. Kawashima, T. Yokoshima, T. Nakanishi, H.-S. Nam, T. Osaka, K. Ohashi

Journal of Magnetics Society of Japan Peer Review Yes 24(4 2) p.699 - 7022000/04-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:Addition of a complexing agent and/or Na2MoO4 to the bath was investigated with a view to increasing the resistivity of CoNiFe soft magnetic thin films. Results showed that the electrical resistivity of CoNiFe thin films was increased by addition of a complexing agent such as sodium tartrate and sodium citrate. These films contained a small amount of carbon of 1 to 2 at%. The addition of Na2MoO4 also resulted in an increase in resistivity of CoNiFe thin films. This Co59Ni12Fe26Mo1C2 thin film had the following properties: Bs = 1.8 T, Hc = 1.6 Oe, ρ = 129 μΩcm.

Ultra-High-Density Magnetic Information Storage Technologies

K. Ohashi, N. Ishiwata, M. Yanagisawa, A. Sato, S. Tsuboi, and H. Hokkyo

NEC Research & Development 41(2) p.160 - 1652000/02-

Detail

Publish Classification:Research paper(bulletin of university, research institution)

Outline:Three approaches used to acheve ultra-high-density recording of 100 Gbit/in2 are discussed. In order to overcome the thermal fluctuation problem of recorded patterns, a write head with Co-Ni-Fe pole has been developed. The Co-Ni-Fe pole generates the strongest write field. The head wrote well in media with a coercivity of 7 kOe, which is sufficiently large for ultra-high-density recording. A narrow gap Co-Ni-Fe head for perpendicular recording has also been developed. The experimental results on contact recording and a double-layer perpendicular medium are also discussed.

Purity of Films and Performance of Recording Heads

Keishi Ohashi, Mikiko Saito, Hiroaki Honjo, Tamaki Toba, Yoshihiro Nonaka, and Nobuyuki Ishiwata

ECS Proceedings; Electrochemical Technology Applications in Electronics III Peer Review Yes PV 99-34p.241 - 2492000-

Detail

Publish Classification:Research paper (international conference proceedings)

Outline:The effect of impurities in CoNiFe films and the performance of CoNiFe pole heads were investigated. Electrodeposition of CoNiFe from a bath containing no sulfur-containing additives (SCAs) produced a pole material with excellent magnetic properties. CoNiFe pole heads generated a strong field of about 10 kOe in a recording medium. These heads did not experience large write instability because of the near-zero magnetostriction of the CoNiFe films. Besides producing good magnetic properties, removal of SCAs from the bath improved corrosion resistance. Moreover, annealing after deposition played an important role in controlling magnetic properties and corrosion resistance. Corrosion resistance was inferior if the film was deposited at a relatively low current density, even when a non-SCA bath was used. However, corrosion resistance of that film was improved by annealing. This improved corrosion resistance suggests that the imperfections associated with adsorption and evolution of hydrogen may play important roles in the corrosion mechanism.

Write Performance of Heads with a 2.1-Tesla CoNiFe Pole

Keishi Ohashi, Noboru Morita, Tadaaki Tsuda, and Yoshihiko Nonaka

IEEE Transactions on Magnetics Peer Review Yes 35(5) p.2538 - 25401999/09-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:We examined the write performance of heads with a CoNiFe/NiFe composite write pole. The saturation induction Bs of the CoNiFe film was 2.1 T (21 kG). The CoNiFe layer thickness was typically 0.5-0.6 um, and the rest of the write pole was composed of Ni80Fe20. The dual high Bs layer structure with the CoNiFe films on both sides of the write gap gave excellent overwrite performance. It was over 30 dB for a medium that had a high coercivity of 560 kA/m (7.0 kOe).

Corrosion properties of electroplated CoNiFe films

Saito, M.; Yamada, K.; Ohashi, K.; Yasue, Y.; Sogawa, Y.; Osaka, T.

Journal of the Electrochemical Society 146(8) p.2845 - 28481999/08-1999/08

DOIScopus

Detail

ISSN:00134651

Outline:Electroplated CoNiFe films with a saturation flux density as high as 2.1 T are potentially useful in high-density magnetic recording heads. We found that films electroplated at a high current density (15 mA/cm2) from a bath without saccharin have a sufficient anodic pitting-corrosion potential (-65 mV). We also found that the pitting-corrosion potential of films electroplated under a low current density (5 mA/cm2) from saccharin-free baths have anodic pitting-corrosion potentials of less than -300 mV. However, the corrosion resistance improved after annealing at temperatures above 100°C. The crystal-grain boundaries in the as-plated film that electroplated under a low current density from saccharin-free baths are not clear (i.e., that the phase is amorphous). But the crystal grain boundaries in the annealed film are clear. Films electroplated from baths containing saccharin also have anodic pitting-corrosion potentials of less than -300 mV. Their corrosion resistance did not improve when they were annealed at 250°C. The deterioration of the corrosion resistance is attributed to the defects that increase the face-centered cubic (111) lattice constant. One of the most important characteristics of a highly corrosion-resistant CoNiFe film is fine crystal structure with very few defects.

Influence of crystalline structure and sulfur inclusion on corrosion properties of electrodeposited CoNiFe soft magnetic films

Osaka, Tetsuya; Takai, Madoka; Sogawa, Yoshimichi; Momma, Toshiyuki; Ohashi, Keishi; Saito, Mikiko; Yamada, Kazuhiko

Journal of the Electrochemical Society 146(6) p.2092 - 20961999/06-1999/06

DOIScopus

Detail

ISSN:00134651

Outline:The corrosion resistance of soft magnetic films is an important property to be considered in the manufacture of magnetic devices. We investigated the corrosion behavior of the electrodeposited CoNiFe film with desired soft magnetic properties by varying the crystalline structure and the amount of included sulfur. The corrosion property in 2.5% NaCl solution depends largely on the sulfur content and also on the structure of the film. Although the CoNiFe film contains more than 13 atom % Fe, the film of face-centered to body-centered cubic mixed crystals exhibits a high anticorrosion property because of very small grain size with essentially no sulfur inclusion (<0.1 atom %).

Effect of Operating Conditions on the Soft Magnetic Properties of Electrodeposited High-Bs CoNiFe Films

Y. Sogawa, S. Mizutani, T. Momma, T. Osaka, M. Saito, K. Ohashi, K. Yamada

Journal of Magnetics Society of Japan Peer Review Yes 23(4 part 2) p.1405 - 14081999/04-

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Detail

Publish Classification:Research paper (scientific journal)

Development of Soft Magnetic Materials with High Bs by the Electroplating Method, and Their Application to an MR Write Core Head

T. Osaka, M. Takai, K. Ohashi

Journal of Magnetics Society of Japan 22(7) p.1182 - 11881998/08-

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New Soft Magnetic CoNiFe Plated Films with High Bs = 2.0-2.1 T

Tetsuya Osaka, Madoka Takai, Katsuyoshi Hayashi, Yoshimichi Sogawa, Keishi Ohashi, Yoshihiko Yasue, Mikiko Saito, and Kazuhiko Yamada

IEEE Transactions on Magnetics Peer Review Yes 34(4) p.1432 - 14341998/07-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:A CoNiFe film with saturation magnetic flux density (Bs) greater than 2.0 tesla (T) has been prepared for the first time as a soft magnetic film; the coercivity (Hc) of the film is less than 160 A/m (2.0 Oe). This success was achieved by formulating a new plating bath and operating conditions to form fine grains. The film has a low Hc of less than 160 A/m, a low saturation magnetostriction (ls) of approximately 10-6, and a high Bs of 2.0-2.1 T. The present invention is expected to contribute to accelerating the development of not only the technology of high-density magnetic recording but also the field of magnetic materials in general.

A soft magnetic CoNiFe film with high saturation magnetic flux density and low coercivity

Osaka, Tetsuya; Takai, Madoka; Hayashi, Katsuyoshi; Ohashi, Keishi; Saito, Mikiko; Yamada, Kazuhiko

Nature 392(6678) p.796 - 7981998/04-1998/04

DOIScopus

Detail

ISSN:00280836

Outline:Magnetic materials are classed as 'soft' if they have a low coercivity (the critical field strength H(c) required to flip the direction of magnetization). Soft magnetic materials are a central component of electromagnetic devices such as step motors, magnetic sensors, transformers and magnetic recording heads. Miniaturization of these devices requires materials that can develop higher saturation flux density, B3, so that the necessary flux densities can be preserved on reducing device dimensions, while simultaneously achieving a low coercivity. Common high-B3 soft magnetic films currently in use are electroplated CoFe-based alloys, electroplated CoNiFe alloys, and sputtered Fe-based nanocrystalline and FeN films. Sputtering is not suitable, however, for fabricating the thick films needed in some applications, for which electrochemical methods are preferred. Here we report the electrochemical preparation of a CoNiFe film with a very high value of B(s) (2.0-2.1 T) and a low coercivity. The favourable properties are achieved by avoiding the need for organic additives in the deposition process, which are typically used to reduce internal stresses. Our films also undergo very small magnetostriction, which is essential to ensure that they are not stressed when an external magnetic field is applied (or conversely, that external stresses do not disrupt the magnetic properties). Our material should find applications in miniaturization of electromechanical devices and in high-density magnetic data storage.

An Advanced Magneto-Resistive Head with A Newly Developed Electroplated High-Bs Write Pole

Hiroshi Gokan, Kaoru Toki, Keishi Ohashi, Takao Maruyama, Mitsuo Abe, and Susumu Mizuno

NEC Research & Development 39(3) p.309 - 3161998/03-

Detail

Publish Classification:Research paper(bulletin of university, research institution)

Outline:A Magneto-Resistive (MR) head with a newly developed electroplated high-Bs CoNiFe write pole has been developed for use in Hard Disk Drives (HDDs). The electroplated film has the leading high saturation magnetization (Bs) of 2.1 T to provide a soft magnetic film suitable for the write element in MR heads. Introducing high-Bs films for the write-pole improves overwrite performance in 2,950 Oe high-Hc media by 17.7 dB. For the read element, a large exchange coupling NiMn film has been developed. This film provides an excellent biasing scheme for maximum asymmetry change during repeated read/write operations is improved by optimizing the write-core design and the magnetostriction of the magnetic layers as well as by optimizing the biasing scheme. Altitude sensitivity, which is defined as the change in flying height when atmospheric pressure is reduced from 1.0 to 0.7 atm, is supressed from 11 to 5 nm by modifying the ABS (Air-Bearing Surface) design to increase the negative pressure induced. Typical read/write characteristics of MR heads with high-Bs write pole designed for 2.6 Gb/in^2 areal-density recording are described. An output-signal voltage of 400 uV/um with excellent signal stability has been obtained.

MR Response Stability on Geometry for an Abutted Junction of the MR Element and Longitudinal Bias Layer

E. Kariyada, S. Kurashina, N. Ikezawa, N. Morita, A. Kota, K. Shimabayashi, K. Ohashi, K. Toki, H. Urai

Journal of Magnetics Society of Japan Peer Review Yes 21(4 part 2) p.253 - 2561997/04-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:Hysteresis and baseline shift are studied in soft-adjacent-layer-biased MR sensors with abutted quasi-permanent magnetic bias. The magnet consists of NiFe/NiMn exchange-coupling films, which apply longitudinal bias field to an MR sensor. Abutted bias-magnet structures with various taper angles fabricated, and the overlap lengths were measured as the length of the MR flat active region covered by the longitudinal bias films. The hysteresis measured from the transfer curve decreases with decreasing overlap length. The repeatable baseline shift in the readback signal was also improved by decreasing the overlap length in the MR sensor.

MR Head Technology Supporting High Recording Density

H. Gokan, H. Urai, K. Toki, K. Ohashi

NEC Technology Journal 49(6) p.23 - 281996/06-

Detail

Publish Classification:Research paper(bulletin of university, research institution)

Evaluation of the Electrical and Mechanical Properties of Hard-Baked Photoresist

M. Saito, K. Ohashi, K. Yamada, K. Seimiya, and T. Ozawa

Journal of Magnetics Society of Japan Peer Review Yes 19(2) p.141 - 1441995-

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Detail

Publish Classification:Research paper (scientific journal)

Outline:The surface structure of a thermally cured photoresist (PR) layer used as a thin-film-head insulation layer greatly affects that layer's insulation resistance (IR) and internal stress. As the carbonyl peak ratio in the PR increases, the IR decreases. In air heat treatment, compressive stress is induced in the PR. These phenomena are explained as follow. Many carbonyl and aromatic ketone groups, which are typical of the hydrophilic group, exist in the PR. Consequently, moisture sorption is induced in the surface of the PR, resulting in swelling of the PR. This stress change is related to the changes in the upper NiFe magnetic domain. It is concluded that supressing change in the PR surface structure improves the head reliability.

Magnetization Dynamics in Thin Film Heads

Keishi Ohashi

Journal of Magnetism and Magnetic Materials Peer Review Yes 134(2 and 3) p.262 - 2671994/06-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:The relationship between domain wall motion and magnetization rotation is investigated. A wall motion mechanism previously proposed by the author is examined. The model gives the novel concept that the energy difference between transition state (magnetization curling) and final state (after wall motion) accelerates the wall motion. The magnetic moments in the region coupled with 90° walls rotate more slowly than those moments in the non-coupled region, hence the magnetic flux change is confined to a narrower portion of central domains at higher frequencies.

Preparation of Electrodeposited FeP Films and Their Soft Magnetic Properties

Tetsuya Osaka, Madoka Takai, Akiyoshi Nakamura, Fujio Asa, Keishi Ohashi, and Hiroaki Tachibana

Journal of the Magnetics Society of Japan Peer Review Yes 18(S1) p.187 - 1901994-

DOI

Detail

Publish Classification:Research paper(bulletin of university, research institution)

Outline:Electrodeposited FeP alloy films were formed, and the most suitable FeP alloy film exhibits a minimum coercivity, 0.2 Oe, and high saturation magnetic flux density, 1.4 T, at the composition of 27at%P. In order to improve the magnetic properties, in particular, the permeability, the magnetic field heat treatment was adopted, and the permeability increased until 1400. The most suitable FeP film was found to be a hyper-fine crystalline structure. The thermal stability of the FeP film was also confirmed to be until 300 degree C annealing without magnetic field in vacuum.

Magnetization Dynamics in Thin Film Head

K. Ohashi

Journal of Magnetics Society of Japan Peer Review Yes 16(S1) p.81 - 841992-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:This paper gives an overview of magnetization dynamics in thin film heads. The relationship between domain wall motion and magnetization rotation is essential in both impedance noise and Barkhausen noise. A model which describes coupled wall motion with magnetization rotation proposed by the author is compared with other models.

Effect of Plated NiFe Composition on Domain Configuration

K. Ohashi, M. Ito, and T. Maruyama

ECS Proceedings; Magnetic Materials, Processes, and Devices Peer Review Yes PV 90-08p.247 - 2581990-

Detail

Publish Classification:Research paper (international conference proceedings)

Outline:This paper describes changes in magnetic domain which vary with the magnetostriction coefficient (a parameter closely related to film composition) in the production of thin film heads. Domain configuration and direction of domain walls are affected by annealing and machining. There are two different mechanisms which change the domain configuration during annealing: deformation of a magnetic film near its edges and deformation of polymer structures under magnetic films. Domain configuration change during machining is connected with the stress of over coat film.

Magnetic Heads

M. Ito, C. Yamada, K. Ohashi, K. Shimabayashi, M. Horiuchi

NEC Technology Journal 41(15) p.41 - 441988/12-

Detail

Publish Classification:Research paper(bulletin of university, research institution)

Outline:This paper presents Magnetic Head technology, which accelerates advances in Magnetic Recording. Tribology and Thin Film Head technology, which are necessary for high recording density, are described, especially from the view point of reliability of hard disk drive operation.

Application of Electroplating to Thin Film Head

K. Ohashi, M. Ito, and M. Watanabe

ECS Proceedings; Electrochemical Technology in Electronics Peer Review Yes Invitation Yes PV 88-23p.525 - 5421988-

Detail

Publish Classification:Research paper (international conference proceedings)

Outline:Electroplating is a crucial step in the production of thin film heads to be used for magnetic disk drives. Anomalous codeposition of NiFe film must be accurately controlled for a stable read/write head operation. Plated NiFe film offers 20% higher voltage output than sputter-depositted film. Research on plating of high saturation magnetization material, which promises improved recording density, has been also performed. Copper film is preffered as a low resistivity conductor for coil windings. It is deposited through micron-size photoresist patterns to provide a high aspect ratio cross section. This paper provides: a review of electroplating in thin film head applications and results of some experiments conducted by the authors.

Magnetic Heads

M. Watanabe, K. Ohashi

NEC Technology Journal 39(9) p.56 - 601986/09-

CiNii

Detail

Publish Classification:Research paper(bulletin of university, research institution)

Outline:Design considerations relating magnetic head, to the one of the most integral parts of the disk dtorage device, are described from the view point of high density recording. Improvements made on the conventional ferrite Winchester transducer and characteristics of the thin-film head as well as its reliability design are reviewed. It is expected that both types of magnetic head can offer competitive features for a variety of future drive development.

Mechanism of 90° Wall Motion in Thin Film Heads

Keishi Ohashi

IEEE Transactions on Magnetics Peer Review Yes 21(5) p.1581 - 15831985/09-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:The interaction between the rotational motion of magnetization and wall movement are investigated for an infinite strip of magnetic film with closure domains. When an external field is applied, the direction of magnetization is assumed to curl parabollicaly near the 90° walls. The 90° wall will move to decrease the energy associated with this curling. This movement can be described by the equation of rotational motion for the wall. The switching time relating to a 90° wall is fairly short (6 - 18 nsec) calculated by solving the equation of motion. It is due to the acceleration of the wall movement by the magnetization rotation.

Magnetic After-Effect in Amorphous Tb-Fe Films

Keishi Ohashi, Hisao Tsuji, Shigeru Tsunashima, and Susumu Uchiyama

Japanese Journal of Applied Physics Peer Review Yes 19(7) p.1333 - 13381980/07-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:Magnetic after-effect in sputter deposited TbxFe1-x (x×0.17~0.24) films is studied. The after-effect is directly observed using polar Kerr magneto-optic effect as a slow propagation of domain walls. The velocity of the domain growth (10-4~10-1 cm/s) changes exponentially with the applied field. The viscosity coefficient Sv≡dM/d ln tcenterdotχ-1 (χ: irreversible susceptibility), which was used in describing Jordan type after-effect, is applied to characterize the after-effect. The value of Sv (22~110 Oe) is inversely proportional to the saturation magnetization at room temperature and decreases with rising temperature. The origin of the slow wall motion is inferred to be the random anisotropy of Tb ion rather than the oxidation of the film surface.

Magnetic Aftereffect Due to Domain Wall Motion in Amorphous TbFe Sputtered Films

K. Ohashi, H. Takagi, S. Tsunashima, S. Uchiyama, and T. Fujii

Journal of Applied Physics Peer Review Yes 50(B3) p.1611 - 16131979/03-

DOI

Detail

Publish Classification:Research paper (scientific journal)

Outline:A very large aftereffect is observed in sputtered amorphous Tb‐Fe films with uniaxial anisotropy perpendicular to the film plane. In the present experiment, the film is first saturated to −Ms by a premagnetizing field Hp (<0), where Ms is the saturation magnetization. Then the applied field is suddenly changed from Hp (<0) to Ha (?0) which is close to the coercive field. With proper choice of the film composition, temperature, Ha and so on, the magnetization changes from −Ms to almost +Ms with the passage of time while Ha is kept constant. The dependences of the aftereffect on the applied field and on the temperature are shown. The domain observation by means of polar Kerr effect reveals that the aftereffect is associated with the slow dendritic growth of the magnetic domains. It is also found that the density of reversed domain nuclei depends on the premagnetizing field Hp.

Books And Publication

'Thin-film Head and the Innovator's Dilemma' in "Electrochemical Engineering: From Discovery to Product" edited by R. C. Alkire et al., Chap. 5.

Keishi Ohashi(Sharing writing)

Wiley-VCH2019/01-2019/01

Detali

Scholarly BookTotal Number of Pages:344Responsible Number of Pages:129-158ISBN:978-3527342068ASIN:3527342060

Group IV Photonics for Sensing and Imaging

K. Ohashi, R. A. Soref, G. Roelkins, H. Minamide, and Y. Ishikawa, editors(Edit)

Cambridge University Press2013/06-

Detali

Scholarly BookISBN:978-1627482417

'Optical Devices ' in "Silicon-Germanium Nanostructures" edited by Y. Shiraki and N. Usami, Chap. 21.

Keishi Ohashi(Sharing writing)

Woodhead Publishing2011/02-

Detali

Scholarly BookISBN:978-1845696894

Lecture And Oral

Next Generation IoT Sensing for Internal Environment

Keishi Ohashi

7th DGIST-Waseda Workshop on Electrochemistry 2019(Unit for Energy and Nanomaterials, Top Global University Project, Waseda University)2019/11/18

Detail

International conferenceOral presentation(general)Venue:Tokyo

Outline: Sensor networks using have started to gather data. With the addition of chemical sensors to existing systems with physical sensors, prescriptions based on medical science would be realized. Bernard pointed out the importance of the internal environment in humans. The constancy of the environment presupposes a perfection of the organism are compensated and brought into balance. Stress is a pattern of disruptive physiological and psychological reactions to events that threaten the ability to cope. Stressors tend to create large changes in metabolism. Selye determined that there is a limited supply of adaptive energy to deal with stress. Epigenetics studies have reported that depression of brain-derived neurotrophic factor is affected by stress hormones. In the presentation, the author presents several recent results on the development of the internal environment sensing system. The system noninvasively monitors several kind of stress markers in saliva. This system is expected to help prevent human depression and will improve livestock productivity.

Trial of Realization of Electrochemical Nanotechnology to Advanced Manufacturing

Keishi Ohashi, Tetsuya Osaka, Daikichi Mukoyama

The 70th Annual Meeting of the International Society of Electrochemistry(International Society of Electrochemistry)Invitation Yes2019/08/08

Detail

International conferenceOral presentation(keynote)Venue:Durban

Outline: The transfer of the new technologies from our university to industries will be introduced, in particular, sensing systems on biosensors and batteries. A biosensing system is commercialized based on a concept of physiological balance for healthcare. The addition of low-cost biochemical sensors to the sensing system would help with scientific prescriptions based on contemporary medicine. As a candidate for a low-cost and robust chemical sensor platform, the ion-sensitive field-effect transistor (ISFET) has long been examined. Besides, we introduced an approach related to battery evaluation by Electrochemical impedance spectroscopy (EIS). After reviewing past our research, our two approaches for new business trials are discussed. One approach is based on the progressiveness of technology that relies on public finance with existing big companies. Another approach is a lean startup based on a customer development model for entrepreneurs.

Detection of four kinds of Stress Biomarkers by Aptamer-Immobilized Field Effect Transistor Biosensor

R. Toyama, S. Kuroiwa, S. Hideshima, N. Kaneko, H. Horii, H. Minagawa, K. Ohashi, T. Momma, T. Osaka

International Symposium on Biological Material Science for Agriculture and Engineering(Tokyo University of Agriculture and Technology)2018/06/27

Detail

International conferencePoster presentationVenue:Tokyo

Gradient tint smart window using metallo-supramolecular polymer

Masayoshi Higuchi, Yuki Seino, Keishi Ohashi

67th Annual Conference of The Society of Polymer Science, Japan(The Society of Polymer Science, Japan)2018/05/24

Detail

National conferenceOral presentation(general)Venue:Nagoya

Outline: Metallo-supramolecular polymer is a new type polymer composed of metal ions and multitopic organic ligands. The polymer is expected to show unique electrochemical and/or optical properties due to the electronic interaction between the metals and ligands through the polymer chain. We found electrochromic properties of polymer and the other functions so far. In this presentation we report gradient tint smart window using the metallo-supramolecular polymer.

Detection of Mental Stress Biomarker by Aptamer-Immobilized FieldEffect Transistor Sensor

Shigeki Kuroiwa, Sho Hideshima, Katsunori Horii, Naoto, Kaneko, Hirotaka Minagawa, Toshiyuki Momma, Takuya Nakanishi, Keishi Ohashi, Tetsuya Osaka, Ryota Takibuchi, Iwao Waga

22nd Topical Meeting of the International Society of Electrochemistry(The International Society of Electrochemistry)2018/04/17

Detail

International conferencePoster presentationVenue:Tokyo

Outline: We detected α-amylase, sIgA, CgA, and cortisol in phosphate buffer using each biosensor.  Increases in the magnitude of response were observed with increases of the biomarkers’ concentration in the range between 1 nmol/dm3 and 100 nmol/dm3, 3 pmol/dm3 and 3 nmol/dm3, 2 nmol/dm3 and 200 nmol/dm3, 1 μmol/dm3 and 1 mmol/dm3, for α-amylase, sIgA, CgA, and cortisol, respectively. FET sensor responded as a gate voltage shift to the change in charge on the gate insulator surface. The observed responses suggested to be the binding of negatively charged α-amylase (isoelectric point (pI) = 6.34), sIgA (pI = 4.8-6.5), CgA (pI = 4.6-4.9) to the corresponding aptamers. Though cortisol is an electrically neutral molecule, a similar behavior toward the increase of negative charge or the decrease of positive charge was observed.

Fabrication of Aptamer-Immobilized Field-Effect Transistor Biosensor for Detecing Stress Biomakers

63. R. Takibuchi, S. Kuroiwa, S. Hideshima, T. Nakanishi, K. Ohashi, T. Momma, T. Osaka

5th DGIST-Waseda Workshop on Electrochemistry2017/12/12

Detail

National conferencePoster presentationVenue:Tokyo

Fabrication of Aptamer-Immobilized Multi-Target Field-Effect Transistor Biosensor for Sensing Mental Stress

Shigeki Kuroiwa, Ryota Takibuchi, Akane Matsuzaka, Sho Hideshima, Naoto Kaneko, Hirotaka Minagawa, Katsunori Horii, Iwao Waga, Takuya Nakanishi, Keishi Ohashi, Toshiyuki Momma, Tetsuya Osaka

232nd ECS Meeting(The Electrochemical Society)2017/10/01

Detail

International conferencePoster presentationVenue:Maryland

Outline: The sensing of biomarkers in the body is very effective for diagnosis of disease and monitoring of human health condition. However, blood sampling of mental stress markers is stressful for those who do not feel serious health concerns when they want to check only their own stress level. We need to measure stress markers noninvasively in our daily lives. Saliva is an ideal biological sample to be taken noninvasively. α-amylase and cortisol are known as stress markers in saliva. Since individual differences in stress response are large, it is important to simultaneously detect multiple markers and evaluate the stress level. In this study, we attempted to fabricate two field effect transistor (FET) biosensors using aptamers against α-amylase and cortisol as indexes of stress. Our purpose was to investigate the characteristics of sensing two types of biomarkers, a protein and a steroid molecule, using aptamer-immobilized FET biosensors. The aptamer against α-amylase and the one against cortisol were obtained after eight rounds of selection by SELEX method from an initial DNA library. The gate insulator (SiO2) of FET was modified with 3-aminopropyltriethoxysilane, followed by addition of glutaraldehyde. Each of two aptamers, which are terminated with amino group, was immobilized on the thus-prepared surface of insulator. We detected α-amylase and cortisol in phosphate buffer using the aptamer against α-amylase and the one against cortisol respectively. An increase in the magnitude of response was observed with an increase of α-amylase concentration in the range between 1 nmol/dm3 and 100 nmol/dm3. FET sensor responded as a gate voltage shift to the change in charge on the gate insulator surface. The observed response was suggested the binding of negatively charged α-amylase (isoelectric point = 6.34) to the aptamer. Though cortisol is an electrically neutral molecule, an increase in the magnitude of response was observed with an increase of cortisol concentration in the range between 1 μmol/dm3 and 1 mmol/dm3. It was a similar behavior toward the increase of negative charge or the decrease of positive charge. The phosphate groups of DNA aptamers and their counter ions have an electrical charge on the gate insulator. This suggests that the cortisol aptamer contracted and its negative charge penetrated Debye length or that the counter ion bound to the aptamer beforehand was removed after the association of cortisol. The concentration of α-amylase in saliva is 1 - 3 μmol/dm3. The sensitivity of this α-amylase sensor is at a practical level. The concentration of cortisol in saliva is 3 - 11 nmol/dm3. This cortisol FET sensor requires optimization of aptamer and refinement of the device for practical application. The quantitative detection of α-amylase and cortisol using aptamer-immobilized FET sensor was achieved. This sensor can be sensitive to a structural change of aptamer induced by the target binding. It was demonstrated that the detection of the neutral target molecule is possible.

Nanoscale Application of Surface Plasmon Resonance

Keishi Ohashi

3rd International Workshop on Chromogenic Materials and Devices(National Institute for Materials Science (NIMS))Invitation Yes2017/09/27

Detail

International conferenceOral presentation(invited, special)Venue:Tokyo

Industrial Trial of a Biosensor Technology

Keishi Ohashi and Tetsuya Osaka

Pacific Rim Meeting on Electrochemical and Solid-State Science 2016(The Electrochemical Society)Invitation Yes2016/10/04

Detail

International conferenceOral presentation(invited, special)Venue:Honolulu, Hawaii

Outline: Sensor network systems using mobile phones with several physical sensors can collect big data related to human health. The addition of low-cost chemical sensors to the sensor system increases the scientific prescription based on contemporary medicine. The authors examine the commercialization of a system based on the concept of physiological balance sensing. Individuals and animals possess biological barrier systems against various stressors. This study offers a system that constantly monitors biological barrier functions on the epithelial layers by using an ion sensitive field-effect transistor (ISFET) sensor and feedback recommendations and precipitations through a smart phone.

Aptamer-Based Biosensors for Rapid Detection of Stress Markers

Naoto Kaneko, Hirotaka Minagawa, Joe Akitomi, Keishi Ohashi, Shigeki Kuroiwa, Shofarul Wustoni, Sho Hideshima, Tetsuya Osaka, Katsunori Horii, and Iwao Waga

The 43rd International Symposium on Nucleic Acids Chemistry2016/09/28

Detail

International conferencePoster presentationVenue:Kumamoto

Outline: Cortisol has been recognized as one of the stress biomarker in evaluating stress related disorders. However, it is difficult to develop the simple test since cortisol is small molecules. In this study, we developed aptamer-based biosensor, constructed with anti-cortisol aptamer and DNAzyme, to detect cortisol by fluorescence detection, colorimetric detection, fluorescence polarization (FP) detection and electrical detection such as field effect transistor (FET) sensor.

Monitoring Biomolecules and Ions with an FET Sensor for Physiological Balance

Keishi Ohashi, Shigeru Kuroiwa, Sho Hideshima, Takuya Nakanishi, Tetsuya Osaka

26th Anniversary World Congress on Biosensors(Elsevier)2016/05/27

Detail

International conferencePoster presentationVenue:Gothenburg

Outline: A concept of physiological balance sensing using a multi-target field-effect transistor (FET) sensor is proposed. Today’s smart phones equip various physical sensors, which has been accelerating the accumulation of human health data. However, more scientific prescription based on contemporary medicine is expected to be pulled out from data bases if low-cost chemical sensors are added to the system. People and animals have inherited biological barrier systems against various stressors. The barriers at the interface between body and external environment, such as skin, gut, and oral cavity, are especially important in the protection of body from external factors. Our plan is to develop a system which constantly monitors the biological barrier functions by using FET sensors. The size of the sensor element is about one millimeter, and is therefore suitable for integration with silicon electronics connecting to the Internet. We already reported a two-target FET sensor chip which detects two different tumor markers. A multiple-target sensor system constructed as the extension of this chip technology is under development. The immune system plays a main role in biological barriers. We have developed an FET immunoglobulin E (IgE) sensor for the examination of egg allergy. Some key molecules for the balance sensing have little or no polarization. Aptamers, which deform to change charge distributions within the Debye length, are under investigation for the detection of such small-molecule hormones. pH is a useful indicator for the physiological balance. A wireless FET sensor system has been developed to monitor skin pH. The system is controlled from a smartphone, and the monitored data is stored in the phone and sent to Cloud. A simple and quick skin pH measurement method was developed to apply to both people and dog. The difference of skin pHs between various sites of a dog will also be presented.

Physiological Balance Sensing Using an FET Sensor System

Keishi Ohashi, Tetsuya Osaka

3rd DGIST-WASEDA Workshop on Electrochemistry2015/12/10

Detail

International conferenceOral presentation(invited, special)Venue:Tokyo

Physiological Balance Sensing in an Unobtrusive Manner

Keishi Ohashi

The Catholic University of Korea & Waseda University 2nd Joint Symposium2015/11/27

Detail

International conferenceOral presentation(invited, special)Venue:Tokyo

Unobtrusive and Wireless Physiological Balance Sensing

Keishi Ohashi, Shigeru Kuroiwa, Sho Hideshima, Takuya Nakanishi, Akane Matsuzaka, Tetsuya Osaka

The 6th Annual Conference on RFID Technology and Application(IEEE)2015/09/18

Detail

International conferencePoster presentationVenue:Tokyo

True Nano, True Business

Keishi Ohashi

The 6th International Symposium on Advanced Materials Development and Integration of Novel Structural Metallic and Inorganic MaterialsInvitation Yes2015/06/09

Detail

International conferenceOral presentation(keynote)Venue:Tokyo

The Final Push to Mainstream; Can Integrated Optics Learn From Integrated Magnetics?

Keishi Ohashi

Evening Discussion Session, International Solid-State Circuits Conference 2012(IEEE)Invitation Yes2012/02/20

Detail

International conferenceSymposium workshop panel(nominated)Venue:San Francisco

Outline: The electronic industry introduced photolithography for fabricating printed circuit boards in the 1930s and semiconductor integrated circuits in the late 1950s. The success stimulated both the optics and magnetics industries. In optics, various micro-optical components have been proposed since the 1960s, and a large assortment of elemental devices using CMOS photonics has been developed. The final push to create a profitable market may be guided by the lessons learned from the hard disk drives (HDDs) in the 1990s. In magnetics, simple replacement of bulk ferrite heads with small integrated thin-film heads using photolithography was not enough to establish a new market. A key technology that enabled small HDDs was the magneto-resistive head, since its read voltage does not depend on the disk velocity. Such enabling technologies for creating a new market in integrated optics will be discussed with the merits produced by the devices operating under different mechanisms.

On-chip Optical Interconnect to Replace Global Electric Interconnect

Keishi Ohashi, Tohru Mogami

OptoElectronics and Communications Conference 2010Invitation Yes2010/07/05

Detail

International conferenceOral presentation(general)

Bonded Photonic Structure Incorporated into a Chip

K. Ohashi, M. Nakada, T. Nakamura

35th European Conference Optical Communication 2009Invitation Yes2009/09/20

Detail

International conferenceSymposium workshop panel(nominated)

Surface Plasmon Antenna for Photo Detection

K. Ohashi, J. Fujikata, T. Ishi, K. Ishihara, D. Okamoto,

Applied Plasmonics Workshop, 4th International Conference on Surface Plasmon Photonics(PLEAS)Invitation Yes2009/06/22

Detail

International conferenceSymposium workshop panel(nominated)

Electro-Optical Ceramic Film for On-Chip Optical Interconnect

K. Ohashi, M. Nakada, T. Shimizu, J. Akedo, H. Tsuda, J. Park

8th Pacific Rim Conference Ceramic and Glass Technology(ACS)Invitation Yes2009/05/31

Detail

International conferenceOral presentation(invited, special)

Silicon Photonics and Plasmonics for On-Chip Interconnection

K. Ohashi

2009 International Seminar on Advanced Semiconductor Materials & Devices(Hokkaido University)Invitation Yes2009/03/02

Detail

International conferenceOral presentation(invited, special)

Plasmonic Coupling for Photonic Device Shrink

K. Ohsahi

Microphotonics Center Fall Meeting(MIT)Invitation Yes2008/12/21

Detail

International conferenceSymposium workshop panel(nominated)

Photodetector Using Surface-Plasmon Antenna for Optical Interconnect

K. Ohashi, J. Fujikata

2008 Materials Research Society Fall Meeting(MRS)Invitation Yes2008/12/01

Detail

Oral presentation(general)

Waveguide-Integrated Si Nano-Photodiode with Surface-Plasmon Antenna and Its Application to On-Chip Optical Clock Signal Distribution

J. Fujikata, K. Nose, J. Ushida, K. Nishi, M. Kinoshita, T. Shimizu, T. Ueno, D. Okamoto, A. Gomyo, M. Mizuno, T. Tsuchizawa, T. Watanabe, K. Yamada, S. Itabashi, K. Ohashi,

5th International Conference on Group IV Photonics 2008(IEEE)Invitation Yes2008/09/17

Detail

Oral presentation(invited, special)

Silicon Photonics and Plasmonics for Electronics

K. Ohashi

14th International Symposium on the Physics of Semiconductors and ApplicationsInvitation Yes2008/08/26

Detail

International conferenceOral presentation(invited, special)

Silicon Photonic Devices and Their Integration

K. Ohashi

International Nano-Optoelectronics Workshop 2008Invitation Yes2008/08/10

Detail

International conferenceOral presentation(invited, special)

Nano-Optics for LSI On-Chip Interconnect

K. Ohashi

International Symposium on Advanced Nanodevice and Nanotechnology 2007Invitation Yes2007/12/03

Detail

International conferenceOral presentation(invited, special)

Optical Interconnect Technology for Computer Systems

K. Ohashi, T. Nakata

Asia-Pacific Optical Communications 2007(SPIE)Invitation Yes2007/11/01

Detail

International conferenceOral presentation(invited, special)

MIRAI’s LSI Chip Optical Interconnect Project

K. Ohashi

4th International Conference on Group IV Photonics 2007(IEEE)Invitation Yes2007/09/18

Detail

International conferenceOral presentation(keynote)

Achieving Convergence between Electronics and Photonics

K. Ohashi

7th International Workshop on Future Information Processing TechnologiesInvitation Yes2007/09/04

Detail

International conferenceOral presentation(invited, special)

Nanophotonics for Networks: from Telecom to LSI

K. Ohashi

2007 Japan-Italy Bilateral Workshop on Photonics for CommunicationInvitation Yes2007/07/05

Detail

International conferenceOral presentation(invited, special)

Optical Interconnect Technologies for High-Speed VLSI Chips Using Silicon Nano-Photonics

K. Ohashi

Silicon Nanoelectronics Workshop 2007(JSAP, IEEE)Invitation Yes2007/06/11

Detail

Oral presentation(general)

LSI On-Chip Optical Interconnects

K. Ohashi, K Nishi, T. Baba

3rd International Nanotechnology Conference on Communication and CooperationInvitation Yes2007/04/18

Detail

International conferencePoster presentationVenue:Belgium

Silicon Photonics for Long-Range and Short-Range Communication

Keishi Ohashi

3rd International Nanotechnology Conference on Communication and CooperationInvitation Yes2007/04/16

Detail

International conferenceOral presentation(invited, special)

Silicon Nanophotodiode

K. Ohashi, J. Fujikata, T. Ishi, K. Nishi, K. Ishihara, M. Mizuno, K. Nose, T. Baba

3rd International Conference on Group IV Photonics 2006(IEEE)Invitation Yes2006/09/13

Detail

International conferenceOral presentation(general)

Development and Applications of a Si Nano-Photodiode with a Surface Plasmon Antenna

K. Ohashi, J. Fujikata, D. Okamoto, T. Ishi, K. Makita, K. Nishi

Asia-Pacific Optical Communications 2006(SPIE)Invitation Yes2006/09/03

Detail

International conferenceOral presentation(invited, special)

Nanotechnology for Storage Devices

K. Ohashi

8th Annual International Conference on Composites EngineeringInvitation Yes2001/08/05

Detail

International conferenceOral presentation(invited, special)

Magnetic Nanotechnology

Keishi Ohashi

Workshop on Magnetism and Electrochemistry(Trinity College Dublin)2001/05/23

Detail

International conferenceSymposium workshop panel(nominated)

Electroplating for Magnetic Head

K. Ohashi

Workshop on Magnetism and Electrochemistry(Trinity College, Dublin)Invitation Yes2001/05/20

Detail

International conferenceOral presentation(invited, special)

Thermal Asperity of TMR Heads for Removable Disk Drives

K. Ohashi, A. Sato, K. Ishihara, T. Matsubara, T. Mitsuzuka, H. Tsuge, N. Ishiwata

8th Joint Magnetsm & Magnetic Materials / International Magnetics Conference(IEEE, American Physical Society)2001/01/08

Detail

International conferenceOral presentation(general)

Purity of Films and Performance of Recording Heads

K. Ohashi, M. Saito, H. Honjo, T. Toba, Y. Nonaka, N. Ishiwata

196th Meeting of Electrochemical Society(ECS)Invitation Yes2000/10/17

Detail

Oral presentation(general)

A Read Head Structure for Magnetic Tunneling Junction

K. Hayashi, E. Fukami, K. Nagahara, M. Nakada, K. Ohashi, K. Matsuda, A. Kamijo, T. Mitsuzuka, and H. Tsuge

International Magnetics Conference 2000(IEEE)Invitation Yes2000/04/09

Detail

Oral presentation(general)

Write Performance of Heads with a 2.1-Tesla CoNiFe Pole

K. Ohashi, N. Morita, T. Tsuda, Y. Nonaka

International Magnetics Conference 1999(IEEE)1999/05/18

Detail

Oral presentation(general)

Microprocessing for Magnetoresistive Heads

K. Ohashi

2nd International Symposium on Electrochemical Microsystem Technology(ISE)Invitation Yes1998/09/08

Detail

International conferenceOral presentation(invited, special)

Newly Developed Inductive Write Head with Electroplated CoNiFe Film

K. Ohashi, Y. Yasue, M. Saito, K. Yamada, T. Osaka, M. Takai, K. Hayashi

7th Joint Magnetism & Magnetic Materials / International Magnetics Conference(IEEE, American Physical Society)1998/06/06

Detail

International conferenceOral presentation(general)

Effect of Plated NiFe Composition on Domain Configuration

K. Ohashi, M. Ito, T. Maruyama

176th Meeting of Electrochemical Society(ECS)1989/10/15

Detail

Oral presentation(general)

Application of Electroplating to Thin Film Head

K. Ohashi, M. Ito, M. Watanabe

172nd Meeting of Electrochemical Society(ECS)Invitation Yes1987/10/18

Detail

Oral presentation(general)

Mechanism of 90-degree Wall Motion in Thin Film Head

K. Ohashi

International Magnetics Conference 1985(IEEE)1985/04/29

Detail

Oral presentation(general)

Research Grants & Projects

Research Fund Acceptance Situation

Providers:Japan Science and Technology AgencySystem:Strategic Basic Research Program

Ultrafast, ultralow-power, ultralarge-area electrochromism2015/10-2021/03

Sharer

Lecture Course

Course TitleSchoolYearTerm
Integrative Nano-Science and Nano-EngineeringGraduate School of Fundamental Science and Engineering2019spring semester
Integrative Nano-Science and Nano-EngineeringGraduate School of Creative Science and Engineering2019spring semester
Integrative Nano-Science and Nano-EngineeringGraduate School of Advanced Science and Engineering2019spring semester
Integrative Nano-Science and Nano-EngineeringGraduate School of Advanced Science and Engineering2019spring semester
Integrative Nano-Science and Nano-EngineeringGraduate School of Advanced Science and Engineering2019spring semester
Seminar on Nano-Electrochemistry AGraduate School of Advanced Science and Engineering2019spring semester
Seminar on Nano-Electrochemistry AGraduate School of Advanced Science and Engineering2019spring semester
Seminar on Nano-Electrochemistry BGraduate School of Advanced Science and Engineering2019fall semester
Seminar on Nano-Electrochemistry BGraduate School of Advanced Science and Engineering2019fall semester
Seminar on Nano-Electrochemistry CGraduate School of Advanced Science and Engineering2019spring semester
Seminar on Nano-Electrochemistry CGraduate School of Advanced Science and Engineering2019spring semester
Seminar on Nano-Electrochemistry DGraduate School of Advanced Science and Engineering2019fall semester
Seminar on Nano-Electrochemistry DGraduate School of Advanced Science and Engineering2019fall semester

Visiting - Interlocking-time or Part-time Lecturers of Other Institutions, etc.

1999/04- 2000/03Graduate School of Nagoya University(Japan)Visiring Lecturer
2004/04- 2006/03Nagoya University(Japan)Visiting Professor
2005/10- 2007/03Nanoelectronics Collaborative Research Center, The University of Tokyo(Japan)Visiting Researcher
2006/04- 2014/03Faculty of Engineering, Nagoya University(Japan)Visiting Lecturer
2008/04- 2014/03Graduate School of Meijo University(Japan)Visiting Lecturer
2008/04- 2020/03Graduate School of the University of Tokyo(Japan)Visiting Lecturer
2009/04- 2020/03Faculty of Engineering, Shibaura Institute of Technology(Japan)Visiting Lecturer
2010/04- 2011/03Fuculty of Engineering, the University of Tokyo(Japan)Visiting Lecturer
2011/04- 2012/03Graduate School of Osaka University(Japan)Visiting Lecturer
2011/04- 2012/03Tsukuba University(Japan)Visiting Lecturer
2012/10- 2017/03Tohoku University(Japan)Visiting Professor