2022/05/18 更新

写真a

ハセガワ ツヨシ
長谷川 剛
所属
理工学術院 先進理工学部
職名
教授

兼担

  • 法学学術院   法学部

  • 理工学術院   大学院先進理工学研究科

学内研究所等

  • 2020年
    -
    2022年

    理工学術院総合研究所   兼任研究員

学歴

  •  
    -
    1987年

    東京工業大学大学院   総合理工学研究科   材料科学専攻  

  •  
    -
    1985年

    東京工業大学   理学部   物理学科  

学位

  • 東京工業大学   博士(理学)

経歴

  • 2016年04月
    -
    2020年03月

    日本学術振興会 学術システム研究センター   数物系科学専門調査班   専門研究員

  • 2015年04月
    -
     

    早稲田大学 理工学術院 教授

  • 2011年04月
    -
    2015年03月

    (独)物質・材料研究機構 原子エレクトロニクスユニット ユニット長(兼務)

  • 2007年10月
    -
    2015年03月

    (独)物質・材料研究機構 国際ナノアーキテクトニクス研究拠点 主任研究者

  • 2006年04月
    -
    2015年03月

    横浜市立大学大学院 客員教授

  • 2012年10月
    -
    2014年05月

    早稲田大学理工学術院 客員教授

  • 2003年01月
    -
    2007年09月

    (独)物質・材料研究機構 原子エレクトロニクスグループ グループリーダー

  • 2003年04月
    -
    2004年03月

    文部科学省科学技術政策研究所 客員研究官

  • 2002年08月
    -
    2003年01月

    (独)物質・材料研究機構 主幹研究員

  • 1999年04月
    -
    2002年07月

    (特)理化学研究所 表面界面工学研究室 先任研究員

  • 1998年08月
    -
    1999年03月

    (株)日立製作所中央研究所 主任研究員

  • 1987年04月
    -
    1998年07月

    (株)日立製作所中央研究所 研究員

▼全件表示

所属学協会

  •  
     
     

    日本物理学会

  •  
     
     

    応用物理学会

  •  
     
     

    日本表面科学会

  •  
     
     

    応用物理学会 薄膜表面物理分科会

 

研究分野

  • ナノマイクロシステム

  • ナノ構造化学

  • 半導体、光物性、原子物理

  • 電気電子材料工学

  • 薄膜、表面界面物性

論文

  • Measurement of changes in resistance of a Ag2+δ S nano-island on removal of dopant δ-Ag atoms

    Nozomi Mishima, Tohru Tsuruoka, Tsuyoshi Hasegawa

    Japanese Journal of Applied Physics   60 ( SE ) SE1001 - SE1001  2021年04月  [査読有り]

    担当区分:最終著者

    DOI

  • Study on a conductive channel of a Pt/NiO/Pt ReRAM by bias application with/without a magnetic field

    Yuki Koga, Tsuyoshi Hasegawa

    Japanese Journal of Applied Physics   60 ( SC ) SCCF03 - SCCF03  2021年04月  [査読有り]

    担当区分:最終著者

    DOI

  • In Situ Reproducible Sharp Tips for Atomic Force Microscopy

    Jo Onoda, Tsuyoshi Hasegawa, Yoshiaki Sugimoto

    Physical Review Applied   15 ( 3 )  2021年03月  [査読有り]

    DOI

  • Changes in the temperature dependence of Ag/Ta2O5/Pt gapless-type atomic switches caused by desorption/adsorption of water molecules from/into the Ta2O5 matrix

    Maiko Mikami, Naoya Tanahashi, Tohru Tsuruoka, Tsuyoshi Hasegawa

    Japanese Journal of Applied Physics   60 ( SC ) SCCF05 - SCCF05  2021年03月  [査読有り]

    担当区分:最終著者

    DOI

  • Emulating neural functions utilizing the larger time constants found in the operation of molecular-gap atomic switches

    Naoya Wada, Tsuyoshi Hasegawa

    Japanese Journal of Applied Physics   60 ( SC ) SCCF01 - SCCF01  2021年02月  [査読有り]

    担当区分:最終著者

    DOI

  • Development of a metal oxide-based molecular-gap atomic switch for unconventional computing

    M. Araki, T. Hasegawa

    Jpn. J. Appl. Phys.   59   040605  2020年  [査読有り]  [招待有り]

    担当区分:最終著者

  • Formation and dissolution of conductive channel in an Ag2S-islands network

    K. Ojima, T. Hasegawa, Y. Naitoh, H. shima, H. Akinaga

    Jpn. J. Appl. Phys.   59   SN1011  2020年  [査読有り]

  • Reliable operation of a molecular-gap atomic switch in a vacuum achieved by covering with an ionic liquid

    C. Arima, Y. Naitoh, H. Shima, H. Akinaga, T. Hasegawa

    Jpn. J. Appl. Phys.   59   SIIF04  2020年  [査読有り]

    担当区分:最終著者

  • SiO2/Ta2O5 heterojunction ECM memristors: Physical nature of their low voltage operation with high stability and uniformity

    X. Guo, Q. Wang, X. Lv, H. Yang, K. Sun, D. Yang, H. Zhang, T. Hasegawa, D. He

    Nanoscale   12   4320 - 4327  2020年  [査読有り]

  • Stable analog resistance change of a molecular-gap atomic switch over a wide range

    A. Kassai, T. Hasegawa

    Jpn. J. Appl. Phys.   59   SIIF01  2020年  [査読有り]

    担当区分:最終著者

  • A nano-mechanical device using a Ag2S-C60 system

    Yuya Ishikawa, Tsuyoshi Hasegawa, Christian Joachim

    Jpn. J. Appl. Phys.   58   SDDF02-1 - SDDF02-4  2019年04月  [査読有り]

    DOI

  • Time-dependent operations in molecular gap atomic switches

    Ayana Suzuki, Tohru Tsuruoka, Tsuyoshi Hasegawa

    Physica Status Solidi B   256   1900068-1 - 1900068-10  2019年04月  [査読有り]

    DOI

  • Resistivity control by the electrochemical removal of dopant atoms from a nanodot

    Wataru Hiraya, Nozomi Mishima, Takaaki Shima, Seishiro Tai, Tohru Tsuruoka, Ilia Valov, Tsuyoshi Hasegawa

    Faraday Discussions   213   29 - 40  2019年01月  [査読有り]

    DOI

  • Oxygen vacancy drift controlled three-terminal ReRAM with a reduction in operating gate bias and leakage current

    Qi Wang, Yaomi Itoh, Tohru Tsuruoka, Masakazu Aono, Deyan He, Tsuyoshi Hasegawa

    Solid State Ionics   328   30 - 34  2018年11月  [査読有り]

    DOI

  • Development of a molecular gap-type atomic switch and its stochastic oepration

    C. Arima, A. Suzuki, A. Kassai, T. Tsuruoka, T. Hasegawa

    J. Appl. Phys.   124   152114-1 - 5  2018年09月  [査読有り]

    DOI

  • The rate limiting process and its activation energy in the forming process of a Cu/Ta2O5/Pt gapless-type atomic switch

    Yuki Shigeoka, Tohru Tsuruoka, Tsuyoshi Hasegawa

    Japanese Journal of Applied Physics   57 ( 3 )  2018年03月  [査読有り]

     概要を見る

    The rate limiting process in first resistive switching, called the "forming process", is determined by measuring the switching time of an as-fabricated Cu/Ta2O5/Pt atomic switch as a function of the ambient temperature and the Ta2O5 thickness. The temperature dependence is well fitted by the Arrhenius equation, suggesting that a certain activation process dominates the switching phenomenon. The switching time increases linearly as the Ta2O5 thickness increases. The results herein clearly suggest that the rate limiting process is the drift of Cu cations in the Ta2O5 layer. We determine that the activation energy is 0.4 eV.

    DOI

  • Nanoarchitectonics for Controlling the Number of Dopant Atoms in Solid Electrolyte Nanodots

    Alpana Nayak, Satomi Unayama, Seishiro Tai, Tohru Tsuruoka, Rainer Waser, Masakazu Aono, Ilia Valov, Tsuyoshi Hasegawa

    Advanced Materials   30 ( 6 )  2018年02月  [査読有り]

    担当区分:最終著者, 責任著者

     概要を見る

    Controlling movements of electrons and holes is the key task in developing today's highly sophisticated information society. As transistors reach their physical limits, the semiconductor industry is seeking the next alternative to sustain its economy and to unfold a new era of human civilization. In this context, a completely new information token, i.e., ions instead of electrons, is promising. The current trend in solid-state nanoionics for applications in energy storage, sensing, and brain-type information processing, requires the ability to control the properties of matter at the ultimate atomic scale. Here, a conceptually novel nanoarchitectonic strategy is proposed for controlling the number of dopant atoms in a solid electrolyte to obtain discrete electrical properties. Using α-Ag2+ δS nanodots with a finite number of nonstoichiometry excess dopants as a model system, a theory matched with experiments is presented that reveals the role of physical parameters, namely, the separation between electrochemical energy levels and the cohesive energy, underlying atomic-scale manipulation of dopants in nanodots. This strategy can be applied to different nanoscale materials as their properties strongly depend on the number of doping atoms/ions, and has the potential to create a new paradigm based on controlled single atom/ion transfer.

    DOI

  • Operating mechanism and resistive switching characteristics of two- and three-terminal atomic switches using a thin metal oxide layer

    Tohru Tsuruoka, Tsuyoshi Hasegawa, Kazuya Terabe, Masakazu Aono

    Journal of Electroceramics   39 ( 1-4 ) 143 - 156  2017年12月  [査読有り]

     概要を見る

    Atomic switches are nanoionic devices that are operated by controlling redox reactions and the local migration of metal ions in solids. The essential mechanism is the growth and shrinkage of a metal filament formed between two electrodes, resulting in repeatable resistive switching between high-resistance and low-resistance states, which can be used for next-generation nonvolatile memories. This review focuses on the operating mechanism and resistive switching characteristics of two- and three-terminal atomic switches using a thin metal oxide layer as an ion-conducting matrix. First, we describe the operating mechanism of a two-terminal atomic switch based on nucleation theory and present the results of temperature dependence and switching speeds to determine the validity of our switching model. Then, we discuss the effects that moisture absorption in the oxide matrix has on the fundamental processes and switching behavior in order to elucidate the importance of the porosity of the oxide matrix. Finally, we demonstrate a three-terminal atomic switch and describe the impact of the anode material or metal-ion species. These findings will contribute to the development of next-generation logic circuits with low-voltage operation and low-power consumption.

    DOI

  • P-type polymer-based Ag2S atomic switch for "tug of war" operation

    Carolin Lutz, Tsuyoshi Hasegawa, Takashi Tsuchiya, Christoph Adelsberger, Ryoma Hayakawa, Toyohiro Chikyow

    Japanese Journal of Applied Physics   56 ( 6 )  2017年06月  [査読有り]

     概要を見る

    The Ag2S gap-type atomic switch based "tug of war" device is a promising element for building a new type of CMOS free neuromorphic computerhardware. Since Ag+ cations are reduced during operation of the device, it was thought that the gap-material should be a n-type polymer. In this study, we revealed that the polymer bithiophene-oligoethyleneoxide (BTOE) doped poly(ethylene oxide) (PEO), which was used as gap-material in the first demonstration of the "tug of war", is a p-type polymer. For this we used impedance spectroscopy and transistor measurements. We elaborate on how the electrochemical processes in the "tug of war" devices could be explained in the case of p-type conductive gap-materials.

    DOI

  • Identification and roles of nonstoichiometric oxygen in amorphous Ta2O5 thin films deposited by electron beam and sputtering processes

    Cedric Mannequin, Tohru Tsuruoka, Tsuyoshi Hasegawa, Masakazu Aono

    APPLIED SURFACE SCIENCE   385   426 - 435  2016年11月  [査読有り]

     概要を見る

    The morphology and composition of tantalum oxide (Ta2O5) thin films prepared by electron-beam (EB) evaporation and radio-frequency sputtering (SP) were investigated by grazing incidence X-ray diffraction (GIXRD), X-ray reflectometry (XRR), atomic force microscopy, Fourier transformed infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). GIXRD revealed an amorphous nature for both films, and XRR showed that the density of the Ta2O5-EB films was lower than that of the Ta2O5-SP films; both films have lower density than the bulk value. A larger amount of molecular water and peroxo species were detected for the Ta2O5-EB films by FTIR performed in ambient atmosphere. XPS analyses performed in vacuum confirmed the presence of hydroxyl groups, but no trace of chemisorbed molecular water was detected. In addition, a higher oxygen nonstoichiometry (higher O/Ta ratio) was found for the EB films. From these results, we conclude that the oxygen nonstoichiometry of the EB film accounted for its lower density and higher amount of absorbed molecular water. The results also suggest the importance of understanding the dependence of the structural and chemical properties of thin amorphous oxide films on the deposition process. (C) 2016 Published by Elsevier B.V.

    DOI

  • Humidity effects on the redox reactions and ionic transport in a Cu/Ta2O5/Pt atomic switch structure

    Tohru Tsuruoka, Ilia Valov, Cedric Mannequin, Tsuyoshi Hasegawa, Rainer Waser, Masakazu Aono

    JAPANESE JOURNAL OF APPLIED PHYSICS   55 ( 6 )  2016年06月  [査読有り]

     概要を見る

    Redox reactions at the Cu/Ta2O5 interface and subsequent Cu ion transport in a Ta2O5 film have been investigated by means of cyclic voltammetry (CV) measurements. Under positive bias to the Cu electrode, Cu is preferentially oxidized to Cu2+ and then to Cu+. Subsequent negative bias causes a reduction of the oxidized Cu ions at the interface. It was found that CV curves change drastically with varied relative humidity levels from 5 to 85%. At higher humidity levels, the ion concentrations and diffusion coefficients, estimated from the CV curves, suggest increased redox reaction rates and a significant contribution of proton conduction to the ionic transport. The results indicate that the redox reactions of moisture are rate-limiting and highlight the importance of water uptake by the matrix oxide film in understanding and controlling the resistive switching behavior of oxide-based atomic switches. (C) 2016 The Japan Society of Applied Physics

    DOI

  • Composition of thin Ta2O5 films deposited by different methods and the effect of humidity on their resistive switching behavior

    Cedric Mannequin, Tohru Tsuruoka, Tsuyoshi Hasegawa, Masakazu Aono

    JAPANESE JOURNAL OF APPLIED PHYSICS   55 ( 6 )  2016年06月  [査読有り]

     概要を見る

    The resistive switching behavior of Cu/Ta2O5/Pt atomic switches, in which the Ta2O5 film was deposited by electron-beam (EB) evaporation and radio-frequency sputtering (SP), was investigated under different relative humidity (RH) levels. Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy measurements revealed that both films possess the oxygen-rich composition and higher water absorption capability of EB films. The Cu/Ta2O5-SP/Pt cell showed a stable, nonvolatile switching behavior in the observed RH range, whereas the Cu/Ta2O5-EB/Pt cell exhibited a similar behavior up to 50% RH, but altered from nonvolatile to volatile switching at higher RH levels. The observed volatile switching behavior of the Cu/Ta2O5-EB/Pt cell can be explained by increased ion migration, assisted by absorbed water and/or proton conduction in hydrated environments. The results indicate that the water uptake ability of the matrix film plays a crucial role in determining the resistive switching behavior of oxide-based atomic switches. (C) 2016 The Japan Society of Applied Physics

    DOI

  • Composition of thin Ta

    Mannequin Cedric, Tsuruoka Tohru, Hasegawa Tsuyoshi, Aono Masakazu

    Jpn. J. Appl. Phys.   55 ( 6 ) 06GG08  2016年05月

     概要を見る

    The resistive switching behavior of Cu/Ta<inf>2</inf>O<inf>5</inf>/Pt atomic switches, in which the Ta<inf>2</inf>O<inf>5</inf>film was deposited by electron-beam (EB) evaporation and radio-frequency sputtering (SP), was investigated under different relative humidity (RH) levels. Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy measurements revealed that both films possess the oxygen-rich composition and higher water absorption capability of EB films. The Cu/Ta<inf>2</inf>O<inf>5</inf>-SP/Pt cell showed a stable, nonvolatile switching behavior in the observed RH range, whereas the Cu/Ta<inf>2</inf>O<inf>5</inf>-EB/Pt cell exhibited a similar behavior up to 50% RH, but altered from nonvolatile to volatile switching at higher RH levels. The observed volatile switching behavior of the Cu/Ta<inf>2</inf>O<inf>5</inf>-EB/Pt cell can be explained by increased ion migration, assisted by absorbed water and/or proton conduction in hydrated environments. The results indicate that the water uptake ability of the matrix film plays a crucial role in determining the resistive switching behavior of oxide-based atomic switches.

    DOI CiNii

  • Decision maker based on atomic switches

    Song-Ju Kim, Tohru Tsuruoka, Tsuyoshi Hasegawa, Masashi Aono, Kazuya Terabe, Masakazu Aono

    AIMS MATERIALS SCIENCE   3 ( 1 ) 245 - 259  2016年

     概要を見る

    We propose a simple model for an atomic switch-based decision maker (ASDM), and show that, as long as its total number of metal atoms is conserved when coupled with suitable operations, an atomic switch system provides a sophisticated "decision-making" capability that is known to be one of the most important intellectual abilities in human beings. We considered a popular decision-making problem studied in the context of reinforcement learning, the multi-armed bandit problem (MAB); the problem of finding, as accurately and quickly as possible, the most profitable option from a set of options that gives stochastic rewards. These decisions are made as dictated by each volume of precipitated metal atoms, which is moved in a manner similar to the fluctuations of a rigid body in a tug-of-war game. The "tug-of-war (TOW) dynamics" of the ASDM exhibits higher efficiency than conventional reinforcement-learning algorithms. We show analytical calculations that validate the statistical reasons for the ASDM to produce such high performance, despite its simplicity. Efficient MAB solvers are useful for many practical applications, because MAB abstracts a variety of decision-making problems in real-world situations where an efficient trial-and-error is required. The proposed scheme will open up a new direction in physics-based analog-computing paradigms, which will include such things as "intelligent nanodevices" based on self-judgment.

    DOI

  • Ag2S atomic switch-based 'tug of war' for decision making

    C. Lutz, T. Hasegawa, T. Chikyow

    NANOSCALE   8 ( 29 ) 14031 - 14036  2016年  [査読有り]

     概要を見る

    For a computing process such as making a decision, a software controlled chip of several transistors is necessary. Inspired by how a single cell amoeba decides its movements, the theoretical 'tug of war' computing model was proposed but not yet implemented in an analogue device suitable for integrated circuits. Based on this model, we now developed a new electronic element for decision making processes, which will have no need for prior programming. The devices are based on the growth and shrinkage of Ag filaments in alpha-Ag2+delta S gap-type atomic switches. Here we present the adapted device design and the new materials. We demonstrate the basic 'tug of war' operation by IV-measurements and Scanning Electron Microscopy (SEM) observation. These devices could be the base for a CMOS-free new computer architecture.

    DOI

  • Redox Reactions at Cu,Ag/Ta2O5 Interfaces and the Effects of Ta2O5 Film Density on the Forming Process in Atomic Switch Structures

    Tohru Tsuruoka, Ilia Valov, Stefan Tappertzhofen, Jan van den Hurk, Tsuyoshi Hasegawa, Rainer Waser, Masakazu Aono

    ADVANCED FUNCTIONAL MATERIALS   25 ( 40 ) 6374 - 6381  2015年10月  [査読有り]

     概要を見る

    Cu and Ag redox reactions at the interfaces with Ta2O5 and the impact of Ta2O5 film density on the forming process of Cu,Ag/Ta2O5/Pt atomic switch structures are investigated. Cyclic voltammetry measurements revealed that under positive bias to the Cu (Ag) electrode, Cu is preferentially oxidized to Cu2+, while Ag is oxidized to Ag+ ions. Subsequent negative bias causes a reduction of oxidized Cu (Ag) ions at the interfaces. The diffusion coefficient of the Cu and Ag ions in the Ta2O5 film is estimated from the results from different bias voltage sweep rates. It is also found that the redox current is enhanced and the forming voltage of the Cu/Ta2O5/Pt cell is reduced when the density of the Ta2O5 film is decreased. This result indicates the importance of the structural properties of the matrix oxide film in understanding and controlling resistive switching behavior.

    DOI

  • Ultra-Low Voltage and Ultra-Low Power Consumption Nonvolatile Operation of a Three-Terminal Atomic Switch

    Qi Wang, Yaomi Itoh, Tohru Tsuruoka, Masakazu Aono, Tsuyoshi Hasegawa

    ADVANCED MATERIALS   27 ( 39 ) 6029 - 6033  2015年10月  [査読有り]

     概要を見る

    Nonvolatile three-terminal operation, with a very small range of bias sweeping (-80 to 250 mV), a high on/off ratio of up to six orders of magnitude, and a very small gate leakage current (&lt; 1 pA), is demonstrated using an Ag (gate)/Ta2O5 (ionic transfer layer)/Pt (source), Pt (drain) three-terminal atomic switch structure.

    DOI

  • Effects of temperature and ambient pressure on the resistive switching behaviour of polymer-based atomic switches

    Saumya R. Mohapatra, Tohru Tsuruoka, Karthik Krishnan, Tsuyoshi Hasegawa, Masakazu Aono

    Journal of Materials Chemistry C   3 ( 22 ) 5715 - 5720  2015年06月

     概要を見る

    Current-voltage measurements demonstrated the effects of temperature on the resistive switching behaviour of a gapless-type atomic switch based on a silver-ion-conductive solid polymer electrolyte (SPE) consisting of a mixture of polyethylene oxide (PEO) and AgClO&lt
    inf&gt
    4&lt
    /inf&gt
    . The operation voltages decreased in magnitude with increased ambient temperature. The reduction of the operation voltages can be explained by the increased conductivity of silver ions in the amorphous PEO-salt complex region of the SPE film. This situation is completely different from a cell with a pure PEO film, in which the increased crystallinity of the PEO film may hinder the ionic conductivity, although similar switching behaviour was observed. It was also found that cells based on SPE and PEO show different behaviours under air and vacuum conditions. This is probably associated with different water uptakes from the ambient surroundings by the SPE and PEO films. The results suggest the importance of the crystallinity and water uptake ability of the matrix polymer film on the resistive switching characteristics.

    DOI

  • Dynamic moderation of an electric field using a SiO2 switching layer in TaOx-based ReRAM

    Qi Wang, Yaomi Itoh, Tohru Tsuruoka, Shintaro Ohtsuka, Tomohiro Shimizu, Shoso Shingubara, Tsuyoshi Hasegawa, Masakazu Aono

    PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS   9 ( 3 ) 166 - 170  2015年03月  [査読有り]

     概要を見る

    ReRAMs using oxygen vacancy drift in their resistive switching are promising candidates as next generation memory devices. One remaining issue is degradation of the on/off ratio down to 102 or less with an increased number of switching cycles. Such degradation is caused by a local hard breakdown in a set process due to a very high electric field formed just before the completion of a conductive filament formation. We found that introducing an ultra-thin SiO2 layer prevents the hard breakdown by dynamical moderation of the electric field formed in the TaOx matrix, resulting in repeated switching while retaining a higher on/off ratio of about 105. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

    DOI

  • Position detection and observation of a conducting filament hidden under a top electrode in a Ta2O5-based atomic switch

    A. Nayak, Q. Wang, Y. Itoh, T. Tsuruoka, T. Hasegawa, L. Boodhoo, H. Mizuta, M. Aono

    Nanotechnology   26   145702  2015年03月

    DOI

  • Nanosecond Fast Switching Processes Observed in Gapless-Type, Ta 2 O 5 –Based Atomic Switches

    Tohru Tsuruoka, Tsuyoshi Hasegawa, Masakazu Aono

    MRS Proceedings   1729  2015年02月  [査読有り]

     概要を見る

    We have investigated the switching mechanisms of Cu(Ag)/Ta2O5/Pt atomic switch cells as a model system. The observed fast switching speeds indicate that oxide-based atomic switches hold potential for fast-switching memory applications.

    DOI

  • Atomic Switch

    Tsuyoshi Hasegawa, Masakazu Aono

    Emerging Nanoelectronic Devices     390 - 404  2015年01月  [査読有り]

     概要を見る

    An atomic switch is a nanoionic device that controls the diffusion of metal ions and their reduction/oxidation processes in the switching operation to form/annihilate a metal atomic bridge. Various types of atomic switches, such as two-terminal and three-terminal atomic switches, have been developed. The novel characteristics, such as their small size, low power consumption, low ON-resistance, and non-volatility, will be useful in improving present-day computers. Novel functions have also been developed in atomic switches, such as learning abilities, photo-sensing abilities, memristive operations, and synaptic functions
    these functions may contribute in the development of new types of neural computing systems.

    DOI

  • Observation of a Ag protrusion on a Ag2S island using a scanning tunneling microscope

    Takeo Ohno, Tsuyoshi Hasegawa

    RESULTS IN PHYSICS   5   182 - 183  2015年  [査読有り]

     概要を見る

    A silver sulfide (Ag2S) island as an ionic conductor in resistive switching memories was formed and a protrusion of silver from the Ag2S formed by an electrochemical reaction was observed using a scanning tunneling microscope. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

    DOI

  • Volatile and nonvolatile selective operation of a two-terminal gap-type atomic switch

    Tsuyoshi Hasegawa, Tohru Tsuruoka, Masakazu Aono

    Proceedings - IEEE International Symposium on Circuits and Systems     1800 - 1803  2014年  [査読有り]

     概要を見る

    Volatile and nonvolatile switching are selectively operated using a two-terminal gap-type atomic switch by choosing a sweeping bias range. The amount of Ag atoms those precipitate from an Ag2S electrode in the turning-on process is a function of a bias. Using a bias larger than the threshold bias, enough number of Ag atoms precipitate to make a bridge to the counter electrode, resulting in the nonvolatile operation. A bias smaller than the threshold bias does not make a bridge, and Ag atoms return to an Ag2S electrode while decreasing a bias to zero, resulting in the volatile operation. The selective operations are enabled by controlling electrochemical potentials. © 2014 IEEE.

    DOI

  • Synaptic Plasticity and Memristive Behavior Operated by Atomic Switches

    Tohru Tsuruoka, Tsuyoshi Hasegawa, Masakazu Aono

    2014 14TH INTERNATIONAL WORKSHOP ON CELLULAR NANOSCALE NETWORKS AND THEIR APPLICATIONS (CNNA)    2014年  [査読有り]

     概要を見る

    We demonstrate that the resistive switching memory, called an atomic switch, emulates the synaptic plasticity underlying short-term and long-term memory formations in the human brain. The change in conductance of the atomic switch is considered analogous to the change in strength of a biological synapse that varies according to stimulating input pulses. The atomic switch also exhibits conventional memristive behavior in which the output depends on the history of input signal. These observations indicate that the atomic switch has potential for use as an essential building block for neural computing systems.

  • Volatile and nonvolatile selective operation of a two-terminal gap-type atomic switch

    Tsuyoshi Hasegawa, Tohru Tsuruoka, Masakazu Aono

    2014 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS (ISCAS)     1800 - 1803  2014年  [査読有り]

     概要を見る

    Volatile and nonvolatile switching are selectively operated using a two-terminal gap-type atomic switch by choosing a sweeping bias range. The amount of Ag atoms those precipitate from an Ag2S electrode in the turning-on process is a function of a bias. Using a bias larger than the threshold bias, enough number of Ag atoms precipitate to make a bridge to the counter electrode, resulting in the nonvolatile operation. A bias smaller than the threshold bias does not make a bridge, and Ag atoms return to an Ag2S electrode while decreasing a bias to zero, resulting in the volatile operation. The selective operations are enabled by controlling electrochemical potentials.

  • Two types of on-state observed in the operation of a redox-based three-terminal device

    Qi Wang, Yaomi Itoh, Tohru Tsuruoka, Tsuyoshi Hasegawa, Satoshi Watanabe, Shu Yamaguchi, Toshiro Hiramoto, Masakazu Aono

    ADVANCED MICRO-DEVICE ENGINEERING IV   596   111 - +  2014年  [査読有り]

     概要を見る

    A redox-based three-terminal device was fabricated using Ta2O5 as the ionic transfer material, and its operation was investigated. We found that application of a negative polarity gate bias, which increases oxygen anions in the channel regions, can make a conductive path between a source electrode and a drain electrode. The insulating state of the pristine device is turned on to a semiconductor state by the application of a negative polarity gate bias. Since turning off to the insulating state could not be achieved, the switching process resembles the soft breakdown of the first turning-on process of oxygen vacancy controlled resistive random access memories, although the polarity of the bias is opposite to that used in the first turning-on process. Further application of a gate bias causes a transition from the semiconductor state to a metal state. Accordingly, there are two types of on-state. It is possible to switch between the semiconductor and metal states.

    DOI

  • Influence of Atmosphere on Photo-Assisted Atomic Switch Operations

    Takami Hino, Tsuyoshi Hasegawa, Hirofumi Tanaka, Tohru Tsuruoka, Takuji Ogawa, Masakazu Aono

    ADVANCED MICRO-DEVICE ENGINEERING IV   596   116 - +  2014年  [査読有り]

     概要を見る

    We conducted light irradiation experiments in air to clarify influence of atmosphere on the operation of a photo-assisted atomic switch. In air, Pt-Ag2S/Ag nanogap electrodes with a PTCDI thin layer in their nanogaps showed current fluctuations with an applied bias of from 1.5 V to 6 V regardless of the bias polarity and with or without light irradiation. This is in contrast to the fact that only two things cause an increase in current that result in the formation of a silver bridge and switching behavior under vacuum, namely, light irradiation and the application of positive bias to the Ag2S/Ag electrode [1]. In addition, photocurrent caused by irradiating a PTCDI thin layer was found to be sensitive to air and to N-2. These results indicate that moisture or other gas molecules in air and in N-2 have an influence on the photo-assisted atomic switching behavior.

    DOI

  • Volatile and nonvolatile selective switching of a photo-assisted initialized atomic switch

    T. Hino, T. Hasegawa, H. Tanaka, T. Tsuruoka, K. Terabe, T. Ogawa, M. Aono

    NANOTECHNOLOGY   24 ( 38 ) 384006  2013年09月  [査読有り]

     概要を見る

    A photo-assisted atomic switch, which has a photoconductive molecular layer in a gap of about 20 nm between an Ag2S electrode and a Pt electrode, is set to a conventional gap-type atomic switch operation mode by light irradiation with the application of a small bias that precipitates Ag atoms from an Ag2S electrode. After this initialization, the switch operates only with application of a bias. In this study, we also found that after the set-operation a photo-assisted initialized atomic switch shows different switching modes depending on the bias range, i.e., volatile switching when the applied bias is smaller than the threshold bias, and nonvolatile switching when the applied bias is larger than the threshold bias. These characteristics can be useful in reconfiguring a circuit such as in neural computing systems.

    DOI

  • Synaptic plasticity and memory functions achieved in a WO3-x-based nanoionics device by using the principle of atomic switch operation

    Rui Yang, Kazuya Terabe, Yiping Yao, Tohru Tsuruoka, Tsuyoshi Hasegawa, James K. Gimzewski, Masakazu Aono

    NANOTECHNOLOGY   24 ( 38 ) 384003  2013年09月  [査読有り]

     概要を見る

    A compact neuromorphic nanodevice with inherent learning and memory properties emulating those of biological synapses is the key to developing artificial neural networks rivaling their biological counterparts. Experimental results showed that memorization with a wide time scale from volatile to permanent can be achieved in a WO3-x-based nanoionics device and can be precisely and cumulatively controlled by adjusting the device's resistance state and input pulse parameters such as the amplitude, interval, and number. This control is analogous to biological synaptic plasticity including short-term plasticity, long-term potentiation, transition from short-term memory to long-term memory, forgetting processes for short-and long-term memory, learning speed, and learning history. A compact WO3-x-based nanoionics device with a simple stacked layer structure should thus be a promising candidate for use as an inorganic synapse in artificial neural networks due to its striking resemblance to the biological synapse.

    DOI

  • Generic Relevance of Counter Charges for Cation-Based Nanoscale Resistive Switching Memories

    Stefan Tappertzhofen, Ilia Valov, Tohru Tsuruoka, Tsuyoshi Hasegawa, Rainer Waser, Masakazu Aono

    ACS NANO   7 ( 7 ) 6396 - 6402  2013年07月  [査読有り]

     概要を見る

    Resistive switching memories (ReRAMs) are the major candidates for replacing the state-of-the-art memory technology in future nanoelectronics. These nonvolatile memory cells are based on nanoionic redox processes and offer prospects for high scalability, ultrafast write and read access, and low power consumption. The interfacial electrochemical reactions of oxidation and reduction of ions necessarily needed for resistive switching result inevitably in nonequilibrium states, which play a fundamental role in the processes involved during device operation. We report on nonequilibrium states in SiO2-based ReRAMs being induced during the resistance transition. It is demonstrated that the formation of metallic cations proceeds in parallel to reduction of moisture, supplied by the ambient. The latter results in the formation of an electromotive force in the range of up to 600 mV. The outcome of the study highlights the hitherto overlooked necessity of a counter charge/reaction to keep the charge electroneutrality in cation-transporting thin films, making it hard to analyze and compare experimental results under different ambient conditions such as water partial pressure. Together with the dependence of the electromotive force on the ambient, these results contribute to the microscopic understanding of the resistive switching phenomena in cation-based ReRAMs.

    DOI

  • Nonvolatile three-terminal operation based on oxygen vacancy drift in a Pt/Ta2O5-x/Pt, Pt structure

    Qi Wang, Yaomi Itoh, Tsuyoshi Hasegawa, Tohru Tsuruoka, Shu Yamaguchi, Satoshi Watanabe, Toshiro Hiramoto, Masakazu Aono

    Applied Physics Letters   102 ( 23 ) 233508  2013年06月

     概要を見る

    Nonvolatile three-terminal operation is demonstrated using a Pt/Ta 2O5-x/Pt, Pt structure, by controlling oxygen vacancy drift to make/annihilate a conductive channel between a source and a drain. The as-fabricated device is in an off-state. Application of a positive gate bias moves oxygen vacancies in a Ta2O5-x layer towards a channel region, making the channel region conductive. The conductive channel remains even after unloading the gate bias. Application of a negative gate bias, which moves the oxygen vacancies back towards the gate electrode, is required to turn off the device. The device shows a high ON/OFF ratio of up to 10 6. © 2013 AIP Publishing LLC.

    DOI

  • Rate-limiting processes in the fast SET operation of a gapless-type Cu-Ta2O5 atomic switch

    T. Tsuruoka, T. Hasegawa, I. Valov, R. Waser, M. Aono

    AIP ADVANCES   3 ( 3 ) 032114  2013年03月  [査読有り]

     概要を見る

    The speed of the SET operation of a Cu/Ta2O5/Pt atomic switch from a high-resistance state to a low-resistance state was measured by transient current measurements under the application of a short voltage pulse. The SET time decreased exponentially with increasing pulse amplitude, reaching as low as 1 ns using moderate pulse voltages. This observation shows that oxide-based atomic switches hold potential for fast-switching memory applications. From a comparison with atomistic nucleation theory, Cu nucleation on the Pt electrode was found to be the likely rate-limiting process determining the SET time. Copyright 2013 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4795140]

    DOI

  • Conductance quantization and synaptic behavior in a Ta2O5-based atomic switch

    Tohru Tsuruoka, Tsuyoshi Hasegawa, Kazuya Terabe, Masakazu Aono

    NANOTECHNOLOGY   23 ( 43 ) 435705  2012年11月  [査読有り]

     概要を見る

    Quantized conductance was observed in a cation-migration-based resistive switching memory cell with a simple metal-insulator-metal (MIM) structure using a thin Ta2O5 layer. The observed conductance changes are attributed to the formation and dissolution of a metal filament with an atomic point contact of different integer multiples in the Ta2O5 layer. The results demonstrate that atomic point contacts can be realized in an oxide-based MIM structure that functions as a nanogap-based atomic switch (Terabe et al 2005 Nature 433 47). By applying consecutive voltage pulses at periodic intervals of different times, we also observed an effect analogous to the long-term potentiation of biological synapses, which shows that the oxide-based atomic switch has potential for use as an essential building block of neural computing systems.

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  • On-Demand Nanodevice with Electrical and Neuromorphic Multifunction Realized by Local Ion Migration

    Rui Yang, Kazuya Terabe, Guangqiang Liu, Tohru Tsuruoka, Tsuyoshi Hasegawa, James K. Gimzewski, Masakazu Aono

    ACS NANO   6 ( 11 ) 9515 - 9521  2012年11月  [査読有り]

     概要を見る

    A potential route to extend Moore's law beyond the physical limits of existing materials and device architectures is to achieve nanotechnology breakthroughs in materials and device concepts. Here, we discuss an on-demand WO3-x-based nanoionic device where electrical and neuromorphic multifunctions are realized through externally induced local migration of oxygen ions. The device is found to possess a wide range of time scales of memorization, resistance switching, and rectification varying from volatile to permanent in a single device, and these can furthermore be realizable in both two- or three-terminal systems. The gradually changing volatile and nonvolatile resistance states are experimentally demonstrated to mimic the human brain's forgetting process for short-term memory and long-term memory. We propose this nanoionic device with its on-demand electrical and neuromorphic multifunction has a unique paradigm shifting potential for the fabrication of configurable circuits, analog: memories, digital-neural fused networks, and more in one device architecture.

    DOI

  • Controlling the Synaptic Plasticity of a Cu2S Gap-Type Atomic Switch

    Alpana Nayak, Takeo Ohno, Tohru Tsuruoka, Kazuya Terabe, Tsuyoshi Hasegawa, James K. Gimzewski, Masakazu Aono

    ADVANCED FUNCTIONAL MATERIALS   22 ( 17 ) 3606 - 3613  2012年09月  [査読有り]

     概要を見る

    It is demonstrated that a Cu2S gap-type atomic switch, referred to as a Cu2S inorganic synapse, emulates the synaptic plasticity underlying the sensory, short-term, and long-term memory formations in the human brain. The change in conductance of the Cu2S inorganic synapse is considered analogous to the change in strength of a biological synaptic connection known as the synaptic plasticity. The plasticity of the Cu2S inorganic synapse is controlled depending on the interval, amplitude, and width of an input voltage pulse stimulation. Interestingly, the plasticity is influenced by the presence of air or moisture. Time-dependent scanning tunneling microscopy images of the Cu-protrusions grown in air and in vacuum provide clear evidence of the influence of air on their stability. Furthermore, the plasticity depends on temperature, such that a long-term memory is achieved much faster at elevated temperatures with shorter or fewer number of input pulses, indicating a close analogy with a biological synapse where elevated temperature increases the degree of synaptic transmission. The ability to control the plasticity of the Cu2S inorganic synapse justifies its potential as an advanced synthetic synapse with air/temperature sensibility for the development of artificial neural networks.

    DOI

  • Flexible resistive switching memory using inkjet printing of a solid polymer electrolyte

    Saumya R. Mohapatra, T. Tsuruoka, T. Hasegawa, K. Terabe, M. Aono

    AIP ADVANCES   2 ( 2 ) 22144  2012年06月  [査読有り]

     概要を見る

    Resistive switching memory cells were fabricated on a plastic substrate via inkjet printing (IJP) of a solid polymer electrolyte (SPE). Using the high contrast between the surface energy of a metal electrode and the substrate, a thin SPE film could be deposited over the electrode by IJP. The fabricated Ag/SPE/Pt cells showed bipolar resistive switching behavior under electrical bias in vacuum and in air, which is attributed to the formation and dissolution of a metal filament between the electrodes. From the standpoint of the switching mechanism, our cell can be referred to as a 'gapless-type atomic switch'. The cells also exhibited stable switching behavior under substrate bending. This device fabrication technique has great potential for flexible switch/memory applications. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4727742]

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  • Electronic State Formation by Surface Atom Removal on a MoS2 Surface

    Nagisa Kodama, Tsuyoshi Hasegawa, Tohru Tsuruoka, Christian Joachim, Masakazu Aono

    JAPANESE JOURNAL OF APPLIED PHYSICS   51 ( 6 ) 06FF07  2012年06月  [査読有り]

     概要を見る

    Removal of a sulfur atom from the topmost layer of a MoS2 surface forms electronic states in the band-gap of an inherently semiconducting material. Scanning tunneling spectroscopy measured at sulfur vacancies, which were made by sulfur atom removal using the high electrical field of a scanning tunneling microscope, shows stepwise increases in the current in a band-gap region, corresponding to the formation of electronic states. The periphery of sulfur vacancies also show linear current-voltage (I/V) characteristics, suggesting that electronic states in the periphery are modified due to the removal of sulfur atoms. (C) 2012 The Japan Society of Applied Physics

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  • Oxygen migration process in the interfaces during bipolar resistance switching behavior of WO3-x-based nanoionics devices

    Rui Yang, Kazuya Terabe, Tohru Tsuruoka, Tsuyoshi Hasegawa, Masakazu Aono

    APPLIED PHYSICS LETTERS   100 ( 23 ) 231603  2012年06月  [査読有り]

     概要を見る

    Bipolar resistance switching (BRS) behavior and the effects of atmosphere (air, vacuum, O-2 gas, or N-2 gas) on BRS behavior occurred in the top and bottom interfaces in the M-(top electrode)/WO3-x/Pt-(bottom electrode) (M = Pt, Au) devices were investigated. Stable BRS only can be obtained in the interface with Pt electrode. And, the top Pt/WO3-x interface exhibited stable BRS only in an oxygen-rich atmosphere (air and O-2 gas). In contrast, the bottom WO3-x/Pt interface showed stable BRS under any atmosphere. Based on the x-ray photoelectron spectroscopy measurement on Pt, Au/WO3-x interfaces, it is identified that the oxygen migration process during resistance switching mainly occurs between the Pt/WO3-x interface and Pt electrode. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4726084]

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  • Atomically controlled electrochemical nucleation at superionic solid electrolyte surfaces

    Ilia Valov, Ina Sapezanskaia, Alpana Nayak, Tohru Tsuruoka, Thomas Bredow, Tsuyoshi Hasegawa, Georgi Staikov, Masakazu Aono, Rainer Waser

    NATURE MATERIALS   11 ( 6 ) 530 - 535  2012年06月  [査読有り]

     概要を見る

    Electrochemical equilibrium and the transfer of mass and charge through interfaces at the atomic scale are of fundamental importance for the microscopic understanding of elementary physicochemical processes. Approaching atomic dimensions, phase instabilities and instrumentation limits restrict the resolution. Here we show an ultimate lateral, mass and charge resolution during electrochemical Ag phase formation at the surface of RbAg4I5 superionic conductor thin films. We found that a small amount of electron donors in the solid electrolyte enables scanning tunnelling microscope measurements and atomically resolved imaging. We demonstrate that Ag critical nucleus formation is rate limiting. The Gibbs energy of this process takes discrete values and the number of atoms of the critical nucleus remains constant over a large range of applied potentials. Our approach is crucial to elucidate the mechanism of atomic switches and highlights the possibility of extending this method to a variety of other electrochemical systems.

    DOI

  • Development and Application of Multiple-Probe Scanning Probe Microscopes

    Tomonobu Nakayama, Osamu Kubo, Yoshitaka Shingaya, Seiji Higuchi, Tsuyoshi Hasegawa, Chun-Sheng Jiang, Taichi Okuda, Yuji Kuwahara, Kazuhiro Takami, Masakazu Aono

    ADVANCED MATERIALS   24 ( 13 ) 1675 - 1692  2012年04月  [査読有り]

     概要を見る

    In the research of advanced materials based on nanoscience and nanotechnology, it is often desirable to measure nanoscale local electrical conductivity at a designated position of a given sample. For this purpose, multiple-probe scanning probe microscopes (MP-SPMs), in which two, three or four scanning tunneling microscope (STM) or atomic force microscope (AFM) probes are operated independently, have been developed. Each probe in an MP-SPM is used not only for observing high-resolution STM or AFM images but also for forming an electrical contact enabling nanoscale local electrical conductivity measurement. The world's first double-probe STM (DP-STM) developed by the authors, which was subsequently modified to a triple-probe STM (TP-STM), has been used to measure the conductivities of one-dimensional metal nanowires and carbon nanotubes and also two-dimensional molecular films. A quadruple-probe STM (QP-STM) has also been developed and used to measure the conductivity of two-dimensional molecular films without the ambiguity of contact resistance between the probe and sample. Moreover, a quadruple-probe AFM (QP-AFM) with four conductive tuning-fork-type self-detection force sensing probes has been developed to measure the conductivity of a nanostructure on an insulating substrate. A general-purpose computer software to control four probes at the same time has also been developed and used in the operation of the QP-AFM. These developments and applications of MP-SPMs are reviewed in this paper.

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  • 局所的なイオン移動を利用したナノイオニクスデバイス−原子スイッチ−

    寺部一弥, 長谷川剛, 鶴岡徹, 青野正和

    電子情報通信学会誌   95 ( 4 ) 299 - 304  2012年

  • アトムトランジスタ

    長谷川剛, 伊藤弥生美, 鶴岡徹, 青野正和

    応用物理, 81(1), 55-58, (2012   81 ( 1 ) 55 - 58  2012年

  • Effects of Moisture on the Switching Characteristics of Oxide-Based, Gapless-Type Atomic Switches

    Tohru Tsuruoka, Kazuya Terabe, Tsuyoshi Hasegawa, Ilia Valov, Rainer Waser, Masakazu Aono

    ADVANCED FUNCTIONAL MATERIALS   22 ( 1 ) 70 - 77  2012年01月  [査読有り]

     概要を見る

    Resistive switching memories based on the formation and dissolution of a metal filament in a simple metal/oxide/metal structure are attractive because of their potential high scalability, low-power consumption, and ease of operation. From the standpoint of the operation mechanism, these types of memory devices are referred to as gapless-type atomic switches or electrochemical metallization cells. It is well known that oxide materials can absorb moisture from the ambient air, which causes shifts in the characteristics of metal-oxide-semiconductor devices. However, the role of ambient moisture on the operation of oxide-based atomic switches has not yet been clarified. In this work, currentvoltage measurements were performed as a function of ambient water vapor pressure and temperature to reveal the effect of moisture on the switching behavior of Cu/oxide/Pt atomic switches using different oxide materials. The main findings are: i) the ionization of Cu at the anode interface is likely to be attributed to chemical oxidation via residual water in the oxide layer, ii) Cu ions migrate along grain boundaries in the oxide layer, where a hydrogen-bond network might be formed by moisture absorption, and iii) the stability of residual water has an impact on the ionization and migration processes and plays a major role in determining the operation voltages. These findings will be important in the microscopic understanding of the switching behavior of oxide-based atomic switches and electrochemical metallization cells.

    DOI

  • Atomic Switch: Atom/Ion Movement Controlled Devices for Beyond Von-Neumann Computers

    Tsuyoshi Hasegawa, Kazuya Terabe, Tohru Tsuruoka, Masakazu Aono

    ADVANCED MATERIALS   24 ( 2 ) 252 - 267  2012年01月  [査読有り]

     概要を見る

    An atomic switch is a nanoionic device that controls the diffusion of metal ions/atoms and their reduction/oxidation processes in the switching operation to form/annihilate a conductive path. Since metal atoms can provide a highly conductive channel even if their cluster size is in the nanometer scale, atomic switches may enable downscaling to smaller than the 11 nm technology node, which is a great challenge for semiconductor devices. Atomic switches also possess novel characteristics, such as high on/off ratios, very low power consumption and non-volatility. The unique operating mechanisms of these devices have enabled the development of various types of atomic switch, such as gap-type and gapless-type two-terminal atomic switches and three-terminal atomic switches. Novel functions, such as selective volatile/nonvolatile, synaptic, memristive, and photo-assisted operations have been demonstrated. Such atomic switch characteristics can not only improve the performance of present-day electronic systems, but also enable development of new types of electronic systems, such as beyond von- Neumann computers.

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  • Sensory and short-term memory formations observed in a Ag2S gap-type atomic switch

    Takeo Ohno, Tsuyoshi Hasegawa, Alpana Nayak, Tohru Tsuruoka, James K. Gimzewski, Masakazu Aono

    APPLIED PHYSICS LETTERS   99 ( 20 ) 203108  2011年11月  [査読有り]

     概要を見る

    Memorization caused by the change in conductance in a Ag2S gap-type atomic switch was investigated as a function of the amplitude and width of input voltage pulses (V-in). The conductance changed little for the first few Vin, but the information of the input was stored as a redistribution of Ag-ions in the Ag2S, indicating the formation of sensory memory. After a certain number of Vin, the conductance increased abruptly followed by a gradual decrease, indicating the formation of short-term memory (STM). We found that the probability of STM formation depends strongly on the amplitude and width of Vin, which resembles the learning behavior of the human brain. (C) 2011 American Institute of Physics. [doi:10.1063/1.3662390]

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  • Bulk and surface nucleation processes in Ag2S conductance switches

    M. Morales-Masis, S. J. van der Molen, T. Hasegawa, J. M. van Ruitenbeek

    PHYSICAL REVIEW B   84 ( 11 ) 115310  2011年09月  [査読有り]

     概要を見る

    We studied metallic Ag formation inside and on the surface of Ag2S thin films, induced by the electric field created with a scanning tunnel microscope (STM) tip. Two clear regimes were observed: cluster formation on the surface at low bias voltages, and full conductance switching at higher bias voltages (V &gt; 70 mV). The bias voltage at which this transition is observed is in agreement with the known threshold voltage for conductance switching at room temperature. We propose a model for the cluster formation at low bias voltage. Scaling of the measured data with the proposed model indicates that the process takes place near steady state, but depends on the STM tip geometry. The growth of the clusters is confirmed by tip retraction measurements and topography scans. This study provides improved understanding of the physical mechanisms that drive conductance switching in solid electrolyte memristive devices.

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  • Short-term plasticity and long-term potentiation mimicked in single inorganic synapses

    Takeo Ohno, Tsuyoshi Hasegawa, Tohru Tsuruoka, Kazuya Terabe, James K. Gimzewski, Masakazu Aono

    NATURE MATERIALS   10 ( 8 ) 591 - 595  2011年08月  [査読有り]

     概要を見る

    Memory is believed to occur in the human brain as a result of two types of synaptic plasticity: short-term plasticity (STP) and long-term potentiation (LTP; refs 1-4). In neuromorphic engineering(5,6), emulation of known neural behaviour has proven to be difficult to implement in software because of the highly complex interconnected nature of thought processes. Here we report the discovery of a Ag2S inorganic synapse, which emulates the synaptic functions of both STP and LTP characteristics through the use of input pulse repetition time. The structure known as an atomic switch(7,8), operating at critical voltages, stores information as STP with a spontaneous decay of conductance level in response to intermittent input stimuli, whereas frequent stimulation results in a transition to LTP. The Ag2S inorganic synapse has interesting characteristics with analogies to an individual biological synapse, and achieves dynamic memorization in a single device without the need of external preprogramming. A psychological model related to the process of memorizing and forgetting is also demonstrated using the inorganic synapses. Our Ag2S element indicates a breakthrough in mimicking synaptic behaviour essential for the further creation of artificial neural systems that emulate characteristics of human memory.

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  • Theoretical investigation of kinetics of a Cu2S-based gap-type atomic switch

    Alpana Nayak, Tohru Tsuruoka, Kazuya Terabe, Tsuyoshi Hasegawa, Masakazu Aono

    APPLIED PHYSICS LETTERS   98 ( 23 ) 233501  2011年06月  [査読有り]

     概要を見る

    Atomic switch, operating by forming and dissolving a metal-protrusion in a nanogap, shows an exponentially large bias dependence and a faster switching with increasing temperature and decreasing off-resistance. These major characteristics are explained with a simple model where the electrochemical potential at the subsurface of solid-electrolyte electrode determines the precipitation rate of metal atoms and the electric-field in the nanogap strongly affects the formation of metal-protrusion. Theoretically calculated switching time, based on this model, well reproduced the measured properties of a Cu2S-based atomic switch as a function of bias, temperature and off-resistance, providing a significant physical insight into the mechanism. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3597154]

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  • Temperature effects on the switching kinetics of a Cu-Ta2O5-based atomic switch’

    T. Tsuruoka, K. Terabe, T. Hasegawa, M. Aono

    Nanotechnology   22 ( 25 ) 254103  2011年06月  [査読有り]

    DOI

  • Switching kinetics of a Cu2S-based gap-type atomic switch

    Alpana Nayak, Tohru Tsuruoka, Kazuya Terabe, Tsuyoshi Hasegawa, Masakazu Aono

    NANOTECHNOLOGY   22 ( 23 ) 235201  2011年06月  [査読有り]

     概要を見る

    The switching time of a Cu2S-based gap-type atomic switch is investigated as a function of temperature, bias voltage, and initial off-resistance. The gap-type atomic switch is realized using a scanning tunneling microscope (STM), in which the formation and annihilation of a Cu-atom bridge in the vacuum gap between the Cu2S electrode and the Pt tip of the STM are controlled by a solid-electrochemical reaction. Increasing the temperature decreases the switching time exponentially with an activation energy of about 1.38 eV. Increasing the bias voltage also shortens the switching time exponentially, exhibiting a greater exponent for the lower bias than for the higher bias. Furthermore, faster switching has been achieved by decreasing the initial off-resistance between the Cu2S electrode and STM tip. On the basis of these results, we suggest that, in addition to the chemical reaction, the electric field in the vacuum gap plays a significant role in the operation of a gap-type atomic switch. This investigation advances our understanding of the operating mechanism of an atomic switch, which is a new concept for future electronic devices.

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  • Chemical Wiring and Soldering toward All-Molecule Electronic Circuitry

    Yuji Okawa, Swapan K. Mandal, Chunping Hu, Yoshitaka Tateyama, Stefan Goedecker, Shigeru Tsukamoto, Tsuyoshi Hasegawa, James K. Gimzewski, Masakazu Aono

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   133 ( 21 ) 8227 - 8233  2011年06月  [査読有り]

     概要を見る

    Key to single-molecule electronics is connecting functional molecules to each other using conductive nanowires. This involves two issues: how to create conductive nanowires at designated positions, and how to ensure chemical bonding between the nanowires and functional molecules. Here, we present a novel method that solves both issues. Relevant functional molecules are placed on a self-assembled monolayer of diacetylene compound. A probe tip of a scanning tunneling microscope is then positioned on the molecular row of the diacetylene compound to which the functional molecule is adsorbed, and a conductive polydiacetylene nanowire is fabricated by initiating chain polymerization by stimulation with the tip. Since the front edge of chain polymerization necessarily has a reactive chemical species, the created polymer nanowire forms chemical bonding with an encountered molecular element. We name this spontaneous reaction "chemical soldering". First-principles theoretical calculations are used to investigate the structures and electronic properties of the connection. We demonstrate that two conductive polymer nanowires are connected to a single phthalocyanine molecule. A resonant tunneling diode formed by this method is discussed.

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  • Three-Terminal Nanometer Metal Switches Utilizing Solid Electrolytes

    Hisao Kawaura, Toshitsugu Sakamoto, Naoki Banno, Shunichi Kaeriyama, Masayuki Mizuno, Kazuya Terabe, Tsuyoshi Hasegawa, Masakazu Aono

    ELECTRONICS AND COMMUNICATIONS IN JAPAN   94 ( 4 ) 55 - 61  2011年04月  [査読有り]

     概要を見る

    We propose a three-terminal nanometer metal switch that utilizes a solid electrolyte where a nanoscale metal filament is stretched and retracted. Its operating principle is based on electrochemical reaction and ion migration in the electrolyte. The fabricated device is composed of a solid electrolyte layer (Cu(2)S), a gate (Cu), a source (Cu), and a drain (Pt). After the Cu filament is formed between the source and the drain by applying the drain voltage, repeatable on/off switching in the drain current is obtained by controlling the gate voltage. The on/off current ratio can be as high as 10(5), and the programmable cycle is around 50. Each state can be kept for up to 40 days. Since the gate is separated from the current path, the switching current can be reduced to 10 mu A, which is two orders of magnitude smaller than that of a two-terminal switch. In this paper, we present the operating principle and electrical characteristics of the three-terminal switches, and discuss how suitable they are for reconfigurable circuits. (C) 2011 Wiley Periodicals, Inc. Electron Comm Jpn, 94(4): 55-61, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10214

    DOI

  • Rate-Determining Factors in the Chain Polymerization of Molecules Initiated by Local Single-Molecule Excitation

    Swapan K. Mandal, Yuji Okawa, Tsuyoshi Hasegawa, Masakazu Aono

    ACS NANO   5 ( 4 ) 2779 - 2786  2011年04月  [査読有り]

     概要を見る

    Spontaneous chain polymerization of molecules initiated by a scanning tunneling microscope tip is studied with a focus on its rate-determining factors. Such chain polymerization that happens in self-assembled monolayers (SAM) of diacetylene compound molecules, which results in a pi-conjugated linear polydiacetylene nanowire, varies in its rate P depending on domains in the SAM and substrate materials. While the arrangement of diacetylene molecules is identical in every domain on a graphite substrate, it varies in different domains on a MoS(2) substrate. This structural variation enables us to investigate how P is affected by molecular geometry. An important determining factor of P is the distance between two carbon atoms which are to be bound by polymerization reaction, R; as R decreases by 0.1 nm, P increases similar to 2 times. P for a MoS(2) substrate Is similar to 4 times higher (with the same value of R) than that for a graphite substrate because of higher mobility of molecules. The exciting correlation of the chain polymerization rate to the geometrical structure of the diacetylene molecules brings a deeper understanding of the mechanism of chain polymerization kinetics. In addition, the fabrication of one-dimensional conjugated polymer nanowires on a semiconducting MoS(2) substrate. as demonstrated here may be of immense Importance in the realization of future molecular devices.

    DOI

  • Memristive operations demonstrated by gap-type atomic switches

    Tsuyoshi Hasegawa, Alpana Nayak, Takeo Ohno, Kazuya Terabe, Tohru Tsuruoka, James K. Gimzewski, Masakazu Aono

    APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING   102 ( 4 ) 811 - 815  2011年03月  [査読有り]

     概要を見る

    We demonstrate memristive operations using gap-type Ag2S atomic switches, in which the growth and shrinkage of an Ag protrusion are controlled by using solid-electrochemical reactions. In addition to conventional memristive operations such as those proposed and demonstrated by resistive random-access memories (ReRAMs) using metal oxide compounds, gap-type Ag2S atomic switches also show new types of memristive operations by storing information from input signals without changing their output until a sufficient number of signals are inputted. The new types of memristive operations resemble the learning process seen in neuroplasticity, where changes occur in the organization of the human brain as a result of experience.

    DOI

  • Atomic switches: atomic-movement-controlled nanodevices for new types of computing

    Takami Hino, Tsuyoshi Hasegawa, Kazuya Terabe, Tohru Tsuruoka, Alpana Nayak, Takeo Ohno, Masakazu Aono

    SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS   12 ( 1 ) 013003  2011年02月  [査読有り]

     概要を見る

    Atomic switches are nanoionic devices that control the diffusion of metal cations and their reduction/oxidation processes in the switching operation to form/annihilate a metal atomic bridge, which is a conductive path between two electrodes in the on-state. In contrast to conventional semiconductor devices, atomic switches can provide a highly conductive channel even if their size is of nanometer order. In addition to their small size and low on-resistance, their nonvolatility has enabled the development of new types of programmable devices, which may achieve all the required functions on a single chip. Three-terminal atomic switches have also been developed, in which the formation and annihilation of a metal atomic bridge between a source electrode and a drain electrode are controlled by a third (gate) electrode. Three-terminal atomic switches are expected to enhance the development of new types of logic circuits, such as nonvolatile logic. The recent development of atomic switches that use a metal oxide as the ionic conductive material has enabled the integration of atomic switches with complementary metal-oxide-semiconductor (CMOS) devices, which will facilitate the commercialization of atomic switches. The novel characteristics of atomic switches, such as their learning and photosensing abilities, are also introduced in the latter part of this review.

    DOI

  • 光アシスト原子スイッチを用いたナノ光センサーの開発

    田中啓文, 長谷川剛, 日野貴美, 青野正和, 小川琢治

    月刊光アライアンス(日刊工業出版)   6   40 - 44  2011年

  • アトムトランジスタの開発

    長谷川剛

    電気協会報   1042   25 - 27  2011年

  • 「情報を記憶する光ナノセンサーの開発」 田中啓文 *、長谷川剛**、日野貴美、青野正和、小川琢治

    月刊画像ラボ(日刊工業出版)   3   60 - 66  2011年

  • ‘Nanoionics switching devices’,

    T. Hasegawa, K. Terabe, M. Aono

    Encyclopedia of Materilas: Science and Technology, Elsevier     1 - 8  2011年

    DOI

  • Volatile/Nonvolatile Dual-Functional Atom Transistor

    Tsuyoshi Hasegawa, Yaomi Itoh, Hirofumi Tanaka, Takami Hino, Tohru Tsuruoka, Kazuya Terabe, Hisao Miyazaki, Kazuhito Tsukagoshi, Takuji Ogawa, Shu Yamaguchi, Masakazu Aono

    APPLIED PHYSICS EXPRESS   4 ( 1 ) 15204  2011年01月  [査読有り]

     概要を見る

    We demonstrate a conceptually new atom transistor operation by electric-field control of the nanoionic state. The new atom transistor possesses novel characteristics, such as dual functionality of selective volatile and nonvolatile operations, very small power consumption (pW), and a high ON/OFF ratio [106 (volatile operation) to 108 (nonvolatile operation)], in addition to complementary metal oxide semiconductor (CMOS) process compatibility enabling the development of future computing systems that fully utilize highly-integrated CMOS technology. Cyclic endurance of 104 times switching was achieved with the prototype. (C) 2011 The Japan Society of Applied Physics

    DOI

  • A Polymer-Electrolyte-Based Atomic Switch

    Shouming Wu, Tohru Tsuruoka, Kazuya Terabe, Tsuyoshi Hasegawa, Jonathan P. Hill, Katsuhiko Ariga, Masakazu Aono

    ADVANCED FUNCTIONAL MATERIALS   21 ( 1 ) 93 - 99  2011年01月  [査読有り]

     概要を見る

    Studies on a resistive switching memory based on a silver-ion-conductive solid polymer electrolyte (SPE) are reported. Simple Ag/SPE/Pt structures containing polyethylene oxide-silver perchlorate complexes exhibit bipolar resistive switching under bias voltage sweeping. The switching behavior depends strongly on the silver perchlorate concentration. From the results of thermal, transport, and electrochemical measurements, it is concluded that the observed switching originates from formation and dissolution of a silver metal filament inside the SPE film caused by electrochemical reactions. This is the first report of an electrochemical "atomic switch" realized using an organic material. The devices also show ON/OFF resistance ratios greater than 10(5), programming speeds higher than 1 mu s, and retention times longer than 1 week. These results suggest that SPE-based electrochemical devices might be suitable for flexible switch and memory applications.

    DOI

  • Toward sub-20 nm hybrid nanofabrication by combining the molecular ruler method and electron beam lithography

    C. B. Li, T. Hasegawa, H. Tanaka, H. Miyazaki, S. Odaka, K. Tsukagoshi, M. Aono

    NANOTECHNOLOGY   21 ( 49 ) 495304  2010年12月  [査読有り]

     概要を見る

    It is of great interest and importance to develop new nanofabrication processes to fabricate sub-20 nm structures with sub-2 nm resolution for next-generation nanoelectronic devices. A combination of electron beam lithography (EBL) and a molecular ruler is one of the promising methods to make these fine structures. Here we successfully develop a hybrid method to fabricate sub-20 nm nanogap devices at the desired positions with a complex structure by developing a post-EBL process, which enabled us to avoid damaging the molecular ruler with the high-energy electron beam, and to fully utilize the EBL resolution. It was found that slight etching of the Ti adhesion layer of the parent metal (Pt) by ACT935J solution assisted the removal of molecular rulers, resulting in improved enhancement in the product yield (over 70%) of nanogap devices.

    DOI

  • The Atomic Switch

    Masakazu Aono, Tsuyoshi Hasegawa

    PROCEEDINGS OF THE IEEE   98 ( 12 ) 2228 - 2236  2010年12月  [査読有り]

     概要を見る

    An atomic switch is a nanoionic device that controls the diffusion of metal ions and their reduction/oxidation processes in the switching operation to form/annihilate a metal atomic bridge, which is a conductive path between two electrodes in an ON-state. Since metal atoms can provide a highly conductive channel even if their size is in the nanometer scale, atomic switches may enable downscaling to smaller than the 11-nm technology node. Two-terminal atomic switches have the potential for use in memories and programmable switches. Three-terminal atomic switches, where the formation/annihilation of a metal atomic bridge between a source electrode and a drain electrode are controlled by a third (gate) electrode, work as nonvolatile transistors. Recent development of two-terminal atomic switches that use a metal oxide as the ionic conductive material, in which a metal atomic bridge is formed, has enabled the integration of atomic switches with complementary metal-oxide-semiconductor (CMOS) devices. Also introduced are the novel characteristics of atomic switches, such as their small size, low power consumption, low ON-resistance, nonvolatility, and learning abilities.

    DOI

  • Forming and switching mechanisms of a cation-migration-based oxide resistive memory

    T. Tsuruoka, K. Terabe, T. Hasegawa, M. Aono

    NANOTECHNOLOGY   21 ( 42 ) 42505  2010年10月  [査読有り]

     概要を見る

    We report detailed current-voltage and current-time measurements to reveal the forming and switching behaviors of Cu/Ta(2)O(5)/Pt nonvolatile resistive memory devices. The devices can be initially SET (from the OFF state to the ON state) when a low positive bias voltage is applied to the Cu electrode. This first SET operation corresponds to the first formation of a metal filament by inhomogeneous nucleation and subsequent growth of Cu on the Pt electrode, based on the migration of Cu ions in the stable Ta(2)O(5) matrix. After the forming, the device exhibits bipolar switching behavior (SET at positive bias and RESET (from the ON state to the OFF state) at negative bias) with increasing the ON resistance from a few hundred Omega to a few k Omega. From the measurements of the temperature stability of the ON states, we concluded that the RESET process consists of the Joule-heating-assisted oxidation of Cu atoms at the thinnest part of the metal filament followed by diffusion and drift of the Cu ions under their own concentration gradient and the applied electric field, disconnecting the metal filament. With ON resistances of the order of a few k Omega, the SET and RESET operations are repeated by the inhomogeneous nucleation and the Joule-heating-assisted dissolution of a small filament on a remaining filament. This switching model is applicable to the operation of cation-migration-based resistive memories using other oxide materials.

    DOI

  • Structural characterization of amorphous Ta2O5 and SiO2-Ta2O5 used as solid electrolyte for nonvolatile switches

    Naoki Banno, Toshitsugu Sakamoto, Noriyuki Iguchi, Masashi Matsumoto, Hideto Imai, Toshinari Ichihashi, Shinji Fujieda, Kazuhiko Tanaka, Satoshi Watanabe, Shu Yamaguchi, Tsuyoshi Hasegawa, Masakazu Aono

    APPLIED PHYSICS LETTERS   97 ( 11 ) 113507  2010年09月  [査読有り]

     概要を見る

    Diffusivity of Cu in amorphous (a-) Ta2O5 is increased by low temperature annealing above 350 degrees C but the increase is suppressed by adding SiO2 to Ta2O5. To clarify the reasons, we investigated the structural difference between a-Ta2O5 and a-SiO2-Ta2O5. The results show that the low temperature annealing does not cause polycrystallization of Ta2O5 but purges weakly bonded oxygen atoms from the bulk and decreases the film density. Adding SiO2 to Ta2O5 is shown to increase the coordination number of Ta-O, which results in the improved thermal stability. (C) 2010 American Institute of Physics. [doi:10.1063/1.3488830]

    DOI

  • Photoassisted Formation of an Atomic Switch

    Takami Hino, Hirofumi Tanaka, Tsuyoshi Hasegawa, Masakazu Aono, Takuji Ogawa

    SMALL   6 ( 16 ) 1745 - 1748  2010年08月  [査読有り]

    DOI

  • Electronic States of Sulfur Vacancies Formed on a MoS2 Surface

    Nagisa Kodama, Tsuyoshi Hasegawa, Yuji Okawa, Tohru Tsuruoka, Christian Joachim, Masakazu Aono

    JAPANESE JOURNAL OF APPLIED PHYSICS   49 ( 8 ) 08LB01  2010年08月  [査読有り]

     概要を見る

    Sulfur vacancies formed on a MoS2 surface have been predicted to have electronic states at the Fermi level, and to work as conductive atomic scale structures. We made sulfur vacancies on a MoS2 surface by removing sulfur atoms using scanning tunneling microscopy (STM) induced field evaporation, and measured the current voltage (I/V) characteristics of the vacancies. The I/V curve measured at the vacancies showed a linear increase at a zero bias region, indicating the existence of electronic states at the Fermi level. On the other hand, the I/V curve measured at a clean surface showed a gap of about 1 eV around the Fermi level, as was expected from the theoretical calculation. We also successfully carried out manipulation of Au nanoislands, which will be used as nanopads to be connected to a sulfur vacancy chain. (C) 2010 The Japan Society of Applied Physics

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  • Size-Tunable UV-Luminescent Silicon Nanocrystals

    Naoto Shirahata, Tsuyoshi Hasegawa, Yoshio Sakka, Tohru Tsuruoka

    SMALL   6 ( 8 ) 915 - 921  2010年04月  [査読有り]

    DOI

  • Learning Abilities Achieved by a Single Solid-State Atomic Switch

    Tsuyoshi Hasegawa, Takeo Ohno, Kazuya Terabe, Tohru Tsuruoka, Tomonobu Nakayama, James K. Gimzewski, Masakazu Aono

    ADVANCED MATERIALS   22 ( 16 ) 1831 - +  2010年04月  [査読有り]

     概要を見る

    Learning abilities are demonstrated using a single solid-state atomic switch, wherein the formation and dissolution of a metal filament are controlled depending on the history of prior switching events. The strength of the memorization level gradually increases when the number of input signals is increased. Once the filament forms a bridge, electrons flow in a ballistic mode and long-term memorization is achieved (see figure).

    DOI

  • Rate-Limiting Processes Determining the Switching Time in a Ag2S Atomic Switch

    Alpana Nayak, Takuro Tamura, Tohru Tsuruoka, Kazuya Terabe, Sumio Hosaka, Tsuyoshi Hasegawa, Masakazu Aono

    JOURNAL OF PHYSICAL CHEMISTRY LETTERS   1 ( 3 ) 604 - 608  2010年02月  [査読有り]

     概要を見る

    The switching time of a Ag2S atomic switch, in which formation and annihilation of a Ag atomic bridge is controlled by a solid-electrochemical reaction in a nanogap between two electrodes, is investigated as a function of bias voltage and temperature. Increasing the bias voltage decreases the switching time exponentially, with a greated exponent for the lower range of bias than that for the higher range. Furthermore, the switching time shortens exponentially with raising temperature, following the Arrhenius relation with activation energy values of 0.58 and 1.32 eV for lower and higher bias ranges, respectively. These results indicate that there are two main processes which govern the rate of switching first the electrochemical reduction Ag++e(-)-&gt; Ag and, second, the diffusion of Ag+ ions. This investigation advances the fundamental understanding of the switching mechanism of the atomic switch which is essential for its successful device application.

    DOI

  • Nanoionics switching device: “Atomic Switches”

    T. Hasegawa, K. Terabe, T. Sakamoto, M. Aono

    MRS Bulletin   34 ( 12 ) 929 - 934  2009年12月  [査読有り]

    DOI

  • 電気化学反応を用いた金属ナノワイヤーの形成とそのデバイス応用

    長谷川剛, 寺部一弥, 阪本利司, 鶴岡徹, 青野正和

    J. Vac. Sci. Jpn.   52 ( 6 ) 340 - 346  2009年

  • Deep Ultraviolet Light-Emitting Organosoluble Polyimides Derived from Siloxane- Containing Aliphatic Dianhydride and Various Aromatic Diamines

    S. Wu, T. Tsuruoka, T. Hasegawa

    Polymer Preprints, Japan   58 ( 1 ) 1452  2009年

  • Cu-ion Diffusivity in SiO2-Ta2O5 Solid Electrolyte and Its Impact on The Yield of Resistance Switching After BEOL Processes

    N. Banno, T. Sakamoto, H. Hada, N. Kasai, N. Iguchi, H. Imai, S. Fujieda, T. Ichihashi, T. Hasegawa, M. Aono

    2009 IEEE INTERNATIONAL RELIABILITY PHYSICS SYMPOSIUM, VOLS 1 AND 2     395 - +  2009年  [査読有り]

     概要を見る

    For stability against the thermal budget of the CMOS BEOL process, we developed a new solid-electrolyte switch that uses a SiO2-Ta2O5 composite as the electrolyte. This switch has high thermal stability because thermal diffusion of Cu+ ions is Suppressed in the composite. Moreover, its switching characteristics after thermal annealing are similar to those of a Ta2O5 switch without annealing. The switch with the SiO2-Ta2O5 composite electrolyte has good ON-state durability against DC current stress; its durability is comparable to that of a single via in interconnects. The switch can be implemented in the local interconnection layers of LSIs.

  • Development of Polymer Electrolytes Based Resistive Switch

    Shouming Wu, Tohru Tsuruoka, Kazuya Terabe, Tsuyoshi Hasegawa, Jonathan P. Hill, Katsuhiko Ariga, Masakazu Aono

    SECOND INTERNATIONAL CONFERENCE ON SMART MATERIALS AND NANOTECHNOLOGY IN ENGINEERING   7493   208 - 211  2009年  [査読有り]

     概要を見る

    The construction of an organic-electronic resistive switch based on polymer electrolytes is the basis to study the interfacial and bulk transport as well as the interaction between ions and electrons/holes at the nanoscale level. Moreover, it could also be potentially applied in novel nanoelectrochemical devices for sensors, fuel cells and batteries, and therefore has attracted much attention in recent years. In this work, we fabricated resistive switching devices with silver-ion-conductive polymer electrolytes. The devices showed bipolar switching behaviors in the current-voltage characteristics for different silver ion concentrations ranging from 1 to 4 wt%. A high resistance up to 1 G Omega in the OFF state and a low resistance with less than tens of k Omega in the ON state can be achieved. We believe that the observed switching results from formation and annihilation of Ag metal filaments inside the polymer film by solid electrochemical reaction. Sequential operations, such as write-read-erase-read, were also demonstrated.

    DOI

  • Diffusivity of Cu Ions in Solid Electrolyte and Its Effect on the Performance of Nanometer-Scale Switch

    Naoki Banno, Toshitsugu Sakamoto, Noriyuki Iguchi, Hiroshi Sunamura, Kazuya Terabe, Tsuyoshi Hasegawa, Masakazu Aono

    IEEE TRANSACTIONS ON ELECTRON DEVICES   55 ( 11 ) 3283 - 3287  2008年11月  [査読有り]

     概要を見る

    A novel solid-electrolyte nonvolatile switch that we previously developed for programmable large-scale-integration circuits turns on or off when a conducting Cu bridge is formed or dissolved in the solid electrolyte. Cu+ ion migration and an electrochemical reaction are involved in the switching process. For logic applications, we need to adjust its turn-on voltage (V-ON), which was too small to maintain the conductance state during logic operations. In this paper, we clarified that V-ON is mainly affected by the rate of Cu+ ion migration in the solid electrolyte. Considering the relationship between the migration rate and V-ON, we replaced the former electrolyte, Cu2-alpha S, with Ta2O5, which enabled us to appropriately adjust V-ON with a smaller Cu+ ion diffusion coefficient.

    DOI

  • A solid electrolyte nanometer switch

    Toshitsugu Sakamoto, Shunichi Kaeriyama, Masayuki Mizuno, Hisao Kawaura, Tsuyoshi Hasegawa, Kazuya Terabe, Masakazu Aono

    ELECTRICAL ENGINEERING IN JAPAN   165 ( 1 ) 68 - 73  2008年10月  [査読有り]

     概要を見る

    We have investigated solid electrolyte switches that utilize electrochemical reactions (deposition and dissolution) of metallic ions. The switch turns off or on when a metallic bridge electrochemically forms or dissolves in the solid electrolyte. Each state is nonvolatile and the switching is repeatable up to 105 cycles. The promising application is a programmable switch in a field programmable logic because of its small size (&lt; 30 nm) and low ON resistance (&lt; 100 92). This paper discusses the electrical characteristics, operation principle, and applications of the solid electrolyte switch. (c) 2008 Wiley Periodicals, Inc.

    DOI

  • 主鎖にシロキサン基を有する高蛍光可溶ポリイミド」

    呉守明, 鶴岡徹, 長谷川剛, 葛 子義, 早川 晃鏡, 柿本 雅明

    Polymer Preprints, Japan   57 ( 2 ) 4113  2008年09月

  • Structural studies of copper sulfide films: effect of ambient atmosphere

    Manisha Kundu, Tsuyoshi Hasegawa, Kazuya Terabe, Kazuhiro Yamamoto, Masakazu Aono

    SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS   9 ( 3 ) 035011  2008年09月  [査読有り]

     概要を見る

    We examined the structural properties of copper sulfide films as a function of the sulfurization time of 70-nm-thick Cu films. Copper sulfide films with various phases such as mixed metallic Cu-chalcocite, chalcocite, roxbyite, and covellite phases were formed with increasing sulfurization time. To evaluate the structural stability of various films, all the films were exposed to the ambient atmosphere for the same amount of time. Although the phase structure and stoichiometry of the films were maintained at a greater depth, the near-surface region of the films was oxidized and covered with overlayers of oxide, hydroxide, and/or sulfate species due to the exposure and reaction with the ambient atmosphere. The oxygen uptake and its reactivity with the copper sulfide film surfaces were enhanced with increasing sulfur content of the films. In addition, the type of divalent state of copper formed on the film surfaces depended on the phase structure, composition, and stoichiometry of the films.

    DOI

  • Resistance switching in anodic oxidized amorphous TiO2 films

    Changhao Liang, Kazuya Terabe, Tsuyoshi Hasegawa, Masakazu Aono

    APPLIED PHYSICS EXPRESS   1 ( 6 ) 064002  2008年06月  [査読有り]

     概要を見る

    A thin amorphous TiO2 layer was prepared using anodic oxidation of Ti. Resistance switching of amorphous TiO2 was investigated by sweeping in a continuous voltage scan and pulse bias voltage. The bipolar switching was observed without the need of a forming process. Switching of the Ti/amorphous-TiO2/Pt based structure showed good endurance. The switching mechanism and current-voltage characteristics were investigated from combinatorial analysis of the conducting filaments' evolution and the space-charge limited current conduction. The oxygen-vacancies migration involved redox processes, which is responsible for the recovery and rupture of sub-TiOx based conducting filaments inside the amorphous TiO2 layer. (C) 2008 The Japan Society of Applied Physics.

    DOI

  • Optical waveguide properties of single indium oxide nanofibers

    T. Tsuruoka, C. H. Liang, K. Terabe, T. Hasegawa

    JOURNAL OF OPTICS A-PURE AND APPLIED OPTICS   10 ( 5 ) 055201  2008年05月  [査読有り]

     概要を見る

    The luminescence and waveguide properties of single In(2)O(3) nanofibers were investigated by means of scanning near-field optical microscopy. The nanofibers showed spatially uniform emission intensity in photoluminescence (PL) images. This emission is associated with a PL emission band centered at similar to 630 nm. We found that this PL light is propagated through the nanofiber over a distance of several hundreds of micrometers. By measuring the PL intensity for different propagating distances, the optical loss of single nanofibers was evaluated. Waveguiding behavior for incident light with different wavelengths in the visible region was also observed. These results indicate that In2O3 nanofibers can be used as good waveguide elements for integrated photonic applications.

    DOI

  • Effect of sulfurization conditions on structural and electrical properties of copper sulfide films

    Manisha Kundu, Tsuyoshi Hasegawa, Kazuya Terabe, Masakazu Aono

    JOURNAL OF APPLIED PHYSICS   103 ( 7 ) 073523  2008年04月  [査読有り]

     概要を見る

    We examined the structural and electrical properties of copper sulfide films as a function of the sulfurization time of 70-nm-thick Cu films. Copper sulfide films with various phases such as mixed metallic Cu-chalcocite, chalcocite, roxbyite, and mixed roxbyite-covellite phases were formed with increasing sulfurization time. The Cu/S atomic percentage ratio of the films decreased with increasing sulfurization time, and films with various compositions such as Cu-rich and stoichiometric copper sulfide with underlying unreacted Cu as well as pure stoichiometric and S-rich copper sulfide were obtained. The surface morphology and the electrical resistivity of the films depended on the chemical phase and composition of the films. The resistivity decreased with increasing Cu deficiency in the films. Distinct switching of the resistance from high to low-state, and vice versa, with the reversal of the bias polarity of the film was observed only for the mixed metallic Cu-chalcocite phased film with underlying Cu. However, the chalcocite film with underlying Cu exhibited a semiconducting behavior. This indicated that excess Cu within the chalcocite film is required for the observation of the switching behavior of the resistance. (c) 2008 American Institute of Physics.

    DOI

  • Origin of green emission from ZnS nanobelts as revealed by scanning near-field optical microscopy

    T. Tsuruoka, C. H. Liang, K. Terabe, T. Hasegawa

    APPLIED PHYSICS LETTERS   92 ( 9 ) 091908  2008年03月  [査読有り]

     概要を見る

    The emission properties of ZnS nanobelts synthesized through thermal evaporation were investigated by means of scanning near-field optical microscopy. The photoluminescence (PL) images of single nanobelts exhibited a bright line along their length. The local light emission spectra measured over the bright lines showed a green emission peak around 535 nm, which was in good agreement with a PL peak obtained for an ensemble of the nanobelts. From careful scanning-electron-microscopy observations of identical nanobelts, we found that the observed green emission is related to line or planar defects of the ZnS nanobelts.

    DOI

  • 固体電解質を用いた3端子型ナノメートル金属スイッチ

    川浦久雄, 阪本利司, 伴野直樹, 帰山隼一, 水野正之, 寺部一弥, 長谷川剛, 青野正和

    電気学会論文誌C   128 ( 6 ) 890 - 895  2008年

  • Atomic force microscopy and theoretical investigation of the lifted-up conformation of polydiacetylene on a graphite substrate

    Yuji Okawa, Daisuke Takajo, Shigeru Tsukamoto, Tsuyoshi Hasegawa, Masakazu Aono

    SOFT MATTER   4 ( 5 ) 1041 - 1047  2008年

     概要を見る

    The structure of a single polydiacetylene compound on a graphite substrate was investigated using atomic force microscopy (AFM). The linear conjugated polydiacetylenes were obtained through chain polymerization of a monomolecular layer of diacetylene compound on a graphite substrate under ultraviolet light irradiation. AFM observations revealed that the polydiacetylenes were imaged higher than the unpolymerized monomer rows. This result supports the 'lifted-up' conformation model, in which the polydiacetylene backbone is geometrically raised. To investigate why the polymer backbone is lifted, we also carried out first-principles density-functional calculations in the local density approximation. These calculations suggested that the steric hindrance between the alkyl side-chains of the monomers and the oligomer caused the lifted-up conformation.

    DOI

  • Resistance switching of an individual Ag2S/Ag nanowire heterostructure

    Changhao Liang, Kazuya Terabe, Tsuyoshi Hasegawa, Masakazu Aono

    NANOTECHNOLOGY   18 ( 48 ) 485202  2007年12月  [査読有り]

     概要を見る

    Ag/Cu-based chalcogenide ionic conductors are candidates for use in applications in resistance- switching and nonvolatile memory devices. We report the investigation of the electrical properties of individual Ag2S/Ag heteronanowires (HNWs) by atomic force microscopy (AFM) using a nanoscale-tip electrode. Hysteretic current-voltage (IV) curves and the polarity-dependent resistance- switching phenomenon in an individual Ag2S/Ag HNW were observed. A local impedance spectroscopy measurement of Ag2S/Ag HNWs was performed to reveal the interface- related electrical characteristics. The DC-bias-dependent impedance spectra suggested the occurrence of charge and mass transfer at the interface of the electrode/mixed conductor. It is proposed that reversible resistance switching originates from the creation and rupture of filament- like conducting pathways inside the Ag2S/Ag HNW.

    DOI

  • Anomalous phase transition and ionic conductivity of AgI nanowire grown using porous alumina template

    Changhao Liang, Kazuya Terabe, Tsuyoshi Hasegawa, Masakazu Aono, Nobuo Iyi

    JOURNAL OF APPLIED PHYSICS   102 ( 12 ) 124308  2007年12月  [査読有り]

     概要を見る

    Silver-iodide (AgI)-based superionic conductors are attracting widespread interest for their potential applications in electrochemical devices such as sensors and batteries. A new kind of nanocomposite with highly ordered AgI nanowires embedded in an anodic-aluminum-oxide (AAO) membrane was fabricated by low-temperature step-electrochemical growth. Structural evolution, phase transition, and ionic conductivity were investigated by x-ray diffraction, differential scanning calorimetry, and impedance measurements. The phase transition from beta/gamma-AgI phase to alpha-AgI phase occurred at temperature of 168 degrees C, that is, higher than that of reported bulk AgI (147 degrees C); abnormally, the alpha to beta/gamma phase-transition temperature on cooling was also depressed as large hysteresis formed. The high-temperature phase, namely, alpha-AgI, remained at temperatures as low as 80 degrees C. The initial highly oriented-growth AgI nanowire disappeared after undergoing heating and cooling processes and a mixture of polycrystalline beta/gamma-AgI and amorphouslike interface phases formed. The cooled AgI-AAO composite displayed ionic conductivity in the order of 10(-2) S cm(-1) at room temperature. This array-structured nanocomposite of AgI-AAO may be further developed for usage as a new type of battery, i.e., "nanobatteries" and "nanosensors" with individual AgI nanowires as basic elements.

    DOI

  • Size-dependent single electron tunneling effect in Au nanoparticles

    R. Negishi, T. Hasegawa, H. Tanaka, K. Terabe, H. Ozawa, T. Ogawa, M. Aono

    SURFACE SCIENCE   601 ( 18 ) 3907 - 3911  2007年09月  [査読有り]

     概要を見る

    We investigated single electron tunneling (SET) behavior of dodecanethiol-coated An nanoparticles of two different sizes (average sizes are 5 nm and 2 nm) using nanogap electrodes, which have a well-defined gap size, at various temperatures. The Coulomb staircases and the Coulomb gap near-zero bias voltage caused by the suppression of the tunneling electrons due to the Coulomb blockade effect were observed in the current-voltage (I-V) curves of both sizes of nanoparticles at a low temperature (10 K). At room temperature, the Coulomb gap was observed only in the I- V curve of the smaller nanoparticles. This result indicates that the charging energy of the smaller nanoparticles is enough to overcome the thermal energy at room temperature. This suggests that it is possible to operate the SET devices at room temperature using the smaller nanoparticles as a Coulomb island. (C) 2007 Elsevier B.V. All rights reserved.

    DOI

  • Control of local ion transport to create unique functional nanodevices based on ionic conductors

    Kazuya Terabe, Tsuyoshi Hasegawa, Changhao Liang, Masakazu Aono

    SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS   8 ( 6 ) 536 - 542  2007年09月  [査読有り]

     概要を見る

    The development of nanometer-scale devices operating under a new principle that could overcome the limitations of current semiconductor devices has attracted interest in recent years. We propose that nanoionic devices that operate by controlling the local transport of ions are promising in this regard. It is possible to control the local transport of ions using the solid electrochemical properties of ionic and electronic mixed conductors. As an example of this concept, here, we report a method of controlling the transport of silver ions of the mixed-conductor silver sulfide (Ag2S) crystal and basic research on nanoionic devices based on this mixed conductor. These devices show unique functions such as atom deposition, resistance switching, and quantum point contact switching. The switches operate through the formation and dissolution of an atomic bridge between the electrodes, and the behavior is realized by control of the local solid-state electrochemical reaction. Potential nanoionic devices utilizing the unique functions and characters that do not exist in conventional semiconductor devices are discussed. (c) 2007 NIMS and Elsevier Ltd. All rights reserved.

    DOI

  • Electronic transport in Ta2O5 resistive switch

    Toshitsugu Sakamoto, Kevin Lister, Naoki Banno, Tsuyoshi Hasegawa, Kazuya Terabe, Masakazu Aono

    APPLIED PHYSICS LETTERS   91 ( 9 ) 092110  2007年08月  [査読有り]

     概要を見る

    The authors examined the electronic transport of a solid electrolyte resistive switch. Using element analysis and the temperature dependence of its electronic transport, they deduced that the conductive path is composed of Cu metal precipitated in the solid electrolyte film by an electrochemical reaction. Furthermore, they observed Coulomb blockade phenomena at 4 K when the switch was in the off state. Their observations and experimental results suggest that the metallic conductive path consists of metallic islands separated by tunneling barriers and that switching between the on and off states originates from modulation in the tunneling barriers.

    DOI

  • AgI/Ag heterojunction nanowires: Facile electrochemical synthesis, photoluminescence, and enhanced ionic conductivity

    Changhao Liang, Kazuya Terabe, Tohru Tsuruoka, Minoru Osada, Tsuyoshi Hasegawa, Masakazu Aono

    ADVANCED FUNCTIONAL MATERIALS   17 ( 9 ) 1466 - 1472  2007年06月  [査読有り]

     概要を見る

    The construction of an electronic-conductor/ionic-conductor heterojunction in a well-defined nanostructure is the basis of studying interfacial and bulk transport and the reactions of ions and electrons at the nanoscale level. An ionic-conductor/metal (AgI/Ag) beterostructured nanowire array is easily fabricated by a template-confined, step-electrochemical technique. The structural and morphological evolution of the AgI/Ag heterostructure before and after its release from the anodic aluminum oxide (AAO) membrane is characterized by scanning electron microscopy, X-ray diffraction, and optical spectroscopy. The structural disordering of released AgI is suggested by the appearance of a broad photoluminescence emission band at longer wavelengths and a short-range-order-like Raman peak. The ionic conductivity of the AgI nanowire embedded inside the insulating AAO membrane is measured as being on the order of 10(-3) S cm(-1), which is an enhancement by two to three orders of magnitude compared with that of bulk polycrystalline AgI at room temperature. This electrochemical method could be useful in fabricating other pure and mixed ionic conductors in heterojunction nanostructures.

    DOI

  • I-V characteristics of single electron tunneling from symmetric and asymmetric double-barrier tunneling junctions

    R. Negishi, T. Hasegawa, K. Terabe, M. Aono, H. Tanaka, T. Ogawa, H. Ozawa

    APPLIED PHYSICS LETTERS   90 ( 22 ) 223112  2007年05月  [査読有り]

     概要を見る

    I-V characteristics of single electron tunneling from a symmetric and an asymmetric double-barrier tunneling junction (DBTJ) were examined. A single Au nanoparticle was trapped in nanogap whose size was precisely controlled using a combination of electron beam lithography and molecular ruler technique. Though the symmetric junction showed a monotonic rise with a bias beyond the Coulomb gap voltage, the asymmetric junction showed Coulomb staircases. The capacitance of the junction estimated from the fitting curves using the Coulomb conventional theory was consistent with the capacitance calculated from the observed structure. The authors quantitatively found the correlation between the electrical and structural properties of DBTJ. (C) 2007 American Institute of Physics.

    DOI

  • Chain polymerization of diacetylene compound multilayer films on the topmost surface initiated by a scanning tunneling microscope tip

    Daisuke Takajo, Yuji Okawa, Tsuyoshi Hasegawa, Masakazu Aono

    LANGMUIR   23 ( 10 ) 5247 - 5250  2007年05月  [査読有り]

     概要を見る

    Chain polymerizations of diacetylene compound multilayer films on graphite substrates were examined with a scanning tunneling microscope (STM) at the liquid/solid interface of the phenyloctane solution. The first layer grew very quickly into many small domains. This was followed by the slow formation of the piled up layers into much larger domains. Chain polymerization on the topmost surface layer could be initiated by applying a pulsed voltage between the STM tip and the substrate, usually producing a long polymer of submicrometer length. In contrast, polymerizations on the underlying layer were never observed. This can be explained by a conformation model in which the polymer backbone is lifted up.

    DOI

  • LSI回路の再構成を可能とするナノブリッジ

    阪本利司, 帰山隼一, 水野正之, 寺部一弥, 長谷川剛, 青野正和

    NEC技報   60 ( 1 ) 73 - 76  2007年

  • Material dependence of switching speed of atomic switches made from silver sulfide and from copper sulfide

    T. Tamura, T. Hasegawa, K. Terabe, T. Nakayama, T. Sakamoto, H. Sunamura, H. Kawaura, S. Hosaka, M. Aono

    PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY   61 ( 1 ) 1157 - 1161  2007年  [査読有り]

     概要を見る

    We developed an atomic switch consisting of an ionic and electronic mixed conductor electrode and a counter metal electrode, having a space of about 1 nm between them. Formation and annihilation of a conductive atomic bridge is controlled using a solid electrochemical reaction, which is caused by applying a certain bias voltage between the electrodes. In this study, we measured the switching time of atomic switches made of silver sulfide and copper sulfide. The switching times were different, and this difference can be attributed to the different activation energies and chemical potentials of the materials.

    DOI

  • A Ta2O5 solid-electrolyte switch with improved reliability

    Toshitsugu Sakamoto, Naoki Banno, Noriyuki Iguchi, Hisao Kawaura, Hiroshi Sunamura, Shinji Fujieda, Kazuya Terabe, Tsuyoshi Hasegawa, Masakazu Aono

    2007 SYMPOSIUM ON VLSI TECHNOLOGY, DIGEST OF TECHNICAL PAPERS     38 - +  2007年  [査読有り]

     概要を見る

    We present a novel solid-electrolyte switch ("NanoBridge") promising for application to field programmable gate array (FPGA). We replace a former solid electrolyte of Cu2S with Ta2O5, which has a Siprocess compatibility,. As a result; we successfully control the turn-on voltage to adapt to CMOS operation. The Ta2O5-NanoBridge exhibits a high reliability of cycling endurance (&gt; 10(4)) and a stability against EM (&gt; 10years at 2.6mA at RT). Furthermore, we demonstrate that the conducting path of the switch is a Cu precipitate with 30nm in diameter, which possibly enables to scale down the switch.

  • Solid-electrolyte nanometer switch

    Naoki Banno, Toshitsugu Sakamoto, Noriyuki Iguchi, Hisao Kawaura, Shunichi Kaeriyama, Masayuki Mizuno, Kozuya Terabe, Tsuyoshi Hasegawa, Masakazu Aono

    IEICE TRANSACTIONS ON ELECTRONICS   E89C ( 11 ) 1492 - 1498  2006年11月  [査読有り]

     概要を見る

    We have developed a solid-electrolyte nonvolatile switch (here we refer as NanoBridge) with a low ON resistance and its small size. When we use a NanoBridge to switch elements in a programmable logic device, the chip size (or die cost) can be reduced and performance (speed and power consumption) can be enhanced. Developing this application required solving a couple of problems. First, the switching voltage of the NanoBridge (similar to 0.3 V) needed to be larger than the operating voltage of the logic circuit (&gt; 1 V). Second, the programming current (&gt; 1 mA) needed to be suppressed to avoid large power consumption. We demonstrate how the Nanobridge enhances the switching voltage and reduces the programming current.

    DOI

  • Template synthesis of M/M2S (M = Ag, Cu) hetero-nanowires by electrochemical technique

    Changhao Liang, Kazuya Terabe, Tsuyoshi Hasegawa, Masakazu Aono

    SOLID STATE IONICS   177 ( 26-32 ) 2527 - 2531  2006年10月  [査読有り]

     概要を見る

    Metal chalcogenide-based mixed ionic-electronic conductors such as Ag2S and Cu2S can be specifically architected for application in nanoelectronic devices. We present a template-confined synthesis of metal chalcogenide (e.g., Ag2S, Cu2S) nanowires for mixed conductor-based nanoelectronics. First, the metal nanowire array was electroplated into pores of a porous alumina membrane. Anodic polarization was then used to transform the metal into the metal sulfide in aqueous hydrosulfide (HS-) solutions. The as-synthesized mixed conductors' hetero-nanowire array was characterized by X-ray diffraction and electron microscopy. Electronic transport measurements show non-linear and reproducible electrical switching characteristics. The high and low resistance states can be reversibly changed by altering the polarity of the applied voltage between the bottom and top electrodes. The electrical-switching behavior is attributed to electric-field-induced accumulation and dissolution of metallic conducting pathways inside the mixed conductors' nanowires. (c) 2006 Elsevier B.V. All rights reserved.

    DOI

  • Formation of metastable silver nanowires of hexagonal structure and their structural transformation under electron beam irradiation

    Changhao Liang, Kazuya Terabe, Tsuyoshi Hasegawa, Masakazu Aono

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS   45 ( 7 ) 6046 - 6048  2006年07月  [査読有り]

     概要を見る

    We fabricated Ag nanowires (AgNWs) of 4H hexagonal structure with a diameter of ca. 20nm using dc clectrodeposition inside an anodic alumina oxide (AAO) membrane at low current density. 4H-AgNWs were formed in scale inside an AAO membrane with a pore diameter of ca. 20 nm. We propose that a. small-pore-size AAO membrane and appropriate growth conditions favor the growth of 4H-Ag. Transmission electron microscopy, (TEM) revealed the coexistence of single-crystalline 4H-AgNWs and fcc-AgNWs. The 4H-AgNWs tended to transform into fcc Ag particles under intense electron beam (EB) irradiation, which may be attributed to the knock-on displacement of Ag atoms by electrons generating defects.

    DOI

  • Fabrication of nanoscale gaps using a combination of self-assembled molecular and electron beam lithographic techniques

    R Negishi, T Hasegawa, K Terabe, M Aono, T Ebihara, H Tanaka, T Ogawa

    APPLIED PHYSICS LETTERS   88 ( 22 ) 223112  2006年05月  [査読有り]

     概要を見る

    We have developed and tested a new method of fabricating nanogaps using a combination of self-assembled molecular and electron beam lithographic techniques. The method enables us to control the gap size with an accuracy of approximately 2 nm and designate the positions where the nanogaps should be formed with high-resolution patterning by using electron beam lithography. We have demonstrated the utility of the fabricated nanogaps by measuring a single electron tunneling phenomenon through dodecanethiol-coated Au nanoparticles placed in the fabricated nanogap.

    DOI

  • Effect of sulfurization conditions and post-deposition annealing treatment on structural and electrical properties of silver sulfide films

    M Kundu, K Terabe, T Hasegawa, M Aono

    JOURNAL OF APPLIED PHYSICS   99 ( 10 ) 103501  2006年05月  [査読有り]

     概要を見る

    We examined the structural and electrical properties of silver sulfide films as a function of the sulfurization time of 70-nm-thick Ag films. Variations in the sulfurization time caused variations in the Ag/S atomic percentage ratio of the silver sulfide films, and as-grown films with various compositions, such as S-rich (Ag/S=1.59), stoichiometric (Ag/S=2), and Ag-rich (Ag/S=2.16) films were formed. Amongst the various as-grown films, Ag ions existed in the most polarizable environment in the Ag-rich films. All the films existed in the acanthite alpha-phase, and the sulfurization conditions did not cause any drastic change in the preferred orientation of this phase. The resistivity of these films strongly depended on the Ag/S ratio. While the resistivity of stoichiometric or S-rich films was about 10(7)-10(8) Omega cm, excess Ag of the Ag-rich film caused a decrease in the resistivity by four orders of magnitude. The Ag/S ratio also played a significant role in our observation of the change in resistance within the films from high- to low-resistance state and vice versa with the reversal of the bias polarity of the film. Distinct switching of the resistance was observed only for the Ag-rich film. We also examined the effects of post-deposition annealing (PDA) of various films at 190 degrees C. PDA caused the formation of Ag-rich films (Ag/S=2.12-2.17) in all cases, and Ag ions existed in a more polarizable environment in all the films as compared with stoichiometric film. All the annealed films contained mixed acanthite alpha-phase and argentite beta-phase. Furthermore, all the films had low resistivities of about 0.01-0.02 Omega cm, which indicated that the coexisting metallic argentite beta-phase of the films significantly improved the conductivity of the films as compared to the as-grown film with similar Ag/S ratio. Clear switching behavior of the resistance could be observed within all the annealed films, thereby indicating that excess Ag in the silver sulfide films is a requirement for observation of such a phenomenon. (c) 2006 American Institute of Physics.

    DOI

  • Switching property of atomic switch controlled by solid electrochemical reaction

    T Tamura, T Hasegawa, K Terabe, T Nakayama, T Sakamoto, H Sunamura, H Kawaura, S Hosaka, M Aono

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   45 ( 12-16 ) L364 - L366  2006年04月  [査読有り]

     概要を見る

    We measured the switching time of an atomic switch that is operated by controlling the formation and annihilation of an atomic bridge in a nanogap between two electrodes using solid electrochemical reaction. The switching time becomes exponentially shorter with increasing the switching bias voltage. This exponential relation indicates that the switching time is determined by the solid electrochemical reaction, which is supported by theoretical estimation using a simple model. These results suggest the possibility that the atomic switch can be operated as fast as semiconductor devices currently used.

    DOI

  • Effect of ion diffusion on switching voltage of solid-electrolyte nanometer switch

    N Banno, T Sakamoto, T Hasegawa, K Terabe, M Aono

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS   45 ( 4B ) 3666 - 3668  2006年04月  [査読有り]

     概要を見る

    A solid electrolyte switch turns on or off when a metallic bridge is formed or dissolved respectively in the solid electrolyte (here we use Cu2-alpha S). For logic applications, the switching voltage (&lt; 0.3 V) should be larger than the operating voltage of the logic circuit (about I V). We reveal that the switching voltage is mainly affected by Cu+ ionic transport in Cu2-alpha S and that a solid electrolyte with an ion diffusion coefficient smaller than that of Cu2-alpha S by several tens of orders of magnitude makes it possible to increase the switching voltage to I V.

    DOI

  • 固体電解質ナノスイッチ

    阪本利司, 帰山隼一, 砂村潤, 水野正之, 川浦久雄, 長谷川剛, 寺部一弥, 青野正和

    電気学会論文誌C「次世代LSIデバイス・プロセス技術の課題と展望」特集   126   714 - 719  2006年

  • 固体メモリー

    阪本利司, 帰山隼一, 長谷川剛, 寺部一弥

    応用物理   75 ( 9 ) 1126 - 1130  2006年

  • 原子スイッチ —原子(イオン)の移動を利用したナノデバイス—

    寺部一弥, 長谷川剛, 中山知信, 青野正和

    表面科学   27 ( 4 ) 232 - 238  2006年

  • 3端子固体電解質ナノスイッチ

    阪本利司, 伴野直樹, 井口憲幸, 帰山隼一, 水野正之, 川浦久雄, 寺部一弥, 長谷川剛, 青野正和

    電子情報通信学会技術研究報告   105   13 - 16  2006年

  • Ionic-electronic conductor nanostructures: Template-confined growth and nonlinear electrical transport

    CH Liang, K Terabe, T Hasegawa, R Negishi, T Tamura, M Aono

    SMALL   1 ( 10 ) 971 - 975  2005年09月  [査読有り]

    DOI

  • 量子化伝導原子スイッチの開発

    寺部一弥, 長谷川剛, 中山知信, 青野正和

    まてりあ   44 ( 9 ) 757 - 763  2005年

  • 固体電気化学反応を利用した実用デバイス「原子スイッチ」の開発

    長谷川剛, 青野正和

    化学と工業   58 ( 11 ) 1336 - 1338  2005年

  • 原子スイッチを用いた実用的論理演算回路の構築

    長谷川剛, 寺部一弥, 中山知信, 坂本利司, 青野正和

    OHM   92 ( 12 ) 10 - 11  2005年

  • 究極的なナノデバイス「原子スイッチ」の開発

    長谷川剛, 寺部一弥, 中山知信, 青野正和

    未来材料   5 ( 6 ) 31 - 37  2005年

  • Three terminal solid-electrolyte nanometer switch

    T Sakamoto, N Banno, N Iguchi, H Kawaura, S Kaeriyama, M Mizuno, K Terabe, T Hasegawa, M Aono

    IEEE INTERNATIONAL ELECTRON DEVICES MEETING 2005, TECHNICAL DIGEST     489 - 492  2005年  [査読有り]

     概要を見る

    We propose a three-terminal solid-electrolyte nanometer switch, where the control gate is separated from the current path. This novel switch resolves the issues arising from large current during switching (&gt; 1mA) in a two-terminal solid-electrolyte switch. We demonstrate that the drain current reversibly switches when a metallic bridge electrochemically forms or dissolves between the source and drain by applying gate voltage. The ON resistance is 200-300 Omega and the ON/OFF current ratio is as high as 10(5). Each state is nonvolatile.

  • Quantized conductance atomic switch

    K Terabe, T Hasegawa, T Nakayama, M Aono

    NATURE   433 ( 7021 ) 47 - 50  2005年01月  [査読有り]

     概要を見る

    A large variety of nanometre-scale devices have been investigated in recent years(1-7) that could overcome the physical and economic limitations of current semiconductor devices(8). To be of technological interest, the energy consumption and fabrication cost of these 'nanodevices' need to be low. Here we report a new type of nanodevice, a quantized conductance atomic switch (QCAS), which satisfies these requirements. The QCAS works by controlling the formation and annihilation of an atomic bridge at the crossing point between two electrodes. The wires are spaced approximately 1 nm apart, and one of the two is a solid electrolyte wire from which the atomic bridges are formed. We demonstrate that such a QCAS can switch between 'on' and 'off ' states at room temperature and in air at a frequency of 1 MHz and at a small operating voltage (600 mV). Basic logic circuits are also easily fabricated by crossing solid electrolyte wires with metal electrodes.

    DOI

  • A nonvolatile programmable solid-electrolyte nanometer switch

    S Kaeriyama, T Sakamoto, H Sunamura, M Mizuno, H Kawaura, T Hasegawa, K Terabe, T Nakayama, M Aono

    IEEE JOURNAL OF SOLID-STATE CIRCUITS   40 ( 1 ) 168 - 176  2005年01月  [査読有り]

     概要を見る

    In this paper, a reconfigurable LSI employing a nonvolatile nanometer-scale switch, NanoBridge, is proposed, and its basic operations are demonstrated. The switch, composed of solid electrolyte copper sulfide, has a &lt;30-nm contact diameter and &lt;100-Ohm on-resistance. Because of its small size, it can be used to create extremely dense field-programmable logic arrays. A 4 x 4 crossbar switch and a 2-input look-up-table circuit are fabricated with 0.18-mum CMOS technology, and operational tests with them have confirmed the switch's potential for use in programmable logic arrays. A 1-kb nonvolatile memory is also presented, and its potential for use as a low-voltage memory device is demonstrated.

    DOI

  • 高性能LSIの機能切り替えを可能にするスイッチ素子

    川浦久雄, 阪本利司, 砂村潤, 帰山隼一, 水野正之, 長谷川剛, 中山知信, 寺部一弥, 青野正和

    工業材料   52 ( 7 ) 46 - 50  2004年

  • 固体電解質を用いたナノスイッチ

    阪本利司, 帰山隼一, 砂村潤, 水野正之, 川浦久雄, 長谷川剛, 中山知信, 寺部一弥, 青野正和

    電子情報通信学会技術研究報告   104   31 - 35  2004年

  • A nonvolatile programmable solid electrolyte nanometer switch

    T Sakamoto, S Kaeriyama, H Sunamura, M Mizuno, H Kawaura, T Hasegawa, K Terabe, T Nakayama, M Aono

    2004 IEEE INTERNATIONAL SOLID-STATE CIRCUITS CONFERENCE, DIGEST OF TECHNICAL PAPERS   47   290 - 291  2004年  [査読有り]

  • Nanometer-scale switches using copper sulfide

    T Sakamoto, H Sunamura, H Kawaura, T Hasegawa, T Nakayama, M Aono

    APPLIED PHYSICS LETTERS   82 ( 18 ) 3032 - 3034  2003年05月  [査読有り]

     概要を見る

    We describe a nanometer-scale switch that uses a copper sulfide film and demonstrate its performance. The switch consists of a copper sulfide film, which is a chalcogenide semiconductor, sandwiched between copper and metal electrodes. Applying a positive or negative voltage to the metal electrode can repeatedly switch its conductance in under 100 mus. Each state can persist without a power supply for months, demonstrating the feasibility of nonvolatile memory with its nanometer scale. While biasing voltages, copper ions can migrate in copper sulfide film and can play an important role in switching. (C) 2003 American Institute of Physics.

    DOI

  • Far-field and near-field optical readings of under-50 nm-sized pits

    S Hosaka, T Shintani, H Koyanagi, K Katoh, T Nishida, T Saiki, T Hasegawa

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS   41 ( 8A ) L884 - L886  2002年08月  [査読有り]

     概要を見る

    In this study, we investigated the limitations of optical reading of very fine pits using conventional optics, immersion lens optics and near-field optics. Using very fine pits &lt; 100 nm in size formed by electron beam writing, a reflection-type depolarization scanning near-field optical microscope (SNOM) read very fine pits &lt; 50 nm in size. On the other hand, far-field optics read fine pits only &gt; 160 nm in size using a lens with a numerical aperture (NA) of 0.95 (17 Gb/in(2)). In addition, an oil immersion lens optics with a NA of 1.4 read fine pits only 100 nm in size (45 Gb/in(2)). Advanced near-field optics is a promising tool for achieving ultrahigh-density optical reading of trillion bits/in(2).

    DOI

  • Formation and disappearance of a nanoscale silver cluster realized by solid electrochemical reaction

    K Terabe, T Nakayama, T Hasegawa, M Aono

    JOURNAL OF APPLIED PHYSICS   91 ( 12 ) 10110 - 10114  2002年06月  [査読有り]

     概要を見る

    We have developed a nanostructuring method using the solid electrochemical reaction induced by a scanning tunneling microscope (STM). This method has some distinctive features that have not previously been obtained by conventional nanostructuring STM methods. The formation and disappearance of the nanostructure are reversible, and the rates can be controlled using STM. These features are realized via a local oxidation/reduction reaction of mobile metal ions in an ionic/electronic mixed conductor. In this study, a crystal of silver sulfide (Ag2S), a mixed conductor, was used as the material for the STM tip. A nanoscale Ag cluster was formed at the apex of the Ag2S tip when a negative bias voltage was applied to the sample. The Ag ions in the Ag2S tip are reduced to Ag atoms by the tunneling electrons from the sample, and the Ag cluster is formed by the precipitation of the Ag atoms at the apex of the tip. The Ag cluster shrank gradually and disappeared when the polarity of the sample bias voltage was switched to positive. Ag atoms in the Ag cluster are oxidized to Ag ions, and the Ag ions redissolve into the Ag2S tip. The formation and disappearance rates of the cluster were controlled by regulating the tunneling current. (C) 2002 American Institute of Physics.

    DOI

  • Ionic/electronic mixed conductor tip of a scanning tunneling microscope as a metal atom source for nanostructuring

    K Terabe, T Nakayama, T Hasegawa, M Aono

    APPLIED PHYSICS LETTERS   80 ( 21 ) 4009 - 4011  2002年05月  [査読有り]

     概要を見る

    Silver sulfide (Ag2S) which has Ag-ionic/electronic mixed conductivity is used for fabricating a tip used for a scanning tunneling microscope. The mixed conductor tip is capable of nanostructuring by depositing Ag atoms continuously on a sample as well as imaging the surface structure. To obtain the surface image, a nanoscale Ag protrusion is formed at an apex of the tip using a local solid electrochemical reaction, working as "a mini-tip." We fabricate a nanoscale line structure on the sample by scanning the Ag2S tip with the protrusion under appropriate bias voltages and tunneling currents. The structuring is thought to be made up of two layers of Ag atoms deposited from the protrusion. (C) 2002 American Institute of Physics.

    DOI

  • Quantum point contact for nano-devices controlled by solid electrochemical reaction

    T. Hasegawa, K. Terabe, T. Nakayama, T. Sakamoto, H. Sunamura, H. Kawaura, M. Aono

    Proc. XVth Int. Cong. on Electron Microscopy, Durban     393 - 394  2002年

  • Quantum point contact switch realized by solid electrochemical reaction

    K. Terabe, T. Hasegawa, T. Nakayama, M. Aono

    Riken Review   37   7 - 8  2001年07月

  • ナノワイヤーの電気伝導

    青野正和, 中山知信, 長谷川剛, 田中啓文, 新ヶ谷義隆, 大川祐司, 桑原裕司, 赤井恵, 寺部一弥

    学術月報   54 ( 10 ) 49 - 55  2001年

  • Quantum Point Contact switch using Solid Electrochemical reaction

    T. Hasegawa, K. Terabe, T. Nakayama, M. Aono

    Extended Abstracts of the 2001 International Conference on Solid State Devices and Materials, Tokyo     564 - 565  2001年

  • Physical and chemical analytical instruments for failure analyses in G-bit devices

    Y Mitsui, F Yano, Y Nakamura, K Kimoto, T Hasegawa, S Kimura, K Asayama

    INTERNATIONAL ELECTRON DEVICES MEETING 1998 - TECHNICAL DIGEST     329 - 332  1998年  [査読有り]

     概要を見る

    The current status and future trend of analytical instruments are discussed. Analytical instruments for failure analyses in sub-1/4 micron dimensions or less, require high spatial resolution and sensitivity at atomic levels. Using new analytical instruments, such as the Nano-prober for electrical characteristics inspection in actual circuits, TEM-EELS for chemical bond analysis of nanometer area and GDS for precise composition analysis, it was found that a SiO2 or TiOx film formed by water from titanic acid (TiOxH2O) produced with titan, water and chlorine, was a cause of high resistivity for a contact (CVD-W/CVD-TiN/Ti/Si) in sub-1/4 micron devices.

    DOI

  • Intrarow diffusion of Au atoms in the Si(111)-(5x2)Au structure

    T Hasegawa, S Hosoki

    PHYSICAL REVIEW B   54 ( 15 ) 10300 - 10303  1996年10月  [査読有り]

     概要を見る

    Intra-row diffusion of Au atoms in the Si(111)-(5x2)Au reconstructed structure has been observed by using high-temperature scanning tunneling microscopy. Loosely bonded Au atoms. which are arranged with 2(n + I)a spacings at room temperature, diffuse in the twofold direction at higher temperatures among adsorbed sites arranged at 2a intervals. These diffusing Au atoms seem to be thr reason there is a nonintegral number of Au atoms in the (5x2) unit cell.

    DOI

  • Dynamic observation of Si-island growth on a Si(111)-7x7 surface by high-temperature scanning tunneling microscopy

    T Hasegawa, W Shimada, H Tochihara, S Hosoki

    JOURNAL OF CRYSTAL GROWTH   166 ( 1-4 ) 314 - 318  1996年09月  [査読有り]

     概要を見る

    Si-island growth on a Si(111)-7 x 7 surface was studied at 350 degrees C in situ using high-temperature scanning tunneling microscopy. At the beginning of growth, deposited Si atoms formed small amorphous clusters within each triangular subunit of the 7 x 7 structure. The amorphous clusters grew, and crystallized islands also appeared as the quantity of deposited Si atoms increased. At the domain boundaries of the 7 x 7 structure, islands tended to begin forming on the unfaulted half of the 7 x 7 structure. These phenomena indicate that cancellation of the stacking fault on the substrate surface dominates island growth.

    DOI

  • STM modification of MoS2 in the nanometer-scale using a gas-solid reaction

    M Kohno, T Doi, T Hasegawa, S Tomimatsu, S Hosoki

    THIN SOLID FILMS   281   588 - 590  1996年08月  [査読有り]

     概要を見る

    We report on the nanometer-scale modification of a MoS2 surface by scanning tunneling microscopy (STM) with an electric field lower than that required for field evaporation by STM. It is known that a Pt-Ir STM tip dissolves H-2 gas into atomic hydrogen which is chemically active. We applied this phenomenon to STM modification to lower the electric field necessary for atom detachment. A Pt-Ir tip was used to dissolve the H-2 gas on the MoS2 surface. The gas-solid reaction enhanced the evaporation of the top-layer sulfur atoms, which were removed at a low electric field of about 2.4 V nm(-1). The present study shows that we can control STM modification well with the same feedback loop as that used for STM observation.

    DOI

  • Stable phase boundaries between the 7x7 and the 5x2 Au structures on a Si(111) surface studied by high-temperature STM

    T Hasegawa, S Hosoki, K Yagi

    SURFACE SCIENCE   355 ( 1-3 ) L295 - L299  1996年06月  [査読有り]

     概要を見る

    Phase boundaries between the 7x7 and the 5x2 Au structures on a Si(111) surface, which were located along the two-fold direction of the 5x2 structure, were dynamically studied using high-temperature scanning tunneling microscopy (STM) during Au deposition at 500 degrees C. Two types of stable phase boundaries were observed depending on the growth direction of the 5x2 domain. The stable phase boundaries had adatoms of the unfaulted half at the edge of the 7x7 side. The formation of an unstable phase boundary was quickly followed by the growth of new rows of the 5x2 structure next to the boundary which formed a stable phase boundary. These results suggest that the stacking fault of the 7x7 structure at a phase boundary is unstable.

    DOI

  • Domain growth of Si(111)-5x2 Au by high-temperature STM

    T Hasegawa, S Hosaka, S Hosoki

    SURFACE SCIENCE   357 ( 1-3 ) 858 - 862  1996年06月  [査読有り]

     概要を見る

    Si(111)-5 x 2 Au reconstruction was studied dynamically at 500 degrees C by high-temperature scanning tunneling microscopy (STM), Transitions of the 5 x 2 domains during growth were observed as invasive erosions of one domain by another. Whenever this occurred, the domain with its 2-fold direction crossing the domain boundary eroded away. This phenomenon suggests that growth in the 2-fold direction has a stronger driving force. Comparison with STM images taken at room temperature shows that the gold atoms seem to diffuse in the 2-fold direction at higher temperatures. The driving force is believed to derive from repulsion between the gold atoms.

    DOI

  • Cu film growth on a Si(111) surface studied by scanning tunneling microscopy

    S Tomimatsu, T Hasegawa, M Kohno, S Hosoki

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   35 ( 6B ) 3730 - 3733  1996年06月  [査読有り]

     概要を見る

    We observed a change in growth mode of Cu, while dynamically observing Cu film growth on a Si(lll)-7 x 7 surface during Cu deposition at room temperature by scanning tunneling microscopy (STM). Initially, Cu atoms were adsorbed mostly on the faulted halves of the 7 x 7 structure. Then, up to about 2 ML coverage, small Cu islands appeared. As the coverage increased from 2 to 3 ML, the growth mode changed into quasi-layer-by-layer growth. With further deposition, 3-D islands having hexagonal terraces grew.

    DOI

  • Fabrication of nanostructures using scanning probe microscopes

    S Hosaka, S Hosoki, T Hasegawa, H Koyanagi, T Shintani, M Miyamoto

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B   13 ( 6 ) 2813 - 2818  1995年11月  [査読有り]

     概要を見る

    We present nanostructure fabrication techniques using field evaporation and local heating in scanning probe microscopes, especially the scanning tunneling microscope (STM), atomic force microscope (AFM), and the scanning near-field optical microscope (SNOM). The detachment of sulfur atoms from the surface of cleaved MoS2 and atomic scale fabrication were demonstrated with a field evaporation in STM. Field evaporation in AFM forms nanometer-sized gold dots on a SiO2/Si substrate. Local heating with SNOM changes a phase of the GeSbTe recording film from amorphous to crystalline, and forms high reflectivity domains 60 nm in diameter. Moreover, we discuss these applications to a semiconductor process and data storage. (C) 1995 American Vacuum Society.

    DOI

  • JUST-ON-SURFACE MAGNETIC FORCE MICROSCOPY

    S HOSAKA, A KIKUKAWA, Y HONDA, T HASEGAWA

    APPLIED PHYSICS LETTERS   65 ( 26 ) 3407 - 3409  1994年12月  [査読有り]

    DOI

  • Initial stages of oxygen adsorption onto a Si(111)-7×7 surface studied by STM

    Tsuyoshi Hasegawa, Makiko Kohno, Sumio Hosaka, Shigeyuki Hosoki

    Surface Science   312 ( 1-2 ) L753 - L756  1994年06月

     概要を見る

    The initial stage of oxygen adsorption onto a Si(111)-7×7 surface has been studied by scanning tunneling microscopy. The substrate was exposed to oxygen under a partial pressure of 1× 10-9 Torr at room temperature during the observation. Dark features, which have been reported as a main channel for oxidation, appeared exclusively in the faulted halves of the DAS structure though bright features appeared in both halves. This difference can be explained by the adsorption site of oxygen. That is, the greater energy difference of the dangling-bonds of adatoms between both halves than that of the back-bonds causes the exclusive appearance of the dark feature, which has an oxygen atom on on-top site in addition to the other in the back-bond. © 1994.

    DOI

  • INITIAL-STAGE OF OXYGEN-ADSORPTION ONTO A SI(111)-7X7 SURFACE STUDIED BY SCANNING-TUNNELING-MICROSCOPY

    T HASEGAWA, M KOHNO, S HOSOKI

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   33 ( 6B ) 3702 - 3705  1994年06月  [査読有り]

     概要を見る

    The initial stage of oxygen adsorption onto a Si(111)-7 x 7 surface has been studied at room temperature by scanning tunneling microscopy. The surface was exposed to oxygen under a partial pressure of 1 x 10(-9) Torr. Initial exposure led to bright and dark features at adatom sites. This dark feature, which was previously reported as a main channel for oxidation, only appeared in the faulted half of the dimer adatom stacking-fault (DAS) structure. The images suggest that the adsorption onto the un-faulted half starts after the faulted half are occupied with oxygen atoms. This clearly indicates that oxygen adsorption occurs at adatom sites with higher energy states.

    DOI

  • DYNAMIC OBSERVATION OF SILICON HOMOEPITAXIAL GROWTH BY HIGH-TEMPERATURE SCANNING-TUNNELING-MICROSCOPY

    T HASEGAWA, M KOHNO, S HOSAKA, S HOSOKI

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B   12 ( 3 ) 2078 - 2081  1994年05月  [査読有り]

     概要を見る

    The dynamic process of Si crystal growth on a Si(111)7X7 surface was studied in situ using high-temperature scanning tunneling microscopy. Si was evaporated onto a Si(111)7X7 surface, kept at 350-degrees-C, and the crystal growth was observed. Both step-flow growth and island growth were observed. In the step-flow growth, the [112BAR] steps became jagged with [112BAR] steps. At the [112BAR] steps, new adatoms appeared in rows along the step edges. In the island growth, the multilayer growth was observed. A rearrangement of adatoms in the first layer was observed when the second layer was formed on the first layer.

    DOI

  • トンネル障壁イメージング(TBI)法によるpoly-Si膜の不純物濃度分布観察

    保坂純男, 相良和彦, 山口宗明, 長谷川剛, 細木茂行

    IONICS   20 ( 9 ) 97 - 102  1994年

  • ULTRAHIGH-VACUUM ATOMIC-FORCE MICROSCOPE USING A PANTOGRAPH INCHWORM MECHANISM

    S HOSAKA, Y HONDA, T. HASEGAWA, T YAMAMOTO, M KONDO

    REVIEW OF SCIENTIFIC INSTRUMENTS   64 ( 12 ) 3524 - 3529  1993年12月  [査読有り]

     概要を見る

    An ultrahigh vacuum atomic force microscope (UHV-AFM) with tunneling current detection has been developed. This microscope uses a new type of pantograph inchworm system. The features of the inchworm system are (i) operation of the clamp in normal clamping mode, (ii) an enlargement of the piezo device stroke for clamper stroke, and (iii) compact system for easy use. Our UHV-AFM has (i) six inchworm movements based on the new mechanism, and (ii) a sharp AFM probe whose tip is machined by a focused ion beam fabrication technique. UHV pressure experiments demonstrate that this system provides a contamination-free surface and can observe atomic resolution AFM images of MoS2 and silicon carbide.

    DOI

  • DYNAMIC OBSERVATION OF SI CRYSTAL-GROWTH ON A SI(111)7X7 SURFACE BY HIGH-TEMPERATURE SCANNING-TUNNELING-MICROSCOPY

    T HASEGAWA, M KOHNO, S HOSAKA, S HOSOKI

    PHYSICAL REVIEW B   48 ( 3 ) 1943 - 1946  1993年07月  [査読有り]

     概要を見る

    The dynamic process of Si crystal growth on a Si(111)7 X 7 surface was studied in situ using high-temperature scanning tunneling microscopy. Si was evaporated onto a Si(111)7 X 7 surface, kept at 350-degrees-C, and the crystal growth was observed. The step-flow growth was observed as the appearance of new adatoms at the step edge. The [112BAR] steps became jagged with [112BAR] steps. At the [112BAR] steps, new adatoms appeared in rows along the step edges.

    DOI

  • 走査型トンネル顕微鏡を用いた表面修飾

    細木茂行, 長谷川剛

    応用物理   62 ( 2 ) 155 - 159  1993年

  • Si(111)の付着金原子による再配列構造

    細木茂行, 長谷川剛

    日本結晶学会誌   35 ( 2 ) 21 - 26  1993年

  • INSITU OBSERVATION OF GOLD ADSORPTION ONTO SI(111)7X7 SURFACE BY SCANNING TUNNELING MICROSCOPY

    T HASEGAWA, S HOSAKA, S HOSOKI

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   31 ( 10B ) L1492 - L1494  1992年10月  [査読有り]

     概要を見る

    Gold adsorption onto a Si(111)7 x 7 surface is studied in situ by Scanning Tunneling Microscopy (STM). Gold is deposited onto the Si(111)7 x 7 surface, kept at 500-degrees-C during the STM observation. The 5 x 2 structure grows at a step edge and expands towards both the higher and lower terraces. Si islands are also formed during the gold deposition. These phenomena are explained by the production and migration of excess Si atoms during the phase transition from the 7 x 7 to the 5 x 2 structure.

    DOI

  • SURFACE MODIFICATION OF MOS2 USING AN STM

    S HOSOKI, S HOSAKA, T HASEGAWA

    APPLIED SURFACE SCIENCE   60-1   643 - 647  1992年08月  [査読有り]

     概要を見る

    Scanning tunneling microscopy is used to modify the surface structure of molybdenum disulfide (MoS2). A natural MoS2 Crystal often has stable point defects. This study shows that surface sulfur atoms are excised by field evaporation and these artificial defects can be used to form characters at room temperature.

    DOI

  • OBSERVATION OF NATURAL OXIDE-GROWTH ON SILICON FACETS USING AN ATOMIC FORCE MICROSCOPE WITH CURRENT MEASUREMENT

    S HOSAKA, H KOYANAGI, T HASEGAWA, S HOSOKI, A HIRAIWA

    JOURNAL OF APPLIED PHYSICS   72 ( 2 ) 688 - 691  1992年07月  [査読有り]

     概要を見る

    Natural oxide growth on silicon facets is observed through an atomic force microscope (AFM) with current measurement. The sample is prepared by means of cleaning and heating a silicon (111) surface with direct electric heating in an ultrahigh vacuum, which creates various facets formed by step bunching. The silicon facets and steps can be observed with the AFM in air. The silicon surface structure and the current distribution can simultaneously be obtained. The results clarify that natural oxide growth on a few special high-index-orientation silicon facets is smaller than that on the other silicon facets ({111}, {110}, {100}, etc.).

    DOI

  • INITIAL-STAGE OF AU ADSORPTION ONTO A SI(111) SURFACE STUDIED BY SCANNING TUNNELING MICROSCOPY

    T HASEGAWA, K TAKATA, S HOSAKA, S HOSOKI

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B   9 ( 2 ) 758 - 760  1991年03月  [査読有り]

     概要を見る

    The initial stage of Au adsorption onto a Si(111) surface (&lt; 0.2 ML) is studied by scanning tunneling microscopy (STM). Au is deposited at room temperature, and then the sample is annealed at 700-degrees-C. At the very early stage Au adsorption, a Au-adsorbed 5 X structure is found not to break a 7 X 7 structure. By increasing the amount of adsorbed Au, the Si substrate itself shows a 5 X structure. Rows of the Au-adsorbed 5 X structure are observed to have grown from the lower side of steps.

    DOI

  • STMによる原子操作の試み

    細木茂行, 保坂純男, 長谷川剛

    表面科学   12 ( 10 ) 623 - 627  1991年

  • DYNAMIC OBSERVATION OF SI(111) SURFACE USING A FAST SCANNING TUNNELING MICROSCOPE

    S HOSAKA, T HASEGAWA, S HOSOKI, K TAKATA

    APPLIED PHYSICS LETTERS   57 ( 2 ) 138 - 140  1990年07月  [査読有り]

    DOI

  • FAST SCANNING TUNNELING MICROSCOPE FOR DYNAMIC OBSERVATION

    S HOSAKA, T HASEGAWA, S HOSOKI, K TAKATA

    REVIEW OF SCIENTIFIC INSTRUMENTS   61 ( 4 ) 1342 - 1343  1990年04月  [査読有り]

    DOI

  • STMを用いたTBI法による不純物濃度分布の観察

    保坂純男, 相良和彦, 長谷川剛, 細木茂行

    Hitachi Scientific Instrument News   55 ( 3 ) 3109 - 3112  1990年

  • TUNNELING BARRIER HEIGHT IMAGING AND POLYCRYSTALLINE SI SURFACE OBSERVATIONS

    S HOSAKA, K SAGARA, T HASEGAWA, K TAKATA, S HOSOKI

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS   8 ( 1 ) 270 - 274  1990年01月  [査読有り]

    DOI

  • AU-INDUCED RECONSTRUCTIONS OF THE SI(111) SURFACE

    T HASEGAWA, K TAKATA, S HOSAKA, S HOSOKI

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS   8 ( 1 ) 241 - 244  1990年01月  [査読有り]

    DOI

  • TUNNELING ACOUSTIC MICROSCOPE

    K TAKATA, J YUGAMI, T HASEGAWA, S HOSAKA, S HOSOKI, T KOMODA

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   28 ( 12 ) L2279 - L2280  1989年12月  [査読有り]

  • TUNNELING ACOUSTIC MICROSCOPE

    K TAKATA, T HASEGAWA, S HOSAKA, S HOSOKI, T KOMODA

    APPLIED PHYSICS LETTERS   55 ( 17 ) 1718 - 1720  1989年10月  [査読有り]

    DOI

  • STMの高性能化と先端プロセスへの応用

    保坂純男, 細木茂行, 長谷川剛, 高田啓二

    真空   32 ( 7 ) 16 - 23  1989年

  • STMによる表面欠陥の観察

    細木茂行, 保坂純男, 高田啓二, 長谷川剛, 野村節生

    表面科学   10 ( 3 ) 156 - 161  1989年

  • EPITAXY OF AU AND AG ON CLEAVED (10, 0) SURFACE OF MOS2

    N IKARASHI, K KOBAYASHI, T HASEGAWA, K YAGI

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS   27 ( 5 ) L750 - L752  1988年05月  [査読有り]

    DOI

  • 走査型トンネル顕微鏡(STM)とその画像

    細木茂行, 保坂純男, 高田啓二, 野村節男, 長谷川剛

    電子情報通信学会誌   88 ( 11 ) 21 - 26  1988年

  • PROFILE AND PLAN-VIEW IMAGING OF RECONSTRUCTED SURFACE-STRUCTURES OF GOLD

    N IKARASHI, K KOBAYASHI, H KOIKE, T. HASEGAWA, K YAGI

    ULTRAMICROSCOPY   26 ( 1-2 ) 195 - 203  1988年  [査読有り]

    DOI

  • ATOMIC RESOLUTION TEM IMAGES OF THE AU(001) RECONSTRUCTED SURFACE

    T HASEGAWA, K KOBAYASHI, N IKARASHI, K TAKAYANAGI, K YAGI

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS   25 ( 5 ) L366 - L368  1986年05月  [査読有り]

    DOI

  • High resolution profile images of the reconstructed structures of Au(001), (110) and (111) surfaces

    T. Hasegawa, N. Ikarashi, K. Kobayashi, K. Takayanagi, K. Yagi

    Proc. XIth Int. Cong. on Electron Microscopy, Kyoto     1345 - 1346  1986年

▼全件表示

書籍等出版物

  • Atomic switch : from invention to practical use and future prospects

    Masakazu Aono, K. Terabe, T. Hasegawa, T. Nakayama, T. Sakamoto, J. K. Gimzewski( 担当: 共編者(共編著者))

    Springer  2020年 ISBN: 9783030348748

  • Resistive switching : From fundamentals of nanoionic redox processes to memristive device applications

    ( 担当: 分担執筆,  担当範囲: Chapter 18 'Atomic Switches', p.515-546)

    Wiley-VCH  2016年03月 ISBN: 3527334173

  • Emerging nanoelectronic devices

    T. Hasegawa, M. Aono( 担当: 分担執筆,  担当範囲: Chapter 19, 'Atomic Switch', p.390-404)

    Wiley  2015年 ISBN: 9781118447741

  • 身のまわりの表面科学

    長谷川剛( 担当: 分担執筆,  担当範囲: 第6章「原子1個を動かす「アトムトランジスタ」とは?」pp.213-215)

    日本表面科学会編、講談社  2015年

  • 「環境・エネルギー材料ハンドブック」、材料編第9章9.1「原子スイッチ材料」、pp. 567-571

    長谷川剛

    オーム社  2011年

  • 'Nanoionics and its device applications’, The Oxford Handbook of NANOSCIENCE AND TECHNOLOGY Vol.3: Applications (A. V. Narlikar &amp; Y. Y. Fu), pp. 294-311

    T. Hasegawa, K. Terabe, T. Sakamoto, M. Aono

    Oxford University Press  2010年

  • 「走査プローブ顕微鏡」、第14章「原子•分子操作」、pp. 412-417.

    大川祐司, 長谷川剛, 青野正和

    共立出版  2009年

  • 「超分子サイエンス&テクノロジー」、第3章・第2節・12「原子スイッチ」

    長谷川剛

    NTS出版  2009年

  • 「ナノプローブ加工技術を用いたナノイオニクス素子の開発」、ナノイオニクス—最新技術とその展望—、pp.268-276

    寺部一弥, 長田実, 長谷川剛

    シーエムシー出版  2008年

  • 「点接触導電体」、ナノテクノロジー大辞典、pp.67-74

    塚本茂, 長谷川剛

    工業調査会  2003年

  • 「原子スイッチ」、ナノテクノロジー大辞典、pp.234-240

    長谷川剛

    工業調査会  2003年

  • 「原子スイッチ」、ナノテクノロジーハンドブック、pp.150-154

    長谷川剛

    オーム社  2003年

  • 「原子スイッチ」、ナノテクノロジー最前線(塚田捷、河津璋)、 pp. 83-87

    青野正和, 寺部一弥, 長谷川剛, 中山知信

    東京教育情報センター  2002年

  • 「STS」、半導体計測評価事典(高柳邦夫、田島道夫、松井純爾)、pp. 331-334、

    細木茂行, 長谷川剛

    サイエンスフォーラム  1994年

▼全件表示

Misc

  • 依頼講演 酸化物ナノ薄膜を用いた原子スイッチ型抵抗変化メモリーとその応用 (シリコン材料・デバイス)

    鶴岡 徹, 長谷川 剛

    電子情報通信学会技術研究報告 = IEICE technical report : 信学技報   114 ( 88 ) 85 - 90  2014年06月

     概要を見る

    酸化物ナノ薄膜中の金属イオン伝導とヘテロ界面の固体電気化学反応を利用した原子スイッチ型抵抗変化メモリーの動作機構解明と機能化に向けた取り組みについて述べる。動作モデルの提案と温度依存性によるモデル妥当性の検証,酸化物中の吸着水の影響などを検討した結果,金属イオンが酸化物ナノ薄膜中でどのように振る舞うかが分かってきた。また,機能化という観点から,原子スイッチの特徴である量子化コンダクタンスとシナプス動作の実現,3端子素子'アトムトランジスタ'への展開についても述べる。

    CiNii

受賞

  • SSDM Award

    2020年09月   'Quantum Point Contact Switch using Solid Electrochemical Reaction'  

    受賞者: T. Hasegawa, K. Terabe, T. Nakayama and M. Aono

  • 第28回つくば賞

    2017年11月   茨城県科学技術振興財団   「原子スイッチの発明と実用化のための研究」  

    受賞者: 寺部一弥, 長谷川剛, 青野正和

  • 第34回(2012年度)応用物理学会優秀論文賞

    2012年08月   応用物理学会   「Volatile/Nonvolatile Dual-Functional Atom Transistor」  

    受賞者: 長谷川剛, 伊藤弥生美, 田中啓文, 日野貴美, 鶴岡徹, 寺部一弥, 宮崎久生, 塚越一仁, 小川琢二, 山口周, 青野正和

  • 物質・材料研究機構理事長賞研究功績賞

    2010年04月   「原子スイッチの発明からその基礎研究ならびに実用化までの顕著な貢献」  

    受賞者: 長谷川剛, 寺部一弥

  • MNC 2008 Award (Most Impressive Presentation)

    2009年11月   ‘Fabrication of Nanostructures Composed of Copper-Phthalocyanine Diacetylene Molecules’  

    受賞者: 大川祐司, 高城大輔, 長谷川剛, 青野正和

  • 第4回 表面科学会会誌賞

    2007年11月   日本表面科学会   「原子スイッチー原子イオンの移動を利用したナノデバイス」  

    受賞者: 寺部一弥, 長谷川剛, 中山知信, 青野正和

  • 文部科学大臣表彰科学技術賞(研究部門)

    2007年04月   「原子スイッチの研究」  

    受賞者: 青野正和, 長谷川剛, 寺部一弥, 中山知信

  • 第13回 高木賞

    2005年03月   未踏科学技術協会インテリジェント材料・システムフォーラム   「ナノイオニクス現象を利用した原子スイッチの開発」  

    受賞者: 寺部一弥, 長谷川剛, 田村拓郎, マニシャクンドゥ, 根岸良太, 梁長浩, 坂本利司, 青野正和

  • 日立製作所・社長技術賞

    2001年   「走査型トンネル顕微鏡を用いた原子操作技術の開発」  

    受賞者: 細木茂行, 保坂純男, 高田啓二, 長谷川剛

  • 精密工学会技術賞

    1991年10月   「高精度STM装置の開発」  

    受賞者: 保坂純男, 細木茂行, 長谷川剛, 高田啓二, 羽崎栄一

▼全件表示

共同研究・競争的資金等の研究課題

  • 超高速・低消費電力ビッグデータ処理を実現・利活用する脳型推論集積システムの研究開発

    NEDO  IoT推進のための横断技術開発プロジェクト 研究代表者:秋永広幸

    研究期間:

    2016年06月
    -
    2021年09月
     

  • 原子圧縮制御型分子シナプス素子の開発

    日本学術振興会  科学研究費補助金 基盤研究(B)

    研究期間:

    2017年04月
    -
    2020年03月
     

     概要を見る

    ディープラーニングでは、シナプスの結合荷重を学習によって変化させることで脳型の情報処理を行っている。シナプス素子の可変抵抗域が大きいほど、より高度で複雑な情報処理が可能となる。本研究では、電極から析出させる金属原子で電極間に挟んだ分子を歪ませることで、連続的に大きな抵抗変化を示す新しいシナプス動作素子の実現を目指している。初年度となる平成29年度は、C60分子を測定対象として、走査型トンネル顕微鏡(STM)の探針の移動(押し付け)によるC60分子の圧縮ならびにそれに伴う電子状態変化計測を行った。その結果、圧縮に起因するバンドギャップの縮みなどC60分子の電子状態変化が観測できた。続いて、電圧印加によって銀原子の析出が可能な硫化銀をSTM探針として用い、探針位置を固定した状態で電圧・電流特性測定を行った。その結果、銀原子の析出する電圧条件でのみC60分子の電子状態が変化した。H30年度は、より清浄な試料の作成と装置改良による観察の高精度化を行った。その結果、金属原子析出量と電子状態変化との定性的な関係を得ることに成功した。金属原子の析出に必要とされるエネルギーおよび観測された電子状態変化に必要なC60分子の圧縮力の理論的考察を行ったところ、ほぼ一致した。これは、当初期待した通りの現象が起こっていることを示唆しており、最終目標にむけて研究が大きく前進した。また、以上の成果を纏めて、国際会議で発表するとともに、論文投稿も行った。本研究の最終目標である「原子圧縮制御型分子シナプス素子」の実現に最も不可欠な、電圧印加のみによるC60分子の圧縮ならびにその電子状態変化の観測に成功した。分担研究者との連携により、現象の定性的な理解に繋がる実験データの取得にも成功したことから、順調に進んでいると判断できる。当初計画に則り、C60分子の圧縮による電子状態変化の詳細を、走査トンネル分光法を用いることで明らかにする。特に、圧縮量と電子状態変化との定量的な関係を明らかにすることに主眼を置いた実験を行う。圧縮量を精密に制御できる走査型トンネル顕微鏡(STM)、圧縮力を精密に制御できる原子間力顕微鏡(AFM)の双方を用いた実験を行い、それぞれで得られた電流電圧測定結果を比較することにより、電気的に圧縮可能な(集積化可能な)原子圧縮制御型分子シナプス素子の学術的基盤を確立する。この精密な実験には、精密な測定手法の開発と清浄な表面を有する試料が不可欠であり、最終年度となるH31年度も上記測定と併せて装置改良と試料作製に関する実験を継続して行っていく

  • 分子被覆硫化銀微粒子による綱引きモデル型情報処理の基本動作実証

    日本学術振興会  科学研究費補助金 新学術領域研究(研究領域提案型)

    研究期間:

    2016年04月
    -
    2018年03月
     

     概要を見る

    本研究では、「硫化銀微粒子から成長可能な銀ワイヤーの高さには限界がある」という前回の公募研究の成果を用いて、集積可能な固体材料による「綱引きモデル」に基づく情報処理システムの動作実証を行うことを目的としている。最終年度となる平成29年度は、分子膜をギャップ層とする素子構造の作製とその動作特性評価に注力した。なお、綱引き動作に基づく銀ナノワイヤーの成長と収縮はこの素子構造では分子膜中で起こる。分子膜中を成長する銀ナノワイヤーの動作を詳細に観察した結果、入力電圧の大きさや頻度に依存した短期記憶や長期記憶に基づく素子動作、ならびに確率動作が起こっていることが判明した。これらは、硫化銀内部の銀イオン分布の時間変化に加えて、分子膜中における銀ワイヤーの成長が容易に起こり、かつ、その崩壊現象も期待通りに起こっていることを示している。これらの現象を用いた情報処理の実現には素子の集積化が不可欠であることから、集積化が容易な縦型素子構造の開発にも取り組んだ。具体的には、銀ナノワイヤーの成長源となる固体電解質電極として、集積化に適した酸化タンタルと銀の共蒸着膜を用い、その上下に分子膜と対向金属電極を配置した素子を作製した。その結果、それぞれの分子膜中での銀ナノワイヤーの成長と収縮の制御には成功したが、綱引き動作の実現には至らなかった。この原因は、固体電解質電極のサイズと分子膜厚の最適化が為されていなかったことにあると考えられる。今後、素子サイズならびに素子作製プロセスの最適化を行うことで、研究をさらに発展させて行く予定である。29年度が最終年度であるため、記入しない。29年度が最終年度であるため、記入しない

  • 電気化学ポテンシャルを利用した原子単位でのドーパント数制御技術の開発

    研究期間:

    2016年04月
    -
    2018年03月
     

     概要を見る

    本研究では、原子単位でのドーパント制御技術の確立を目指して、電気化学ポテンシャルを利用したナノ構造体からの不純物原子の取り出し・注入に関する研究を行った。モデル材料である硫化銀ならびに金属酸化物である酸化タンタルを用いてナノドットを形成し、走査型トンネル顕微鏡を用いた電位制御により、不純物原子の取り出しや注入が可能であることを実証した。さらに、取り出したドーパント原子の量に依存した伝導度変化の測定にも成功し、提案した手法の有用性と汎用性を明らかにした

  • 分子被覆硫化銀微粒子による綱引きモデル型情報処理の基本動作実証

    日本学術振興会  科学研究費補助金 新学術領域研究(研究領域提案型)

    研究期間:

    2016年04月
    -
    2018年03月
     

     概要を見る

    本研究では、「硫化銀微粒子から成長可能な銀ワイヤーの高さには限界がある」という前回の公募研究の成果を用いて、集積可能な固体材料による「綱引きモデル」に基づく情報処理システムの動作実証を行うことを目的としている。最終年度となる平成29年度は、分子膜をギャップ層とする素子構造の作製とその動作特性評価に注力した。なお、綱引き動作に基づく銀ナノワイヤーの成長と収縮はこの素子構造では分子膜中で起こる。分子膜中を成長する銀ナノワイヤーの動作を詳細に観察した結果、入力電圧の大きさや頻度に依存した短期記憶や長期記憶に基づく素子動作、ならびに確率動作が起こっていることが判明した。これらは、硫化銀内部の銀イオン分布の時間変化に加えて、分子膜中における銀ワイヤーの成長が容易に起こり、かつ、その崩壊現象も期待通りに起こっていることを示している。これらの現象を用いた情報処理の実現には素子の集積化が不可欠であることから、集積化が容易な縦型素子構造の開発にも取り組んだ。具体的には、銀ナノワイヤーの成長源となる固体電解質電極として、集積化に適した酸化タンタルと銀の共蒸着膜を用い、その上下に分子膜と対向金属電極を配置した素子を作製した。その結果、それぞれの分子膜中での銀ナノワイヤーの成長と収縮の制御には成功したが、綱引き動作の実現には至らなかった。この原因は、固体電解質電極のサイズと分子膜厚の最適化が為されていなかったことにあると考えられる。今後、素子サイズならびに素子作製プロセスの最適化を行うことで、研究をさらに発展させて行く予定である。29年度が最終年度であるため、記入しない。29年度が最終年度であるため、記入しない

  • ビッグデータ処理を加速・利活用する脳型推論システムの研究開発

    NEDO  エネルギー・環境新技術先導プログラム 研究代表者:秋永広幸

    研究期間:

    2016年01月
    -
    2017年01月
     

  • 分子・原子の協働による新しい情報処理システム

    研究期間:

    2014年04月
    -
    2016年03月
     

     概要を見る

    本研究では、分子機能を利用した単一原子輸送現象の実現と、それを利用した分子と原子の協働による新しい情報処理システムの開発を行う。具体的には、最近、光機能性分子をスイッチング動作に利用することで、原子単位での金属原子析出の制御が可能であることを示唆する結果が得られていることから、本研究では、1)電位制御による原子単位での析出を実現、続いて、2)分子機能を利用した原子単位での析出と輸送の制御を行う。この分子と原子の協働現象を利用することで、信号の揺らぎやバラツキを積極的に利用して動作するネットワーク型の新しい情報処理システムを構築する。平成27年度は、ナノドットからの析出可能な金属原子数が印加電圧とナノドットのサイズに依存することを明らかにした昨年度の成果を利用して、綱引きモデルに基づくネットワーク形成の可能性を検証する実験を行った。ひとつのナノドットに複数の電極を対向して配置することは現在の微細加工技術では困難があるため、サブミクロンサイズの硫化銀アイランドに対して、その左右に金属電極を配置した構造で動作実証を行うこととした。硫化銀アイランドのサイズが大きいため、伸張可能な金属フィラメントの長さも長くなる。このため、硫化銀アイランドと対向金属電極間の距離を数百ナノメートルに設定し、かつ、電極間に金属フィラメントの伸張を可能とする固体電解質ポリマーを配置した。実験の結果、硫化銀アイランドから右に配置した対向電極にフィラメントが伸張した場合、左に配置した対向電極に向かって伸びていたフィラメントが縮む現象が観測された。これはまさに左右の対向電極間における綱引き動作であり、今年度の目標を達成することができた。得られた成果を基に論文を執筆、投稿した。27年度が最終年度であるため、記入しない。27年度が最終年度であるため、記入しない

  • 原子移動型素子を用いたニューロン動作に関する研究

    研究期間:

    2012年04月
    -
    2015年03月
     

     概要を見る

    原子/イオンの移動とその酸化・還元反応を制御して動作する原子移動型素子を基盤技術として用い、脳型コンピューターを実現する上で不可欠なニューロン動作素子の開発を目指した。その結果、ニューロン動作を特徴づける3つの基本現象、「入力信号の蓄積」、「発火」、「発火後の自己減衰」の実現に成功した。今後、シナプス動作素子との集積化を行うことで、本成果が脳型コンピューターの実現に寄与することが期待される

  • 3端子型原子移動不揮発性デバイス「アトムトランジスター」の開発

    科学技術振興機構  戦略的創造研究推進事業(CREST)

    研究期間:

    2009年10月
    -
    2015年03月
     

  • 不揮発性アトムトランジスタを用いた低消費ロジックシステム

    科学技術振興機構  戦略的国際科学技術協力推進事業 日英研究交流

    研究期間:

    2011年05月
    -
    2014年03月
     

  • 固体電解質原子スイッチ動作における電荷移動と交換に関する研究

    科学技術振興機構  戦略的国際科学技術協力推進事業 日独研究交流

    研究期間:

    2008年10月
    -
    2012年03月
     

  • 原子移動型素子を用いたニューロン動作に関する研究

    村田学術振興財団  研究助成

    研究期間:

    2011年
    -
    2012年
     

  • 原子スイッチを用いた次世代プログラマブル論理演算デバイスの開発

    文部科学省  キーテクノロジー研究開発の推進「ナノテクノロジー・材料を中心とした癒合新分野研究開発」 研究代表者:青野正和

    研究期間:

    2005年08月
    -
    2010年03月
     

  • ナノ量子導体アレープロジェクト

    科学技術振興機構  戦略的創造研究推進事業 ICORPタイプ 研究代表者:青野正和

    研究期間:

    2003年03月
    -
    2008年03月
     

  • 固体電解質ナノスイッチを用いた学習機能回路の研究

    三菱財団自然科学研究助成 

    研究期間:

    2005年
    -
    2006年
     

  • 新しい量子効果スイッチの機能素子化

    科学技術振興機構  基礎的研究発展推進事業(SORST) 研究代表者:青野正和

    研究期間:

    2001年04月
    -
    2005年03月
     

  • 人工ナノ構造の機能探索プロジェクト

    新技術事業団  戦略的基礎研究推進事業(CREST) 研究代表者:青野正和

    研究期間:

    1999年04月
    -
    2000年03月
     

  • ナノプローブ加工技術を用いたナノイオニクス素子の開発

     概要を見る

    ナノスケールでのイオンの移動を制御することによって生じるナノ現象の探索とそれを利用した新規ナノデバイスの開発を目指した。初めに、多孔質アルミナをテンプレートに用いた電気化学堆積法によりイオン伝導体ナノワイヤ結晶の作製技術を開発した。次に、ナノプローブ技術を用いて電気的特性やナノ構造の評価を行い、ユニークなナノ現象を見出した。このナノワイヤ結晶の応用展開として高密度ナノスイッチ素子および原子付与のためのナノプローブを開発した

  • 原子スイッチの多機能化に関する研究

     概要を見る

    固体電気化学反応を用いて電極間での金属原子架橋の形成と消滅を制御して動作する原子スイッチの多機能化を目指した。その結果、一定の入力信号が到達するまでは素子内部に入力情報を蓄え、一定の入力信号が到達して初めて出力動作をする学習機能や、電源オフと同時に初期状態に戻る揮発性動作と、電源オフでも状態を保持する不揮発性動作の選択動作の開発に成功した。これらは脳型コンピューターなどの開発への貢献が期待できる

▼全件表示

特定課題研究

  • 拡散障壁上昇による動作電圧の低減と保持特性の向上の同時実現

    2021年  

     概要を見る

    デバイス動作電圧の低減は、省エネルギー化を実現する上で最も有効な手段である。例えば抵抗変化メモリでは、イオン拡散障壁の小さい材料系を用いることで動作電圧を低減できる。ただし、拡散障壁を下げ過ぎると熱エネルギーによる誤動作が発生してしまう。本研究ではこの常識を覆し、イオン拡散障壁を逆に高くすることで動作電圧を低減できることの原理実証に取り組んだ。具体的には、金属フィラメントの形成と消滅を制御して動作する原子スイッチを用いることで、拡散障壁を高くすればオフ動作時にイオンが遠くまで熱拡散しないこと、それゆえ次の動作時の電圧が小さくなることを実験的および理論的に明らかにした。

  • 原子圧縮制御型分子シナプス素子の開発

    2020年  

     概要を見る

    素子機能を利用したスパイクタイミング依存可塑性とその応用に関する研究を行った。金属イオンの拡散とその酸化還元反応を利用してナノギャップ中に金属原子を析出させるギャップ型原子スイッチでは、印加電圧のオンオフに伴い電極内の金属イオンが行きつ戻りつする。電極表面直下の金属イオン濃度が臨界値に達すると金属原子の析出が始まることから、パルス電圧印加間隔に依存して析出量が決まることが期待された。この特性を利用すれば生体シナプスにおける特徴的な機能「スパイクタイミング依存可塑性」を再現できると考え、シナプス素子構造を試作し、パルス印加実験を行った。その結果、基本的な動作実証に成功した。

  • 幅広い抵抗領域で連続的に変化するシナプス動作素子の開発

    2016年  

     概要を見る

    金属酸化物系材料を主材料とするギャップ型原子スイッチを実現し、半導体回路との集積化を可能とすることで、脳型情報処理技術の飛躍的な発展に資することを目的として研究を行った。金属酸化物として酸化タンタルを用い、析出・固溶金属として銀および銅を用いて試料を作製した。原子間力顕微鏡を用いてスイッチング動作の基本現象である金属原子の析出と固溶の制御が可能であることを確認した。さらに、ギャップ層として有機分子薄膜を用いて素子構造を作製し、その素子動作の実証実験を行った。その結果、硫化物を用いた従来型のギャップ型原子スイッチと同等の素子動作を実現することができた。以上により、本研究の目的をすべて達成することができた。

  • 単一イオン輸送制御とその情報処理応用に関する基礎研究

    2015年  

     概要を見る

    本研究では、単一イオン輸送制御とその情報処理応用を目指して、ナノ球リソグラフィーを用いた固体電解質ナノドットの作製と、同ナノドットからのイオン取り出し実験を行った。その結果、電位制御によるイオン取り出しとその輸送が可能であることを示唆する実験結果が得られた。

  • 単一イオン輸送制御とその情報処理応用に関する基礎研究

    2015年  

     概要を見る

    本研究では、単一イオン輸送制御とその情報処理応用を目指して、イオンの供給源となるナノドットの作製手法の開発を行った。具体的には、ナノ球リソグラフィー法を用いたイオン伝導体ナノドットを作製するプロセスを確立した。

 

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