Hiroshi Shimada
| Department of Engineering Science | Professor |
| Cluster III (Fundamental Science and Engineering) | Professor |
- Profile:
1997年10月－2002年09月 科学技術振興事業団 戦略的基礎研究事業 研究員
1998年08月－1999年01月 文部省在外研究員（Chalmers University of Technology (Sweden)）
1999年06月－1999年08月 Chalmers University of Technology (Sweden) 客員研究員
2003年04月－2007年03月 電気通信大学COE「コヒーレント光科学の展開」事業推進担当者
Researcher Information
Research Keyword
Field Of Study
Career
- 01 Apr. 2018
電気通信大学 大学院, 情報理工学研究科, 教授 - 01 Apr. 2010 - 31 Mar. 2018
電気通信大学 大学院, 情報理工学研究科, 准教授 - 01 Apr. 2007 - 31 Mar. 2010
電気通信大学, 電気通信学部, 准教授 - 01 Apr. 2003 - 31 Mar. 2006
電気通信大学, 電気通信学部, 助教授 - 01 Apr. 1989 - 31 Mar. 2003
東京大学, 低温センター, 助手 - Jun. 1999 - Aug. 1999
Chalmers University of Technology, 客員研究員 - Sep. 1998 - Jan. 1999
Chalmers University of Technology, 客員研究員
Educational Background
Research Activity Information
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Paper
- Asymmetry of the Breakdown near Hot Spots in the Quantum Hall Regime in a Specially Shaped GaAs/AlGaAs Sample
Hiroshi Hirai; Hiroshi Shimada
Journal of the Physical Society of Japan, 93, 044709, Mar. 2024, Peer-reviwed
Scientific journal, English - Evaluation of True Random Number Sequences Generated by Utilizing Timing Jitters in Superconducting Integrated Circuits
Kenta Sato; Naonori Sega; Hiroshi Shimada; Yoshinao Mizugaki
Journal of Physics: Conference Series, IOP Publishing, 2545, 1, 012022-012022, 01 Jul. 2023, Abstract
A Hardware Random Number Generator (HRNG), which generates true random number sequences, is studied. In superconducting Single Flux Quantum (SFQ) circuitry, HRNGs that utilized timing jitters in trigger signals have been demonstrated. In this paper, we propose an HRNG with two oscillators to enhance stability against variation of oscillator frequencies. We investigate the characteristics of random numbers generated with the proposed HRNG not only by numerical simulation but also by experiments using Nb test circuits. In the numerical simulation, the probability of “1” in random number sequences has a local minimum of “1” output probability at conditions where fclk (the clock oscillator frequency) and fgate (the gate oscillator frequency) are approximately equal (fclk ≈ fgate) for fclk ≤ 60 GHz. It is also found that pass rates for the FIPS140-2 random number tests are little affected by variations of fclk at fgate = 69.2 GHz. The random number generation rate for fclk = 60 GHz and fgate = 43 GHz reaches 3.98 GHz. In experimental measurements, random numbers of 1 Mbits generated by a test circuit pass the SP800-22 random number tests at fclk = 48.79 GHz and fgate = 19.81 GHz.
Scientific journal - マイクロコントローラを利用した金ナノ粒子誘電泳動の自動停止機構
浦江哲也; 島田 宏; 水柿義直
電子情報通信学会 和文論文誌C, 電子情報通信学会, J105-C, 11, 339-341, 01 Nov. 2022, Peer-reviwed
Scientific journal, Japanese - Sensitive phonon detection using a single Cooper-pair transistor
Jutarat Tanarom; Takuma Watanabe; Yoshinao Mizugaki; Hiroshi Shimada
Applied Physics Express, The Japan Society of Applied Physics, 15, 21 Apr. 2022, Peer-reviwed
Scientific journal, English - Detection of phonons with a single Cooper-pair transistor
Jutarat Tanarom; Yoshinao Mizugaki; Hiroshi Shimada
IEICE Technical Report, 電子情報通信学会, SCE2021-3, 10-13, Aug. 2021
Scientific journal, Japanese - Enhanced Operation Frequencies of Bipolar Double-Flux-Quantum Amplifiers Fabricated Using 10-kA/cm2 Nb/AlOx/Nb Integration Process
Y. Somei; H. Shimada; Y. Mizugaki
Japanese Journal of Applied Physics, Japan Society of Applied Physics, Institute of Physics, 60, 7, 073001-1-073001-7, 01 Jul. 2021, Peer-reviwed
Scientific journal, English - Scalability of supercurrent modulable with single Cooper-pair transistors connected in parallel
Jutarat Tanarom; Yoshinao Mizugaki; Hiroshi Shimada
Japanese Journal of Applied Physics, Japan Society of Applied Physics, 60, 074003-1-074003-7, 24 Jun. 2021, Peer-reviwed
Scientific journal, English - Nanoscale Tunnel Junctions and Metallic Single-Electron Transistors via Shadow Evaporation and In Situ Atomic Layer Deposition of Tunnel Barriers
H. Shimada; T. Koike; K. Kikkawa; H. Konno; N. Ito; R. Kobayashi; Y. Mizugaki; K. Kanomata; M. Miura; F. Hirose
ACS Applied Nano Materials, American Chemical Society, 4, 2, 1401-1410, 12 Feb. 2021, Peer-reviwed
Scientific journal, English - Rescaling of applied oscillating voltages in small Josephson junctions
Godwill Mbiti Kanyolo; Hiroshi Shimada
Journal of Physics Communications, IOP Publishing, 4, 10, 105007-1-105007-29, 12 Oct. 2020, Peer-reviwed
Scientific journal, English - Current Distributions in the Vicinity of Electrical Contacts with a Two Dimensional Electron Gas under High Magnetic Fields
Hiroshi Hirai; Hiroshi Shimada
Journal of Physical Society of Japan, Physical Society of Japan, 89, 11, 114701-1-114701-7, 02 Oct. 2020, Peer-reviwed
Scientific journal, English - Design and Error-Rate Evaluation of RSFQ Logic Gates Comprising a Toggle Storage Loop
K. Yamazaki; H. Shimada; Y. Mizugaki
Journal of Physics: Conference Series, IOP, 1590, 012042-1-012042-7, 31 Jul. 2020, Peer-reviwed
International conference proceedings, English - Cooper‑Pair Tunneling in Small Josephson Junction Arrays Under Radio‑Frequency Irradiation
G. M. Kanyolo; K. Takeda; Y. Mizugaki; T. Kato; H. Shimada
Journal of Low Temperature Physics, Springer, 201, 3-4, 269-284, 13 Jun. 2020, Peer-reviwed
Scientific journal, English - Design and Operation of Distributed Double-SQUID Amplifier for RSFQ Circuits
K. Higuchi; H. Shimada; Y. Mizugaki
Journal of Physics: Conference Series, IOP, 1293, 012060-1-012060-7, 15 Oct. 2019, Peer-reviwed
International conference proceedings, English - 微小Josephson接合列の輻射検出器としての利用性の評価
鈴木俊貴; カニョロ ゴドゥウィリ ビティ; 西垣宏志; 水柿義直; 島田 宏
信学技報, 119, SCE2019-11, 02 Aug. 2019
Scientific journal, Japanese - Evaluation of inter-particle distance of gold nanoparticles dispersed on silane-treated substrates to fabricate dithiol-connected arrays
T. Yagai; K. Matsumoto; M. Moriyabashi; M. Moriya; H. Shimada; A. Hirano-Iwata; F. Hirose; Y. Mizugaki
Japanese Journal of Applied Physics, 58, SD, SDDF09-1-SDDF09-6, Jun. 2019, Peer-reviwed, © 2019 The Japan Society of Applied Physics. Small tunnel junctions using gold nanoparticles (GNPs) as electrodes have been studied to fabricate single-electron devices. GNPs connected via dithiol molecules have been used as small tunnel junctions, and a two-stage dispersion method was used to fabricate dithiol-connected GNP arrays. In this process, the GNPs were fixed on silane-treated substrates by immersing the substrate in a colloidal gold solution. For fabricating dithiol-connected arrays, the inter-particle distance of the dispersed GNPs must be smaller than the GNP diameter. Consequently, the inter-particle distance controlled by the immersion time (T IM1) was evaluated. For T IM1 values exceeding 8 h, the inter-particle distance was less than the GNP diameter. A second dispersion of GNPs after treating samples with dithiol realized particle connections. For the GNP arrays produced with T IM1 values greater than 8 h, the I-V characteristics were measured at 77 K, and the yield of devices exhibiting nonlinear I-V curves was 23%.
Scientific journal, English - 1000-fold double-flux-quantum voltage multiplier employing directional propagation of flux quanta through asymmetrically-damped junction branches
Y. Mizugaki; Y. Arai; T. Watanabe; H. Shimada
IEEE Transactions on Applied Superconductivity, IEEE, 29, 5, 1400105-1-1400105-5, 28 Jan. 2019, Peer-reviwed
Scientific journal, English - Single-electron charging effects observed in arrays of gold nanoparticles formed by dielectrophoresis between SAM-coated electrodes
M. Moribayashi; T. Yagai; M. Moriya; H. Shimada; A. Hirano-Iwata; F. Hirose; Y. Mizugaki
AIP Conference Proceedings, 2067, 020019-1-020019-8, Jan. 2019, Peer-reviwed, © 2019 Author(s). In the fabrication of single-electron (SE) devices with gold nanoparticles (GNPs), one of the technical challenges is the arrangement of GNPs into a gap between electrodes. We employed dielectrophoresis (DEP) for the GNP arrangement because it allowed flexible fabrication conditions. When we tried to arrange GNPs into a gap between electrodes, we often had an excessive current during DEP, which resulted in poor fabrication yields. It suggested that the Joule heat generated by the excessive current could break or fused arrays of GNPs when the electrodes were bridged through the arrays. In order to solve this problem, we coated the electrode surfaces with a self-assembled monolayer (SAM) of dithiol, by which high resistance between GNPs and electrodes was realized. That is, suppression of excess currents and improvement of fabrication yield were confirmed. We also demonstrated that a sample device fabricated by using this method exhibited not only the Coulomb blockade but also the Coulomb oscillation.
International conference proceedings - Numerical simulation of single-electron tunneling in random arrays of small tunnel junctions formed by percolation of conductive nanoparticles
Y. Mizugaki; H. Shimada; A. Hirano-Iwata; F. Hirose
IEICE Transactions on Electronics, E101-C, 10, 836-839, Oct. 2018, Peer-reviwed, Copyright © 2018 The Institute of Electronics, Information and Communication Engineers. We numerically simulated electrical properties, i.e., the resistance and Coulomb blockade threshold, of randomly-placed conductive nanoparticles. In simulation, tunnel junctions were assumed to be formed between neighboring particle-particle and particle-electrode connections. On a plane of triangle 100 × 100 grids, three electrodes, the drain, source, and gate, were defined. After random placements of conductive particles, the connection between the drain and source electrodes were evaluated with keeping the gate electrode disconnected. The resistance was obtained by use of a SPICE-like simulator, whereas the Coulomb blockade threshold was determined from the current-voltage characteristics simulated using a Monte-Carlo simulator. Strong linear correlation between the resistance and threshold voltage was confirmed, which agreed with results for uniform one-dimensional arrays.
Scientific journal - One-dimensional array of small tunnel junctions fabricated using 30-nm-diameter gold nanoparticles placed in a 140-nm-wide resist groove
Yoshinao Mizugaki; Kazuhiko Matsumoto; Masataka Moriya; Hiroshi Shimada; Ayumi Hirano-Iwata; Fumihiko Hirose
Japanese Journal of Applied Physics, 57, 9, 098006-1-098006-3, Aug. 2018, Peer-reviwed, © 2018 The Japan Society of Applied Physics. We present percolative arrays of gold nanoparticles (NPs) formed in a resist groove. To enhance the connection probability, the width of the resist groove (140 nm) was designed to be approximately five times larger than the diameter of gold NPs (30 nm). Two-stage deposition of gold NPs was employed to form bridge connections between the source and drain electrodes. Dithiol molecules coated on surfaces of gold NPs worked as tunnel barriers. 5 of 12 samples exhibited Coulomb blockade characteristics, in one of which the gate response was confirmed.
Scientific journal, English - Double-Flux-Quantum Amplifier with a Single-Flux-Biasing Line
Y. Arai; T. Watanabe; K. Higuchi; H. Shimada; Y. Mizugaki
Journal of Physics: Conference Series, IOP, 1054, 012062-1-012062-8, Jul. 2018, Peer-reviwed
International conference proceedings, English - Magnetoresistance in single-electron transistors comprising a superconducting island with ferromagnetic leads
Yoshinao Mizugaki; Masashi Takiguchi; Nobuyuki Tamura; Hiroshi Shimada
Journal of Physics: Conference Series, Institute of Physics Publishing, 969, 1, 012154-1-012154-6, 19 Apr. 2018, Peer-reviwed, We report electric and magnetic field responses of single-electron transistors (SETs) comprising a superconducting island with ferromagnetic (FM) leads. We fabricated two SETs, one of which had relatively high resistance and the other had relatively low resistance. The SETs had two states for the gate charge: SET-ON or SET-OFF. They also had two states for the FM lead magnetization: parallel (P) or anti-parallel (AP) configuration. Current-voltage characteristics of four SET states ("P &
SET-ON," "P &
SET-OFF," "AP &
SET-ON," and "AP &
SET-OFF") were measured at approximately 0.1 K in a compact dilution refrigerator. Magnetoresistance ratio (MRR) values were obtained for the SET-ON and SET-OFF states, respectively. The higher-resistance SET1 exhibited positive MRR values for all measured bias voltages. The MRR enhancement was confirmed for the SET-OFF state, which agreed well with the co-Tunneling model. The lower-resistance SET2, on the other hand, exhibited negative and positive MRR values for higher and lower bias voltage conditions, respectively. The bias voltage for the MRR polarity reversal was changed by the gate voltage. It was also confirmed that the co-Tunneling model was partially valid for negative MRR values.
International conference proceedings, English - Thermally-fluctuated single-flux-quantum pulse intervals reflected in input-output characteristics of a double-flux-quantum amplifier
Yoshinao Mizugaki; Yoshiaki Urai; Hiroshi Shimada
Journal of Physics: Conference Series, Institute of Physics Publishing, 871, 1, 012066-1-012066-6, 26 Jul. 2017, Peer-reviwed, A double-flux-quantum amplifier (DFQA) is a voltage multiplier of quantum accuracy, which we have employed at the final stage of a single-flux-quantum (SFQ) digital-to-analog converter (DAC). We recently found that experimental input-output (IO) characteristics of DFQAs were always slightly different from numerical results assuming ideally-periodic SFQ pulse trains. That is, experimental IO characteristics obtained using an over-biasing method were gradually deteriorated near their maximum operation voltages. Numerical simulation including the over-biasing method at a finite temperature suggested that the difference was likely to be attributed to thermally-fluctuated intervals of input SFQ pulses.
International conference proceedings, English - Single-Flux-Quantum Bipolar Digital-to-Analog Converter Comprising Polarity-Switchable Double-Flux-Quantum Amplifier
Yoshinao Mizugaki; Tomoki Watanabe; Hiroshi Shimada
IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 27, 4, 1400104-1-1400104-4, Jun. 2017, Peer-reviwed, We present a single-flux-quantum (SFQ)-based digital-to-analog converter (DAC) generating bipolar output voltages, in which the key component is a polarity-switchable double-flux-quantum amplifier (PS-DFQA). The DAC comprised a dc/SFQ converter, an 8-bit variable pulse-number multiplier (PNM), and a +/- 8-fold PS-DFQA integrated on a single chip. SFQ pulse-frequency modulation was employed to realize variable output voltage amplitude, for which the multiplication factor of the variable-PNM was controlled by a commercial data generator situated at room temperature. The variable-PNM realized 8-bit resolution with a multiplication factor between 0 and 255. Bias currents fed to the +8-fold PS-DFQA were polarity switched in synchronization with the digital code for the variable-PNM. The whole circuits including I/O elements were designed using SFQ cell libraries, and fabricated using a niobium integration process. Sinusoidal bipolar voltage waveform of 0.38 mV(pp) was demonstrated using a reference signal source of 43.94 MHz.
Scientific journal, English - Sharp Switching Characteristics of Single Electron Transistor with Discretized Charge Input
Masashi Takiguchi; Hiroshi Shimada; Yoshinao Mizugaki
APPLIED SCIENCES-BASEL, MDPI AG, 6, 8, 214-1-214-8, Aug. 2016, Peer-reviwed, For the low-power consumption analog and digital circuit applications based on a single-electron transistor, enhancement of its switching performance is required. Our previous works analytically and numerically demonstrated that a discretized charge input device, which comprised a tunnel junction and two capacitors, improved the gain characteristics of single-electron devices. We report the design and fabrication of an aluminum-based single-electron transistor having the discretized charge input function. Flat-plate and interdigital geometries were employed for adjusting capacitances of grounded and the coupling capacitors. The sample exhibited clear switching on input-output characteristics at the finite temperature.
Scientific journal, English - Bloch Oscillation in a One-Dimensional Array of Small Josephson Junctions
Hiroshi Shimada; Shunsuke Katori; Srinivas Gandrothula; Tomoaki Deguchi; Yoshinao Mizugaki
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 85, 7, 074706-1-074706-6, Jul. 2016, Peer-reviwed, A distinct Bloch nose was demonstrated in the current-voltage characteristics of a one-dimensional array of 20 small Josephson junctions. Arrays of direct-current superconducting quantum interference device (dc-SQUID) structures were used as leads to the array of junctions, and the environmental impedance was tuned with a magnetic field. The observed Bloch nose had a negative differential resistance of its magnitude of as large as 14.3 M Omega, a blockade voltage of 0.36 mV, and a decrease in voltage of 0.21 mV due to the Bloch oscillation, all of which are larger than those obtained in a single junction by more than one order. The observed Bloch oscillation was quantitatively described on the basis of the Bloch oscillation of each single junction in combination with the charge soliton model in a long array. Unexpected constant-current spikes, whose origin lay in the dc-SQUID in the leads, were also observed to be superposed on the current-voltage characteristics when the Coulomb blockade appeared.
Scientific journal, English - Experimental demonstration of single-flux-quantum sequential-access mask ROM
Yoshinao Mizugaki; Kazunao Sawada; Tomoki Watanabe; Hiroshi Shimada
IEICE ELECTRONICS EXPRESS, IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, 13, 12, 20160342-1-20160342-6, Jun. 2016, Peer-reviwed, We present a superconducting single-flux-quantum (SFQ) mask ROM comprising 2-bit storage cells and a sequential-access driver. Four types of storage cells for 2-bit data ("00," "10," "01," "11") are adopted for reduction of the cell dimensions, whereas the sequential access is suitable for a single-chip quantum voltage waveform generator implemented with an SFQ-based digital-to-analog converter. 2-bit storage cells of 60 x 70 mu m(2) are fabricated using a niobium integration technology and tested in liquid helium. Operation of a sequential-access mask ROM with data of 8 bits x 6 words is also demonstrated.
Scientific journal, English - Superconducting bipolar digital-to-analog converter equipped with dual double-flux-quantum amplifier
Yoshinao Mizugaki; Tomoki Watanabe; Hiroshi Shimada
IEICE ELECTRONICS EXPRESS, IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, 13, 10, 20160242-1-6, May 2016, Peer-reviwed, Precise voltage generation is a unique feature of superconducting single-flux-quantum (SFQ) circuits, and hence, several SFQ-based digital-to-analog converters (DACs) have been designed for metrological applications. In this letter, we propose a dual double-flux-quantum amplifier (dual-DFQA) that extends DAC output voltage from unipolar to bipolar. An SFQ-based DAC comprising a 4-bit variable pulse number multiplier and a +/- 20-fold dual-DFQA is fabricated using a niobium integration technology. A 1-kHz, +/- 0.29-mV sinusoidal voltage waveform is successfully synthesized.
Scientific journal, English - Improvement of Single-Electron Digital Logic Gates by Utilizing Input Discretizers
Tran Thi Thu Huong; Hiroshi Shimada; Yoshinao Mizugaki
IEICE TRANSACTIONS ON ELECTRONICS, IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, E99C, 2, 285-292, Feb. 2016, Peer-reviwed, We numerically demonstrated the improvement of single-electron (SE) digital logic gates by utilizing SE input discretizers (IDs). The parameters of the IDs were adjusted to achieve SE tunneling at the threshold voltage designed for switching. An SE four-junction inverter (FJI) with an ID (ID-FJI) had steep switching characteristics between the high and low output voltage levels. The limiting temperature and the critical parameter margins were evaluated. An SE NAND gate with IDs also achieved abrupt switching characteristics between output logic levels.
Scientific journal, English - Change in the characteristics of an array of small Josephson junctions with an application of high frequency/microwave radiation
Kanyolo G. M.; Mizugaki Y.; Shimada H.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, 71, 1064-1064, 2016,Coulomb閉塞を示すAl/AlOx/Alの微小Josephson接合を20個直列に一次元配列した素子を作製し、高周波照射に伴うその直流特性の変化を入力パワーを変えて測定した。1 MHz〜3 GHzでは、Coulomb閉塞の電圧幅は周波数によらずに印加された交流電圧振幅に比例して減少することを見出した。この結果は、古典領域の多光子吸収過程によるCooper対電荷ソリトンの注入閾電圧の低下によるものと理解でき、高周波/マイクロ波パワー検出器としての応用可能性を示唆する。
Japanese - Tunneling transport in capacitively coupled arrays of small Josephson junctions
Matsudo K.; Nishigaki H.; Mizugaki Y.; Shimada H.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, 71, 1066-1066, 2016,微小ジョセフソン接合の1次元配列2本を静電的に結合した素子においては結合の強弱、印加磁場、バイアス電圧に応じて様々な電流誘引現象が見られる。今回、結合容量が先行研究より大きな素子を作製し、測定を行った。一方の配列を零バイアスに固定し、他方に有限バイアスを与えると、低バイアス時に顕著な逆方向の電流誘引が観測された。この逆方向の誘引電流は、弱い磁場の印加で消失した。この誘引の起源はクーパー対の励起子輸送であることが示唆される。
Japanese - Detection of emission from a superconducting single-electron transistor by an array of small Josephson junctions
Nishigaki H.; Kanyolo G. M.; Mizugaki Y.; Shimada H.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, 71, 1065-1065, 2016,微小Josephson接合の1次元配列では、マイクロ波を照射すると電流電圧特性に存在するCoulombギャップがマイクロ波電圧に比例して減少する。この特性変化に基づいて、微小Josephson接合列はマイクロ波検出器となり得る。微小Josephson接合列をオンチップの輻射強度検出器とし、輻射源として超伝導単一電子トランジスタ(SSET)を用いて、SSETの特性変化に応じた輻射検出を行った結果を報告する。
Japanese - Pulse Response of Mutually-Coupled dc-to-SFQ Converter Investigated using an On-Chip Pulse Generator
Tomoki Watanabe; Yoshiaki Urai; Hiroshi Shimada; Yoshinao Mizugaki
IEICE TRANSACTIONS ON ELECTRONICS, IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, E98C, 3, 238-241, Mar. 2015, Peer-reviwed, A readout technique using single-flux-quantum (SFQ) circuits enables superconducting single photon detectors (SSPDs) to operate at further high-speed, where a mutually-coupled dc-to-SFQ (MC-dc/SFQ) converter is used as an interface between SSPDs and SFQ circuits. In this work, we investigated pulse response of the MC-dc/SFQ converter. We employed on-chip pulse generators to evaluate pulse response of the MC-dc/SFQ converter for various pulses. The MC-dc/SFQ converter correctly operated for the pulse current with the amplitude of 52 mu A and the width of 179 ps. In addition, we examined influence of the pulse amplitude and width to operation of the MC-dc/SFQ converter by numerical simulation. The simulation results indicated that the MC-dc/SFQ converter had wide operation margins for pulse current with amplitudes of 30-60 mu A irrespective of the pulse widths.
Scientific journal, English - 21aBK-10 Observation of Bloch oscillation and current plateaus in a linear array of small Josephson junctions
Shimada H.; Katori S.; Deguchi T.; Mizugaki Y.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 70, 1269-1269, 2015
Japanese - Quantum Interference in DC-SQUIDs Comprising Two Sub-Micron Aluminum Josephson Junctions: Deviation from Classical Model
Koji Miura; Kento Kikuchi; Hiroshi Shimada; Yoshinao Mizugaki
Proceedings of the 27th International Symposium on Superconductivity (ISS 2014), ELSEVIER SCIENCE BV, 65, 177-180, 2015, Peer-reviwed, In a small Josephson junction, the critical current is often found experimentally to be smaller than the value expected from the Ambegaokar-Baratoff theory because of the quantum phase fluctuations. We also observed in our previous study that the quantum interference in a dc-SQUID comprising sub-micron Al junctions deviated from the classical model. In this work, we have fabricated 13 devices having different values of maximal critical currents, and evaluated their quantum interference patterns. The quantum interference of 12 among 13 devices has deviated from the classical model. It is confirmed that their maximal critical currents (I-csq,I-max) are reduced from the values (I-csq0) predicted by the Ambegaokar-Baratoff theory. Besides, the quantum interference for I-csq,I-max / I-csq0 < 0.4 agrees with the modified quantum-interference model. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
International conference proceedings, English - Design and operation of a 9-bit single-flux-quantum pulse-frequency modulation digital-to-analog converter
Yoshinao Mizugaki; Yoshitaka Takahashi; Hiroshi Shimada; Masaaki Maezawa
Proceedings of the 27th International Symposium on Superconductivity (ISS 2014), ELSEVIER SCIENCE BV, 65, 209-212, 2015, Peer-reviwed, We designed and operated a 9-bit single-flux-quantum (SFQ) digital-to-analog converter (DAC). SFQ pulse-frequency modulation (PFM) was employed for generation of variable quantum output voltage, where a 9-bit variable pulse number multiplier and a 100-fold voltage multiplier were the key components. Test chips were fabricated using a Nb Josephson integration technology. Arbitrary voltage waveforms were synthesized with the maximum voltage of 2.54 mV. For ac voltage standard applications, relationships between the DAC resolution and the synthesized waveform frequency are discussed. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
International conference proceedings, English - Design and Operation of ROM-Dedicated Single-Flux-Quantum Cell Comprising Splitters and Confluence Buffers
Kazunao Sawada; Tomoki Watanabe; Hiroshi Shimada; Yoshinao Mizugaki
2015 15TH INTERNATIONAL SUPERCONDUCTIVE ELECTRONICS CONFERENCE (ISEC), IEEE, -DS-P12, 2015, Peer-reviwed, We have developed a single-flux-quantum (SFQ) read only memory (ROM) cell. The developed SFQ ROM cell has compatibility with an existing cell library. It comprises splitters and confluence buffers. For large integration, we have merged two 1-bit cells into one cell with peripheral elements, and we have optimized circuit parameters with an automatic optimization tool. The cell area is approximately 50% of our preliminary SFQ sequential ROM cell using the CONNECT cell library. A test circuit was fabricated using a 25 mu A/mu m(2) Nb integration process. We have confirmed correct operation for all six I/O ports. The measured bias margins were almost the same magnitude as the simulation result.
International conference proceedings, English - 4-bit Bipolar Triangle Voltage Waveform Generator Using Single-Flux-Quantum Circuit
Tomoki Watanabe; Yoshitaka Takahashi; Hiroshi Shimada; Masaaki Maezawa; Yoshinao Mizugaki
Proceedings of the 27th International Symposium on Superconductivity (ISS 2014), ELSEVIER SCIENCE BV, 65, 213-216, 2015, Peer-reviwed, SFQ digital-to-analog converters (DACs) are one of the candidates for AC voltage standards. We have proposed SFQ-DACs based on frequency modulation (FM). Bipolar output is required for applications of AC voltage standards, while our previous SFQ-DACs generated only positive voltages. In this paper, we present our design of a 4-bit bipolar triangle voltage waveform generator comprising an SFQ-DAC. The waveform generator has two output ports. Synthesized half-period waveforms are alternately generated in one of the output ports. The bipolar output is realized by observing the differential voltage between the ports. We confirmed a 72-mu V-PP bipolar triangle voltage waveform at the frequency of 35.7 Hz. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
International conference proceedings, English - Modified Double-Flux-Quantum Amplifier for Bipolar Voltage Multiplication
Tomoki Watanabe; Hiroshi Shimada; Yoshinao Mizugaki
2015 15TH INTERNATIONAL SUPERCONDUCTIVE ELECTRONICS CONFERENCE (ISEC), IEEE, -DS-P13, 2015, Peer-reviwed, Single-flux-quantum (SFQ) circuits can generate highly accurate average voltage. We have developed SFQ digitalto- analog converters (DACs) for application of new ac voltage standards. In this paper, we present a bipolar voltage amplifier (BVA) based on a double flux quantum amplifier (DFQA) for generation of intrinsic bipolar voltage in an SFQ-DAC. The BVA realizes the identical multiplication factors for the positive and negative output, whereas the conventional DFQA has different multiplication factors in the bipolar output. The BVA can be used for the output stage of the SFQ-DAC. We have designed a 19-fold BVA and confirmed that the 19-fold BVA operated for input frequency of up to 31.2 GHz in positive voltage output and 33.6 GHz in negative voltage output.
International conference proceedings, English - Towards precise current-multiplication based on the quantum current-mirror effect
Kouichi Takeda; Kenji Miyawaki; Srinivas Gandrothula; Chihiro Ishida; Ayano Hagiwara; Yoshinao Mizugaki; Hirhoshi Shimada
IEICE Technical Report, The Institute of Electronics, Information and Communication Engineerings, SCE2014-49, 1-6, Jan. 2015
Symposium, Japanese - Characterization of superconducting single-electron transistors with small Al/AlOx/V Josephson junctions
Hiroshi Shimada; Kenji Miyawaki; Ayano Hagiwara; Kouichi Takeda; Yoshinao Mizugaki
SUPERCONDUCTOR SCIENCE & TECHNOLOGY, IOP PUBLISHING LTD, 27, 11, 115015-1-115015-8, Nov. 2014, Peer-reviwed, Superconducting single-electron transistors (SSETs) composed of small Al/AlOx/V junctions were fabricated, and their transport properties were investigated. The device with an Al island exhibited a supercurrent that was 2e-periodic in the gate charge while that with a V island showed a periodicity of e, where e is an elementary charge. The Josephson-quasiparticle (JQP)cycle current appeared at the bias voltage V in the range. Delta(Al) + Ec < e vertical bar V vertical bar < Delta(Al) + 3E(c), where. Delta(Al) is the superconducting gap of Al and Ec is the charging energy of an elementary charge. This is different from the commonly accepted range for the JQP current such as that in the case of an all Al SSET. There also appeared a large leakage current at 2 Delta(Al) <= e vertical bar V vertical bar < 2(Delta(V) + Delta(Al)+ E-c), where Delta V is the superconducting gap of V. All these properties are accounted for by considering the finite subgap quasiparticle density of states in the V electrode.
Scientific journal, English - 9 bit superconductive single-flux-quantum digital-to-analogue converter
Y. Mizugaki; Y. Takahashi; H. Shimada; M. Maezawa
ELECTRONICS LETTERS, INST ENGINEERING TECHNOLOGY-IET, 50, 22, 1637-1638, Oct. 2014, Peer-reviwed, The design and operation of a 9 bit superconductive single-flux-quantum (SFQ) digital-to-analogue converter (DAC) are presented. The DAC comprises a 9 bit variable SFQ pulse number multiplier and a 100-fold voltage multiplier. An SFQ pulse-frequency modulation technique is employed for coding the analogue output voltage. The DAC is fabricated using an Nb Josephson integration technology. Its output voltage waveform, the amplitude of which is up to 2.54 mV(pp), is controlled by digital input signals from a room-temperature data generator.
Scientific journal, English - Input-output characteristics of a 999-stage double-flux-quantum amplifier designed for 1000-fold voltage multiplication
Yoshinao Mizugaki; Yusuke Sato; Hiroshi Shimada; Masaaki Maezawa
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 53, 5, 053101-1-053101-4, May 2014, Peer-reviwed, We evaluate the input output characteristics of a 1000-fold voltage multiplier designed for single-flux-quantum (SFQ) digital-to-analog converters. The voltage multiplication is based on the double-flux-quantum amplifier (DFQA) that was originally proposed by Herr in 2005. We have designed and fabricated a 999-stage DFQA using a Nb/AlOx/Nb integration technology. In experiments, we have used two methods of feeding the input SFQ pulse train. The one is an overbiasing method, i.e., the input SFQ pulse train is generated at an overbiased input junction. A 1000-fold voltage multiplication with errors less than +/- 1% has been confirmed for input voltages of up to 27 mu V, of which the corresponding Josephson frequency is 13 GHz. In the other method, a dc/SFQ converter is used for feeding the input SFQ pulse train. A 1000-fold voltage multiplication with an error of -0.03% has been obtained for an input frequency of 600 MHz, of which the corresponding Josephson voltage is 1.2 mu V. In experiments, errors in measured voltages are likely to limit the accuracy in evaluation of the multiplication factor. (C) 2014 The Japan Society of Applied Physics
Scientific journal, English - Correlation between polarity of magnetoresistance ratio and tunnel resistance in ferromagnetic single-electron transistor with superconductive island
Masashi Takiguchi; Hiroshi Shimada; Yoshinao Mizugaki
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 53, 4, 043101-1-043101-4, Apr. 2014, Peer-reviwed, We report on the correlation between the polarity of magnetoresitance ratios and the tunnel resistance observed in ferromagnetic single-electron transistors with a superconductive island (FM-SC-FM SETs). Negative magnetoresistance ratios are observed at approximately the superconductive gap voltages, which indicates that an excessive number of spin-polarized quasiparticles accumulated in a superconductive island suppress the superconductive gaps. Since the spin polarization in a superconductor decays with time, the spin injection rate should be high enough to observe the suppression of superconductive gaps. The spin injection rate at a certain bias voltage is inversely proportional to the tunnel resistance; hence, the polarity of magnetoresistance ratio should correlate with the tunnel resistance. We fabricated 26 FM-SC-FM SETs. Samples having tunnel resistances lower than 100 k Omega exhibited negative magnetoresistance ratios, while samples having tunnel resistances higher than 600 k Omega exhibited positive magnetoresistance ratios. (C) 2014 The Japan Society of Applied Physics
Scientific journal, English - Demonstration of 6-bit, 0.20-mV(pp) Quasi-Triangle Voltage Waveform Generator Based on Pulse-Frequency Modulation
Yoshitaka Takahashi; Hiroshi Shimada; Masaaki Maezawa; Yoshinao Mizugaki
IEICE TRANSACTIONS ON ELECTRONICS, IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, E97C, 3, 194-197, Mar. 2014, Peer-reviwed, We present our design and operation of a 6-bit quasi-triangle voltage waveform generator comprising three circuit blocks; an improved variable Pulse Number Multiplier (variable-PNM), a Code Generator (CG), and-a Double-Flux-Quantum Amplifier (DFQA). They are integrated into a single chip using a niobium Josephson junction technology. While the multiplication factor of our previous m-bit variable-PNM was limited between 2(m-1) and 2(m), that of the improved one is extended between 1 and 2(m). Correct operations of the 6-bit variable-PNM are confirmed in low-speed testing with respect to the codes from the CG, whereas generation of a 6-bit, 0.20 mV(pp) quasi-triangle voltage waveform is demonstrated with the 10-fold DFQA in high-speed testing.
Scientific journal, English - Precision improvement of the current multiplier based on the quantum current-mirror effect
Kouichi Takeda; Chihiro Ishida; Srinivas Gandrothula; Yoshinao Mizugaki; Hiroshi Shimada
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 53, 2, 023101-1-023101-7, Feb. 2014, Peer-reviwed, The relationship between the coupling strength and the uncertainty in current duplication was investigated for the quantum current-mirror effect in capacitively coupled arrays of small Josephson junctions. With the increase in the coupling factor kappa, defined as kappa = C-c/C, with C-c being the coupling capacitance and C the capacitance of the junction, the uncertainty decreased rapidly, especially at kappa > 1, and the standard deviation of the error reached as low as the order of 10 fA at kappa similar or equal to 2.4. On this basis, we fabricated a 10-fold current multiplier composed of 11 simple arrays of junctions coupled more strongly (kappa similar or equal to 0.5), using a plate-capacitor structure, than a previously studied multiplier (kappa similar or equal to 0.01). It demonstrated more precise current-multiplication behavior than the previous multiplier with no intentional coupling structure, and the standard deviation of the error in current multiplication was decreased to less than 1/10 of the previous result. (C) 2014 The Japan Society of Applied Physics
Scientific journal, English - Design and operation of 6-bit, 0.25-mV(pp) quasi-sine voltage waveform generator based on SFQ pulse-frequency modulation
Yoshitaka Takahashi; Hiroshi Shimada; Masaaki Maezawa; Yoshinao Mizugaki
PROCEEDINGS OF THE 26TH INTERNATIONAL SYMPOSIUM ON SUPERCONDUCTIVITY (ISS 2013), ELSEVIER SCIENCE BV, 58, 220-223, 2014, Peer-reviwed, A digital-to-analogue converter (DAC) consisting of single-flux-quantum (SFQ) circuitry is known to generate accurate analogue voltages defined by the Josephson relationship. We have been developing SFQ-DACs of the pulse-frequency modulation (PFM) type. Toward voltage standard applications of SFQ-DACs, we have set the target values for the voltage amplitude and resolution at 20 mV(pp) and 10 bits, respectively. So far, we have reported a 5-bit, 10-mu V-pp quasi-sine voltage waveform generator comprising a PFM-type SFQ-DAC integrated with an on-chip digital code generator. Its small peak-to-peak voltage amplitude was due to the lack of an on-chip voltage multiplier (VM). In this paper, we present a 6-bit, 0.25-mV(pp) quasisine voltage waveform generator integrated with a 10-fold VM. The resolution is improved by introducing efficient logic sequences into the SFQ-DAC. (C) 2014 The Authors. Published by Elsevier B.V.
International conference proceedings, English - Zero-crossing Shapiro step generated in a niobium in-line Josephson gate
Yoshinao Mizugaki; Haruna Takahashi; Hiroshi Shimada
IEICE ELECTRONICS EXPRESS, IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, 11, 6, 1-5, 2014, Peer-reviwed, We demonstrate a zero-crossing Shapiro step generated in a magnetically-coupled Josephson gate, where a long Josephson junction and a control line are placed in-line. The operation is based on the imbalanced evolution of the junction phases owing to the different amplitudes of the positive and negative critical current. A test circuit was fabricated using a Nb/AlOx/Nb junction technology. When we applied a rf signal of 15.2 GHz, we observed a Shapiro step that crossed the zero-current axis at the voltage position of the 1st order. The experimental results were quantitatively reproduced by simulation.
Scientific journal, English - Polarity Reversal of Tunnel Magnetoresistance Observed in Lateral Co-Al-Co Single-Electron Transistor
Masashi Takiguchi; Takayuki Sato; Hiroshi Shimada; Yoshinao Mizugaki
JPS Conference Proceedings, The Physical Society of Japan, 1, 012004-1-012004-5, 2014, Peer-reviwed, Polarity reversal of tunnel magnetoresistance is a unique feature of double-tunnel-junction systems
comprising a superconducting (SC) middle electrode sandwiched by two ferromagnetic (FM) outer
electrodes. Yang et al. demonstrated a good agreement between experimental and theoretical tunnel
magnetoresistance in vertically-stacked FM/SC/FM double tunnel junctions, in which the SC layer
was 4.5-nm-thick Al. In this paper, we present the polarity reversal of tunnel magnetoresistance in
Co-Al-Co double tunnel junctions, where two Co electrodes are laterally placed with spacing of 570
nm. The tunnel magnetoresistance is negative at the bias voltages near the SC gap voltage, whereas
it is positive at higher bias voltages. The results demonstrate that the long spin lifetime in the SC Al
electrode enables us to observe the spin accumulation even in the lateral structure.
International conference proceedings, English - 5-Bit Quasi-Sinusoidal Voltage Waveform Synthesized Using Single-Flux-Quantum Pulse-Frequency Modulation
Yoshinao Mizugaki; Keisuke Kuroiwa; Masataka Moriya; Hiroshi Shimada; Masaaki Maezawa
IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 23, 3, 1300804, Jun. 2013, Peer-reviwed, Synthesis of sinusoidal voltage waveform is a unique application in single-flux-quantum (SFQ) digital electronics. In this paper, the authors present a waveform synthesizer based on SFQ pulse-frequency modulation. It comprises a variable SFQ pulse-number-multiplier (PNM) and a code generator (CG) integrated on the same chip. The output voltage is determined by the multiplication factor in the variable-PNM, which is controlled by the code from the CG instead of room-temperature electronics. The variable-PNM realizes 5-bit resolution with the multiplication factors between 33 and 64. The CG generates the 5-bit codes for 16-step quasi-sinusoidal waveform. The whole circuits including I/O elements are designed using an SFQ digital cell library, and fabricated using a niobium integration process. The modulation of the multiplication factor for the 16-step quasi-sinusoidal waveform is confirmed by counting SFQ pulses in the low-speed testing, whereas the voltage waveform of 11 mu V peak-to-valley is demonstrated using a high-speed SFQ input of 156.25 MHz.
Scientific journal, English - Bias-voltage dependence of magnetoresistance enhancement in a single-electron transistor comprising two cobalt leads and an aluminum island
Yoshinao Mizugaki; Nobuyuki Tamura; Hiroshi Shimada
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 113, 15, 156101, Apr. 2013, Peer-reviwed, We present the magnetoresistance enhancement observed in a Co-Al-Co single-electron transistor (SET). The parallel and anti-parallel alignments of the magnetic domains in the Co leads are realized at the external field of 1.9 kOe by using magnetic hysteresis. The magnetoresistance ratio (MRR) is obtained as functions of the bias voltages for the on- and off-state SET, respectively. The results demonstrate that the MRR is enhanced in the off- state SET under the low biasing conditions. The theory including cotunneling processes is likely to explain the enhancement quantitatively. (C) 2013 AIP Publishing LLC.
Scientific journal, English - Design and operation of 1000-fold voltage multiplier based on double-flux-quantum amplifier
Y. Sato; M. Moriya; H. Shimada; Y. Mizugaki; M. Maezawa
PROCEEDINGS OF THE 25TH INTERNATIONAL SYMPOSIUM ON SUPERCONDUCTIVITY (ISS2012), ELSEVIER SCIENCE BV, 45, 221-224, 2013, Peer-reviwed, Rapid-single-flux-quantum digital-to-analogue converters (RSFQ-DACs) are now under development for ac voltage standard applications. The voltage multiplier (VM), which precisely amplifies the input voltage, is a key component for RSFQ-DACs. Because the amount of bias current for a conventional VM increases in proportion to its multiplication factor, we have been looking for a VM device which is operated on a different principle. In this paper, we report our design of a 1000-fold VM comprising double flux quantum amplifiers (DFQAs) of which the amount of bias current is independent of its multiplication factor. Test circuits were fabricated using a 2.5 kA/cm(2) Nb process. We confirm that the experimental results demonstrate the 1000-fold operation up to 13.2 GHz input SFQ pulse repetition frequency. (C) 2013 The Authors. Published by Elsevier B.V.
International conference proceedings, English - Effect of charging energy on critical current of dc-SQUID comprising two sub-micron aluminum Josephson junctions
Y. Mizugaki; K. Kikuchi; M. Moriya; H. Shimada
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 484, 206-208, Jan. 2013, Peer-reviwed, Tiny Al/AlOx/Al tunnel junctions are widely used in single-electron, single-Cooper-pair, and quantum-bit devices. A crucial parameter for such devices is the charging energy of a single electron or a single Cooper-pair in the junctions, and hence, determination of the junction capacitance is quite important. In this paper, we report our experiments to determine the capacitance of sub-micron Al tunnel junctions. We employ a SQUID resonance technique. Differently from the work reported by Deppe et al. [4], the loop inductance is obtained by not only numerical calculation but also experimental results of quantum interference, which eliminates uncertainty about the field penetration depth of Al thin films. The specific capacitance is obtained as 54 fF/mu m(2). We have also found that the critical current of the dc-SQUID is smaller than the value given by the classical theory for large Josephson junctions. Calculation including the charging energy effect provides better fitting to the experiments, where the critical current is assumed to be proportional to the square root of the ratio of the Josephson coupling energy to the charging energy. (C) 2012 Elsevier B.V. All rights reserved.
Scientific journal, English - Current Multiplication Using Arrays of Small Josephson Junctions
Srinivas Gandrothula; Kenta Nakamura; Masashi Takiguchi; Yoshinao Mizugaki; Hiroshi Shimada
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 51, 12, 123101, Dec. 2012, Peer-reviwed, We report our observation of a current-multiplication trend in a new class of current-multiplier designs based on the quantum current-mirror effect in coupled arrays of small Josephson junctions. We demonstrate an extension of the current doubler device to 8- and 10-fold current multipliers by including additional Josephson junction arrays with simplified device geometry. The devices showed the expected current-multiplication trend at low temperatures where the charging effect was dominant. The magnitude of the current that exhibited such a multiplication trend was as large as 0.8 nA. (C) 2012 The Japan Society of Applied Physics
Scientific journal, English - Drag Current Reversal in Capacitively Coupled Arrays of Small Josephson Junctions
Hiroshi Shimada; Chihiro Ishida; Yoshinao Mizugaki
PHYSICAL REVIEW LETTERS, AMER PHYSICAL SOC, 109, 19, 196801, Nov. 2012, Peer-reviwed, The current-voltage characteristics of two long capacitively coupled one-dimensional arrays of small Josephson junctions were measured, where the coupling capacitance was comparable with the capacitance of the junction. The current in both arrays was simultaneously measured at various applied magnetic fields with the voltage applied to only one of the arrays. The current was induced in the unbiased array beyond the threshold voltage for the Coulomb blockade of the biased array. The direction of the induced current is the same as that of the current in the other array when the applied magnetic field is small and Cooper-pair tunneling is dominant, while it changes to the opposite direction when the applied magnetic field is large and single-electron tunneling is dominant. This suggests that the current induction mechanism between arrays of small Josephson junctions is substantially different from that in arrays of small normal tunnel junctions.
Scientific journal, English - Estimation of Nb Junction Temperature Raised Due to Thermal Heat from Bias Resistor
Keisuke Kuroiwa; Masaki Kadowaki; Masataka Moriya; Hiroshi Shimada; Yoshinao Mizugaki
IEICE TRANSACTIONS ON ELECTRONICS, IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, E95C, 3, 355-359, Mar. 2012, Peer-reviwed, Superconducting integrated circuits should be operated at low temperature below a half of their critical temperatures. Thermal heat from a bias resistor could rise the temperature in Josephson junctions, and would reduce their critical currents. In this study, we estimate the temperature in a Josephson junction heated by a bias resistor at the bath temperature of 4.2 K, and introduce a parameter beta that connects the thermal heat from a bias resistor and the temperature elevation of a Josephson junction. By using beta, the temperature in the Josephson junction can be estimated as functions of the current through the resistor.
Scientific journal, English - 強磁性リード電極を有する単一電子トランジスタでの磁気抵抗比増大効果の観測
田村伸行; 菊池健人; 守屋雅隆; 小林忠行; 島田宏; 水柿義直
IEICE Technical Report, ED2009-204, SDM2009-201, 2010, Peer-reviwed
Scientific journal, Japanese - ホットエレクトロン効果を考慮した微小トンネル接合二次元アレーの微分コンダクタンス特性
田村伸行; 滝口将志; 島田宏; 水柿義直
電子情報通信学会論文誌Ｃ, The Institute of Electronics, Information and Communication Engineers, J92-C, 9, 534-536, Sep. 2009, Peer-reviwed, ホットエレクトロン効果を考慮した微小トンネル接合二次元アレーの特性式を提案し,実験結果とのフィッティングを行ったところ良い一致が得られた.
Scientific journal, Japanese - Differential conductance characteristic of two dimensional tunnel junctions array considered hot electron effects
N. Tamura; M. Takiguchi; H. Shimada; Y. Mizugaki
IEICE Transactions on Electronics, The Institute of Electronics, Information and Communication Engineers, J92-C, 9, 534-536, Sep. 2009, Peer-reviwed, ホットエレクトロン効果を考慮した微小トンネル接合二次元アレーの特性式を提案し,実験結果とのフィッティングを行ったところ良い一致が得られた.
Scientific journal, English - Electric Characteristics of Li2O-Doped TiO2 Nanocrystalline Film and Its Application to Dye-Sensitized Solar Cells
Masahiro Nada; Tomohiro Gonda; Qing Shen; Hiroshi Shimada; Taro Toyoda; Naoki Kobayashi
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 48, 2, 0255505-1～4, Feb. 2009, Peer-reviwed, The effects of Li2O doping on TiO2 nanocrystalline film are investigated to improve the conversion efficiency of dye-sensitized solar cells (DSC), while considering the mechanism of electric conduction in the TiO2 nanocrystalline film. The temperature dependence of carrier concentration and electric conductivity of Li2O-doped TiO2 nanocrystalline film are determined by Hall effect and high-impedance conductivity measurements. At the doping condition of 4.5 x 10(-5) molar ratio of Li2O to TiO2, the electric conductivity at room temperature is maximum, which is almost two orders of magnitude higher than that of the undoped sample. The conduction type and carrier concentration at 500 K are n-type and 1.75 x 10(13) cm(-3), respectively. From the temperature dependence of the electron concentration, the donor depth is estimated as 1.0 eV. By applying Li2O doping to DSC, the conversion efficiency and open-circuit voltage are maximum at the highest conductivity of the Li2O-doped TiO2 layer. (C) 2009 The Japan Society of Applied Physics
Scientific journal, English - Current Doublers Based on the Quantum Current-Mirror Effect
Hiroshi Shimada; Sumio Hanadou; Takuma Kawa; Hiroto Kido; Yoshinao Mizugaki
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOCIETY APPLIED PHYSICS, 47, 10, 8131-8136, Oct. 2008, Peer-reviwed, Two types of current doublers, which operate in a sub-nanoampere range, have been fabricated as prototypes of a precise current multiplier for metrological application. The current doubling function of the devices is based on the quantum current-mirror effect in coupled arrays of small Josephson junctions. Both types of devices comprise three arrays of small Josephson junctions: the first device has two serial short arrays coupled to one long array, and the second device has three arrays of the same size arranged in parallel. The arrays for the current input are the long array in the first device and one of the three arrays in the second device, and a parallel connection of the other two arrays in each device forms the output port. In both types of devices, a current fed to the input array is doubled in the output circuit, which includes the connected arrays, up to about 100pA with the accuracy <=+/- 3pA, which is the uncertainty of the measurement system, by correlated tunnelings of Cooper-pair charge solitons in the arrays. The feasibility of producing a current Multiplier has been ascertained on the basis of this effect. [DOI: 10.1143/JJAP.47.8131]
Scientific journal, English - Single-Electron Devices With Input Discretizer
Yoshinao Mizugaki; Masashi Takiguchi; Shota Hayami; Akio Kawai; Masataka Moriya; Kouichi Usami; Tadayuki Kobayashi; Hiroshi Shimada
IEEE TRANSACTIONS ON NANOTECHNOLOGY, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 7, 5, 601-606, Sep. 2008, Peer-reviwed, We propose an input discretizer for single-electron (SE) devices. The input discretizer is composed of one small tunnel junction and two capacitances. Adjusting the capacitances to be equal discretizes the gate charge with interval of a half of the elementary charge e, which enhances the performance of SE devices. An SE transistor with the input discretizer has abrupt switchings of the Coulomb blockade thresholds, resulting in steep responses to the input signal. An SE turnstile with the input discretizer enhances its operation margins for the application of a digital-to-analog converter element. Both analytical and numerical results are presented.
Scientific journal, English - Tunnel magnetoresistance in ferromagnet-superconductor-ferromagnet single-electron transistors with different lead Spacings up to 50 mu m
Yoshinao Mizugaki; Hidemitsu Hakii; Masataka Moriya; Kouichi Usami; Tadayuki Kobayashi; Hiroshi Shimada
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, INST PURE APPLIED PHYSICS, 46, 36-40, L901-L903, Oct. 2007, Peer-reviwed, We fabricated single-electron transistors (SETs) with ferromagnetic (FM) Co leads and superconducting (SC) Al islands, and measured their tunnel magnetoresistances. Under the antiparallel magnetization state of the two FM leads, current increase due to the SC gap suppression by spin accumulation was observed. Tunnel magnetoresistance ratios of the antiparallel state to the parallel state were investigated for 10 FM SETs with different spacings between the two FM leads, from 0.35 to 50 mu m. Spin valve effects were confirmed in the SETs with an FM lead spacing not only on the submicron order but also of 50 mu m.
Scientific journal, English - Current correlation in single-electron current mirror electromagnetically dual to Josephson voltage mirror
Yoshinao Mizugaki; Masafumi Itoh; Hiroshi Shimada
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 46, 9B, 6237-6242, Sep. 2007, Peer-reviwed, The electromagnetic duality between single-electron devices and Josephson devices sometimes helps us to develop new electron devices. In this article, a single-electron turnstile is discussed as a dual device to a de superconducting quantum interference device (dc-SQUID). From the viewpoint of the device characteristics, a,single-electron turnstile has better duality to a dc-SQUID than a single-electron transistor. Next, a current mirror based on single-electron turnstiles is introduced as a dual circuit corresponding to a Josephson voltage mirror. A test circuit of a current mirror was fabricated using electron beam lithography and aluminum shadow evaporation. Although the precise current mirror operation was not obtained, we observed two currents approaching each other. Simulation based on the Monte Carlo method succeeded in reproducing the experimental results. Numerical results indicate that insufficient capacitive coupling, nonnegligible parasitic capacitances, and short array length deteriorate the current mirror operation.
Scientific journal, English - Current Multiplication Based on the Quantum Current-Mirror Effect
Hiroshi Shimada; Takuma Kawai; Yoshinao Mizugaki
IEEE Transactions on Applied Superconductivity, 17, 2, 602-604, Jul. 2007, Peer-reviwed
Scientific journal, English - Optimization of asymmetric single-electron transistor generating ac-induced dc current
Yoshinao Mizugakia; Akio Kawai; Masataka Moriya; Kouichi Usami; Tadayuki Kobayashi; Hiroshi Shimada
IEICE ELECTRONICS EXPRESS, IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, 4, 11, 345-350, Jun. 2007, Peer-reviwed, Charge tunneling events in an ac-voltage-driven asymmetric single-electron transistor (aSET) under appropriate gate charge are rectified due to the tilted Coulomb blockade (CB) diagram, which induces finite dc electric current even under zero dc biasing. We demonstrate dependence of the dc current upon the gate charge and the amplitude of the ac voltage by means of numerical simulation based on the Monte Carlo method. Device parameters of the aSET optimized for generation of the ac-induced dc current are derived by both analytical and numerical methods.
Scientific journal, English - Coulomb blockade conditions for detailed model of single-electron turnstile device including finite self-capacitances of island electrodes
Asaki Mizuta; Masataka Moriya; Kouichi Usami; Tadayuki Kobayashi; Hiroshi Shimada; Yoshinao Mizugaki
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 46, 5A, 3144-3148, May 2007, Peer-reviwed, We propose a detailed model of a single-electron turnstile device in which each island electrode has a finite self-capacitance. The Coulomb blockade (CB) regions are obtained by calculating the free energy of the system, and are graphically presented in the gate-charge versus bias-voltage plane. We confirm the CB regions obtained to be octagonal, instead of the quadrilateral CB regions obtained in the conventional model.
Scientific journal, English - Monte Carlo study of charge transport in slantingly coupled arrays of small tunnel junctions
Y Mizugaki; H Shimada
PHYSICAL REVIEW B, AMERICAN PHYSICAL SOC, 71, 11, 115103-1~7, Mar. 2005, Peer-reviwed, We present a numerical investigation on the charge transport in capacitively coupled arrays of small tunnel junctions in the case of slanted coupling. Current-voltage characteristics of the arrays having various coupling capacitance (C-c) are simulated using the Monte Carlo method. In contrast to the case of straight coupled arrays, slantingly coupled arrays exhibit the current mirror effect using a coupling capacitance as small as C-c/C similar or equal to 0.1, where C is the junction capacitance. However, when C-c is too large (C-c/C>1), electron-electron or hole-hole chains are formed in each array, which deteriorate the current mirror effect. Conditions for the formation of such chains are derived from analysis of a simplified model of slantingly coupled arrays.
Scientific journal, English - Driving the single-electron device with a magnetic field (invited)
H Shimada; K Ono; Y Ootuka
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 93, 10, 8259-8264, May 2003, Peer-reviwed, The single-electron devices some of whose electrodes are composed of ferromagnetic metals can be driven with a magnetic field. It is based on the fact that a ferromagnetic electrode has a function as a magnetochemical or magnetoelectric coupling component in the device through the Zeeman effect on the electron spins in it. Double- and triple-small-junction devices composed of Ni and Co electrodes showed conductance oscillations typical to the single-electron device when the applied magnetic field was swept, illustrating the magnetic-field control of the device operation. A single-electron box and a single-electron pump driven with a magnetic field are described based on the functions of the ferromagnetic electrodes. (C) 2003 American Institute of Physics.
Scientific journal, English - Ferromagnetic Single-Electron Pump
Hiroshi Shimada; Youiti Ootuka
Abstract in International Symposium on Mesoscopic Superconductivity and Spintronics (MS+S2002), 6-1～2, Mar. 2002
International conference proceedings, English - Magnetic-field-driven single-electron pump
H Shimada; Y Ootuka
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 64, 23, 235418-1~6, Dec. 2001, Peer-reviwed, A ferromagnetic triple-tunnel-junction device whose island electrodes or lead electrodes are composed of ferromagnetic metals with different coercive forces can be operated as a single-electron pump by applying an ac magnetic field. This device utilizes the magnetic-field-induced shift of chemical potential and magnetization reversal in the ferromagnetic electrode as its basic mechanisms in addition to the single-electron charging effect. We describe principle of its operation in terms of the orthodox theory of the single-electron tunneling, and further examine the role of the domain-wall propagation during the magnetization reversal in the operation of the device and intrinsic limitation of the operation frequency.
Scientific journal, English - Current mirror effect and correlated cooper-pair transport in coupled arrays of small Josephson junctions
H Shimada; P Delsing
PHYSICAL REVIEW LETTERS, AMERICAN PHYSICAL SOC, 85, 15, 3253-3256, Oct. 2000, Peer-reviwed, We have measured the transport properties of capacitively coupled one-dimensional arrays of small aluminum Josephson junctions. Under suitable biasing conditions, the samples act as current mirrors; the currents in the two arrays couple to each other and become equally large. The coupling is found both for currents flowing in the same direction and in opposite directions. We have also measured the time dependent fluctuations of the currents in the two arrays, and we find a strong correlation or anticorrelation of the fluctuations depending on the relative direction of the two currents.
Scientific journal, English - Quantum charge fluctuations in quantum dots
H Shimada; Y Ootuka; S Kobayashi; S Katsumoto; A Endo
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 69, 3, 828-835, Mar. 2000, Peer-reviwed, Influence of the quantum charge fluctuations in a quantum dot on its charging effect has been investigated by using a quantum-dot device having four quantum point contacts (QPC's) which connect the dot to the reservoirs. The charging effect was detectable at combined tunnel conductance of four QPC's up to near 8e(2)/h beyond the intuitive criterion e(2)/h. We observed anomalously nonlinear dependences of the conductances at the tops (G(top)) and bottoms (G(bot)) of the Coulomb oscillation on the tunnel conductances of QPC's, G(QPC)'s The result on G(top) indicates that a transition from Coulombically regulated tunnelings to non-correlated tunnelings occurs by increasing G(QPC)'s. The result on G(bot) shows the existence of leakage conductance beyond the 2nd-order cotunneling contribution. The offset voltage in the current-voltage characteristics of the device showed significant decrease with the increase of G(QPC)'s, indicating the shrinkage of the effective charging energy. The results on G(top) and G(bot) can be explained in the light of the shrinkage of the effective charging energy.
Scientific journal, English - Spin polarization and magneto-Coulomb oscillations in ferromagnetic single electron devices
K Ono; H Shimada; Y Ootuka
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 67, 8, 2852-2856, Aug. 1998, Peer-reviwed, magneto-Coulomb oscillation due to the single electron repopulation induced by external magnetic field, observed in a ferromagnetic single electron transistor is examined in various ferromagnetic single electron devices. In case of double- and triple-junction devices made of Ni and Co electrodes, the single electron repopulation always occurs from Ni to Co electrodes with increasing magnetic field, irrespective of the configurations of the electrodes. The period of the magneto-Coulomb oscillation is proportional to the single electron charging energy. All these features are consistently explained by the mechanism that the Zeeman effect induces changes of the Fermi energy of the ferromagnetic metal having a non-zero spin polarizations. Experimentally determined spin polarizations are negative for both Ni and Co and the magnitude is larger for Ni than Co as expected from the calculated hand structures.
Scientific journal, English - Magneto-Coulomb oscillation in ferromagnetic single electron transistors
H Shimada; K Ono; Y Ootuka
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 67, 4, 1359-1370, Apr. 1998, Peer-reviwed, The mechanism of the magneto-Coulomb oscillation in ferromagnetic single electron transistors (SET's) is theoretically considered. Variations in the chemical potentials of the conduction electrons in the ferromagnetic island electrode and the ferromagnetic lead electrodes in magnetic fields cause changes in the free energy of the island electrode of the SET. This is a plausible origin of the conductance oscillation of the SET in sweeping an applied magnetic field.
Scientific journal, English - Enhanced magnetic valve effect and magneto-Coulomb oscillations in ferromagnetic single electron transistor
K Ono; H Shimada; Y Ootuka
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 66, 5, 1261-1264, May 1997, Peer-reviwed, We report on magnetotransport properties of a ferromagnetic single electron transistor (SET) in which tunnel resistance RT changes about 3.6-3.8% by the magnetic valve effect. We find that the magnetic valve effect is enhanced in the Coulomb blockade region: The magnetoresistance (MR) ratio of the off-state of the SET is more than 40%, while that of the on-state is 4.0%. A mechanism of enhancement by the higher-order tunneling process is proposed. Furthermore, we find a monotonic phase shift of the Coulomb oscillations induced by the magnetic field, which results in magneto-Coulomb oscillations with fixed gate voltage. A simple explanation for this effect based on a magnetic-field-induced change in the Fermi energy of the spin-polarized electrons in an island electrode is given.
Scientific journal, English - DYNAMICS OF HOT-ELECTRONS ACCUMULATED IN THE VELOCITY SPACE OF CDS WITH ACOUSTIC-PHONON INTERACTIONS
H SHIMADA; T MASUMI
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 62, 9, 3203-3215, Sep. 1993, Peer-reviwed, Transport phenomena of photoexcited electrons in CdS have been investigated at crossed electric and magnetic fields. Dynamics of electrons at the so-called ''accumulation'' area in the velocity space, escaping from the LO-phonon emission, has been clarified in a view of the hot electron effect at strong transverse magnetic fields, particularly in the case of interaction with acoustic phonons, both the deformation-potential coupling and piezoelectric coupling included.
Scientific journal, English - Nonlinear Optical Phenomena in Cyclotron Resonance of Positive Holes and Electrons in Cu2O
Taizo Masumi; Hiroshi Shimada
Journal of the Physical Society of Japan, 60, 11, 3629-3632, Nov. 1991, Peer-reviwed
Scientific journal, English - Hall Mobility of Positive Holes in Cu2O
Hiroshi Shimada; Taizo Masumi
Lead, Journal of the Physical Society of Japan, 58, 5, 1717-1724, May 1989, Peer-reviwed
Scientific journal, English - A Novel Spectral Photoconductivity of the Ca-Sr-Bi-Cu-O System Correlative with Superconductivity
Taizo Masumi; Hidetoshi Minami; Hiroshi Shimada
Journal of the Physical Society of Japan, 57, 8, 2674-2677, Aug. 1988, Peer-reviwed
Scientific journal, English - A Novel Spectral Photoconductivity of the Ba-Pb-Bi-O System Correlative with Superconductivity
Taizo Masumi; Hiroshi Shimada; Hidetoshi Minami
Journal of the Physical Society of Japan, 57, 8, 2670-2673, Aug. 1988, Peer-reviwed
Scientific journal, English - A Novel Spectral Photoconductivity of the La-Cu-O Correlative with Superconductivity
Taizo Masumi; Hidetoshi Minami; Hiroshi Shimada
Journal of the Physical Society of Japan, 56, 9, 3013-3016, Sep. 1987, Peer-reviwed
Scientific journal, English - A Novel Spectral Photoconductivity of the Y-Cu-O, Y-Ba-Cu-O Correlative with Superconductivity
Taizo Masumi; Hiroshi Shimada; Hidetoshi Minami
Journal of the Physical Society of Japan, 56, 9, 3009-3012, Sep. 1987, Peer-reviwed
Scientific journal, English
MISC
- Fabrication of resistively-coupled single-electron device using an array of gold nanoparticles
Tran Thi Thu Huong; Kazuhiko Matsumoto; Masataka Moriya; Hiroshi Shimada; Yasuo Kimura; Ayumi Hirano-Iwata; Yoshinao Mizugaki
We demonstrated one type of single-electron device that exhibited electrical characteristics similar to those of resistively-coupled SE transistor (R-SET) at 77 K and room temperature (287 K). Three Au electrodes on an oxidized Si chip served as drain, source, and gate electrodes were formed using electron-beam lithography and evaporation techniques. A narrow (70-nm-wide) gate electrode was patterned using thermal evaporation, whereas wide (800-nm-wide) drain and source electrodes were made using shadow evaporation. Subsequently, aqueous solution of citric acid and 15-nm-diameter gold nanoparticles (Au NPs) and toluene solution of 3-nm-diameter Au NPs chemisorbed via decanethiol were dropped on the chip to make the connections between the electrodes. Current-voltage characteristics between the drain and source electrodes exhibited Coulomb blockade (CB) at both 77 and 287 K. Dependence of the CB region on the gate voltage was similar to that of an R-SET. Simulation results of the model based on the scanning electron microscopy image of the device could reproduce the characteristics like the R-SET., SPRINGER, Aug. 2017, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 123, 8, English, 0947-8396, 1432-0630, 85026775337, WOS:000407570900011 - Gate-tuned negative differential resistance observed at room temperature in an array of gold nanoparticles
Tran Thi Thu Huong; Kazuhiko Matsumoto; Masataka Moriya; Hiroshi Shimada; Yasuo Kimura; Ayumi Hirano-Iwata; Yoshinao Mizugaki
We fabricated a single-electron (SE) device using gold nanoparticles (Au NPs). Drain, source, and gate electrodes on a SiO2/Si substrate were formed using electron beam lithography (EBL) and thermal evaporation of Au. Subsequently, solutions of 3-nm-diameter and 5-nm-diameter Au NPs were dropped on the device to make current paths through Au NPs among the electrodes. Measurements of the device exhibited negative differential resistance (NDR) in the current-voltage characteristics between the drain and source electrodes at room temperature (298 K). The NDR behavior was tuned by applying a gate voltage., SPRINGER, Apr. 2017, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 123, 4, English, 0947-8396, 1432-0630, 85016328097, WOS:000397581200053 - Fabrication of single-electron devices using dispersed nanoparticles and fitting experimental results to values calculated based on percolation model
Masataka Moriya; Tran Thi Thu Huong; Kazuhiko Matsumoto; Hiroshi Shimada; Yasuo Kimura; Ayumi Hirano-Iwata; Yoshinao Mizugaki
We calculated the connection probability, P-C, between electrodes on the basis of the triangular lattice percolation model for investigating the effect of distance variation between electrodes and the electrode width on fabricated capacitively coupled single-electron transistors. Single-electron devices were fabricated via the dispersion of gold nanoparticles (NPs). The NPs were dispersed via the repeated dropping of an NP solution onto a chip. The experimental results were fitted to the calculated values, and the fitting parameters were compared with the occupation probability, P-O, which was estimated for one drop of the NP solution. On the basis of curves of the drain current versus the drain-source voltage (I-D-V-DS) measured at 77 K, the current was suppressed at approximately 0 V., SPRINGER, Aug. 2016, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 122, 8, English, 0947-8396, 1432-0630, 84979573645, WOS:000380667500042 - Fabrication of high temperature capacitively-and resistively-coupled single electron transistors using gold nanoparticles
H. T. T. Tran; K. Matsumoto; M. Moriya; H. Shimada; Y. Kimura; A. Hirano-Iwata; Y. Mizugaki
We fabricated single electron transistors (SETs) by using gold nanoparticles as their islands. With a simple method of the fabrication, characteristics of capacitively-and resistively-coupled SETs (C-SETs and R-SETs) were achieved at 77 K and room temperature., IEEE, 2016, 2016 IEEE 16TH INTERNATIONAL CONFERENCE ON NANOTECHNOLOGY (IEEE-NANO), 131-134, English, 85006856529, WOS:000391840000038
Lectures, oral presentations, etc.
- SiO2/Si基板上の超伝導デバイス間におけるフォノン伝播の研究
飯塚竜也; 水柿義直; 島田宏
Oral presentation, Japanese, 2023年 第84回 応用物理学会秋季学術講演会
22 Sep. 2023
19 Sep. 2023- 23 Sep. 2023 - 単一Cooper対トランジスタによるフォノンの高感度検出
島田 宏; Jutarat Tanarom; 水柿 義直
Oral presentation, Japanese, 第70回応用物理学会春季学術講演会
17 Mar. 2023
15 Mar. 2023- 18 Mar. 2023 - 希釈冷凍温度で動作するラテラル型過減衰Al/AlOx/Al接合の作製
星野将弥; 水柿義直; 島田宏
Oral presentation, Japanese, 電子情報通信学会 超伝導エレクトロニクス研究会, 東北大学 電気通信研究所, Domestic conference
04 Nov. 2022 - Sensitive phonon detection by use of a single Cooper-pair transistor
H. Shimada; J. Tanarom; T. Watanabe; T. Iizuka; Y. Mizugaki
Poster presentation, English, Applied Superconductivity Conference (ASC2022), International conference
24 Oct. 2022 - Phonon Detection with a Supercurrent through a Single Cooper-pair Transistor
H. Shimada; J. Tanarom; T. Iizuka; Y. Mizugaki
Poster presentation, English, 29th International Conference on Low Temperature Physics, Sapporo, Japan, https://www.lt29.jp, International conference
22 Aug. 2022 - Gate-controlled supercurrent in vertical ultra-short superconductor/MoS2/superconductor junctions
Yung-Hsiang Tsai; Yun-Lien Hsieh; Chien-Han Chen; Hiroshi Shimada; Wen-Hao Chang; Cen-Shawn Wu; Watson Kuo
Poster presentation, English, 29th International Conference on Low Temperature Physics, International conference
22 Aug. 2022 - Phonon detection using a single Cooper-pair transistor
ジュタラト タナロ-ム; 水柿義直; 島田 宏
Oral presentation, English, 電子情報通信学会超伝導エレクトロニクス研究会, Domestic conference
06 Aug. 2021 - 原子層堆積法を援用した斜め蒸着法による単一電子素子の作製
小池威廣; 今野寛己; 水柿義直; 島田 宏; 三浦正範; 鹿又健作; 廣瀬文彦
Oral presentation, Japanese, 第81回応用物理学会秋季学術講演会, Domestic conference
09 Sep. 2020 - Study on the Cooper-pair transistor as a fast supercurrent switch
Jutarat Tanarom; Hiroshi Shimada
Oral presentation, English, 第81回応用物理学会秋季学術講演会, Domestic conference
09 Sep. 2020 - フォノン照射による微小Josephson接合列の特性変化
渡邉拓磨; 水柿義直; 島田宏
Oral presentation, Japanese, 日本物理学会第75回年次大会, 日本物理学会, Domestic conference
Mar. 2020 - Applicability of small Josephson junction arrays as radiation detectors
T. Suzuki; G. M. Kanyolo; H. Nishigaki; Y. Mizugaki; H. Shimada
Poster presentation, English, International Symposium on Hybrid Quantum Systems 2019 (HQS2019), Matsue, Shimane, Japan, https://www.hqs2019.org/, International conference
02 Dec. 2019 - Application of the Cooper-pair transistor as a supercurrent switch for superconducting circuits
Jutarat Tanarom; Hiroshi Shimada
Poster presentation, English, International School and Symposium on Nanoscale Transport and phTonics (ISNTT2019), NTT Basic Research Laboratories, Atsugi, Kanagawa, http://www.brl.ntt.co.jp/event/isntt2019/, International conference
20 Nov. 2019 - Long Range Current Correlation for Adjacent Small Josephson Junction Devices
Takuma Watanabe; Yoshinao Mizugaki; Hiroshi Shimada
Poster presentation, English, International School and Symposium on Nanoscale Transport and phTonics (ISNTT2019), NTT Basic Research Laboratories, Atsugi, Kanagawa, Japan, http://www.brl.ntt.co.jp/event/isntt2019/, International conference
20 Nov. 2019 - 微小Josephson接合列の輻射検出器としての利用性の評価
鈴木俊貴; Kanyolo Godwill Mbiti; 西垣宏志; 水柿義直; 島田宏
Oral presentation, Japanese, 第80回応用物理学会秋季学術講演会, 応用物理学会, 北海道大学 札幌キャンパス, Domestic conference
19 Sep. 2019 - 微小Josephson接合列の輻射検出器としての利用性の評価
鈴木俊貴; カニョロ・ゴドゥウィリ・ビティ; 西垣宏志; 水柿義直; 島田宏
Oral presentation, Japanese, 電子情報通信学会超伝導エレクトロニクス研究会, Domestic conference
09 Aug. 2019 - The Lifting of Coulomb Blockade by Alternating Voltages in Small Josephson junctions with Electromagnetic Environment-based Renormalization Effects
G. M. Kanyolo; H. Shimada
Oral presentation, English, 日本物理学会第74会年次大会, 九州大学伊都キャンパス, Domestic conference
17 Mar. 2019 - 強く容量結合した短い微小ジョセフソン接合列における電流誘引現象
村井飛天; 水柿義直; 島田宏
Oral presentation, Japanese, 日本物理学会第74回年次大会, 九州大学伊都キャンパス, Domestic conference
17 Mar. 2019 - 原子層堆積法を援用した微小トンネル接合素子の形成装置の開発
今野寛己; 島田 宏
Poster presentation, Japanese, 新学術領域「ハイブリッド量子科学」第８回領域会議, 沖縄科学技術大学院大学, Domestic conference
09 Jan. 2019 - The radio-frequency response of linear arrays of mesoscopic Josephson junctions
G.M. Kanyolo; H. Nishigaki; Y. Mizugaki; H. Shimada
Poster presentation, English, International Symposium on Frontiers of Quantum Transport in Nano Science, Institute of Industrial Science, Kashiwa Campus, University of Tokyo, International conference
08 Nov. 2018 - Correlation of currents in remote arrays of small Josephson junctions through the quasiparticle excitation
Takuma Watanabe; Yoshinao Mizugaki; Hiroshi Shimada
Poster presentation, English, International Symposium on Frontiers of Quantum Transport in Nano Science, Institute of Industrial Science, Kashiwa Campus, University of Tokyo, International conference
08 Nov. 2018 - 室温ALD法を援用した斜め蒸着法による微小トンネル接合の作製
吉川圭介; 伊藤直輝; 今野寛己; 水柿義直; 島田宏; 鹿又健作; 廣瀬文彦
Oral presentation, Japanese, 第65回応用物理学会春季学術講演会, 応用物理学会, Domestic conference
17 Mar. 2018 - Excitons in capacitively coupled chains of small Josephson junctions
H. Shimada; K. Matsudo; C. Ishida; H. Murai; Y. Mizugaki
Poster presentation, English, International Symposium on Nanoscale Transport and phoTonics (ISNTT2017), NTT Basic Research Laboratory, Atsugi, Kanagawa, Japan, http://www.brl.ntt.co.jp/event/isntt2017, International conference
14 Nov. 2017 - Fabrication of Mesoscopic Tunnel Junctions by Use of In-situ Low-temperature Atomic Layer Deposition for Tunnel Barriers
K. Kikkawa; N. Ito; H. Shimada
Poster presentation, English, International Symposium on Novel Energy Nanomaterials, Catalysts and Surfaces for Future Earth（NENCS）, The Unniversity of Electro-Communications, Chofu, Tokyo, Japan, http://www.iwasawalab.pc.uec.ac.jp/uec.int.symp/, International conference
29 Oct. 2017 - Fabrication of Mesoscopic Tunnel Junctions by Use of In-situ Low-temperatureAtomic Layer Deposition for Tunnel Barriers
K. Kikkawa; N. Ito; H. Shimada
Poster presentation, English, International Symposium on Novel Energy Nanomaterials, Catalysts and Surfaces for Future Earth（NENCS）, The Unniversity of Electro-Communications, Chofu, Tokyo, Japan, http://www.iwasawalab.pc.uec.ac.jp/uec.int.symp/, International conference
29 Oct. 2017 - The radio-frequency response of linear arrays of mesoscopic Josephson junctions and its application
G. M. Kanyolo; H. Nishigaki; Y. Mizugaki; H. Shimada
Poster presentation, English, 28th International Conference on Low Temperature Physics, Swedish Exhibition Center, Gothenburg, Sweden, http://lt28.se, International conference
10 Aug. 2017 - Cooper-pair excitons and quasiparticle excitons in capacitively coupled chains of small Josephson junctions
H. Shimada; K. Matsudo; C. Ishida; Y. Mizugaki
Poster presentation, English, 28th International Conference on Low Temperature Physics, Swedish Exhibition Center, Gothenburg, Sweden, http://lt28.se, International conference
10 Aug. 2017 - 容量結合した微小ジョセフソン接合列におけるトンネル伝導(2)
松戸広太; 村井飛天; 水柿義直; 島田宏
Oral presentation, Japanese, 日本物理学会 第72回年次大会, 日本物理学会, 大阪負豊中市, Domestic conference
17 Mar. 2017 - 1次元微小Josephson接合列の高周波印加に伴う直流特性変化
Godwill Mbiti Kanyolo; 水柿義直; 島田宏
Oral presentation, Japanese, 日本物理学会2016年秋季大会, Domestic conference
13 Sep. 2016 - 微小Josephson接合列による超伝導単一電子トランジスタからの輻射検出
西垣宏志; Godwill Mbiti Kanyolo; 水柿義直; 島田宏
Oral presentation, Japanese, 日本物理学会2016秋季大会, Domestic conference
13 Sep. 2016 - 容量結合した微小ジョセフソン接合列におけるトンネル伝導
松戸広太; 西垣宏志; 水柿義直; 島田宏
Oral presentation, Japanese, 日本物理学会2016秋季大会, Domestic conference
13 Sep. 2016 - Co/Al/Co単一電子トランジスタにおけるトンネル磁気抵抗の静電的制御
田中歩; 小林竜介; 辻道尚貴; 島田宏
Oral presentation, Japanese, 第76回応用物理学会秋季学術講演会, Domestic conference
16 Sep. 2015 - Electrostatic control of tunnel-magnetoresistance polarity in ferromagnetic single-electron transistors
Hiroshi Shimada
Invited oral presentation, English, 2015 Interanational Conference on Low Dimensional Science, Invited, National Changhua University of Education, Changhua, Taiwan, International conference
11 Sep. 2015 - Long Range Induction between Josephson Junction Arrays via Microwave Photon Emission and Absorption
Wei-Chen Chien; Cheng-An Jiang; Jia-Yu Hong; Yung-Fu Chen; Cen-Shawn Wu; Hiroshi Shimada; Watson Kuo
Oral presentation, English, Progress In Electromagnetics Research Symposium 2015, International conference
08 Jul. 2015 - 微小Josephson接合列におけるBloch振動と電流プラトーの観測
島田宏; 鹿取俊介; 出口智明; 水柿義直
Oral presentation, Japanese, 日本物理学会第70回年次大会, Domestic conference
21 Mar. 2015 - 二重微小Josephson接合における接合間のトンネル過程の相互作用
松原明志; 水柿義直; 島田宏
Oral presentation, Japanese, 日本物理学会第70回年次大会, 早稲田大学、東京, Domestic conference
21 Mar. 2015 - 量子電流ミラー効果に基づく高精度な電流整数倍器の実現に向けた研究
武田晃一; 宮脇健至; ガンドロシュラ・スリニワス; 石田千尋; 萩原彩乃; 水柿義直; 島田宏
Oral presentation, Japanese, 電子情報通信学会超伝導エレクトロニクス研究会, 電子情報通信学会超伝導エレクトロニクス研究専門委員会, 機会振興会館、東京, Domestic conference
22 Jan. 2015 - Manipulating Cooper pairs by using linear arrays of small Josephson junctions
Hiroshi Shimada
Oral presentation, English, The Second International Workshop MIPT-UEC, Invited, UEC, UEC, Tokyo, International conference
20 Oct. 2014 - 微小なAl/AlOx/V接合を用いた超伝導単一電子トランジスタ
宮脇健至; 水柿義直; 島田宏
Oral presentation, Japanese, 第75回応用物理学会秋季学術講演会, Domestic conference
19 Sep. 2014 - Ni/Al/Ni単一電子トランジスタにおけるトンネル磁気抵抗の静電的な極性制御
小林竜介; 辻道尚貴; 島田宏
Oral presentation, Japanese, 第75回応用物理学会秋季学術講演会, Domestic conference
19 Sep. 2014 - 量子電流ミラー効果における電流誘引過程の非局所性
武田晃一; 水柿義直; 島田宏
Oral presentation, Japanese, 日本物理学会2014年秋季大会, Domestic conference
09 Sep. 2014 - Observation of Bloch oscillation and current plateaus in an array of small Josephson junctions embedded in dc-SQUID network
Srinivas Gandrothula; Shunsuke Katori; Tomoaki Deguchi; Yoshinao Mizugaki; Hiroshi Shimada
Poster presentation, English, 3rd International Conference on Nanotek and Expo, Las Vegas, USA, International conference
02 Dec. 2013 - Towards precise current multiplication by use of linear arrays of small Josephson junctions
K. Takeda; S. Gandrothula; Y. Mizugaki; H. Shimada
Oral presentation, English, International Symposium on Nanoscale Transport and Technology, NTT Atsugi R&D Center, Atsugi, Kanagawa, Japan, International conference
27 Nov. 2013 - Observation of Bloch oscillation and current plateaus in an array of small Josephson junctions embedded in dc-SQUID network
Srinivas Gandrothula; Shunsuke Katori; Tomoaki Deguchi; Yoshinao Mizugaki; Hiroshi Shimada
Poster presentation, English, International Symposium on Nanoscale Transport and Technology, NTT Atsugi R&D Center, Atsugi, Kanagawa, Japan, International conference
27 Nov. 2013 - Current Induction Phenomena in Capacitively Coupled Linear Arrays of Small Josephson Junctions
Hiroshi Shimada
Oral presentation, English, The First International Workshop MIPT-UEC, Invited, Lebedev Institute, Moscow, International conference
01 Nov. 2013 - 微小ジョセフソン接合列間の量子電流ミラー効果に見られる二面性
島田宏; 武田晃一; 水柿義直
Oral presentation, Japanese, 電子情報通信学会2013年ソサエティ大会, 電子情報通信学会, 福岡工業大学, Domestic conference
19 Sep. 2013 - 量子電流ミラー効果に基づく微小電流の整数倍器
武田晃一; 水柿義直; 島田 宏
Oral presentation, Japanese, 電子情報通信学会2013年ソサエティ大会, 電子情報通信学会, 福岡工業大学, Domestic conference
19 Sep. 2013 - 微小Josephson接合列におけるBloch振動と電流プラトー
出口智明; 鹿取俊介; Srinivas Gandrothula; 水柿義直; 島田宏
Oral presentation, Japanese, 第74回応用物理学会秋季講演会, 応用物理学会, 同志社大学京田辺キャンパス, Domestic conference
18 Sep. 2013 - Current Induction Phenomena in Capacitively Coupled Linear Arrays of Small Josephson Junctions
Hiroshi Shimada
Invited oral presentation, English, Low Dimensional Science 2013 Conference, Invited, National Chung Hsing University, Huisun Forest, Nantou Taiwan, International conference
09 Sep. 2013 - 微小Josephson接合列を用いた電流整数倍器の高精度化
武田晃一; 水柿義直; 島田宏
Oral presentation, Japanese, 応用物理学会,第60回応用物理学会春季学術講演会, 応用物理学会, 神奈川工科大学, Domestic conference
28 Mar. 2013 - Al/AlOx/V Josephson接合を用いた単一Cooper対素子
宮脇健至; 萩原彩乃; 小谷祥生; 水柿義直; 島田宏
Oral presentation, Japanese, 電子情報通信学会,電子情報通信学会総合大会
22 Mar. 2013 - DC/SFQ変換器をSFQ入力に用いた1000倍電圧増倍回路の増倍率評価
佐藤裕介; 守屋雅隆; 島田宏; 水柿義直; 前澤正明
Oral presentation, Japanese, 電子情報通信学会,電子情報通信学会総合大会
Mar. 2013 - Current Induction Phenomena between arrays of small Josephson Junctions
Chihiro Ishida; Yoshinao Mizugaki; Hiroshi Shimada
Oral presentation, Japanese, Physical Society of Japan
Mar. 2012 - アンダーダンプ接合でのSFQ反射を利用する電圧増倍器の増倍率評価
Y. Sato; M. Moriya; H. Shimada; Y. Mizugaki; M. Maezawa
Oral presentation, Japanese, 電子情報通信学会,2012年総合大会
Mar. 2012 - Current steps in a mesoscopic Josephson junction embedded in a Josephson-junction network
Srinivas Gandrothula; Yoshinao Mizugaki; Hiroshi Shimada
Oral presentation, English, 応用物理学会,第59回応用物理学関係連合講演会
Mar. 2012 - 強く容量結合した微小Josephson接合列における電流誘引現象
石田千尋; 水柿義直; 島田宏
Public symposium, Japanese, 東京農工大学・電気通信大学第８回合同シンポジウム
Dec. 2011 - 4-Step Quasi-Sine Waveform Synthesizer Based on 3-Bit Variable Pulse Number Multiplier
Y. Mizugaki; K. Kuroiwa; M. Moriya; H. Shimada; M. Maezawa
Oral presentation, English, The 6th East Asia Symposium on Superconductor Electronics
Oct. 2011 - The Quantum Current Mirror Based 10-Time Current Multiplier
Srinivas Gandrothula; Yoshinao Mizugaki; Hiroshi Shimada
Oral presentation, English, Superconductivity Centennial Conference
Sep. 2011 - Current Induction in Strongly Coupled Arrays of Small Josephson Junctions
Hiroshi Shimada; Chihiro Ishida; Yoshinao Mizugaki
Oral presentation, English, The 26th International Conference on Low Temperature Physics
Aug. 2011 - 10-Time Current Multiplier Based on the Quantum Current Mirror
Srinivas Gandrothula; Yoshinao Mizugaki; Hiroshi Shimada
Oral presentation, English, 応用物理学会,第58回応用物理関係連合講演会
Mar. 2011 - Li-doped TiO2ナノ結晶薄膜の電気的特性評価と色素増感太陽電池への応用
名田允洋; 権田智洋; 沈青; 島田宏; 豊田太郎; 小林直樹
Oral presentation, Japanese, 第69回応用物理学会学術講演会
Sep. 2008 - 量子電流ミラー効果を用いた微小電流２倍器
島田宏; 花堂純央; 水柿義直
Public symposium, Japanese, 第４回合同シンポジウム「コヒーレント光科学とナノ未来材料」, 電気通信大学・東京農工大学ＣＯＥ, 小金井市
Dec. 2007 - Precise dc-current duplication and multiplication with arrays of small Josephson junctions
H. Shimada; S. Hanadou; Y. Mizugaki
Public symposium, English, International Symposium on Coherent Optical Science, UEC 21th Century COE Program, Chofu-shi
Dec. 2007 - 交流電圧駆動された単一電子トランジスタでの直流電流生成と素子パラメータの最適化
水柿義直; 河合章生; 守屋雅隆; 宇佐美興一; 小林忠行; 島田宏
Oral presentation, Japanese, 第68回応用物理学会学術講演会
Sep. 2007 - 量子電流ミラー効果に基づいた微小電流２倍器(II)
花堂純央; 島田宏; 水柿義直
Oral presentation, Japanese, 第68回応用物理学会学術講演会
Sep. 2007 - 量子電流ミラー効果に基づいた微小電流２倍器
島田宏; 河合卓磨; 水柿義直
Oral presentation, Japanese, 第54回応用物理学関係連合講演会
Mar. 2007 - 量子電流ミラー効果を用いた微小電流２倍器
島田宏; 水柿義直
Public symposium, Japanese, 第３回合同シンポジウム「ナノ未来材料とコヒーレント光科学」, 電気通信大学・東京農工大学ＣＯＥ, 調布市
Dec. 2006 - 単一電子トランジスタを用いた微小強磁性金属の物性研究
石本英彦; 水柿義直; 島田宏
Public symposium, Japanese, 第３回合同シンポジウム「ナノ未来材料とコヒーレント光科学」, 電気通信大学・東京農工大学ＣＯＥ, 調布市
Dec. 2006 - 単一電子デバイスのクーロンブロッケイド領域設計法に関する研究
水田元紀; 島田宏; 水柿義直
Public symposium, Japanese, 第３回合同シンポジウム「ナノ未来材料とコヒーレント光科学」, 電気通信大学・東京農工大学ＣＯＥ, 調布市
Dec. 2006 - 量子電流ミラー効果による電流２倍器の試作
河合卓磨; 島田宏
Public symposium, Japanese, 第２回合同シンポジウム「ナノ未来材料とコヒーレント光科学」, 電気通信大学・東京農工大学ＣＯＥ, 小金井市
Dec. 2005 - 単電子ターンスタイル素子の電流ミラー回路応用
伊藤正史; 水田元紀; 島田宏; 水柿義直
Public symposium, Japanese, 第２回合同シンポジウム「ナノ未来材料とコヒーレント光科学」, 電気通信大学・東京農工大学ＣＯＥ, 小金井市
Dec. 2005 - 量子電流ミラー効果と電流の計量標準
島田宏
Public symposium, Japanese, 合同シンポジウム「ナノ未来材料とコヒーレント光科学」, 電気通信大学・東京農工大学ＣＯＥ, 調布市
Dec. 2004 - 量子電流ミラー（鏡）効果と量子電流標準器
島田宏
Public symposium, Japanese, 公開シンポジウム「コヒーレント光科学の展開」, 電気通信大学２１世紀ＣＯＥ, 調布市
Dec. 2003 - Driving the single-electron device with a magnetic field
Hiroshi Shimada; Keiji Ono; Youiti Ootuka
Invited oral presentation, English, Journal of Applied Physics, Tampa, International conference
May 2003
Courses
Research Themes
- 単電子制御による量子標準・極限計測技術の開発
藤原 聡; 山端 元音; 金子 晋久; 島田 宏
日本学術振興会, 科学研究費助成事業, 日本電信電話株式会社NTT物性科学基礎研究所, 基盤研究(A), 18H03871
01 Apr. 2018 - 31 Mar. 2021 - Detection of a single-flux-quantum at 4.2 K by means of a ultra-charge-sensitive single-electron device
MIZUGAKI Yoshinao; SHIMADA Hiroshi
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Electro-Communications, Grant-in-Aid for Challenging Exploratory Research, A superconducting quantum interference device (SQUID) is commonly used for detection of a single-flux-quantum (SFQ) in a superconducting loop. A SQUID, however, occupies a relatively large area. On the other hand, a single-electron (SE) device is a ultra-small and ultra-charge-sensitive sensor, which is expected to detect an SFQ. In this research project, we integrated an SFQ digital circuit with an SE device that would work as an SFQ detector. SFQ digital circuits were made of niobium superconductors, whereas gold nano-particles were employed for island electrodes of SE devices. SFQ circuits and SE devices developed in this research project demonstrated new functionality, resulting in several publications. Unfortunately, the whole circuit including an SFQ digital circuit and an SE device did not work as we expected. The reason was insufficient sensitivity of the SE device on the SFQ circuit., 15K13999
01 Apr. 2015 - 31 Mar. 2017 - Development of fast high-sensitivity scanning charge microscope
SHIMADA Hiroshi; OOTUKA Youiti
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Tokyo, Grant-in-Aid for Scientific Research (A), The goal of this project is to develop a versatile fast scanning charge microscope which utilizes the single-electron transistor as its charge sensor and works at 2K. We have introduced a low-temperature scanning shear-force microscope as the basic servo scanning system for the charge microscope. The shear force microscope uses as its force sensor a sharpened optical fiber that is fixed on a quartz oscillator on the sensor head. We have developed a fabrication process of a single-electron transistor on the tip of the sharpened optical fiber. The process comprises a sharpening process of an optical fiber by using a selective etching technique of a dispersion- compensation fiber, and a formation of double small tunnel junctions on the tip of the sharpened fiber mostly by means of a vacuum-evaporation deposition. We have also developed versatile fast-measuring circuits of the single-electron transistor. The main part of the circuits is a current amplifier that is composed of an operational amplifier (opamp) and it measures a conductance of a measured device. Generally a conductance measurement with a voltage biasing is less influenced by the stray capacitance of the signal cable than the resistance measurement with a current biasing. We have further reduced the influence of the stray capacitance of the signal cable by using a C-MOS based opamp (TLC4501) and putting the amplifier near the sensor device in liquid He and making the signal cable short, or by using a tri-axial signal cable and driving its middle conductor with a voltage follower at the voltage of the signal line and reducing the stray capacitance effectively. Unfortunately we have spent a lot of effort and time on the development of the fabrication process of the charge sensor, and we have not succeeded in integrating all the elements described above and constructing the charge microscope itself during the period of the project., 12355002
2000 - 2002 - Invesigation on Mesoscopic Ferromagnetic Metals by Using Single Electron Transistor
SHIMADA Hiroshi
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Tokyo, Grant-in-Aid for Scientific Research (C), In this project we have investigated the behavior of ferromagnetic single electron transistors (FSET's) in a magnetic field. With the term 'ferromagnetic single electron transistor' we mean a single electron transistor part of whose electrode is made of ferromagnetic metals, and in such a system we discovered a conductance oscillation almost periodic in applied magnetic field, which we call 'magneto-Coulomb oscillation (MCO)'. That was the start point of this project. In this project, we have especially clarified the mechanism of MCO from both experimental and theoretical point of view. We have also explored the possible application of this phenomenon as a tool to investigate the electronic structure of ferromagnetic metals and as a basis for functional operations of FSE devices. We have constructed a model to elucidate the phenomenon of MCO. In the model the origin of the magnetic-field induced conductance oscillation consists in the Zeemann effect and the spin polarization of the valence electrons in ferromagnetic metals. These two factors induce a change in chemical potential of the ferromagnetic metal in a magnetic field, just in a same way as by a gate potential in usual nonmagnetic SET's. We experimentally examined this model for Ni/Co/Ni, Co/Ni/Co, Al/Co/Al, Al/Al/Al, Al/Ni/Al and Ni/Al/Ni FSET's, and have found semi-quantitative consistency with the model. By using this phenomenon conversely, we can determine a thermodynamic coefficient of a ferromagnetic metal (∂ζ/∂H)ィイD2NィエD2, where ζ is the chemical potential, H means the magnetic field and N is the number of electrons in the ferromagnet. We have demonstrated this for Al/Co/Al, Al/Ni/Al and Ni/Al/Ni SET's. We have also indicated a possible operation of ferromagnetic single electron devices as magnetic-field driven functional devices utilizing MCO mechanism and magnetization reversal., 10640331
1998 - 1999 - 速度変調トランジスタ素子型試料を用いた量子ホール効果の破綻現象の研究
島田 宏
日本学術振興会, 科学研究費助成事業, 東京大学, 奨励研究(A), 量子ホール効果のブレークダウン現象がバルクの効果であるか、あるいは試料端の効果であるかという問題は、量子ホール効果状態下での試料中の電流分布の問題と関連して研究されてきている。これまで量子ホール効果のブレークダウンの臨界電流値の試料幅依存性からブレークダウンがバルク、試料端のどちらで起こる場合もあり、両者を分ける隠れたパラメータがあることが指摘されて来ている。 この研究では、GaAs/AlGaAsの場合にその一つの可能性として、接合界面から離れたドープ層のイオン化不純物により2次元電子が受けるポテンシャル揺らぎの効果に着目し、基板上面、下面両方にゲート電極を設けた速度変調トランジスタ構造の素子を用い、2次元電子の波動関数の接合界面に対する相対的な位置を変化させて、ポテンシャル揺らぎの強度を変化させて、量子ホール効果のブレークダウンの臨界電流値の試料幅依存性を調べることを目指して研究を行った。 実験は、速度変調トランジスタ構造型素子の作製、下面ゲート用高圧回路の作製、高圧用強磁場クライオスタットの作製等を経て行った。 ポテンシャル揺らぎの強度変調の影響を押さえるためには、他のパラメータの変化を抑えた上で測定を行う必要があるため、現段階では、速度変調トランジスタ型素子の上面、下面ゲートによる電子濃度、電子移動度の制御を行っており、目的とした測定まで至っていない。, 08740230
1996 - 1996 - 強磁性金属を用いた微小トンネル接合の単電子帯電効果と磁化
大塚 洋一; 島田 宏
日本学術振興会, 科学研究費助成事業, 東京大学, 重点領域研究, これまでの実験で、微小な接合面積をもつNi/NiO/Coトンネル接合が2次元的に配列した系の電気抵抗を測定し、一電子帯電効果が支配的となる極低温・低バイアス電流の下では保磁力差型の磁気抵抗が最大40%に達するほど大きくなることを見いだしていた。この磁気抵抗の巨大化の原因をはっきりさせるため、より単純な単一電子トランジスター(SET)構造を強磁性体で作製し、T=20mKにおける電流・電圧特性の磁場、ゲート電圧依存性等を測定した。 試料となるSETは、島状電極がCo、ソース、ドレイン電極がNiでできており、ソース・ドレイン各電極と島状電極とは接合面積約0.02μm^2のNiOのトンネル接合でつながっている。これはSi_3N_4薄膜を微細加工して作った蒸着マスクを用い、斜め蒸着法によりSi基板上に作製した。 この試料のソース・ドレイン抵抗を様々なソースドレイン電圧、ゲート電圧、磁場に対して調べ、以下の知見を得た。 (1)高温においてスピンバルプ効果による約4%の磁気抵抗を示す。 (2)一電子帯電効果が支配的となる低温で、磁気抵抗は40%程度まで巨大化する。 (3)低温でも高バイアスにおける微分抵抗に見られる磁気抵抗は高温とほぼ同程度である。 (4)ゲート電圧による明確なクーロン振動を示す。 (5)SETのオフ抵抗は巨大磁気抵抗を示すのに対して、オン抵抗には巨大化は見られない。 (6)磁場によってクーロン振動の振幅のみならず位相が変わる。則ち、外部磁場によってSETのスイッチが起こる(磁場クーロン振動)。 このうち、特に(5、6)はこれまでに報告のない新しい発見である。磁気抵抗の巨大化には高次のトンネル効果による有効帯電エネルギーの減少が、また磁気クーロン振動については強磁性物質中の各スピン状態に対応する状態密度の差によって生じる化学ポテンシャルの磁場による変動が原因するものと考えている。, 08247206
1996 - 1996 - 1次元同期ポテンシャルの加わった2次元電子系の電流磁気効果
島田 宏
日本学術振興会, 科学研究費助成事業, 東京大学, 奨励研究(A), GaAs/AlGaAsヘテロ接合界面の2次元電子系を用いて、まず、電圧印加・電流測定により界面に垂直な強磁場中で対角伝導率、非対角伝導率を測定するための試料および測定用回路を作製した。これらを用い予備実験として、量子化 Hall 伝導率の測定を試みた。Hall 伝導率のプラトーの観測はでき、測定回路が予想通り機能していることがわかった。しかし、Si-MOS FET の場合に比べると、試料の電流端子の端子抵抗を、無視できる程度に小さくすることができなかった。端子と2次元電子系とのオーミック接触は、文献に見られる最も良好な材料で行ったが、接触抵抗は20-30Ωmm程度に留まり、これは伝導率の絶対値を問題にする場合には不十分である。 これらの予備実験の後、2次元電子系に1次元周期ポテンシャルの加わった試料を次のように作製した。用いたヘテロ基板の2次元電子系の4.2Kでの平均自由行程は3-10μmであり、これに対して摂動ポテンシャルの周期は可能な限り短い方がよいので、電子線描画装置を用いて安定してレジストに描画出来た最短の0.3μm周期の縞状構造を描画し、これを軽くウェット・エッチして電子系に周期的な摂動ポテンシャルを加えることを試みた。周期構造を作製した後電圧印加・電流測定用の整形プロセスを施した試料いくつかにつき、電圧印加型の電流磁気効果測定をし、目的とする共鳴による伝導度振動の観測を試みたが、これまでのところ観測に成功していない。AFMを用いて作製した周期構造を観察してみたところ、エッチングした部分にかなり凹凸が見られ、これらがランダムポテンシャルを作り、伝導度振動を観測できない一因となっていることが考えられる。これに対し電子線描画後の酸素プラズマによる試料表面の浄化やエッチャントの種類を変えるなどの改善を試みている。, 06740244
1994 - 1994 - 微細加工による準周期構造の電子状態の研究
大塚 洋一; 多田 哲也; 島田 宏
日本学術振興会, 科学研究費助成事業, 東京大学, 重点領域研究, 準周期的ポテンシャル中の電子がどのような状態にあるか、それが周期的あるいは不規則的な場合とどのように異なるかは興味深い問題である。本研究は1次元準周期ポテンシャル中の電子状態を実験的に探ることを目的としている。試料は変調ド-プ型のAlGaAs/GaAs単一ヘテロ接合界面に生じる高易動度2次元電子ガスとし、基板上1次元方向にいわゆるHEMT構造で細線ゲ-トを作製し、これによって2次元電子系に強度可変にポテンシャル障壁列を導入する。作製した金ゲ-トの線幅は約0.1μmであり、間隔が0.809μmと0.500μmとのフィボナッチ列を構成している。また比較対照のため、周期的に並んだゲ-トを有する試料も 作製した。液体ヘリウム温度において電気伝導を測定した結果、周期的障壁列をもつ試料で、障壁による干渉効果と考えられるサブストレ-トバイアス依存性を見出した。しかし準周期系についてはそのような構造を見つけるに至らなかった。電子の平均自由行程長が不十分であること、測定温度が高いこと等が問題であると考えられ、これらを克服するために一層の努力が必要である。 波動コヒ-レンス長さがより長い波動系を用いれば、この困難の少ない実験が出来る。我々は超流動ヘリウム薄膜中の第3音波に対する準周期的障壁列の影響を調べた。ガラス及びシリコンウエハを基板とし、その上にリソグラフィ-によりアルミニウム線を周期的及びフィボナッチ的に設けた。この上の第3音波を測定した所、その透過スペクトルに多くの難透過領域がみられた。特に準周期系ではその構造は自己相似的でありネストしている。このスペクトルはシュミレ-ションによるものとよく一致し、難透過領域の指数付けを行なうことが出来る。, 02212203
1990 - 1990