Author
Akira Toriumi
Other affiliations: Hokkaido University, National Institute of Advanced Industrial Science and Technology, Dresden University of Technology
Bio: Akira Toriumi is an academic researcher from University of Tokyo. The author has contributed to research in topics: Electron mobility & High-κ dielectric. The author has an hindex of 50, co-authored 399 publications receiving 9145 citations. Previous affiliations of Akira Toriumi include Hokkaido University & National Institute of Advanced Industrial Science and Technology.
Topics: Electron mobility, High-κ dielectric, Dielectric, Germanium, Graphene
Papers published on a yearly basis
Papers
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TL;DR: In this article, Ohmic and Schottky properties of metal/germanium (Ge) junction have been investigated and it has been shown that Fermi level at metal/Ge interface is intrinsically pinned at the charge neutrality level (CNL) characterized by the metal-induced gap states model.
Abstract: The purpose of this paper is to understand metal/germanium (Ge) junction characteristics. Electrode metals with a wide work function range were deposited on Ge. All metal/p-Ge and metal/n-Ge junctions have shown Ohmic and Schottky characteristics, respectively, with the strong Fermi-level pinning. The charge neutrality level (CNL) at metal/Ge interface is close to the branch point calculated for the bulk Ge. Moreover, the pinning level is hardly modulated by annealing in forming gas, forming metal-germanide/Ge interfaces or changing the substrate orientation. These results suggest that Fermi level at metal/Ge interface is intrinsically pinned at the CNL characterized by the metal-induced gap states model.
411 citations
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TL;DR: In this paper, the authors examined the contact properties between metal and graphene and found that the current flow preferentially entered graphene at the edge of the contact metal, and the analysis using the cross-bridge Kelvin (CBK) structure suggested that a transition from the edge conduction to area conduction occurred for a contact length shorter than the transfer length of ∼1 μm.
Abstract: The contact properties between metal and graphene were examined. The electrical measurement on a multiprobe device with different contact areas revealed that the current flow preferentially entered graphene at the edge of the contact metal. The analysis using the cross-bridge Kelvin (CBK) structure suggested that a transition from the edge conduction to area conduction occurred for a contact length shorter than the transfer length of ∼1 μm. The contact resistivity for Ni was measured as ∼5×10−6 Ω cm2 using the CBK. A simple calculation suggests that a contact resistivity less than 10−9 Ω cm2 is required for miniaturized graphene field effect transistors.
304 citations
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TL;DR: In this paper, the authors proposed a model for the physical origin of the dipole formed at high-k/SiO2 interface, where the bonding energy relaxation at the interface explains why the oxygen density difference is the driving force of the oxygen movement.
Abstract: A model for the physical origin of the dipole formed at high-k/SiO2 interface is proposed. In our model, an areal density difference of oxygen atoms at high-k/SiO2 interface is considered as an intrinsic origin of the dipole formation. The oxygen movement from higher-oxygen-density side to a lower-oxygen-density one will determine the direction of interface dipole. The bonding energy relaxation at the interface explains why the oxygen density difference is the driving force of the oxygen movement. Our model enables the prediction of the dipole directions for candidate gate dielectrics, including those so far not reported.
292 citations
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TL;DR: In this paper, the authors examined the contact properties between metal and graphene and found that the current flow preferentially entered graphene at the edge of the contact metal, and the analysis using the crossbridge Kelvin structure (CBK) suggested that a transition from the edge conduction to area conduction occurred for a contact length shorter than the transfer length of ~1 micron.
Abstract: The contact properties between metal and graphene were examined. The electrical measurement on a multiprobe device with different contact areas revealed that the current flow preferentially entered graphene at the edge of the contact metal. The analysis using the cross-bridge Kelvin structure (CBK) suggested that a transition from the edge conduction to area conduction occurred for a contact length shorter than the transfer length of ~1 micron. The contact resistivity for Ni was measured as ~5*10-6 Ohmcm2 using the CBK. A simple calculation suggests that a contact resistivity less than 10-9 Ohmcm2 is required for miniaturized graphene field effect transistors.
286 citations
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TL;DR: In this paper, a gradual change of Schottky barrier heights with increasing insulating film thickness has been found, which supports that the origin of Fermi level pinning at the metal/germanium junction is caused by the metal-induced gap states.
Abstract: At any metal/germanium (Ge) interfaces, Schottky junctions to n-Ge and ohmic ones to p-Ge are formed by the strong Fermi level pinning to the valence band edge of Ge. In this paper, we report that Schottky-ohmic characteristics are reversed by inserting an ultra-thin oxide film into the metal/Ge interface. A gradual change of Schottky barrier heights (SBHs) with increasing insulating film thickness has been found, which supports that the origin of Fermi level pinning at the metal/Ge junction is caused by the metal-induced gap states. Furthermore, the SBH change enables us to operate metal source/drain Ge n-channel metal–oxide–semiconductor field effect transistors (n-MOSFETs) without any impurity doping. We demonstrate the metal source/drain Ge n-MOSFET with a peak mobility of 270 cm2/(Vs).
201 citations
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TL;DR: Ultraensitive monolayer MoS2 phototransistors with improved device mobility and ON current are demonstrated, showing important potential for applications in MoS 2-based integrated optoelectronic circuits, light sensing, biomedical imaging, video recording and spectroscopy.
Abstract: A very sensitive photodector based on molybdenum disulphide with potential for integrated optoelectronic circuits, light sensing, biomedical imaging, video recording or spectroscopy is now demonstrated.
4,212 citations
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University of Cambridge1, Istituto Italiano di Tecnologia2, Lancaster University3, University of Manchester4, Catalan Institution for Research and Advanced Studies5, Technical University of Denmark6, Nokia7, Queen Mary University of London8, University of Trento9, fondazione bruno kessler10, Technische Universität München11, Polytechnic University of Milan12, Centre national de la recherche scientifique13, University of Trieste14, University of Ioannina15, University of Geneva16, Trinity College, Dublin17, Texas Instruments18, University of Paris19, Spanish National Research Council20, Leiden University21, Delft University of Technology22, University of Patras23, École Normale Supérieure24, Radboud University Nijmegen25, Nest Labs26, Airbus UK27, Seoul National University28, Yonsei University29, University of Oxford30, Chalmers University of Technology31, University of Groningen32, STMicroelectronics33, Chemnitz University of Technology34, Max Planck Society35, Aalto University36
TL;DR: An overview of the key aspects of graphene and related materials, ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries are provided.
Abstract: We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.
2,560 citations
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TL;DR: Tunnels based on ultrathin semiconducting films or nanowires could achieve a 100-fold power reduction over complementary metal–oxide–semiconductor transistors, so integrating tunnel FETs with CMOS technology could improve low-power integrated circuits.
Abstract: Power dissipation is a fundamental problem for nanoelectronic circuits. Scaling the supply voltage reduces the energy needed for switching, but the field-effect transistors (FETs) in today's integrated circuits require at least 60 mV of gate voltage to increase the current by one order of magnitude at room temperature. Tunnel FETs avoid this limit by using quantum-mechanical band-to-band tunnelling, rather than thermal injection, to inject charge carriers into the device channel. Tunnel FETs based on ultrathin semiconducting films or nanowires could achieve a 100-fold power reduction over complementary metal-oxide-semiconductor (CMOS) transistors, so integrating tunnel FETs with CMOS technology could improve low-power integrated circuits.
2,390 citations
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TL;DR: In this paper, the surface chemistry of the trimethylaluminum/water ALD process is reviewed, with an aim to combine the information obtained in different types of investigations, such as growth experiments on flat substrates and reaction chemistry investigation on high-surface-area materials.
Abstract: Atomic layer deposition(ALD), a chemical vapor deposition technique based on sequential self-terminating gas–solid reactions, has for about four decades been applied for manufacturing conformal inorganic material layers with thickness down to the nanometer range. Despite the numerous successful applications of material growth by ALD, many physicochemical processes that control ALD growth are not yet sufficiently understood. To increase understanding of ALD processes, overviews are needed not only of the existing ALD processes and their applications, but also of the knowledge of the surface chemistry of specific ALD processes. This work aims to start the overviews on specific ALD processes by reviewing the experimental information available on the surface chemistry of the trimethylaluminum/water process. This process is generally known as a rather ideal ALD process, and plenty of information is available on its surface chemistry. This in-depth summary of the surface chemistry of one representative ALD process aims also to provide a view on the current status of understanding the surface chemistry of ALD, in general. The review starts by describing the basic characteristics of ALD, discussing the history of ALD—including the question who made the first ALD experiments—and giving an overview of the two-reactant ALD processes investigated to date. Second, the basic concepts related to the surface chemistry of ALD are described from a generic viewpoint applicable to all ALD processes based on compound reactants. This description includes physicochemical requirements for self-terminating reactions,reaction kinetics, typical chemisorption mechanisms, factors causing saturation, reasons for growth of less than a monolayer per cycle, effect of the temperature and number of cycles on the growth per cycle (GPC), and the growth mode. A comparison is made of three models available for estimating the sterically allowed value of GPC in ALD. Third, the experimental information on the surface chemistry in the trimethylaluminum/water ALD process are reviewed using the concepts developed in the second part of this review. The results are reviewed critically, with an aim to combine the information obtained in different types of investigations, such as growth experiments on flat substrates and reaction chemistry investigation on high-surface-area materials. Although the surface chemistry of the trimethylaluminum/water ALD process is rather well understood, systematic investigations of the reaction kinetics and the growth mode on different substrates are still missing. The last part of the review is devoted to discussing issues which may hamper surface chemistry investigations of ALD, such as problematic historical assumptions, nonstandard terminology, and the effect of experimental conditions on the surface chemistry of ALD. I hope that this review can help the newcomer get acquainted with the exciting and challenging field of surface chemistry of ALD and can serve as a useful guide for the specialist towards the fifth decade of ALD research.
2,212 citations
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TL;DR: In this paper, it was shown that crystalline phases with ferroelectric behavior can be formed in thin thin films of SiO2 doped hafnium oxide, which is suitable for field effect transistors and capacitors due to its excellent compatibility to silicon technology.
Abstract: We report that crystalline phases with ferroelectric behavior can be formed in thin films of SiO2 doped hafnium oxide. Films with a thickness of 10 nm and with less than 4 mol. % of SiO2 crystallize in a monoclinic/tetragonal phase mixture. We observed that the formation of the monoclinic phase is inhibited if crystallization occurs under mechanical encapsulation and an orthorhombic phase is obtained. This phase shows a distinct piezoelectric response, while polarization measurements exhibit a remanent polarization above 10 μC/cm2 at a coercive field of 1 MV/cm, suggesting that this phase is ferroelectric. Ferroelectric hafnium oxide is ideally suited for ferroelectric field effect transistors and capacitors due to its excellent compatibility to silicon technology.
1,631 citations