Language：Others   Publishing type：Research paper (scientific journal)  

Ultra-low-power switching circuits based on a binary pattern generator with spiking neurons

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/aelm.202100842

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0028620

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/aelm.201901356

Language：English   Publishing type：Research paper (other academic)  

High-speed low-energy heat signal processing via digital-compatible binary switch with metal-insulator transitions.

DOI： 10.1109/IEDM19573.2019.8993502

Language：English   Publishing type：Research paper (scientific journal)  

Hydrogenation of the wide-gap oxide semiconductor as a room-temperature and 3D-compatible electron doping technique.

DOI： 10.1063/1.5055302

Language：English   Publishing type：Research paper (other academic)  

Analog Spike Processing with High Scalability and Low Energy Consumption Using Thermal Degree of Freedom in Phase Transition Materials.

DOI： 10.1109/VLSIT.2018.8510649

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/smll.201603113

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/IEDM.2016.7838540

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssa.201600006

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/ncomms10104

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/ncomms7759

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.91.205102

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/nl504169m

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/NMAT2946

Language：English   Publishing type：Research paper (scientific journal)  

Recent advances in neural network-based computing have enabled human-like information processing in areas such as image classification and voice recognition. However, many neural networks run on conventional computers that operate at GHz clock frequency and consume considerable power compared to biological neural networks, such as human brains, which work with a much slower spiking rate. Although many electronic devices aiming to emulate the energy efficiency of biological neural networks have been explored, achieving long timescales while maintaining scalability remains an important challenge. In this study, a field-effect transistor based on the oxide semiconductor strontium titanate (SrTiO3) achieves leaky integration on a long timescale by leveraging the drift-diffusion of oxygen vacancies in this material. Experimental analysis and finite-element model simulations reveal the mechanism behind the leaky integration of the SrTiO3 transistor. With a timescale in the order of one second, which is close to that of biological neuron activity, this transistor is a promising component for biomimicking neuromorphic computing.

DOI： 10.1002/adma.202407326

PubMed

researchmap

Language：Others   Publishing type：Research paper (other academic)  

DOI： 10.1109/mcsoc60832.2023.00018

Language：Others   Publishing type：Research paper (other academic)  

DOI： 10.23919/vlsitechnologyandcir57934.2023.10185412

Language：Others   Publishing type：Research paper (scientific journal)  

CMOS-based area-and-power-efficient neuron and synapse circuits for time-domain analog spiking neural networks

DOI： 10.1063/5.0136627

Language：Others   Publishing type：Research paper (scientific journal)  

Abstract

Spiking neural networks (SNNs) inspired by biological neurons enable a more realistic mimicry of the human brain. To realize SNNs similar to large-scale biological networks, neuron circuits with high area efficiency are essential. In this paper, we propose a compact leaky integrate-and-fire (LIF) neuron circuit with a long and tunable time constant, which consists of a capacitor and two pseudo resistors (PRs). The prototype chip was fabricated with TSMC 65 nm CMOS technology, and it occupies a die area of 1392 μm². The fabricated LIF neuron has a power consumption of 6 μW and a leak time constant of up to 1.2 ms (the resistance of PR is up to 600 MΩ). In addition, the time constants are tunable by changing the bias voltage of PRs. Overall, this proposed neuron circuit facilitates the very-large-scale integration of adaptive SNNs, which is crucial for the implementation of bio-scale brain-inspired computing.

DOI： 10.35848/1347-4065/ac43e4

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.18494/SAM3863

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/led.2021.3077466

Language：Others   Publishing type：Research paper (scientific journal)  

Temperature dependence of resistivity increases induced by thiols adsorption in gold nanosheets

DOI： 10.35848/1347-4065/abd6de

Language：English   Publishing type：Research paper (scientific journal)  

Understanding of Fermi level pinning at metal/germanium interface based on semiconductor structure

Language：English  

Impact of defects in self-assembled monolayer on humidity sensing by molecular functionalized transistors

Language：English   Publishing type：Research paper (scientific journal)  

Reaction of GeO2 with Ge and crystallization of GeO2 on Ge

Language：English   Publishing type：Research paper (scientific journal)  

Electron‐Doping Mottronics in Strongly Correlated Perovskite

Language：English   Publishing type：Research paper (scientific journal)  

Heteroepitaxial vertical perovskite hot-electron transistors down to the monolayer limit.

Language：English   Publishing type：Research paper (scientific journal)  

In this work, we investigated the band alignment at bismuth (Bi)/germanium (Ge) and Bi/silicon (Si) interfaces to understand the mechanism of strong Fermi level pinning (FLP) at element metal/Ge and/Si interfaces. Bi/Ge and/Si interfaces exhibit almost ideal alignment deviating from the trend of strong FLP at element metal/Ge and/Si interfaces. This result suggests that the strong FLP at element metal/Ge and/Si interfaces is mainly caused by the metal-induced gap states (MIGS) in case of the free electron density of metal, and that the weak FLP at direct metal/Ge and/Si interfaces including germanide/Ge and silicide/Si interfaces is comprehensively understandable from the MIGS in case of low electron density. Furthermore, we also discuss impacts of interface structures on the band alignment at the MIGS-weakened interface.

DOI： 10.1063/1.5115535

Language：Others  

Delta-temperatural electronic transportation achieved in metastable perovskite rare-earth nickelate thin films

DOI： 10.1039/c9tc02327e

Language：Others  

Overcoming synthetic metastabilities and revealing metal-to-insulator transition & thermistor bi-functionalities for d-band correlation perovskite nickelates

DOI： 10.1039/c9mh00008a

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5052712

Language：English   Publishing type：Research paper (other academic)  

Anomalous Spectral Shape Evolution of Ge Raman Shift in Oxidation of SiGe.

DOI： 10.1109/EDTM.2018.8421461

Language：English  

A reliable method to apply biaxial strain over a wide range of values with minimal dislocation generation is critical for the study of strain dependent physical properties in oxide thin films and heterostructures. In this work, we systematically controlled the strain state in a perovskite manganite thin film by as much as 1% using a new ultrathin strain-releasing buffer layer Sr3Al2O6, and observed signatures of accompanying magnetic and metal–insulator transitions. The near-zero strain state is achieved within five nanometers of buffer layer thickness, substantially thinner than any oxide epitaxial buffer layers that can continuously tune the film strain states. Furthermore, the majority of misfit dislocations were confined to the Sr3Al2O6 layer, structurally decoupling defects in the film from the substrate.

DOI： 10.1002/pssr.201700339

Language：English   Publishing type：Research paper (other academic)  

Rigidity enhancement of GeO2by Y doping for reliable Ge gate stacks

DOI： 10.1109/EDTM.2018.8421529

Language：English   Publishing type：Research paper (other academic)  

Potential Influence of Surface Atomic Disorder on Fermi-level Pinning at Metal/SiGe Interface

DOI： 10.1109/EDTM.2018.8421410

Language：English   Publishing type：Research paper (scientific journal)  

The ferroelectric properties of ultrathin Y-doped HfO2 films were investigated. Ferroelectricity was demonstrated experimentally in 3 nm-thick Y-doped HfO2 via direct detection of displacement currents during polarization switching. The dependence on the HfO2 thickness within the 30 to 3 nm range revealed that the ferroelectric properties decrease rapidly below a critical thickness. In the ultrathin HfO2 region, methods such as higher Y doping or metal capping annealing were required to further stabilize the ferroelectric phase. These methods could be used to enhance the switchable polarization (Psw) to 35 μC/cm2 in 5 nm- and 10 μC/cm2 in 3 nm-thick Y-doped HfO2. This paper indicates that HfO2 ferroelectricity is scalable even in the ultrathin region.

DOI： 10.1063/1.5017094

Language：English   Publishing type：Research paper (other academic)  

5-nm-Thick ferroelectric Y-doped HfO2 was intensively studied. The thickness dependence of ferroelectric properties indicates that stable ferroelectric characteristics are maintained down to 5-nm-thick by taking care of doping and capping effects. Furthermore, the cycling performance shows no wake-up behavior, no obvious degradation after 108 cycles. These results not only enable us to use ferroelectric HfO2 for practical application, but also point out intrinsic properties in ultrathin ferroelectric HfO2 film from materials science point of view.

DOI： 10.1109/IEDM.2017.8268508

Language：English   Publishing type：Research paper (scientific journal)  

Strong electron-correlations can result in un-conventional transportation behaviour, such as metalinsulator transitions, high temperature superconductivity and bad metal conduction. Here we report a distinct transportation characteristic achieved by actively coupling the carriers with randomly distributed lattice-dipoles for strain-distorted SrNbxTi1-xO3. The strong electron correlations split the conduction band, and lead to a distinguished thermal-emitted carrier transportation with an activation energy of similar to 10(-2) eV. Further consistency was demonstrated by the respective changes in orbital configurations observed in near edge X-ray absorption fine structures. The present investigation demonstrates new mechanisms for regulating the carrier transportation using polaronic electron correlations.

DOI： 10.1039/c7cp06495k

Language：English   Publishing type：Research paper (other academic)  

Reconsideration of Metal Work Function at Metal/Semiconductor Interface
Fermi-level pinning (FLP) at metal/semiconductor interface, which is deviated from ideal Schottky-Mott limit, has been discussed for several decades based on various intrinsic and extrinsic models, and it has commonly been considered that the origin of FLP is ascribed only to semiconductor side. In this paper, we discuss FLP from the viewpoint of work function of metal. We focus on a fact that both of surface term of vacuum work function at metal/vacuum interface and intrinsic metal induced gap states (MIGS) at metal/semiconductor interface are described as a common physics of wave function tailing from metal. This suggests that the MIGS is regarded as a surface term of work function of metal at metal/semiconductor interface rather than interface states. Namely, the FLP caused by MIGS seems corresponded to modulation of work function. We also discuss how to control the work function modulation from both semiconductor and metal sides taking germanium as an example.

DOI： 10.1149/08004.0107ecst

Language：English   Publishing type：Research paper (scientific journal)  

The dopant-induced ferroelectric HfO2 formation has been systematically investigated by using cation (Sc, Y, Nb, Al, Si, Ge, and Zr) and anion (N) dopants. Both differences and similarities are discussed among various dopants by focusing on two major factors, the oxygen vacancy (Vo) and the dopant ionic size. First, the doping concentration dependence of the remanent polarization in 27 (+/-2) nm HfO2 films is quantitatively estimated. Then, by comparing the polarization result with the structural transformation in doped HfO2, the pathway of the dopant-induced HfO2 phase transition is discussed among monoclinic, ferroelectric orthorhombic, tetragonal, and cubic phases. Finally, it is addressed that a dopant species independent phase transition route may exist in HfO2 owing to the same kinetic transition process, in which the ferroelectric phase seems to be at an intermediate state between tetragonal and monoclinic phases. Published by AIP Publishing.

DOI： 10.1063/1.5003918

Language：English   Publishing type：Research paper (scientific journal)  

Thermal oxidation kinetics of Ge was investigated by the O-18 tracing study and re-oxidation experiments of the SiO2/GeO2 stacked oxide-layer. The results suggest that Ge oxidation kinetics is completely different from that expected from the Deal-Grove model and that Ge is oxidized by GeO2 on Ge instead of O-2 at the interface. This oxidation process forms large amounts of oxygen vacancies in GeO2, which facilitate the diffusion of oxygen atoms in GeO2. This means that oxygen atoms diffuse through GeO2 with an exchange type of process. Based on experimental results, a possible kinetics for Ge oxidation is discussed. Published by AIP Publishing.

DOI： 10.1063/1.4997298

Language：English   Publishing type：Research paper (scientific journal)  

A bonding technique via passivating interlayer formation is proposed for bulkmaterial heterojunction fabrication. n(+)Si/pGe heterojunctions were fabricated by a ribbon bonding with interfaces passivated by an amorphous interlayer. With a highest process temperature as low as 150. degrees C, the bonded junctions exhibited rectifying characteristics with a turn-on voltage of 0.3 V as an ideal Si/Ge heterojunction and an ideality factor of 2.15. This technique shows a great potential for bulk material heterojunction formation, especially when ultimately abrupt junctions and low temperature processes are needed.

DOI： 10.1109/LED.2017.2699658

Language：English   Publishing type：Research paper (scientific journal)  

Localized refrigeration and power generation via thermoelectric technology rely on efficient thermoelectric materials with high performance at room temperature. Although the two-dimensional electron gas (2DEG)-related materials exhibit ultrahigh thermoelectric performance near room temperature, such performance is only preserved at thicknesses within subnanometer scales, limited by the requirement of two-dimensional size confinements. Here we report ultrahigh thermoelectric performance similar to 2DEG-related materials but achieved in SrNb0.2Ti0.8O3 oxide films with a submicrometer-scale thickness by regulating strain induced lattice polarizations and interfacial polarizations. A large figure of merit, zT, and power factor (similar to 10(2)-10(3) mu W cm(-1) K-2) were achieved near room temperature, and the maximum zT is estimated to be similar to 1.6 for a 49 nm thick film. These performances exceed those of the existing n-type thermoelectric materials for room-temperature uses and the reported best oxide materials beyond subnanometer scales. The earth-abundant elemental composition of the oxide film paves the way toward potential applications in thermoelectric thin film devices with a microscale thickness.

DOI： 10.1021/acsenergylett.7b00197

Language：English   Publishing type：Research paper (scientific journal)  

This work thermodynamically and experimentally generalizes the interfacial SiO2 scavenging in HfO2 gate stacks from on Si to on other channel materials including SiGe and SiC and proposes a generalized formulation for this process. By paying attention to the Si chemical potential in the SiO2 interfacial layer (SiO2-IL) significantly affected by the substrate, it clarifies that Si in the substrate is indispensable to trigger the scavenging process. Thanks to this understanding, we demonstrate that the scavenging is extendable to next generation of channel materials containing Si such as SiGe and SiC with well-controlled high-k gate stacks. In addition, via formulating the diffusion-reaction-diffusion kinetics, an analytical relation like the Deal-Grove model is obtained for SiO2-IL scavenging in high-k gate stacks. Published by AIP Publishing.

DOI： 10.1063/1.4979711

Language：English   Publishing type：Research paper (other academic)  

This work discusses the general relationship for cation and anion doping effects on the HfO2 para-/ferroelectric transition, which will provide us a helpful instruction for precise HfO2 ferroelectricity design. In addition, ferroelectric N-doped HfO2 has been demonstrated as a gate dielectric film on an oxide semiconductor for ferroelectric field-effect transistors (FeFETs).

DOI： 10.1109/IEDM.2016.7838477

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/IEDM.2016.7838477

Language：English   Publishing type：Research paper (scientific journal)  

We report that nitrogen (N) doping can drive the ferroelectricity of HfO2. It was found that N doping can cause the transition from a monoclinic phase to a highly symmetric phase. The role of N doping is discussed from the viewpoints of charge balance and bond-constraining effects. The former is responsible for the structural transformation from a paraelectric phase to a ferroelectric phase by forming an oxygen vacancy. In addition, Hf-N and N-O bonds with covalent characteristics have strong effects on HfO2 structural and electrical properties, and thus contribute to a marked HfO2 para-/ferroelectric transition. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/APEX.9.091501

Language：English   Publishing type：Research paper (scientific journal)  

Metal/dielectric interface properties of Au/SrTiO3 (STO) and SrRuO3/SrTiO3 (SRO/STO) interfaces were investigated using metal/STO/heavily Nb-doped STO (0.5 wt% Nb:STO) capacitors. The observed interfacial capacitance at SRO/STO accords with results predicted theoretically, whereas that at the Au/STO interface is strongly suppressed, suggesting an intrinsic low-k (dielectric constant) interfacial layer formation at the Au/STO interface owing to in situ evaporated Au after STO film deposition. Furthermore, metal/0.01 wt% Nb:STO junctions were also analyzed. It was found that the SRO/Nb: STO junction forms an ideal Schottky dipole, whereas the Au/Nb: STO junction exhibits anomalous electrical properties. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.08PB04

Language：English   Publishing type：Research paper (scientific journal)  

The element metal/germanium (Ge) interface exhibits a strong Fermi level pinning (FLP), which is usually characterized on the basis of Ge side semiconductor properties. In this work, we demonstrate that metal properties significantly affect the Schottky barrier height (SBH) on Ge. Metallic germanides show both FLP alleviation and a clear substrate orientation dependence of SBH on Ge, despite the nearly perfect FLP and very slight orientation dependence in the element metal case. As a result, ohmic characteristics are observed at germanide/n-Ge (111) junctions. The metal properties required to alleviate the FLP on Ge are also discussed. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/APEX.9.081201

Language：English   Publishing type：Research paper (scientific journal)  

We report on the impact of TiN interfaces on the ferroelectricity of nondoped HfO2. Ferroelectric properties of nondoped HfO2 in TiN/HfO2/TiN stacks are shown in capacitance-voltage and polarization-voltage characteristics. The Curie temperature is also estimated to be around 500 degrees C. The ferroelectricity of nondoped HfO2 clearly appears by thinning HfO2 film down to > 35 nm. We directly revealed in thermal treatments that the ferroelectric HfO2 film on TiN was maintained by covering the top surface of HfO2 with TiN, while it was followed by a phase transition to the paraelectric phase in the case of the open surface of HfO2. Thus, it is concluded that the ferroelectricity in nondoped HfO2 in this study was mainly driven by both of top and bottom TiN interfaces. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.08PB01

Language：English   Publishing type：Research paper (other academic)  

To realize scaled Ge CMOS device, there are several challenges of junction formation in nMOSFET. (Fermi level pinning, activation and diffusion of n-type impurities and junction leakage, etc.) In this paper, we report recent progresses of controllability of band alignment at metal/Ge interface, understanding of n-type impurity activation in Ge, and impact of oxygen in Ge on n(+)/p junction leakage.

DOI： 10.1109/IWJT.2015.7467098

Language：English   Publishing type：Research paper (scientific journal)  

We discuss the impact of free carriers on the zone-center optical phonon frequency in germanium (Ge). By taking advantage of the Ge-on-insulator structure, we measured the Raman spectroscopy by applying back-gate bias. Phonon softening by accumulating holes in Ge film was clearly observed. This fact strongly suggests that the phonon softening in heavily-doped Ge is mainly attributed to the free carrier effect rather than the dopant atom counterpart. Furthermore, we propose that the free carrier effect on phonon softening is simply understandable from the viewpoint of covalent bonding modification by free carriers. (C) 2016 Author(s).

DOI： 10.1063/1.4941072

Language：English   Publishing type：Research paper (other academic)  

We investigate impacts of free carriers on phonon frequency of zone-center optical phonon in Germanium (Ge). By taking advantage of Ge-on-insulator structure, Raman measurement with applying the back-gate bias was performed. The phonon softening was clearly observed by increasing hole density. It is also pointed out that the phonon softening in heavily-doped Ge is mainly attributed to the free carrier effect rather than dopant atom one. Furthermore, we show that the free carrier effect on phonon softening can be simply and reasonably interpreted from the view point of modification of the covalent bonding by free carriers.

DOI： 10.1149/06910.0075ecst

Language：English   Publishing type：Research paper (other academic)  

This work clarifies roles of substrate-Si in SiO2-IL scavenging in HfO2/SiO2/Si gate stack experimentally, and points out a coupling effect of oxygen vacancy (V-O) with SiO2/Si interface from thermodynamic viewpoint.

Language：English   Publishing type：Research paper (scientific journal)  

In this study, what occurs at the SiO2/substrate interface and how Si atoms in SiO2 behave in interfacial SiO2 scavenging in a HfO2 gate stack have been investigated. Since the same scavenging occurs on both Si and SiC substrates, the SiC substrate is used to study the role of the substrate. The characterizations of the SiO2/SiC interface show no Si growth on the substrate and no consumption of the substrate in the SiO2 scavenging. Isotope tracing experiments for a HfO2/SiO2/Si stack further demonstrate that atomic Si is generated in scavenging and diffuses out through the HfO2 layer. On the basis of these findings, the reaction at the SiO2/substrate interface is thermodynamically discussed. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/APEX.8.061304

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (scientific journal)  

We demonstrate that direct-gap photoluminescence (PL) analysis is useful for the nondestructive, fast, and in-line characterization of the oxide/germanium (Ge) interface without making actual devices. The fact that Ge has a quasi-direct gap enables us to utilize direct-gap PL intensity as a good indicator for interface quality estimation. We experimentally confirm the validity of the present analysis, by comparing PL spectra with capacitance-voltage characteristics. The impact of the band bending at the interface on PL intensity is also discussed. Furthermore, the effect of forming gas annealing at oxide/Ge interfaces is discussed by taking advantage of the present method. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/APEX.8.051301

Language：English   Publishing type：Research paper (other academic)  

The scavenging kinetics of ultra-thin-SiO&lt
inf&gt
2&lt
/inf&gt
interface layer (IL) in HfO&lt
inf&gt
2&lt
/inf&gt
/SiO&lt
inf&gt
2&lt
/inf&gt
/Si stacks is investigated by focusing on SiO&lt
inf&gt
2&lt
/inf&gt
/Si interface reaction in addition to both O and Si atom kinetics. SiO&lt
inf&gt
2&lt
/inf&gt
/Si interface serves as a stage that the oxygen vacancy (VO) is converted to Si release from SiO&lt
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2&lt
/inf&gt
with the help of Si substrate. Based on both diffusion kinetics and possible reaction, an analytical model for two-stage SiO&lt
inf&gt
2&lt
/inf&gt
-IL scavenging in high-k gate stack is proposed.

DOI： 10.1109/IEDM.2014.7047094

Language：English   Publishing type：Research paper (scientific journal)  

The scavenging kinetics of an ultra-thin SiO2 interface layer (SiO2-IL) in an HfO2/SiO2/Si stack is discussed by focusing on the substrate effect in addition to oxygen diffusion. O-18 tracing experiments demonstrate that the O-atom moves from the SiO2-IL to the HfO2 layer during scavenging. SiO2-IL scavenging with various substrates (Si, SiC, and sapphire) has been found to be significantly different, which suggests that the Si in the substrate is also necessary to continuously cause the scavenging. Based on these findings and thermodynamic considerations, a kinetic model where oxygen vacancy (VO) transferred from the HfO2 reacts with the SiO2, which is in contact with the Si-substrate, is proposed for the SiO2-IL scavenging. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4901172

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.1109/ISTDM.2014.6874698

Language：English   Publishing type：Research paper (other academic)  

This work discusses effects of the substrate on the scavenging of SiO2 interface layer (SiO2-IL) in HfO2 gate stacks. We propose a model that SiO2-IL scavenging occurs through the reaction of the oxygen vacancy (V-O) transferred from HfO2 to SiO2 with oxygen formed at SiO2/substrate interface.

DOI： 10.1109/SNW.2014.7348532

Language：English   Publishing type：Research paper (scientific journal)  

We demonstrate that Ge(100), (110), and (111) Ge surfaces are planarized with atomic level step and terrace structures in H-2 annealing. The temperature required for such planarization is different among the three orientations. The step edge structure on the Ge(100) surface is composed of alternate smooth and rough steps (S-a + S-b steps) owing to the (2 x 1) reconstruction on that surface. It is also shown that the terrace widths on the Ge(110) and (111) surfaces are on average controlled by adjusting the off-angle from the respective surface orientation. (C) 2014 The Japan Society of Applied Physics

DOI： 10.7567/APEX.7.051301

Language：English   Publishing type：Research paper (scientific journal)  

The ultra-thin SiO2 interface layer (SiO2-IL) in the HfO2/SiO2/Si stack was found to be reduced during the ultra-high vacuum (UHV) annealing. Along with thin SiO2-IL reduction in UHV, SiO desorption and silicide formation also took place. The thermal desorption spectroscopy and X-ray photoelectron spectroscopy results showed that the SiO2-IL reduction occurred at temperatures lower than the temperature showing SiO desorption and silicidation by accurately controlling the annealing conditions. The mechanism of SiO2-IL reduction can be explained by the oxygen diffusion through oxygen vacancies in HfO2 generated in the gate stack formation and thermal treatment. It is also understandable that the silicidation process is associated with the inhomogeneous SiO desorption. (c) 2013 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.tsf.2013.10.142

Language：English   Publishing type：Research paper (scientific journal)  

Electronic changes at polar interfaces between transition metal oxides offer the tantalizing possibility to stabilize novel ground states yet can also cause unintended reconstructions in devices. The nature of these interfacial reconstructions should be qualitatively different for metallic and insulating films as the electrostatic boundary conditions and compensation mechanisms are distinct. Here we directly quantify with atomic-resolution the charge distribution for manganite-titanate interfaces traversing the metal-insulator transition. By measuring the concentration and valence of the cations, we find an intrinsic interfacial electronic reconstruction in the insulating films. The total charge observed for the insulating manganite films quantitatively agrees with that needed to cancel the polar catastrophe. As the manganite becomes metallic with increased hole doping, the total charge build-up and its spatial range drop substantially. Direct quantification of the intrinsic charge transfer and spatial width should lay the framework for devices harnessing these unique electronic phases.

DOI： 10.1038/ncomms4464

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/IEDM.2013.6724610

Language：English   Publishing type：Research paper (other academic)  

In germanium (Ge) MOSFET technology, surface planarization is a serious concern for mobility enhancement at high carrier density, reliability improvement of gate dielectrics and morphology control for non-planar FETs. In this work, (111)-oriented Ge substrates were annealed at 350-750 degrees C in pure H-2 atmosphere, and the surface structure and morphology were analyzed with atomic force microscopy. A step and terrace structure was observed on the surface after the H-2 annealing above 500 degrees C. The terrace width is controllable by the off-angle of the initial surface within 0.3 degrees at least. The roughness root mean square (RMS) at 100 x 100 nm on single terrace is similar to 0.05 nm which is almost our detection limit, which implies that the single terrace on H-2 annealed Ge (111) is atomically flat. Furthermore, even though the initial surface roughness RMS is intentionally increased up to 0.6 nm, atomically flat terrace structure could be obtained by the H-2 annealing.

DOI： 10.1149/05809.0201ecst

Language：English   Publishing type：Research paper (scientific journal)  

Coexistence of two-dimensional and three-dimensional Shubnikov-de Haas oscillations in Ar+-irradiated KTaO3
We report electron doping in the surface vicinity of KTaO3 by inducing oxygen vacancies via Ar+ irradiation. The doped electrons have high mobility (&gt
104 cm2/Vs) at low temperatures, and exhibit Shubnikov-de Haas oscillations with both two- and three-dimensional components. A disparity of the extracted in-plane effective mass, compared to the bulk values, suggests mixing of the orbital characters. Our observations demonstrate that Ar+ irradiation serves as a flexible tool to study low-dimensional quantum transport in 5d semiconducting oxides. ©2013 American Physical Society.

DOI： 10.1103/PhysRevB.88.085102

Language：English   Publishing type：Research paper (scientific journal)  

Oxide heterointerfaces are ideal for investigating strong correlation effects to electron transport, relevant for oxide-electronics. Using hot-electrons, we probe electron transport perpendicular to the La0.7Sr0.3MnO3 (LSMO)- Nb-doped SrTiO3 (Nb:STO) interface and find the characteristic hot-electron attenuation length in LSMO to be 1.48 +/- 0.10 unit cells (u.c.) at -1.9 V, increasing to 2.02 +/- 0.16 u.c. at -1.3 V at room temperature. Theoretical analysis of this energy dispersion reveals the dominance of electron-electron and polaron scattering. Direct visualization of the local electron transport shows different transmission at the terraces and at the step-edges.

DOI： 10.1038/srep01274

Language：Others  

Design of interfacial dipole in perovskite oxides and its application to transistors

Language：English   Publishing type：Research paper (scientific journal)  

The transport and magnetic properties of La0.7Sr0.3MnO3 thin-films grown by pulsed laser deposition on (LaAlO3)(0.3)(SrAl0.5Ta0.5O3)(0.7) single crystal substrates have been investigated. A systematic series with various thicknesses of La0.7Sr0.3MnO3 was used to establish a phase diagram which showed a clear difference compared to films grown on SrTiO3 substrates, highlighting the importance of film thickness, and substrate strain. At 8 unit cells, the boundary between the metallic and insulating groundstates, a second abrupt metal-insulator transition was observed at low temperatures, which could be tuned by magnetic field, and was interpreted as a signature of electronic phase separation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3628659]

DOI： 10.1063/1.3628659

Language：English   Publishing type：Research paper (scientific journal)  

Biased conducting-up atomic force microscopy (AFM) has been shown to write and erase nanoscale metallic lines at the LaAlO3/SrTiO3 interface Using various AFM modes, we show the mechanism of conductivity switching is the writing of surface charge These charges are stably deposited on a wide range of LaAlO3 thicknesses, including bulk crystals. A strong asymmetry with writing polarity was found for 1 and 2 unit cells of LaAlO3, providing experimental evidence for a theoretically predicted built-in potential

DOI： 10.1021/nl1012695

Language：English   Publishing type：Research paper (scientific journal)  

Precipitates formed during the growth of manganite thin films by pulsed laser deposition have been an obstacle for fabricating high quality devices incorporating these ferromagnetic metals. In order to analyze the nature of these precipitates, we have investigated their spectroscopic and structural properties by scanning transmission electron microscopy. For LaMnO3 films, crystallites of Mn3O4 are found to segregate out from stoichiometric films to accommodate a net cation off-stoichiometry during growth. By tuning the laser spot conditions, these precipitates can be eliminated.

DOI： 10.1063/1.3193667

Language：English   Publishing type：Research paper (scientific journal)  

In order to investigate the interface termination dependence of perovskite band alignments, we have studied the Schottky barrier height at La0.7Sr0.3MnO3/Nb:SrTiO3 (001) heterointerfaces. As the Nb:SrTiO3 semiconductor was varied from TiO2 termination to SrO termination by variable insertion of a SrMnO3 layer, a large systematic increase in the Schottky barrier height was observed. This can be ascribed to the evolution of the interface dipole induced to screen the polar discontinuity at the interface, which gives a large internal degree of freedom for tuning band diagrams in oxides.

DOI： 10.1103/PhysRevB.79.073101

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Trends in Power Supply Circuit Technology for Widespread Use of Energy Harvesting

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Design of neuromorphic information devices using protons

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Designing neuromorphic devices using protons

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Edge AI using spiking neural networks and its application to energy harvesting

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Neuromorphic Functional Design Using Solid-State Proton Devices

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Neuromorphic Devices Using Oxide Heterostructures and Protons

Presentation type：Oral presentation (invited, special)  

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Presentation type：Oral presentation (invited, special)  

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Neuromorphic information processing using proton

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Research on low power electronics based on neuron circuits and materials properties

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Codesign of materials and circuits for neuromorphic edge computing

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Presentation type：Oral presentation (invited, special)  

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Presentation type：Oral presentation (invited, special)  

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Presentation type：Oral presentation (invited, special)  

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Presentation type：Oral presentation (invited, special)  

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Engineering Artificial Interface Dipoles at Oxide Heterointerfaces.

Language：English   Publishing type：Internal/External technical report, pre-print, etc.  

Other Link： http://pfwww.kek.jp/acr/2014pdf/part_a/14ah1_2.pdf

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Other Link： http://www.fbi-award.jp/sentan/jusyou/2012/3.pdf

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Controlling Band Alignments by Engineering Interface Dipoles at Perovskite Oxide Heterointerfaces.