arXiv subjects

Masataka Imura

Publications and source records attributed to Masataka Imura.

7 recordsLinked to original sources

arXiv2023

A high-performance deep reservoir computing experimentally demonstrated with ion-gating reservoirs

While physical reservoir computing (PRC) is a promising way to achieve low power consumption neuromorphic computing, its computational performance is still insufficient at a practical level. One promising approach to improving PRC performance is deep reservoir computing (deep-RC), in which the component reservoirs are multi-layered. However, all of the deep-RC schemes reported so far have been effective only for simulation reservoirs and limited PRCs, and there have been no reports of nanodevice implementations. Here, as the first nanodevice implementation of Deep-RC, we report a demonstration of deep physical reservoir computing using an ion gating reservoir (IGR), which is a small and high-performance physical reservoir. While previously reported Deep-RC scheme did not improve the performance of IGR, our Deep-IGR achieved a normalized mean squared error of 0.0092 on a second-order nonlinear autoregressive moving average task, with is the best performance of any physical reservoir so far reported. More importantly, the device outperformed full simulation reservoir computing. The dramatic performance improvement of the IGR with our deep-RC architecture paves the way for high-performance, large-scale, physical neural network devices.

physics.app-ph↗

arXiv2022

Edge-Of-Chaos Learning Achieved by Ion-Electron Coupled Dynamics in an Ion-Gating Reservoir

Physical reservoir computing has recently been attracting attention for its ability to significantly reduce the computational resources required to process time-series data. However, the physical reservoirs that have been reported to date have had insufficient expression power, and most of them have a large volume, which makes their practical application difficult. Herein we describe the development of a Li+-electrolyte based ion-gating reservoir (IGR), with ion-electron coupled dynamics, for use in high performance physical reservoir computing. A variety of synaptic responses were obtained in response to past experience, which responses were stored as transient charge density patterns in an electric double layer, at the Li+-electrolyte/diamond interface. Performance, which was tested using a nonlinear autoregressive moving-average (NARMA) task, was found to be excellent, with a NMSE of 0.023 for NARMA2, which is the highest for any physical reservoir reported to date. The maximum Lyapunov exponent of the IGR was 0.0083: the edge of chaos state enabling the best computational capacity. The IGR described herein opens the way for high-performance and integrated neural network devices.

cs.ET↗

arXiv2021

High-Mobility p-Channel Wide Bandgap Transistors Based on h-BN/Diamond Heterostructures

Field-effect transistors made of wide-bandgap semiconductors can operate at high voltages, temperatures and frequencies with low energy losses, and have been of increasing importance in power and high-frequency electronics. However, the poor performance of p-channel transistors compared with that of n-channel transistors has constrained the production of energy-efficient complimentary circuits with integrated n- and p-channel transistors. The p-type surface conductivity of hydrogen-terminated diamond offers great potential for solving this problem, but surface transfer doping, which is commonly believed to be essential for generating the conductivity, limits the performance of transistors made of hydrogen-terminated diamond because it requires the presence of ionized surface acceptors, which cause hole scattering. Here, we report on fabrication of a p-channel wide-bandgap heterojunction field-effect transistor consisting of a hydrogen-terminated diamond channel and hexagonal boron nitride ($h$-BN) gate insulator, without relying on surface transfer doping. Despite its reduced density of surface acceptors, the transistor has the lowest sheet resistance ($1.4$ k$Ω$) and largest on-current ($1600$ $μ$m mA mm$^{-1}$) among p-channel wide-bandgap transistors, owing to the highest hole mobility (room-temperature Hall mobility: $680$ cm$^2$V$^{-1}$s$^{-1}$). Importantly, the transistor also shows normally-off behavior, with a high on/off ratio exceeding $10^8$. These characteristics are suited for low-loss switching and can be explained on the basis of standard transport and transistor models. This new approach to making diamond transistors paves the way to future wide-bandgap semiconductor electronics.

cond-mat.mtrl-sci↗

arXiv2020

Charge-carrier mobility in hydrogen-terminated diamond field-effect transistors

Diamond field-effect transistors (FETs) have potential applications in power electronics and high-output high-frequency amplifications. In such applications, high charge-carrier mobility is desirable for a reduced loss and high-speed operation. We have recently fabricated diamond FETs with a hexagonal-boron-nitride gate dielectric and observed a high mobility above 300 cm$^{2}$V$^{-1}$s$^{-1}$. In this study, we examine which scattering mechanism limits the mobility of our FETs through theoretical calculations. Our calculations reveal that the dominant carrier scattering is caused by surface charged impurities with the density of $\approx$1$\times10^{12}$ cm$^{-2}$, and suggest a possible increase in mobility over 1000 cm$^{2}$V$^{-1}$s$^{-1}$ by reducing the impurities.

cond-mat.mes-hall↗

arXiv2019

Quantum oscillations in diamond field effect transistors with a h-BN gate dielectric

Diamond has attracted attention as a next-generation semiconductor because of its various exceptional properties such as a wide bandgap and high breakdown electric field. Diamond field effect transistors, for example, have been extensively investigated for high-power and high-frequency electronic applications. The quality of their charge transport (i.e., mobility), however, has been limited due to charged impurities near the diamond surface. Here, we fabricate diamond field effect transistors by using a monocrystalline hexagonal boron nitride as a gate dielectric. The resulting high mobility of charge carriers allows us to observe quantum oscillations in both the longitudinal and Hall resistivities. The oscillations provide important information on the fundamental properties of the charge carriers, such as effective mass, lifetime, and dimensionality. Our results indicate the presence of a high-quality two-dimensional hole gas at the diamond surface and thus pave the way for studies of quantum transport in diamond and the development of low-loss and high-speed devices.

cond-mat.mes-hall↗

arXiv2014

Interactive Art To Go

Traditional artworks like paintings, photographs, or films can be reproduced by conventional media like printing or video. This makes visitors of museums possible to purchase postcards, posters, books, and DVDs of pictures and/or movies shown at the exhibition. However, newly developing arts so called interactive art, or new media art, has not been able to be reproduced due to limitation of functionalities of the conventional media. In this article, the authors report a novel approach of sharing such interactive art outside the exhibition, so that the visitors of the museum can take a copy to home, and even share it with non-visitors. The authors build up their new projector-and-camera (ProCam) based interactive artwork for exhibition at Museum of Contemporary Art Tokyo (MOT) by using Apple's iPhone. The exactly same software driving this artwork was downloadable from Apple's App Store -- thus all visitors or even non-visitors could enjoy the same experience at home or wherever they like.

cs.HC↗

arXiv2014

Function + Action = Interaction

This article presents the mathematical background of general interactive systems. The first principle of designing a large system is to _divide and conquer_, which implies that we could possibly reduce human error if we divided a large system in smaller subsystems. Interactive systems are, however, often composed of many subsystems that are _organically_ connected to one another and thus difficult to divide. In other words, we cannot apply a framework of set theory to the programming of interactive systems. We can overcome this difficulty by applying a framework of category theory (Kleisli category) to the programming, but this requires highly abstract mathematics, which is not very popular. In this article we introduce the fundamental idea of category theory using only lambda calculus, and then demonstrate how it can be used in the practical design of an interactive system. Finally, we mention how this discussion relates to category theory.

cs.HC↗