Showing papers in "Japanese Journal of Applied Physics in 2020"

Physical reservoir computing—an introductory perspective

Abstract: Understanding the fundamental relationships between physics and its information-processing capability has been an active research topic for many years. Physical reservoir computing is a recently introduced framework that allows one to exploit the complex dynamics of physical systems as information-processing devices. This framework is particularly suited for edge computing devices, in which information processing is incorporated at the edge (e.g., into sensors) in a decentralized manner to reduce the adaptation delay caused by data transmission overhead. This paper aims to illustrate the potentials of the framework using examples from soft robotics and to provide a concise overview focusing on the basic motivations for introducing it, which stem from a number of fields, including machine learning, nonlinear dynamical systems, biological science, materials science, and physics.

Review on ferroelectric/polar metals

Abstract: The possibility of reconciliation between seemingly mutually exclusive properties in one system can not only lead to theoretical breakthroughs but also potential novel applications. The research on the coexistence of two purportedly contra-indicated properties, ferroelectricity/polarity and conductivity, proposed by Anderson and Blount over 50 years ago was recently revitalized by the discovery of the first unambiguous polar metal LiOsO3 and further fueled by the demonstration of the first switchable ferroelectric metal WTe2. In this review, we first discuss the reasons why the coexistence of ferroelectricity/polarity and conductivity have been deemed incompatible, followed by a review on the history of ferroelectric/polar metals. Secondly, we review the important milestones along with the corresponding mechanisms for the ferroelectric/polar metallic phases in these materials. Thirdly, we summarize the design approaches for ferroelectric/polar metals. Finally, we discuss the prospects and potential applications of ferroelectric/polar metals.

Demonstration of 1200 V/1.4 mΩ cm2 vertical GaN planar MOSFET fabricated by an all ion implantation process

Abstract: We present a vertical GaN planar MOSFET fabricated by an all ion implantation process. The fabricated MOSFET shows an on-resistance of 2.78 mΩ cm2 and a breakdown voltage of 1200 V, by applying the short cell pitch design to reduce the on-resistance and a Mg and N sequential implantation to improve the breakdown voltage of the pn-junction. By evaluating each on-resistance component in the fabricated vertical GaN planar MOSFET using the simultaneously formed test structures, an effective on-resistance of the active region excluding the source parasitic resistance is 1.4 mΩ cm2. Consequently, it was demonstrated that an all ion implantation process can fabricate a vertical GaN planar MOSFET with a high breakdown voltage and low on-resistance. This result will greatly contribute to the realization of GaN power devices.

A high throughput molecular screening for organic electronics via machine learning: present status and perspective

Abstract: Organic electronics such as organic field-effect transistors (OFET), organic light-emitting diodes (OLED), and organic photovoltaics (OPV) have flourished over the last three decades, largely due to the development of new conjugated materials. Their designs have evolved through incremental modification and stepwise inspiration by researchers; however, a complete survey of the large molecular space is experimentally intractable. Machine learning (ML), based on the rapidly growing field of artificial intelligence technology, offers high throughput material exploration that is more efficient than high-cost quantum chemical calculations. This review describes the present status and perspective of ML-based development (materials informatics) of organic electronics. Although the complexity of OFET, OLED, and OPV makes revealing their structure-property relationships difficult, a cooperative approach incorporating virtual ML, human consideration, and fast experimental screening may help to navigate growth and development in the organic electronics field.

Assembly of van der Waals heterostructures: exfoliation, searching, and stacking of 2D materials

Abstract: The fascinating point of 2D and layered materials is that they can be assembled into van der Waals (vdW) heterostructures, in which atomic layers are integrated by vdW force. There are almost infinite potential combinations in vdW heterostructures owing to the multiple degrees of freedom, i.e., the choice of materials, stacking order, and lateral orientation angle at the interfaces. In this article, we review the fabrication technique of vdW heterostructures, which has played an essential role in the development of the 2D materials research field. First, we describe the primary technique of mechanical exfoliation to fabricate and identify high-quality atomic layers. We then discuss the assembly of atomic layers into vdW heterostructures. Finally, we introduce the recent advancement of fabrication techniques using autonomous robotic assembly. We hope this article would help the readers to acquire basic knowledge of vdW assembly and motivate them to fabricate vdW heterostructures.

Beyond silicene: synthesis of germanene, stanene and plumbene

Abstract: Twenty five years after the first theoretical prediction of two-dimensional (2D) honeycomb-like silicon and germanium, now coined silicene and germanene, the last Group 14 artificial cousin of graphene has been synthesized, thus terminating the lineage from silicene (2012) to germanene (2014), stanene (2015), and finally plumbene (2019). Here, we describe the realizations and review the tantalizing properties of these outstanding novel 2D materials.

GaN power IC technology on p-GaN gate HEMT platform

Abstract: GaN power ICs provide an elegant solution for high-frequency power switching applications. This paper will first discuss GaN power integration platform, which requires not only high-voltage power switch, but also peripheral low-voltage transistors, diodes, resistors, capacitors, etc. The low-voltage components are preferably fabricated using the same process steps as the power switch to be cost effective. As an example of GaN power IC, an integrated gate driving circuit is demonstrated. By adopting a charge pump unit, the novel gate driver in this work enables rail-to-rail output voltage, fast switching speed and enhanced reliability. For the design of GaN power ICs, the unique device physics of GaN power devices should be carefully considered. The Vth of the GaN power transistor is found to be bias-dependent and exhibit dynamic behavior during power switching operation. The mechanism of this dynamic Vth will be explained and its impact on circuit operation will be illustrated.

Effect of field cooling AC poling on electrical and physical properties for Pb(Mg1/3Nb2/3)O3-PbTiO3-based single crystals manufactured by a continuous-feeding Bridgman process

Abstract: We have designed and fabricated a compact, 250 cm3 electric field cooling alternate current poling (FC ACP) system and obtained an enhanced dielectric permittivity (e T 33/e 0) of 7920 which was 10 to 33% larger than that of high temperature (HT) ACP of 0.70Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 (PMNT) single crystal (SC) with phase change temperature (T pc) of 93 °C. However, when the FC ACP temperature from 200 to 35 °C was applied for 0.31Pb(In1/2Nb1/2)O3-0.43Pb(Mg1/3Nb2/3)O3-0.26PbTiO3 (PIMNT) SC with a T pc of 136 °C, the e T 33/e 0 decreased by 55% compared with that of HT ACP. Temperature dependence of the e T 33/e 0 and phase analysis by X-ray diffraction of these SCs produced by a continuous-feeding Bridgman process showed clear different properties. We conclude the effects of FC ACP on the electrical and physical properties are different from the compositions, T pc, Curie temperature, etc., and it is required to find the best FC ACP condition according to each SC.

Luminescence and scintillation properties of (C6H5(CH2)2NH3)2(Ba,Pb)Br4 with self-organized bi-dimensional quantum-well structures

Abstract: (C6H5(CH2)4NH3)2Ba x Pb1−x Br4 (x = 0, 0.1, 0.25 and 0.5) crystals were prepared by the solvent diffusion method to evaluate the scintillation properties. The samples exhibit photoluminescence and scintillation with a sharp emission peaking around 440 nm due to excitons, and the decay time is dominantly several nanoseconds. The pulse height spectrum under 137Cs gamma-ray irradiation demonstrates that the scintillation light yields of (C6H5(CH2)2NH3)2Ba0.25Pb0.75Br4 and (C6H5(CH2)2NH3)2Ba0.5Pb0.5Br4 crystals are approximately 19 000 ph MeV−1.

Relationship between cold plasma treatment-induced changes in radish seed germination and phytohormone balance

Abstract: This study aimed to estimate the dependence of the effects of radish (Raphanus sativus) seed irradiation with atmospheric cold plasma (CP) on physiological seed condition or dormancy status. Seeds were treated for different durations with a scalable dielectric barrier discharge (DBD) device. The relationship between the effect of CP on germination kinetics with changes in the content of phytohormones in seeds stored for different periods of time after harvesting (1, 5, and 7 months) was estimated. CP treatment efficiently stimulated germination only in freshly harvested (not after-ripened seeds), and these changes correlated with a decrease in abscisic acid (ABA) and an increase in gibberellin (GA) content. CP treatment induced a fast decrease in ABA content and ABA/GA ratio in after-ripened seeds (5 months after harvesting) but did not stimulate germination. Primary evidence of direct ABA modification by the reactive compounds from the gaseous phase of CP was obtained.

Mass production of plasma activated water by an atmospheric pressure plasma

Abstract: We report on the mass production of plasma activated water (PAW) by a non-thermal atmospheric pressure plasma. As a non-thermal plasma source, we used planar dielectric barrier discharge (DBD) and two types cylindrical DBDs. The manufacturing characteristics of PAW were investigated for each DBD type. The results show that the radical transfer characteristics from plasma to water have a dominant effect on the PAW properties. Of the two cylindrical DBD reactors, the "direct" type in which the mesh electrode was replaced with the conductor (Al) showed superior characteristics over "indirect" type. DBD reactor with an Al electrode with the length of 1 m long achieved a PAW production capacity of 520 liters per hour and production efficiency of 65 l kWh−1. Such a large-capacity PAW manufacturing device can be applied to various industries including agriculture, sterilization, and water treatment.

Impact of radish sprouts seeds coat color on the electron paramagnetic resonance signals after plasma treatment

Abstract: Recently, cold atmospheric plasma (CAP) treatment on seed germination has emerged as a useful technique to increase agriculture production, although, the mechanism of the cold plasma in seed germination is still under investigation. In this work, we studied the role of pigments in the seed coat of radish sprouts on the electron spin resonance (ESR) signals before and after CAP treatment. Radish sprouts seeds having gray color show enhanced ESR signals after the CAP treatment, whereas, no increased ESR signals were observed for brown color seeds of radish sprouts as compared to their respective control seeds. These results reveal that seeds from the same harvest year having different seed coat colors show different responses to the plasma treatment. Although ESR signal intensity can vary with the harvest year, the change in ESR signal intensity after plasma treatment depends on the seed coat color. Independently on the harvest year (2017 and 2018), CAP increased ESR signals stronger in the grey seeds in comparison to the brown ones. The results indicated that seed coat color may be an important variable for understanding differences in the extent of CAP effects on seeds.

Evaluation methods for materials for power ultrasonic applications

Abstract: This paper is focused on evaluation methods for materials at high amplitudes of ultrasonic vibrations. First, basic concepts on piezoelectric ultrasonic transducers utilized in power applications are introduced as well as horns and vibration converters. Second, an electrical equivalent circuit model of piezoelectric transducers is described. Then, a standard method to measure the output acoustic power of ultrasonic transducer is demonstrated. Third, the electromechanical coupling factor and quality factor are defined. The last half of this paper is dedicated to the transient method and quality factor measurement under high vibration strain. The quality factor and piezoelectric constant of piezoelectric ceramics are discussed as functions of vibration strain with the transient method. Next, an evaluation method for the quality factor of non-piezoelectric materials is proposed on the basis of the definition of quality factor. Ultrasonic characteristics of several metals and polymers are explored using the proposed method.

Estimation of viscoelasticity of radial artery via simultaneous measurement of changes in pressure and diameter using a single ultrasound probe

Abstract: To establish an evaluation index for vascular endothelial function, we developed an ultrasonic probe that can measure changes in blood pressure and blood vessel diameter at the same position in the radial artery. Based on phantom experiments, the pressure waveforms measured using the piezoelectric effect of the ultrasonic probe element and those using a pressure sensor exhibited a high correlation (correlation coefficient: r = 0.979 – 0.999). We confirmed the continuous measurement of the relationship between changes in blood pressure and the diameter from the in vivo experiments. We could then estimate the changes in viscoelasticity by calibrating the output from the probe element to the absolute blood pressure values in advance. The average coefficients of variations were 0.02 and 0.24 for elasticity and viscosity, respectively. This study demonstrated the possibility of measuring changes in the viscoelastic moduli of the radial arterial wall due to flow-mediated dilation using the developed ultrasonic probe.