High-NA extreme ultraviolet (EUV) lithography is currently in development. Fabrication of exposure tools and optics with a numerical aperture (NA) equal to 0.55 has started at ASML and Carl Zeiss. Lenses with such high NA will have very small depths-of-focus, which will require improved focus systems and significant improvements in wafer flatness during processing. Lenses are anamorphic to address mask 3D issues, which results in wafer field sizes of 26 mm × 16.5 mm, half that of lower NA EUV tools and optical scanners. Production of large die will require stitching. Computational infrastructure is being created to support high-NA lithography, including simulators that use Tatian polynomials to characterize the aberrations of lenses with central obscurations. High resolution resists that meet the line-edge roughness and defect requirements for high-volume manufacturing also need to be developed. High power light sources will also be needed to limit photon shot noise.
The Japan Society of Applied Physics (JSAP) serves as an academic interface between science and engineering and an interactive platform for academia and the industry. JSAP is a "conduit" for the transfer of fundamental concepts to the industry for development and technological applications.
JSAP was established as an official academic society in 1946, and since then, it has been one of the leading academic societies in Japan. The society's interests cover a broad variety of scientific and technological fields, and JSAP continues to explore state-of-the-art and interdisciplinary topics.
To this end, the JSAP holds annual conferences; publishes scientific journals; actively sponsors events, symposia, and festivals related to science education; and compiles information related to state-of-the-art technology for the public.
ISSN: 1347-4065
The Japanese Journal of Applied Physics (JJAP) is an international journal for the advancement and dissemination of knowledge in all fields of applied physics.
Open all abstracts, in this tab
Harry J. Levinson 2022 Jpn. J. Appl. Phys. 61 SD0803
Kohei Nakajima 2020 Jpn. J. Appl. Phys. 59 060501
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.
Yasuhiro Iwamura et al 2024 Jpn. J. Appl. Phys. 63 037001
Anomalously large heat generation phenomena that cannot be explained by any known chemical processes were discovered: Ni-based nano-structured multilayer metal composites were preloaded with hydrogen gas and heated rapidly to diffuse hydrogen and trigger the heat generation reaction. Maximum energy released per total hydrogen absorption was over 10 keV H–1 and no gamma rays or neutrons, which are harmful to the human body, were observed. It is possible to intentionally induce the heat burst phenomenon, which can increase the amount of heat generated without any new energy input. This can be applied to reaction control as well as to improving the accuracy of heat generation evaluation. A common feature, that regions of very high oxygen concentrations are observed in places, was observed in the heat-producing samples. At this time, however, the discussion of this oxygen concentration as nuclear in origin must exclude the possibility of many chemical processes.
Ruizhe Zhang and Yuhao Zhang 2023 Jpn. J. Appl. Phys. 62 SC0806
Breakdown voltage (BV) is arguably one of the most critical parameters for power devices. While avalanche breakdown is prevailing in silicon and silicon carbide devices, it is lacking in many wide bandgap (WBG) and ultra-wide bandgap (UWBG) devices, such as the gallium nitride high electron mobility transistor and existing UWBG devices, due to the deployment of junction-less device structures or the inherent material challenges of forming p-n junctions. This paper starts with a survey of avalanche and non-avalanche breakdown mechanisms in WBG and UWBG devices, followed by the distinction between the static and dynamic BV. Various BV characterization methods, including the static and pulse I–V sweep, unclamped and clamped inductive switching, as well as continuous overvoltage switching, are comparatively introduced. The device physics behind the time- and frequency-dependent BV as well as the enabling device structures for avalanche breakdown are also discussed. The paper concludes by identifying research gaps for understanding the breakdown of WBG and UWBG power devices.
Makoto Kambara et al 2023 Jpn. J. Appl. Phys. 62 SA0803
Low-temperature plasma-processing technologies are essential for material synthesis and device fabrication. Not only the utilization but also the development of plasma-related products and services requires an understanding of the multiscale hierarchies of complex behaviors of plasma-related phenomena, including plasma generation in physics and chemistry, transport of energy and mass through the sheath region, and morphology- and geometry-dependent surface reactions. Low-temperature plasma science and technology play a pivotal role in the exploration of new applications and in the development and control of plasma-processing methods. Presently, science-based and data-driven approaches to control systems are progressing with the state-of-the-art deep learning, machine learning, and artificial intelligence. In this review, researchers in material science and plasma processing, review and discuss the requirements and challenges of research and development in these fields. In particular, the prediction of plasma parameters and the discovery of processing recipes are asserted by outlining the emerging science-based, data-driven approaches, which are called plasma informatics.
Tsunenobu Kimoto 2015 Jpn. J. Appl. Phys. 54 040103
Power semiconductor devices are key components in power conversion systems. Silicon carbide (SiC) has received increasing attention as a wide-bandgap semiconductor suitable for high-voltage and low-loss power devices. Through recent progress in the crystal growth and process technology of SiC, the production of medium-voltage (600–1700 V) SiC Schottky barrier diodes (SBDs) and power metal–oxide–semiconductor field-effect transistors (MOSFETs) has started. However, basic understanding of the material properties, defect electronics, and the reliability of SiC devices is still poor. In this review paper, the features and present status of SiC power devices are briefly described. Then, several important aspects of the material science and device physics of SiC, such as impurity doping, extended and point defects, and the impact of such defects on device performance and reliability, are reviewed. Fundamental issues regarding SiC SBDs and power MOSFETs are also discussed.
Yuan Qin et al 2023 Jpn. J. Appl. Phys. 62 SF0801
Benefitted from progress on the large-diameter Ga2O3 wafers and Ga2O3 processing techniques, the Ga2O3 power device technology has witnessed fast advances toward power electronics applications. Recently, reports on large-area (ampere-class) Ga2O3 power devices have emerged globally, and the scope of these works have gone well beyond the bare-die device demonstration into the device packaging, circuit testing, and ruggedness evaluation. These results have placed Ga2O3 in a unique position as the only ultra-wide bandgap semiconductor reaching these indispensable milestones for power device development. This paper presents a timely review on the state-of-the-art of the ampere-class Ga2O3 power devices (current up to >100 A and voltage up to >2000 V), including their static electrical performance, switching characteristics, packaging and thermal management, and the overcurrent/overvoltage ruggedness and reliability. Exciting research opportunities and critical technological gaps are also discussed.
Kazuhito Hashimoto et al 2005 Jpn. J. Appl. Phys. 44 8269
Photocatalysis has recently become a common word and various products using photocatalytic functions have been commercialized. Among many candidates for photocatalysts, TiO2 is almost the only material suitable for industrial use at present and also probably in the future. This is because TiO2 has the most efficient photoactivity, the highest stability and the lowest cost. More significantly, it has been used as a white pigment from ancient times, and thus, its safety to humans and the environment is guaranteed by history. There are two types of photochemical reaction proceeding on a TiO2 surface when irradiated with ultraviolet light. One includes the photo-induced redox reactions of adsorbed substances, and the other is the photo-induced hydrophilic conversion of TiO2 itself. The former type has been known since the early part of the 20th century, but the latter was found only at the end of the century. The combination of these two functions has opened up various novel applications of TiO2, particularly in the field of building materials. Here, we review the progress of the scientific research on TiO2 photocatalysis as well as its industrial applications, and describe future prospects of this field mainly based on the present authors' work.
Zhe Zhuang et al 2022 Jpn. J. Appl. Phys. 61 SA0809
InGaN-based LEDs are efficient light sources in the blue–green light range and have been successfully commercialized in the last decades. Extending their spectral range to the red region causes a significant reduction in LED efficiency. This challenge hinders the integration of red, green, and blue LEDs based on III-nitride materials, especially for full-color micro-LED displays. We review our recent progress on InGaN-based red LEDs with different chip sizes from hundreds to tens of micrometers, including the epitaxial structures, device fabrication, and optical performance (peak wavelength, full-width at half-maximum, light output power, efficiency, temperature stability, and color coordinates).
Norio Nakamura et al 2023 Jpn. J. Appl. Phys. 62 SG0809
The development of a high-power EUV light source is very important in EUV lithography to overcome the stochastic effects for higher throughput and higher numerical aperture (NA) in the future. We have designed and studied a high-power EUV free-electron laser (FEL) based on energy-recovery linac (ERL) for future lithography. We show that the EUV-FEL light source has many advantages, such as extremely high EUV power without tin debris, upgradability to a Beyond EUV (BEUV) FEL, polarization controllability for high-NA lithography, low electricity consumption, and low construction and running costs per scanner, as compared to the laser-produced plasma source used for the present EUV lithography exposure tool. Furthermore, the demonstration of proof of concept (PoC) of the EUV-FEL is in progress using the IR-FEL in the Compact ERL (cERL) at the High Energy Accelerator Research Organization. In this paper, we present the EUV-FEL light source for future lithography and progress in the PoC of the EUV-FEL.
Open all abstracts, in this tab
Min Liang et al 2024 Jpn. J. Appl. Phys. 63 052005
The design and fabrication processes of the stimulated Brillouin laser (SBL) are complex, and it is affected by many factors such as temperature and resonance shift. In this study, we have fabricated a Brillouin laser using a fiber ring resonator with Q factor = 7.1 × 108 and resonance depth (h) = 96%. The free spectral range automatic feedback control technology is proposed to realize the accurate matching of the resonant mode and the Stokes mode. The influence of temperature on the SBL frequency shift is suppressed. The fluctuation range of SBL's frequency decreases by 5 times. The maximum steady state output of the SBL at the best matching position is realized, and the output power fluctuation range decreases by 15 times. The power stability of the SBL reaches 4.85 × 10−6, which is improved by two orders of magnitude. This simple scheme provides convenience for the application of the SBL, such as sensing and other applications.
Kai E. Thomenius 2024 Jpn. J. Appl. Phys. 63 050807
From its earliest appearance in the 1950s, ultrasound has received much continuous attention by the research community. In this review paper, the evolution of the field will be discussed throughout its various hardware and software implementations with the goal of establishing the state-of-the-art for the present. This supplies a convenient launching point to consider possible directions for future research. A useful tool for this assessment is an analysis of the focus areas of various disciplines at medical ultrasound conferences and their relative frequencies. The assumption behind this methodology is that each topic has received much attention from academic faculties, technical program committees, journal editorial boards, and grant review processes. This evaluation suggests that ultrasound beamformation is becoming increasingly based on computational methods more along the lines of computed tomography or magnetic resonance imaging. As part of the process, select traditional challenges are starting to be translated into clinical practice.
Xuchen Gao et al 2024 Jpn. J. Appl. Phys. 63 054003
Using numerical simulation tools, this work systematically investigates the impact of bulk defects in the drift layer on GaN-based trench metal–insulator–semiconductor barrier-controlled Schottky rectifiers. Investigations show that in forward conduction, the acceptor-type defects significantly increase the on-resistance (Ron.sp). When the device is in reverse blocking mode, donor-type defects tend to weaken the charge-coupling effect, leading to early breakdown of the device, while acceptor-type defects show the opposite feature. In addition, our report identifies that the reverse blocking effect is significantly impacted when the defects are located in the region with maximum electric field magnitude. We also find that the acceptor-type traps generate a remarkable charging/discharging effect, which will destabilize the dynamic forward conduction process. Hence, we numerically prove that bulk defects should be avoided in actual power diodes.
Hiromasa Shimizu et al 2024 Jpn. J. Appl. Phys. 63 052004
We report improved photothermal heating efficiency of Si plasmonic waveguide heaters integrated with ring resonators by enhancing the interaction of the propagating light and metal with a thinner buffer layer. The resonance wavelength was shifted towards a longer wavelength by inputting transverse magnetic mode light, and the amount of shift was influenced by the length of the region deposited with the Co thin film and the gap of the directional coupler. The local temperature rise of 580 K was achieved by injecting 6.3 mW of light, and photothermal conversion efficiency as high as 106 K mW−1 was obtained in a Si plasmonic waveguide deposited with 0.5 μm long Co thin films, showing improvement compared with previous devices. Discussion on the heating efficiency based on the propagation loss and cavity loss in the ring resonators is given based on experimental results, to realize compact photothermal waveguide heaters for various applications.
Soomin Kim and Seongjae Cho 2024 Jpn. J. Appl. Phys. 63 054002
In advanced MOSFET design, a vertical-channel structure provides the advantages of a smaller footprint of the transistor cell and stronger immunity against short-channel effects by introducing higher freedom in determining the channel length. For these reasons, vertical devices are still predicted to be an upcoming solution in the most recent technology roadmap. However, due to the cell-to-cell or wafer-to-wafer processing deviation that inevitably exists, it can be quite challenging to locate the gate edges at the exact positions that maximize the device performance. In this work, a series of technology computer-aided design (TCAD) device simulations have been carried out to investigate the effects of gate underlap and overlap structures on the device performance of vertical-channel MOSFETs. The device characterizations were conducted from the aspects of both DC and HF operations for higher completeness of this work, since both are not usually optimized at the same time under the same structural and processing conditions. Under the underlap condition, slight degradation in the on-state current (Ion) drivability was observed. On the other hand, a noticeable off-state current (Ioff) increase was witnessed under the underlap conduction. It is explicitly demonstrated that excessive gate underlap results in non-ideal effects, including degradation of the subthreshold swing (S), worsening of drain-induced barrier lowering, and lowering of the maximum transconductance (gm,Max). In the HF analyses, although fT and fmax remained high under overlap and gate–drain alignment conditions, it was observed that both were likely to deteriorate under underlap conditions. As a result, a processing margin in the anisotropic etching of the gate can be obtained for the optimization of the DC and HF performance of vertical-channel MOSFETs, paving the way for a wide variety of low-power and high-speed analog and digital applications.
Open all abstracts, in this tab
Kai E. Thomenius 2024 Jpn. J. Appl. Phys. 63 050807
From its earliest appearance in the 1950s, ultrasound has received much continuous attention by the research community. In this review paper, the evolution of the field will be discussed throughout its various hardware and software implementations with the goal of establishing the state-of-the-art for the present. This supplies a convenient launching point to consider possible directions for future research. A useful tool for this assessment is an analysis of the focus areas of various disciplines at medical ultrasound conferences and their relative frequencies. The assumption behind this methodology is that each topic has received much attention from academic faculties, technical program committees, journal editorial boards, and grant review processes. This evaluation suggests that ultrasound beamformation is becoming increasingly based on computational methods more along the lines of computed tomography or magnetic resonance imaging. As part of the process, select traditional challenges are starting to be translated into clinical practice.
Yasuyuki Yokota 2024 Jpn. J. Appl. Phys. 63 050806
In recent years, electrochemical devices have become increasingly important, and atomic- and molecular-scale understanding of the electronic and ionic transfers and chemical reactions at the electrode/electrolyte interface is required. While electrochemical scanning tunneling microscopy (EC-STM) has long enabled atomic-resolution observations in real space, it is difficult to identify reaction products and evaluate their electronic states at the interface in the electrochemical environment because of various limitations imposed by the presence of electrolyte solutions in the measurement. In this perspective review, we present our recent progresses with in situ (EC-STM combined with near-field spectroscopy) and ex situ (precise measurements in ultrahigh vacuum after electrode emersion) experiments for elucidating the microscopic properties of the electrochemical interfaces. Current issues and future perspective of both techniques are also discussed in detail.
Lingke Xu et al 2024 Jpn. J. Appl. Phys. 63 050805
Famous for their two-dimensional magnetism, the transition-metal halides with significant anisotropy and correlated d-electrons have been reduced to a low dimension and caught substantial attention in recent years. At the same time, owing to the excellent capability of discerning various degrees of freedom in solid-state systems, a scanning tunneling microscope greatly advances the understanding of low-dimensional transition-metal halides and their heterostructures by providing key results regarding structural, electronic, and magnetic properties. Here, we review the key insights about the fabrication methods, crystallography, strongly correlated electronic structures, and magnetic orders of low-dimensional revealed by scanning tunneling microscope, and introduce the latest discoveries of emergent physics under the interplay between dimensionality confinement, many-body correlation, and quantum-coupling mechanisms.
Toshiki Ito et al 2024 Jpn. J. Appl. Phys. 63 050804
Field-by-field-type UV nanoimprint lithography equipped with an on-demand inkjet dispense system, known as jet and flash imprint lithography (JFIL), has been developed. In JFIL, the inkjet resist drops still remain independent of each other when imprinting a mold, so that the ambient gas is trapped among the resist drops to generate bubbles. It takes time for the trapped bubbles to disappear, and the bubbles sometimes remain in the cured resist film to cause open defects. The waiting time for the disappearance of the gas results in low throughput and the remaining bubbles cause defect problems in JFIL. The fast disappearance of trapped bubbles was demonstrated in the case when carbon dioxide gas was used as the ambient gas. On the basis of fluid mechanics, combined-drop JFIL and its resist material was developed, in which the resist drops were combined with each other prior to imprinting to minimize trapped gas volume.
Takahiro Kozawa 2024 Jpn. J. Appl. Phys. 63 050101
The high-volume production of semiconductor devices with EUV lithography started in 2019. During the development of EUV lithography, the resist materials had always been ranked high in the focus area for its realization. The trade-off relationships between the resolution, line width roughness, and sensitivity were the most serious problem. EUV lithography started with the use of chemically amplified resists after the material chemistry was optimized on the basis of radiation chemistry. The increase of numerical aperture has been scheduled to enhance the optical resolution. For the realization of next-generation lithography, the suppression of stochastic effects is the most important issue. A highly absorptive material is key to the suppression of stochastic effects. The development of next-generation EUV resists has progressed around chemically amplified resists, metal oxide resists, and main-chain-scission-type resists. EUV resists are reviewed from the viewpoint of the material design for the suppression of stochastic effects.
Open all abstracts, in this tab
WANG et al
Air gap discharge is one of the basic scientific problems in the field of high voltage engineering. The homogeneous electric field 1.5 mm air gap negative streamer at overvoltage and atmospheric pressure is observed by a high-speed 4-channel framing camera. The ultra-high temporal resolution images of a single negative stream are captured (exposure time is 5 ns, and inter-frame delay is no more than 0.1 ns). It is observed that the negative streamer formed in the middle of the air gap and growth bidirectionally towards both electrodes. At the same time, the electrical measurement is also carried out.
XIE et al
Power splitter is one of the fundamental elements in photonic integrated circuit. Among various power splitter structures, nano-pixel-based ones have attracted attention because of the flexible design capability. As there is no rigid design rule in nano-pixel layout, inverse design algorithms are employed to realize the target function. Machine-learning needs in general criteria during design process, and one typical criterial is the device excess loss. For the designing of 1×N power splitter, it is not sufficient in consideration of power valance among N output-ports. In this study, we propose an electric field profile evaluation method which evaluate the total field profile at the device facet in addition to the excess loss. We exploit the criteria including above method to design 1 × 4 power splitter. As a result, the simulated results show all four 0th order modes and the output power are 24.490%, 24.494% with excess loss of 0.1 dB..
Matsuura et al
This paper reveals that ultrasonic jet atomization using a diaphragm enables to enclose microplastics in water into atomized mist, emitting them into the air. In particular, a strong correlation is found between the size of the atomized mist and the acrylic particles enclosed in the mist: Acrylic particles with an average diameter of 1.5㎛ or smaller are selectively enclosed in the atomized mist with average diameter of 2.2㎛. The results of this study can be applicable to the process of analyzing microplastics dispersed in rivers, lakes, and oceans for separating particles of a targeted diameter from numerous particles of different diameters without aggregation. This paper also reveals one aspect of atomization mechanism that has not been achieved for more than 60 years.
Tsukahara et al
A porous two-dimensional metal-organic network (2D-MON) on the substrate captures deposited metal atoms and metal clusters grow in the pores of the 2D-MON. We found that the growth mechanisms of Ag, In, and Pd clusters in the 2D-MON synthesized from 1,3,5-tris(4-bromophenyl)benzene molecules on Ag(111) are different from each other, and the difference derives from the interaction of an adatom with the 2D-MON. Ag and Pd clusters grow from the 2D-MON since the interaction of Ag and Pd adatoms with the 2D-MON is attractive. In clusters grow inside of the pores of the 2D-MON since the interaction between an In adatom and the 2D-MON is repulsive. The growth process of metal clusters is determined by the element-specific behavior of metal adatoms in the pores, taking into account interactions with the 2D-MON.
nishimura et al
A silicon (Si) protrusion, grown on a narrow path of a Si(001) wafer by surface melting via resistive heating, was sharpened by applying a local high electric field under a magnetic field during the growth. The electric field caused local stress to the surface-melted Si, which was pulled upward along the field. Consequently, the melted Si formed a sharper protrusion on solidification, with an apex surrounded by {001}, {113}, and {111} facets. The field emission from the protrusions was measured. The onset voltage of the emission from protrusions was lower when they were grown under the electric field. We used Fowler–Nordheim plots to characterize the emission current and voltage conversion factor, β. The results indicated that the application of electric field is beneficial to sharpening Si protrusions grown from Si melt. Such protrusions surrounded by facets are suitable for field emission electron sources with a confined emission area.
Trending on Altmetric
Open all abstracts, in this tab
Bingzhuo WANG et al 2024 Jpn. J. Appl. Phys.
Air gap discharge is one of the basic scientific problems in the field of high voltage engineering. The homogeneous electric field 1.5 mm air gap negative streamer at overvoltage and atmospheric pressure is observed by a high-speed 4-channel framing camera. The ultra-high temporal resolution images of a single negative stream are captured (exposure time is 5 ns, and inter-frame delay is no more than 0.1 ns). It is observed that the negative streamer formed in the middle of the air gap and growth bidirectionally towards both electrodes. At the same time, the electrical measurement is also carried out.
Soomin Kim and Seongjae Cho 2024 Jpn. J. Appl. Phys. 63 054002
In advanced MOSFET design, a vertical-channel structure provides the advantages of a smaller footprint of the transistor cell and stronger immunity against short-channel effects by introducing higher freedom in determining the channel length. For these reasons, vertical devices are still predicted to be an upcoming solution in the most recent technology roadmap. However, due to the cell-to-cell or wafer-to-wafer processing deviation that inevitably exists, it can be quite challenging to locate the gate edges at the exact positions that maximize the device performance. In this work, a series of technology computer-aided design (TCAD) device simulations have been carried out to investigate the effects of gate underlap and overlap structures on the device performance of vertical-channel MOSFETs. The device characterizations were conducted from the aspects of both DC and HF operations for higher completeness of this work, since both are not usually optimized at the same time under the same structural and processing conditions. Under the underlap condition, slight degradation in the on-state current (Ion) drivability was observed. On the other hand, a noticeable off-state current (Ioff) increase was witnessed under the underlap conduction. It is explicitly demonstrated that excessive gate underlap results in non-ideal effects, including degradation of the subthreshold swing (S), worsening of drain-induced barrier lowering, and lowering of the maximum transconductance (gm,Max). In the HF analyses, although fT and fmax remained high under overlap and gate–drain alignment conditions, it was observed that both were likely to deteriorate under underlap conditions. As a result, a processing margin in the anisotropic etching of the gate can be obtained for the optimization of the DC and HF performance of vertical-channel MOSFETs, paving the way for a wide variety of low-power and high-speed analog and digital applications.
Tatsuya Kitazawa et al 2024 Jpn. J. Appl. Phys. 63 055508
This study investigates the effects of sulfur atomic defects and crystallinity on the thermal conductivity of MoS2 thin films. Utilizing scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), and Raman spectroscopy, we examined MoS2 films, several nanometers thick, deposited on Si/SiO2 substrates. These films were prepared via a combination of RF magnetron sputtering and sulfur vapor annealing (SVA) treatment. Structural analyses, including cross-sectional STEM and in-plane and out-of-plane XRD measurements, revealed an increase in the S/Mo ratio and grain size of the MoS2 films following SVA treatment. Notably, the in-plane thermal conductivity of MoS2 films treated with SVA was found to be at least an order of magnitude higher than that of films without SVA treatment. This research suggests that the in-plane thermal conductivity of MoS2 thin films can be significantly enhanced through crystallinity improvement via SVA treatment.
Gisya Abdi et al 2024 Jpn. J. Appl. Phys. 63 050803
Reservoir computing is an unconventional computing paradigm that uses system complexity and dynamics as a computational medium. Currently, it is the leading computational paradigm in the fields of unconventional in materia computing. This review briefly outlines the theory behind the term 'reservoir computing,' presents the basis for the evaluation of reservoirs, and presents a cultural reference of reservoir computing in a haiku. The summary highlights recent advances in physical reservoir computing and points out the importance of the drive, usually neglected in physical implementations of reservoir computing. However, drive signals may further simplify the training of reservoirs' readout layer training, thus contributing to improved performance of reservoir computer performance.
Konrad Seidel et al 2024 Jpn. J. Appl. Phys. 63 050802
In this work the integration of ferroelectric (FE) devices for advanced in-memory computing applications is demonstrated based on the FeMFET memory cell concept. In contrast to FeFET having the FE layer directly embedded in the gate-stack, the FeMFET consists of a separated ferroelectric capacitor which can be integrated in the chip-interconnect layers. Optimization of the FE material stack under such lower thermal budget constraints will be discussed as well as the significant performance improvement and reduction of variability by application of superlattice FE-stacks and further optimization knobs. The low memory state variability is important for accurate multiply-accumulate (MAC) operation. Such improvements are demonstrated on a memory array test chip including functional verification of MAC operation along a FeMFET-based array column with good accuracy over high dynamic current range.
Jun Wu et al 2024 Jpn. J. Appl. Phys. 63 056501
This paper reports on a fabrication process suitable for ultra-low resonant frequency inertial MEMS sensors. The low resonant frequency is achieved by electrically tunable springs and a heavy mass formed by through-silicon deep reactive-ion etching (DRIE) applied to a silicon-on-glass. A thermal issue of through-silicon DRIE (TSD) stemming from the low-resonant-frequency structure is circumvented by two methods: introducing cooling time between the DRIE steps, and adopting a metal hard mask. A blade dicing method suited for this process is also presented. To monitor the verticality of TSD, a non-destructive taper detection method that utilizes a capacitance–voltage (CV) curve is proposed and verified.
Shogo Matsuda and Shigeki Matsuo 2024 Jpn. J. Appl. Phys. 63 052001
In this study, we used femtosecond laser-assisted etching (FLAE) to drill through glass vias (TGVs) in 0.3 mm thick non-alkali glass substrates. In FLAE, the focus of the femtosecond laser pulses is scanned to modify the material along a preprogrammed pattern, and the modified region is preferentially removed by chemical etching. We found that the scanning strategy affected the etching rate along the laser-modified lines. Among four types of scanning strategies tested, the strategy 〈du〉—that is, scanning in a downward direction followed by an upward direction—obtained the highest etching rate. In this case, the etching rate along the laser-modified line was approximately 10 times larger than that of the unmodified region.
Akihiko Teshigahara et al 2024 Jpn. J. Appl. Phys. 63 055501
A ScAlN thin film is one of the key materials of MEMS and high-frequency filters used in new-generation communication devices. Piezoelectricity can be improved by increasing Sc concentration. However, abnormal grains often appear at high Sc concentrations, degrading crystallinity and piezoelectricity. Herein, we demonstrated that underlayer roughness considerably affects the emergence of abnormal grains in a Sc0.4Al0.6N thin film formed via reactive DC sputtering. Dry etching with Ar plasma can effectively reduce the surface roughness of amorphous SiN and polycrystalline Si. Sc0.4Al0.6N thin films deposited on amorphous SiN and polycrystalline Si with sufficient flat surfaces exhibited a low density of abnormal grains, high crystallinity and piezoelectricity, and low loss tangent. Moreover, such high-quality thin films were obtained on a borophosphosilicate glass flattened using a reflow process without Ar etching. Therefore, underlayer roughness played an important role. The findings can help enable the large-scale production of highly doped ScAlN thin films.
Noah Austin-Bingamon et al 2024 Jpn. J. Appl. Phys. 63 04SP84
The effective quality factor of the cantilever plays a fundamental role in dynamic mode atomic force microscopy. Here we present a technique to modify the quality factor of an atomic force microscopy cantilever within a Fabry–Perot optical interferometer. The experimental setup uses two separate laser sources to detect and excite the oscillation of the cantilever. While the intensity modulation of the excitation laser drives the oscillation of the cantilever, the average intensity can be used to modify the quality factor via optomechanical force without changing the fiber-cantilever cavity length. The technique enables users to optimize the quality factor for different types of measurements without influencing the deflection measurement sensitivity. An unexpected frequency shift was observed and modelled as temperature dependence of the cantilever's Young's modulus, which was validated using finite element simulation. The model was used to compensate for the thermal frequency shift. The simulation provided relations between optical power, temperature, and frequency shift.
Aleksandr Zozulia et al 2024 Jpn. J. Appl. Phys. 63 04SP78
Wafer bonding is a key process in heterogeneous photonic integration and benzocyclobutene (BCB) is widely used for adhesive wafer-to-wafer bonding when it comes to handling complex topography on both wafers. However, until now a major drawback of bonding with BCB was the high thermal impedance of lasers due to the low thermal conductivity of BCB. We demonstrate, that by optimizing the membrane device topography and introducing the BCB reflow step into the process flow it is possible to achieve full planarization of 1 μm topography at the wafer scale while ensuring only 135 nm of BCB between the laser p-contact and the substrate. We show experimentally, that the thermal impedance of 500 μm long distributed feedback (DFB) laser was reduced from 585 to 271 K W−1 when bonded to Si substrate, and to 174 K W−1 when bonded to SiC substrate using the new method.
Open all abstracts, in this tab
Junpei Igarashi et al 2024 Jpn. J. Appl. Phys. 63 05SP17
A hydrogen gas sensor based on a silicon microring resonator (MRR) with a Pt–SiO2 thin film as a hydrogen-sensitive film is proposed and investigated to realize a high-sensitivity hydrogen sensor. The sensor detects hydrogen on the basis of the resonant wavelength shift caused by the reaction heat generated in the Pt–SiO2 film. In the hydrogen exposure measurement, resonant wavelength shifts of approximately 5.0 and 2.4 nm were observed at hydrogen concentrations of 4.0 and 0.4 vol%, respectively, showing the high sensitivity of the proposed sensor. In addition, an MRR sensor with an upper Al2O3 cladding layer is proposed and its higher sensitivity is theoretically demonstrated.
Kei Sato et al 2024 Jpn. J. Appl. Phys. 63 04SP76
In this study, precious metal/tungsten trioxide (WO3) composite particles in which palladium (Pd) and platinum (Pt) were loaded on WO3 particles were synthesized via the ultrasonic reduction method. The surface observation of the synthesized composite materials was performed and their photocatalytic performance under visible light irradiation was evaluated from the decomposition rate of methylene blue in aqueous solution. From the TEM image, it was found that the Pd/WO3 composite particles synthesized by the ultrasonic reduction method had a structure in which Pd nanoparticles were supported on WO3 particles. The photocatalytic performance of Pd/WO3 and Pt/WO3 increased with increasing contents of Pd and Pt. When synthesizing Pd(0.5 wt%)/WO3 particles by ultrasonic reduction method, the photocatalytic activity was improved by feeding Pd equivalent to 0.17 wt% per feed three times at regular time intervals, rather than by feeding 0.5 wt% of Pd at a time.
Hideaki Numata et al 2024 Jpn. J. Appl. Phys. 63 04SP73
A 100 nm wide superconducting niobium (Nb) interconnect was fabricated by a 300 mm wafer process for Cryo-CMOS and superconducting digital logic applications. A low pressure and long throw sputtering was adopted for the Nb deposition, resulting in good superconductivity of the 50 nm thick Nb film with a critical temperature (Tc) of 8.3 K. The interconnects had a titanium nitride (TiN)/Nb stack structure, and a double-layer hard mask was used for the dry etching process. The exposed area of Nb film was minimized to decrease the effects of plasma damage during fabrication and atmosphere. The developed 100 nm wide and 50 nm thick Nb interconnect showed good superconductivity with a Tc of 7.8 K and a critical current of 3.2 mA at 4.2 K. These results are promising for Cryo-CMOS and superconducting digital logic applications in the 4 K stage.
Keisuke Yamamoto et al 2024 Jpn. J. Appl. Phys. 63 04SP32
Ge-on-Insulator (GOI) is considered to be a necessary structure for novel Ge-based devices. This paper proposes an alternative approach for fabricating GOI based on the Ge-on-Nothing (GeON) template. In this approach, a regular macropore array is formed by lithography and dry etching. These pores close and merge upon annealing, forming a suspended monocrystalline Ge membrane on one buried void. GOI is fabricated by direct bonding of GeON on Si carrier substrates, using an oxide bonding interface, and subsequent detachment. The fabricated GOI shows uniform physical properties as demonstrated using micro-photoluminescence measurements. Its electrical characteristics and cross-sectional structure are superior to those of Smart-CutTM GOI. To demonstrate its application potential, back-gate GOI capacitors and MOSFETs are fabricated. Their characteristics nicely agree with the theoretically calculated one and show typical MOSFET operations, respectively, which indicates promising Ge crystallinity. This method, therefore, shows the potential to provide high-quality GOI for advanced Ge application devices.
Kohei Iino and Tomohiro Kita 2024 Jpn. J. Appl. Phys. 63 04SP21
We developed a compact thermo-optic Mach–Zehnder interferometer switch with a direct heating heater using multimode interference and achieved a sufficiently low thermal crosstalk performance. Large-scale switch systems, such as optical neural networks, require thermo-optical switches with low power consumption, fast switching speed, compact size, and low thermal crosstalk. This switch is equipped with a heater that directly heats the Si core waveguide, which is a structure that connects non-doped Si wires between phase shifters and a heatsink. As a result, a significant miniaturization with a phase shifter length of approximately 7 μm, low π-phase shift power consumption of less than 20 mW, and fast switching in sub-microseconds were achieved. The improved phase shifter showed a very small figure of merit of 8.89 mWμs. Simultaneously, transmission spectrum measurements of nearby ring resonators show that the thermal crosstalk is significantly reduced even at a distance of only 30 μm. This device can contribute to the overall circuit performance and footprint reduction in large-scale optical integrated circuits and optical neural network configurations.
Haruki Matsuo et al 2024 Jpn. J. Appl. Phys. 63 04SP19
Two metal-induced lateral crystallization (MILC) methods are proposed as candidate techniques to enhance cell current in future ultra-high-density NAND-type 3D flash memory devices. The channel crystallinity differs depending on the MILC method. In a single MILC, the channel is composed of single-crystal Si, whereas in a regional MILC, the channel comprises multiple crystal grains that are larger than those of the conventional polycrystalline Si. Using transmission electron microscopy, the inhibiting factor of MILC was modeled to reveal that the two MILC approaches result in different cell current distributions that are related to their degree of crystallinity. A comparison of these two cell current distributions in a 3D flash memory with over 900 word-line stacks showed that the single MILC delivers a higher median cell current with outliers on the lower side. In contrast, the regional MILC delivers a lower median cell current without outliers on the lower side.
Naoko Misawa et al 2024 Jpn. J. Appl. Phys. 63 03SP83
This paper comprehensively analyses dual integration of approximate random weight generator (ARWG) and computation-in-memory for event-based neuromorphic computing. ARWG can generate approximate random weights and perform multiply-accumulate (MAC) operation for reservoir computing (RC) and random weight spiking neural network (SNN). Because of using device variation to generate random weights, ARWG does not require any random number generators (RNGs). Because RC and random weight SNN allow approximate randomness, ARWG only needs to generate approximate random weights, which does not require error-correcting code to correct weights to make the randomness accurate. Moreover, ARWG has a read port for MAC operation. In this paper, the randomness of random weights generated by the proposed ARWG is evaluated by Hamming distance and Hamming weight. As a result, this paper reveals that the randomness required for ARWG is much lower than that for physically unclonable functions and RNGs, and thus the proposed ARWG achieves high recognition accuracy.
Kaori Yamamoto et al 2024 Jpn. J. Appl. Phys. 63 03SP14
By modulating a ζ potential of graphene FET (G-EFT), the sensitivity of G-FET could be enhanced than that without modulation. Therefore, 1 × 107 FFU ml−1 SARS-CoV-2 was detected using G-FET modified with the ζ potential modulator which is the cation polymer with the positive charge. This method is based on the relationship between the surface charge and the sensitivity, in which the highest sensitivity is obtained when the ζ potential is 0 and/or the surface charge is almost 0. In this study, the microfluidic channel was installed on G-FET to get the precise result because it could wash away the free-floating virus and the physical adsorbed virus. 32 G-FETs including the reference FETs were integrated on the silicon substrate and the precise results were obtained by subtracting the noise terms.
Naoko Misawa et al 2024 Jpn. J. Appl. Phys. 63 03SP05
This paper proposes a design methodology for a compact edge vision transformer (ViT) Computation-in-Memory (CiM). ViT has attracted much attention for its high inference accuracy. However, to achieve high inference accuracy, the conventional ViT requires fine-tuning many parameters with pre-trained models on large datasets and a large number of matrix multiplications in inference. Thus, to map ViT to non-volatile memory (NVM)-based CiM compactly for edge applications (IoT/Mobile devices) in inference, this paper analyses fine-tuning in training, clipping, and quantization in inference. The proposed compact edge ViT CiM can be optimized by three design methods according to use cases considering the required fine-tuning time, ease of setting memory bit precision, and memory error tolerance of ViT CiM. As a result, in CIFAR-10, the most compact type successfully reduces the total memory size of ViT by 85.8% compared with the conventional ViT. Furthermore, the high accuracy type and high error-tolerant type improve inference accuracy by 4.4% and memory-error tolerance by more than four times compared with convolutional neural networks, respectively.
Sung-Won Youn et al 2024 Jpn. J. Appl. Phys. 63 03SP06
Plasmonic color is a structural color generated via preferential light absorption and scattering in dielectric nanostructures. In this study, a large plasmonic color image was successfully fabricated by an electron beam lithography (EBL) system. A software program, referred to as P-color in this study, was developed to facilitate the conversion of a desired color bitmap image to a GDS file composed of multiple nano-patterns to realize plasmonic color. The relationship between the color, width, and pitch of the pattern structures was investigated under different area-dose conditions during EBL as basic data for plasmonic color image design. After establishing conversion techniques for both the large-capacity GDS and EBL files, a plasmonic color image sample with a size of 60 mm × 40 mm area (which is difficult to fabricate using a conventional point-type EBL system) was successfully fabricated.