The 50 most-cited articles in Japanese Journal of Applied Physics, 2024

Abstract 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.

Abstract Since the last decade, research on plasma catalysis has attracted keen attention as an emerging type of low-carbon technology. An advantage of plasma is to facilitate non-equilibrium reaction fields on a large scale, which is inaccessible by conventional thermal approaches. Stable molecules such as CO2 and CH4 are activated by electrical energy, paving the way for low-temperature chemistry that departs from energy-intensive heat-dependent systems. Moreover, the power-to-chemical concept could gain momentum with plasma technologies that are driven by renewable energy. Currently, research is accelerating with application initiatives, but at the same time the importance of scientific understanding of plasma catalytic reactions is being recognized more than ever. This review article offers an overview of various plasma technologies in the “plasma alone” and “plasma–catalyst combination” context. Plasma–catalyst combination technology, known as “plasma catalysis”, is discussed further to dry methane reforming (CH4 + CO2 = 2CO + 2H2) and the reverse water gas shift reaction (CO2…

Abstract This paper presents a tutorial and review of Static Random Access Memory-based compute-in-memory (CIM) circuits, with a focus on both digital CIM (DCIM) and analog CIM (ACIM) implementations. We explore the fundamental concepts, architectures, and operational principles of CIM technology. The review compares DCIM and ACIM approaches, examining their respective advantages and challenges. DCIM offers high computational precision and process scaling benefits, while ACIM provides superior power and area efficiency, particularly for medium-precision applications. We analyze various ACIM implementations, including current-based, time-based, and charge-based approaches, with a detailed look at charge-based ACIMs. The paper also discusses emerging hybrid CIM architectures that combine DCIM and ACIM to leverage the strengths of both approaches.

Abstract The impact of H2 gas flow in the reactive sputtering process to 60 nm-thick ferroelectric Al1−x Sc x N films is investigated with x of 0.26 (high-Sc) and 0.12 (low-Sc). Al1−x Sc x N films exhibit clear ferroelectric switching, confirming the robustness against reducing ambient. The dielectric constants (ε i) as well as the leakage current decrease, and the breakdown field (E BD) increases with H2 flow. Although the remanent polarization (P r) decreases with H2 flow, the wake-up effect is suppressed for the high-Sc film, and the fatigue effect is weakened for the low-Sc film. By probing the change in the coercive field (E c) after the switching cycle test, we anticipate oxygen impurities bonded to Sc and Al atoms are the source of wake-up and fatigue effects, respectively. As a result, a high endurance cycle of 2 × 107 times was achieved for low-Sc films with H2 flow.

Abstract The bulk photovoltaic (PV) effect in ferroelectric materials has attracted worldwide attention for novel optoelectronic applications utilizing above-bandgap photovoltages, light-polarization-dependent photocurrents, photocurrent generation by terahertz light, etc. One of the drawbacks is its weak photoresponse under visible-light irradiation, and thereby the development of visible-light-active ferroelectrics has been an important issue. In this review, firstly, we introduce the history, mechanisms, and physical features of the bulk PV effect. Secondly, we summarize the properties of representative ferroelectric oxides and two-dimensional nanomaterials. Moreover, we describe a material design for enhancing the visible-light photoresponse based on bandgap tuning and gap-state engineering. Finally, we discuss future prospects of ferroelectric PV devices with a high conversion efficiency.

Abstract Silicon carbide (SiC) is widely used in power semiconductor devices; however, basal plane dislocations (BPDs) degrade device performance, through a mechanism called bipolar degradation. Recently, we proposed that proton implantation could suppress BPD expansion by reducing BPD mobility. We considered three potential mechanisms: the hydrogen presence around BPDs, point defects induced by implantation, and carrier lifetime reduction. In this study, we discuss the mechanisms of proton implantation and its applicability to SiC power device production.

Abstract We explored the potential of an optoelectronic frequency hopping system within the 300 GHz band, leveraging a tunable distributed feedback laser array and uni-traveling carrier photodiode. Our experiments successfully achieved a 10-channel terahertz (THz) frequency hopping, marking a significant advancement in THz secure communication technologies. Notably, the system exhibited a rapid frequency-hopping capability with a short transition time of 0.8 ms between channels, ranging from 288 to 331 GHz. Further, we conducted data transmission tests at a rate of 5 Gbit s −1 across several channels. The results were promising, showing each channel maintained a clear eye pattern and a low bit error rate, crucial factors for reliable and secure data transmission. These findings not only demonstrate the efficacy of our system but also open new avenues for high-speed, secure THz communication.

Abstract Cutting-edge thin film studies using multiple-angle incidence resolution spectrometry (MAIRS) are introduced from the principle to forefront applications in a wide variety of research fields covering semiconductor material with respect to nanoarchitectonics. MAIRS basically reveals quantitatively optical anisotropy in thin films, which is mostly used for quantitative molecular orientation analysis of each chemical group for chemistry purposes. This works powerfully especially when the material has poor crystallinity that cannot be analyzed by X-ray diffraction. As a matter of fact, MAIRS works in a role that compensates for the diffraction techniques, and the combination of MAIRS and the diffraction techniques has already been established as the most powerful technique not to miss the molecular aggregation structure in thin films. In this review, in addition, another application for physics purposes is also introduced where phonon in thin films is discriminated from normal infrared absorption bands by using the MAIRS technique.

Abstract We investigated the effectiveness of poling processes for Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals (SCs) produced using a continuous feeding Bridgman method, which is known to produce a high property uniformity. The four studied poling processes are: (I) standard direct current poling (STD-DCP); (II) low-voltage field-cooling DCP (LV-FCP); (III) high-voltage field-cooling DCP (HV-FCP); and (IV) mid-temperature alternating current poling (MT-ACP). The highest free dielectric constant (ε 33 T/ε 0) and piezoelectric constant (d 33) were obtained by MT-ACP (ε 33 T/ε 0 = 11 000, d 33 = 3000 pC/N), followed by LV-FCP (ε 33 T/ε 0 = 7500, d 33 = 2400 pC/N), HV-FCP (ε 33 T/ε 0 = 6250, d 33 = 1850 pC/N), and STD-DCP (ε 33 T/ε 0 = 6200, d 33 = 1800 pC/N). The LV-FCP SC showed a 21% and 33% increase in ε 33 T/ε 0 and d 33 compared to that of the STD-DCP SC; however, this was not as much as the 77% and 67% improvement of the MT-ACP SC. These results provide guidance for SC transducers.

Abstract High aspect ratio SiO2/SiN (ON) stacked layer etching using hydrofluorocarbon gases was conducted with various ratios of H, F, and C to achieve higher etching rates and precise profile control. The experimental gases were C3HF5, C4HF5, C4H2F4, C4H2F6, C4H4F6 and C5H2F10. The oxygen gas flow rate and mixing ratio were optimized to maximize mask selectivity while avoiding clogging at the top of the mask. For comparison, C4F6/CH2F2/Ar/O2, and C4F6/C4F8/CH2F2/Ar/O2 were used as reference gas mixtures. The initial screening narrowed the candidate pool to 3 gases: C3HF5, C4H2F6, and C4H4F6. At equivalent power, the C3HF5 condition achieved a 15% faster ON etch rate, and C4H2F6 achieved a 9% faster ON etch rate compared to the reference condition. Only C4H4F6 showed a worse ON etch rate than the reference (∼33%) due to severe mask clogging. Furthermore, C3HF5 achieved a 29% faster ON etch rate under high power conditions. It also achieved a 57% faster ON etch rate without excessively compromising selectivity or bow CD expansion after optimization. We report detailed comparisons of…

Abstract This study explores the factors governing the peel strength characteristics between a cycloolefin polymer (COP) film and a copper plating layer with a copper seed layer, for applying to antenna circuits in 6 G communications. The peel strength depended on the surface modification methods as pretreatment for copper seed layer formation: vacuum ultraviolet (VUV) irradiation and oxygen plasma treatment. VUV irradiation induced a modified layer with brittleness on the COP surface, leading to substrate failure. Conversely, oxygen plasma treatment formed a quite thin modified layer and facilitated Cu2O formation by bonding functional groups on the topmost COP surface with copper in the seed layer at the interface between the COP film and the copper plating layer, resulting in interface failure rather than substrate failure. Therefore, enhancing peel strength involves preventing the formation of a modified layer on the surface and generating a significant quantity of functional groups on the topmost surface.

Abstract In this work, the optical efficiency of III-nitride blue micro-LEDs ( μ LEDs) ranged from 5 × 5 to 60 × 60 μ m 2 with different sidewall treatments at low current density range was investigated. The results showed dielectric sidewall passivation using atomic layer deposition (ALD) has superior optical enhancement compared to conventional RF sputtering, where most of the enhancement occurred at low current density range. Additionally, the use of ALD sidewall passivation and chemical treatment offered significant efficiency improvement for different sizes of μ LEDs at operating less than 1 A cm −2 and the devices without sidewall treatments did not emit light. The effect of sidewall treatments to the effective Shockley–Read–Hall (SRH) nonradiative recombination coefficient, or the effective A coefficient from the ABC model, was estimated. The effective SRH nonradiative recombination coefficient was suppressed by two orders of magnitude for devices with sidewall treatments compared to devices without sidewall passivation.

Abstract We have investigated how the parameters of an input gate voltage (V g) waveform and a drain voltage (V d) impact the performance of reservoir computing (RC) using a Hf0.5Zr0.5O2 ferroelectric FET (FeFET). The RC performance is maximized by the high swing amplitude of the V g and the most symmetrical polarization switching condition in the triangular-shaped input waveform, obtained by the center V g of 0.5 V, because of the enhanced polarization switching of the FeFETs. Regarding the V d dependence, the amount of the drain current and polarization switching have a trade-off relationship. As a result, a moderate V d of 1.0 V becomes optimum in terms of the RC performance because a difference in drain current responses between different gate input patterns is maximized with this V d. Furthermore, high computing capacities are achieved by combining the above optimal bias condition with drain current responses to both original and inverted gate input patterns.

Abstract The propagation and resonance properties of longitudinal leaky surface acoustic waves (LLSAW) on a bonded structure comprising an X-cut LiNbO 3 (LN) thin plate and a 4H-SiC support substrate were theoretically investigated. Strong LLSAW responses with high Q factors were obtained at the LN thin-plate thickness h where the LLSAW phase velocity was slower than the bulk shear wave of 4H-SiC of 7126 m s −1 , and fractional bandwidth (FBW) of 9%–10% was obtained for Al film thickness normalized by wavelength of h Al / λ = 0.06–0.07 and h / λ = 0.30–0.40. Moreover, even at h / λ with a faster phase velocity than the bulk shear wave of 4H-SiC, strong LLSAW responses without spurious response owing to the LLSAW higher-order mode were obtained. Finally, h Al / λ = 0.031 and h / λ = 0.19 were determined to obtain a phase velocity of 7800 m s −1 , high Q factors, and FBW of 7.6%.

Abstract 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.

Abstract This paper proposes a procedure for measuring transmitter–receiver (Tx–Rx) distance using acoustic communication signals to realize communication and positioning underwater with the same signal and device. Specifically, we focus on an underwater acoustic communication using orthogonal signal division multiplexing, where a pilot signal and messages are placed in the time–frequency domain. In this paper, we show that measurements of both Tx–Rx distance and speed are available by utilizing the pilot signal. We conducted a sea trial and evaluated the performance of the proposed method. During the experiment, the Tx–Rx distance was 50–550 m. The obtained results suggest that the proposed method can measure the Tx–Rx distance and speed in a specific environment. The mean absolute error and the standard deviation error of ranging are 4.0 and 2.7 m, respectively, while those of measurement speed are 0.13 and 0.22 m s−1, respectively.

Abstract The control of the electrical properties and the growth mechanism of the NiO films were investigated by Li addition using the spray pyrolysis method. In addition, to enhance the uniformity and flatness of the NiO films, the electric field applied spray pyrolysis named electrostatic spray deposition (ESD) process was applied. Experimental results suggest that a certain amount of Li acts as an interstitial on the Ni sites in the NiO film and enhances crystal growth. Moreover, excessive Li additions resulted in Li segregation into NiO crystal defects, whereas the resistivity decreases and the promotion of crystal growth was not inhibited regardless of the presence of Li on the NiO film up to a Li concentration of 10 at.%. Furthermore, ESD was confirmed to deposit highly flat NiO films. These results represent the initial step toward the practical application of visible-light-transparent devices using spray deposition.

Abstract Germanium (Ge) has high mobility and is more suitable for low-temperature device processes than silicon (Si); thus, it has attracted attention as an upper-layer transistor for monolithic three-dimensional (M3D) integration. We evaluated in detail the crystalline quality of extremely thin polycrystalline-Ge (poly-Ge) thin films thinner than 15 nm fabricated by metal-induced crystallization using copper (Cu-MIC) at 400 °C using micro-Raman scattering, in-plane X-ray diffraction, transmission electron microscopy (TEM), TEM energy dispersive X-ray spectroscopy, and TEM electron diffraction. Additionally, the films were applied to p-ch double-gate (DG) poly-Ge thin-film transistors (TFTs), and their performance was evaluated. As a result, a high I on/I off ratio of 2.8 × 103 was realized by crystallization at 400 °C with a ratio equal to that of crystallization at 500 °C. This study demonstrated the feasibility of Cu-MIC DG poly-Ge TFTs for M3D applications.

Abstract We are on the eve of the next big step in lithography technology with the introduction of high numerical aperture EUV. The change from NA 0.33–0.55 in EUV lithography is an increase of 67%, which is the largest jump in the last decades, and puts tight requirements on focus and edge placement. Moreover, the lithography system has changed from fully isomorphic, i.e. same demagnification in all directions, to an anamorphic system, i.e. the demagnification in scan direction has doubled with respect to the slit direction. At imec we are fostering the ecosystem surrounding the lithography tool. In this paper we focus on the imaging and mask innovations supporting the EUV ecosystem, which are categorized into four areas: novel absorber masks, stitching, mask variability, and innovative imaging solutions. The current drivers of IC manufacturers implementing (high NA) EUV lithography (EUVL) are reduction of the EUV exposure dose and decrease in wafer stochastics. We discuss how these four areas have the potential to deliver in EUVL an increase in productivity, an improvement in the…

Abstract Ultra-small (10 μm) InGaN-based red microLEDs (625 nm at 1 A cm−2) are necessary for modern displays. However, an increase in surface-area-to-volume ratio with a decrease in the micro-LED size resulting in higher surface recombination causes a drop in efficiency with device size. In this letter, we demonstrate microLEDs from 60 μm down to 3 μm with significantly reduced sidewall-related efficiency reduction using a two-step passivation technique using Al2O3 and Si3N4. The peak on-wafer EQE changes from 0.21% to 0.35% as the device size reduces from 60 to 3 μm, possibly due to improved light extraction efficiency for smaller mesa-widths.

Abstract This review focuses on controlling interface charges and traps to obtain minimal channel resistance and stable enhancement-mode operation in GaN MOSFETs. Interface traps reduce the free electron density and act as Coulomb scattering centers, thus reducing the channel mobility. Oxide traps cause instability of threshold voltage (V th) by trapping electrons or holes under gate bias. In addition, the V th is affected by the overall distribution of interface charges. The first key is a design of a bilayer structure to simultaneously obtain good insulating properties and interface properties. The other key is the optimization of post-deposition annealing to minimize oxide traps and interface fixed charges. Consequently, the gate structure of an AlSiO/AlN/p-type GaN has been designed. Reductions in V th as a result of polarization charges can be eliminated using an m-plane trench channel, resulting in a channel mobility of 150 cm2 V–1s–1 and V th of 1.3 V.

Abstract The expansion of single Shockley-type stacking faults (1SSFs) was observed in 4H-SiC below the ion-implanted region of hydrogen or fluorine under ultraviolet illumination, and it was found that 1SSF expansion slowed, the expansion angle decreased, and the termination of 1SSF expansion became deeper as the dose of implanted ions was increased. A comparison of implanted ion species revealed that fluorine ion implantation more strongly suppresses 1SSF expansion under ultraviolet illumination than hydrogen ion implantation. The thermal stability of hydrogen and fluorine was also compared by using depth profiles of the implanted species concentrations before and after annealing. Fluorine was found to have superior thermal stability to that of hydrogen.

Abstract Dry etching and deposition of Si and Si dielectric films are critical processes for achieving high performance in advanced CMOS devices. To accurately predict and control fluctuations in these process properties during mass production, it is essential that the dry process simulation technology considers various factors. These include fluctuations in plasma–chamber wall interaction, effects of by-products on critical dimensions, Si recess dependence on wafer open area ratios and local pattern structures, the time-dependent distribution of plasma-induced damage associated with feature-scale profiles, and film properties such as density, permeability, and adhesion. Addressing these considerations can overcome issues with conventional simulations that lack the accuracy required for mass production. This paper reviews these advanced simulation technologies and discusses the perspective of the fusion of physical models with machine learning, incorporating real-time monitoring in manufacturing equipment, known as process informatics. This approach is anticipated to usher in the…

Abstract The noncontact acoustic inspection method using acoustic irradiation induced vibration and a scanning laser Doppler vibrometer can detect internal defects in the surface layer of concrete structures, etc, over long distances and without contact. Since this method uses flexural vibration in principle, it can be used as an alternative method to tapping inspection. Therefore, there has been an increase in requests for realizing movement measurement. Thus, an experiment was conducted to verify whether movement measurement was possible by mounting multiple LDVs and sound sources that did not have scanning mechanisms on a moving cart. The experimental results revealed that by using cross-correlation processing between the emitted and received waveforms, it is possible to perform movement measurements at low speeds of about 2 km h−1.

Abstract A quartz crystal microbalance (QCM) sensor can detect various physical and chemical properties, including biomolecules, gases, external forces, and so on, through changes in its resonance frequency. Because of the extremely high temperature stability of the resonance frequency, no thermostatic device is required, making the entire system compact. The sensitivity is governed by the thinness of the quartz resonator, and a wireless-electrodeless approach has achieved much thinner resonators. This review introduces recent advances in wireless-electrodeless QCM sensors for studying real-time biomolecules and target-gas detection.

Abstract We evaluated the effectiveness of a low-current-consumption amplifier for a compressed-sensing (CS) framework in wearable electroencephalography (EEG) recording devices. The amplifier uses a capacitively coupled chopper instrumentation amplifier (CCIA) architecture which is often used for low-noise amplifier (LNA) to achieve low consumption and low-noise characteristics. According to measurements of the designed CCIA, the power consumption was 0.36 μW/channel, and the input referred noise (IRN) was 4.47 μVrms. The measured IRN and simulations were used to confirm the effect of CCIA noise on the CS-based EEG measurement framework. The difference in the normalized mean squared error at CR = 4 to the uncompressed conditions could be reduced to 0.008. The findings show that even with the LNA specialized for low power consumption, a slight signal degradation is observed when the compression ratio is increased up to 4 in the CS framework by utilizing the sparsity of EEG in the frequency domain.

Abstract We demonstrated fully vertical Schottky barrier diodes (SBDs) that have a Si-doped AlN drift layer directly grown on an n-type 4H-SiC substrate by metal-organic CVD. The AlN SBD with a Ni anode showed a clear rectifying characteristic at 300–500 K and a rectification ratio of about 10–2. We found that the leakage current of the vertical AlN-on-SiC devices is affected by defects in the AlN drift layer and Schottky interface.

Abstract The AC poling cycle dependence of Mn-doped Pb(Mg 1/3 Nb 2/3 )O 3 -0.3Pb(Zr.Ti)O 3 (PMN-0.3PZT) single crystals (SC) produced via the solid-state crystal growth (SSCG) method was investigated. The piezoelectric strain and charge constants, d 33 ＝ 1130 pC/N, g 33 = 42.7 × 10 −3 Vm/N, and mechanical quality factor Q m = 800 were obtained under conditions of 1 Hz, bipolar sine wave, 7.5 kV cm −1 electric field, and 6000 cycles. In contrast to the conventional Bridgman process SC, the low-density and high Q m SSCG SC necessitates a substantial number of AC cycles due to the presence of pores within the SC. In addition, the ACP SC showed a 13 °C increase in the phase change temperature T rt compared to the DC-poled SC. This information on ACP SSCG SCs with improved thermal stability, low acoustic impedance, and enhanced receiving efficiency attributable to high g 33 offers new insight into high-frequency ultrasonic devices.

Abstract We investigated the effectiveness of AC poling (ACP) processes for [001] direction oriented Pb(Zn 1/3 Nb 2/3 )O 3 -0.055PbTiO 3 (PZN-PT) single crystals (SCs) and obtained a dielectric constant ε 33 T / ε 0 of 6680 and piezoelectric strain constant d 33 of 2760 pC/N, a piezoelectric charge constant g 33 of 46.7 × 10 −3 Vm/N, and a figure of merit (FOM) ( d 33 × g 33 ) of 129 × 10 −12 m 2 /N. These values were 19%, 31%, 10%, and 45% higher than those of DC poling PZN-PT SC, respectively. The phase change temperature T pc , Curie temperature T c , and acoustic impedance ( Z 33 ) of the ACP PZN-PT SC were 121 °C, 165 °C, and 30.5 MRayls, respectively. Compared with Pb(Mg 1/3 Nb 2/3 )O 3 −0.3PbTiO 3 SCs, the higher T pc , T c , and FOM and lower Z 33 of the PZN-PT SCs enable the applications in high temperature with superior Z 33 matching to water and human body than conventional Pb(Mg 1/3 Nb 2/3 )O 3 −0.3PbTiO 3 SCs , and these findings are vital for a wide range of ultrasonic transducer applications.

Abstract We reported the growth of (AlGa)2O3 layers on (10 10 ̅ ) α-Al2O3 substrates using cold-wall metalorganic chemical vapor deposition, and the electrical characterization of Si-doped (AlGa)2O3 layers. In the Ga2O3 growth, the α phase was dominant at low growth temperature, achieving the growth rate of 2.4 μm h−1 at 650 °C. Sheet resistance and electrical conductivity of the Ga2O3 layers with a Si concentration of 3 × 1020 cm−3 were 1 × 104 Ω/square and 8.3 S cm−1, respectively, at the measurement temperature of 500 °C. The Al composition in the (AlGa)2O3 layers was controlled from 0% to 74%. In our initial attempts, we obtained electrically conductive α-(AlGa)2O3 layers by Si doping (2 × 10−9 S cm−1 in the sample with an Al composition of 56%). Hybrid functional calculations suggest the conductivities are limited by compensation of Si through cation vacancy complexes, and not by the significant amounts of co-incorporated C and N that are predicted to be electrically passivated by hydrogen.

Abstract This is a review of proton devices for neuromorphic information processing. While solid-state devices utilizing various ions have been widely studied for non-volatile memory, the proton, which is the smallest ion, has been relatively overlooked despite its advantage of being able to move through various solids at RT. With this advantage, it should be possible to control proton kinetics not only for fast analog memory function, but also for real-time neuromorphic information processing in the same time scale as humans. Here, after briefing the neuromorphic concept and the basic proton behavior in solid-state devices, we review the proton devices that have been reported so far, classifying them according to their device structures. The benchmark clearly shows the time scales of proton relaxation ranges from several milliseconds to hundreds of seconds, and completely match the time scales for expected neuromorphic functions. The incorporation of proton degrees of freedom in electronic devices will also facilitate access to electrochemical phenomena and subsequent phase…

Abstract We present our systematic theoretical study by performing ab initio calculations to clarify the behavior of adsorption for constituent atoms such as Al and N on a vicinal AlN(0001) surface with step edges and kinks during metal-organic vapor-phase epitaxy (MOVPE). The calculations reveal that the surface reconstruction affects the adsorption of Al and N adatoms near the kinks and step edges. Furthermore, we find the incorporation of an Al adatom at the kink and that of N adatoms not only at the kink but also in the terrace regions. The calculated results give some insights for an atomic-scale understanding of the step-flow growth during the MOVPE growth of AlN.

Abstract We developed a method of nonlinear three-wave interaction using shear-vertical-wave point-focusing electromagnetic acoustic transducers (SV-wave PF-EMATs). EMATs can excite and detect ultrasonic waves without couplants through interaction between electromagnetic fields and solid mechanics and are generally unsuitable for the nonlinear ultrasound measurement due to their low signal conversion efficiency. However, our originally developed PF-EMAT can focus SV waves at a focal point in phase, achieving a large local displacement. Here, two PF-EMATs with different driving frequencies are placed facing each other so as to match their focal points, where the focused SV waves intersect to induce the third waves with the frequencies of the sum and difference of the incident frequencies through the nonlinear three-wave interaction. We demonstrate that the local nonlinearity can be measured by this method with EMATs and demonstrate its applicability to evaluation of fatigue damage in a fatigue crack initiation phase with aluminum alloy specimens.

Abstract Nucleation and grain growth are discussed as a means of clarifying the mechanism of the rapid solid-phase crystallization (SPC) process of H2-doped amorphous indium oxide (InO x :H) films. H2-doping in InO x :H films reduced nucleation density at 250 °C from 4.1 to 1.1 μm−2, resulting in an increase in grain size and Hall mobility of the polycrystalline (poly)-InO x :H films. Lateral growth rate from the nucleus was estimated to be 220 nm min−1 for the InO x :H film at 250 °C. Thus, an amorphous InO x :H film could be converted to a poly-InO x :H film within 3 min owing to a fast lateral growth rate from the nucleus. Almost the same grain size, Hall mobility, and carrier density could be obtained from the poly-InO x :H films after annealing at 250 °C for only 3 min irrespective of the ramp rate. The results demonstrated the wide range of the processing window for SPC for poly-InO x :H films.

Abstract In recent years, physical reservoir computing has attracted much attention because of its low computational cost and low power consumption. In terms of social implementation of artificial intelligence, physical reservoir has a potential to meet the request, such as the need for AI robots to process information related to tactile sensation. It has been reported that a Ag2S polycrystalline thin film retains short-term memory and non-linearity when used as a physical reservoir. In this study, we applied the technique to tactile sensation by combining with a pressure sensor attached to a robot arm. In the object grasping task, a Ag2S physical reservoir enabled the objective recognition with the accuracy of 81.3%, although the task failed with linear regression of the direct output from the pressure sensor. We also demonstrate the potential of the system to detect anomalies in object grabbing.

Abstract This paper presents research results on AlN/AlGaN heterojunction field-effect transistors (HFETs) with a high-AlN-mole-fraction Al0.72Ga0.28N channel grown on a single-crystal AlN substrate by metalorganic chemical vapor deposition. Material evaluation results confirmed that the grown AlGaN layer was 100% coherently grown for the underlying AlN substrate and thereby had superior crystal quality as well as the substrate. The fabricated AlGaN-channel HFETs with a gate length of 2 μm exhibited pinch-off characteristics with the max. current density (I DS_MAX) of 21 mA mm−1, the on-state resistance of 250 Ωmm, the peak transconductance of 4.5 mS mm−1 with the threshold voltage of –4.6 V, and the on/off ratio of 4 × 10−5. The temperature dependence of DC characteristics confirmed that the I DS_MAX decreased by 15% and the off-leakage current increased from 60 nA mm−1 to 10 μA mm−1 within the temperature range from room temperature to 200 °C.

Abstract In this work, we report the reduced gate leakage current by using aluminum oxide (Al2O3) and gallium oxide (Ga2O3) as a bi-layer gate stack for GaN MOS-HEMT on a silicon substrate up to 450 °C. The bi-layer gate stack MOS-HEMTs suppressed the gate leakage by more than four orders of magnitude compared to only Al2O3-based GaN MOS-HEMT at 450 °C. The low gate leakage current is attributed to the reduced oxygen vacancies present in the Ga2O3 layer, which effectively impede the conduction path of the Poole-Frenkel emission at high temperatures, thereby enhancing the overall performance of GaN HEMTs.

Abstract Positrons entered into living organisms can form positronium (Ps), a bound state with electrons. Most of the triplet Ps (ortho-Ps) in insulating materials annihilate with electrons in surrounding molecules, and then the ortho-Ps lifetime varies depending on the surrounding electron density. The ortho-Ps lifetime may add new biological information to positron emission tomography (PET) scan information. In order to discuss the feasibility of quantifying (free) radicals in vivo by the Ps lifetime, we used a clinical PET system to make ortho-Ps lifetime measurements in aqueous solutions containing radicals. The results suggested that differences in radical concentrations in aqueous solutions of the order of a few mM could be quantified by the Ps lifetime if the counting statistic of the detection time difference spectra was more than 108 events. This concentration was much higher than the radical concentration generated in the physiological functions of living organisms. Therefore, we concluded that quantification of radicals generated in vivo by using the Ps lifetime is very…

Abstract High-quality unintentionally doped (UID) (001) β -Ga 2 O 3 homoepitaxial films were grown on native substrates through metalorganic CVD. The surface parallel grooves were repaired under low temperature and pressure conditions, reaching the surface roughness of 2.22 nm and the high electron mobility of 74.6 cm 2 /Vs. Enhancement-mode MOSFETs were fabricated on the UID β -Ga 2 O 3 film, showing a positive turn-on threshold gate voltage of 4.2 V and a breakdown voltage of 673 V. These results can serve as a reference for (001)-oriented lateral Ga 2 O 3 power transistors and may contribute to the development of Ga 2 O 3 power devices.

Abstract In this paper, the memory characteristics of In-Ga-Zn-O (IGZO)-channel ferroelectric FETs (FeFETs) with stackable vertical channel-all-around structure are investigated by technology computer-aided design (TCAD) simulation. The simulated drain current–gate voltage (I DS–V GS) curves of the IGZO FeFET show an on–off ratio of up to 107 and a memory window of 1.76 V, proving that ferroelectric hafnium oxide (FE-HfO2) is suitable for a 2T0C transistor. To solve the potential current-sharing problem of the 2T0C dynamic random access memory (DRAM) array, an advanced operation design methodology is proposed, which utilizes the bipolar polarization characteristics of FE-HfO2. This solution shows a remarkable current ratio between data “1” and data “0”, not only demonstrating the feasibility of the IGZO-based FeFET on 2T0C DRAM memory cells, but also providing an array design guideline for highly reliable 2T0C memory applications.

Abstract Here we aimed to enhance azimuth estimation to accurately locate a communication partner’s position by utilizing a low-resolution underwater acoustic lens system for communication. We proposed a method to accurately estimate the direction-of-arrival (DoA) by finding the center of gravity of the focal distribution using two adjacent elements of the transducer array. Ranging was to be based on time-of-flight (ToF). The method’s effectiveness was evaluated by two-dimensional finite difference time domain simulation. The lens’s focused sound field was calculated and the array was designed based on the result. DoA and ToF were estimated from the received signals and evaluated by comparing them with the true values under conditions involving 1-, 2-, and 3- users. The results confirmed DoA estimation with an error of almost 4°, even when using a lens system with an azimuth resolution of 10°. As the number of users increased, the maximum error value increased, though slightly.

Abstract Acceptor Mn-doped Pb(Mg1/3Nb2/3)O3-Pb(ZrTi)O3 (PMN-PZT) single crystals (SCs) grown by a solid state crystal growth (SSCG) process electrode with Ag at 650 °C showed a high piezoelectric coefficient (d 33) of 520 pC N−1 at 25 °C by self-poling, i.e. without any additional poling process. Upon heating above the Curie temperature (T c), the impedance characteristics’ oscillation peak due to piezoelectricity disappears. However, as the temperature falls below T c, these oscillation peaks reemerge around T c. And when the temperature is further lowered to around RT, the impedance characteristics return to almost the original state. The d 33 values of the non-poled SCs, initially 520 pC N−1, increased to 910 pC N−1 after DC poling (DCP) and to 1170 pC N−1 after field cooling (FC)-DCP. These values surpass those of commercially available high-Qm PZT ceramics. These high-Qm PMN-PZT single crystals developed using the SSCG method demonstrate huge potential for future transducer applications.

Abstract Manganese telluride (MnTe) is an intriguing polymorphic semiconductor. Among them, the metastable β-MnTe phase, characterized by a wurtzite-type structure, has been successfully fabricated as a sputtered film on substrates. However, bulk or free-standing β-MnTe without substrates has never been realized. In this study, we fabricated a β-MnTe flake using a lift-off process. Notably, the X-ray diffraction patterns of the flake sample approached the predicted peak positions of bulk β-MnTe, indicating strain relaxation. This study represents a pioneering experimental success in demonstrating a bulk-like β-MnTe. Furthermore, we conducted thermal analyses associated with the β→α transformation through differential scanning calorimetry. The β-MnTe flake exhibited a lower transformation temperature than films, suggesting diminished thermal stability of the β phase. The enthalpy change was quantitatively determined as −45.1 kJ mol−1, which arises from the substantial volume change. These experimental demonstrations are expected to contribute to the application of free-standing…

Abstract This study investigates a scheme utilizing a ring transducer for an acoustic underwater propulsion system. Acoustic underwater propulsion systems are well suited for the inspection and repair of underwater robots due to their small size, high power density, and simple structure. Previous research has focused on self-propelled swimmers utilizing disc transducers. However, the radial vibration component of disc transducers makes it difficult to provide propulsion for an acoustic underwater propulsion system driven by an acoustic driving force. Pure longitudinal vibration requires a greater thickness to achieve the same vibration area, resulting in higher impedance and reduced driving efficiency. In this paper, simulation, and measurements of vibration distribution demonstrate that a ring transducer exhibits a vibration distribution closely resembling pure longitudinal vibration. A prototype swimmer using a ring transducer was fabricated for experimental evaluation through measurements of admittance characteristics, zero-speed propulsion, and no-load speed in water.

Abstract In this paper, we propose an effective method for optimizing mask design using an enhanced genetic algorithm (GA), significantly boosting digital micromirror device (DMD) maskless lithography performance. After a thorough evaluation of various optimization techniques, we determined that the simulated annealing-enhanced GA (SA-GA) offers superior improvements in lithography simulations, thus optimizing mask design more effectively. Our findings reveal that this method achieves up to 88% and 75% enhancement in simulation accuracy for circular and heart-shaped patterns, respectively, surpassing the results of conventional Hopkins lithography simulations. The remarkable effect of improved GA in enhancing the quality of DMD digital lithography shows that it will have great potential in micro-fabrication applications, and paves the way for the realization of high-fidelity and efficient DMD digital lithography technology, which has excellent versatility and adaptability in the field of microelectronics manufacturing.

Abstract This paper describes a design technique for serpentine spring with the edge span beam L /2. In order to improve design accuracy, we investigate the key structure parameters influenced by the fabrication process for MEMS device, comparing finite element analysis (FEA) and analytical models. It is found that the Fedder model as the analytical model is suitable for the spring constant characteristics of FEA with the edge span beam L /2. Further, the thickness and width are found to be the key structure parameters and the dominant factor of variation regarding the serpentine spring. Based on the analysis, we propose a spring design technique. The experimental results show that the variation between the measured data of 4.46 N m −1 and the design value of 4.15 N m −1 was 7.5%, satisfying the target of ±10%. It is confirmed that the proposed technique can establish the serpentine spring for high sensitivity gold proof-mass MEMS accelerometers.

Abstract Liquid biopsies for cancer diagnosis using exosomes have been studied. Separating cancer cell-derived exosomes from a sample mixture is crucial, especially when they do not dominate the sample at an early stage of cancer. A method based on their electrical properties could provide a simpler separation than immune-affinity methods. We have identified the differences in electrical properties of cancerous exosomes from those of normal ones, suggesting the possibility for their dielectrophoresis (DEP) based separation. This study separated cancerous exosomes from a mixture of normal exosomes. The DEP of fluorescence-labeled exosomes suspended in aqueous media with varying electrical conductivities was investigated. The observed DEP was quantitatively evaluated using the normalization method accounting for the fluorescence fading effect. The results showed that the cancerous exosomes were preferentially concentrated under the appropriate conditions. This suggests that DEP can enable the selective capture of cancer exosomes without chemical labeling.

Abstract Nanoimprint lithography (NIL) is promising for the processing of dual damascene structures fabricated in back-end-of-line layers, and initial development began with a simple single-level process to evaluate NIL’s suitability. In this work, a test element group (TEG) pattern with a 70 nm half-pitch was selected, and copper (Cu) filling and chemical-mechanical polishing were performed after NIL pattern transfer. The results were compared with those obtained from the same TEG layout and processes but using ArF immersion lithography instead of NIL. Those obtained by NIL showed high pattern fidelity for all the designed layouts, whereas the resist patterns varied from the designed shape for ArF immersion lithography. The line resistances of Cu interconnects patterned by NIL showed good cumulative distributions at line widths ranging from 60 nm to 78 nm in 2 nm increments, without line breaks or space narrowing of SiO2. NIL showed potential for interconnect patterning with high-precision line width control.

Abstract A monovalent copper ion (Cu+) with the same valence as formamidinium is focused on the present work, and the effects of A-site inorganic cations on the electronic structures and device performance are discussed from the experiments and the first-principles calculations. The addition of inorganic cations increased the conversion efficiencies, and the copper-doped device showed the highest conversion efficiency. In particular, the hysteresis of current density–voltage characteristics was significantly suppressed by the addition of Cu+, which would be due to suppression of iodine ion (I−) diffusion by electrostatic interaction between Cu+ and I−. The addition of rubidium or cesium contributed to the increase in short-circuit current density by suppressing decomposition of perovskite crystals and formation of PbI2.