Japanese Journal of Applied Physics

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.

The present study aims to detect helium-3 in nickel-based metal nano-composites doped with zirconia, which exhibited anomalous heat generation when exposed to hydrogen gas at approximately 450 °C. Two complementary analytical techniques were employed: nuclear reaction analysis utilizing 1.4 MeV deuteron beams from a tandem accelerator, and thermal desorption spectrometry using a quadrupole mass spectrometer. Both methods successfully detected helium-3 in the samples. Given the extreme rarity of this isotope, its presence strongly suggests the occurrence of nuclear reactions within the nickel-containing materials. These findings lend support to the 4 hydrogen/tetrahedral symmetric condensate (4H/TSC) model, which uniquely predicts helium-3 as one of the primary reaction products.

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.

Metal oxide semiconductor (MOX) chemiresistive gas sensors used in gas alarms have contributed to the safe use of city gas and liquid petroleum gas. In this study, we successfully fabricated hot-wire-type MOX sensors using micro-electro-mechanical systems (MEMS) technology. The hot-wire type structure, in which an electrode plays dual roles in detecting and heating, was adopted for efficient production. Owing to the miniaturization together with the thermal insulation, the sensors exhibited a fast thermal response. The average power consumption of the sensor in the pulsed operation was less than 100 μW. The sensor exhibited high sensitivity of more than 100 mV to 3000 ppm methane and showed low cross-sensitivity to interference gases such as ethanol and hydrogen. These sensing properties were retained for more than five years, demonstrating excellent long-term stability of the sensors.

Thin films of ferroelectric materials have been investigated for various applications because of their high dielectric constants, as well as piezoelectric and ferroelectric properties. Ferroelectricity has been explored for memory applications because of its two stable states after releasing an electric field, depending on the direction. Perovskite-based ferroelectrics have been studied for the last 30 years for these applications and have already been commercialized. However, the degradation of their ferroelectricity with decreasing film thickness (below about 30 nm) makes high-density memory applications difficult. A recent "discovery" of novel ferroelectrics, e.g., fluorite-type structure HfO₂-based films and wurtzite structure AlN-, GaN-, and ZnO-based films, have enabled significant reductions in film thickness without noticeable degradation. In this article, we discuss the status and challenges of these novel non-perovskite-based ferroelectric films mainly for memory device applications.

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.

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.

The structural stability and miscibility of ScAlN are theoretically investigated on the basis of density functional calculations. The calculations demonstrate that the relative stability between wurtzite and rocksalt structures depends on Sc composition. The lattice constraint of AlN and GaN substrates enhances the stability of the wurtzite structure as well as the miscibility of ScAlN alloys. Furthermore, the calculated energy barrier for polarization switching is also influenced by the lattice constraint. The results give insights into understanding the effect of substrate on structural stability and miscibility of ScAlN alloys.

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.

Modern dynamic random-access memories (DRAMs) have ultra-high densities due to the high integration of cell arrays, and the length of word-line (WL) has become considerably longer. In particular, maintaining the uniform line profile in the WL of modern 10 nm-class DRAMs is extremely challenging. In this paper, our goal is to investigate the causes of the WL break and propose a new method to solve it. We discuss a novel gate oxide (Gox) formation technology that is able to relieve the WL wiggling and disconnection. 10 nm-class DRAMs are fabricated with the novel Gox technology, and their structure and characteristics are studied.

This study investigates the dependence of the translational velocity of lipid-coated microbubbles in an ultrasound field on the viscosity of the surrounding Newtonian fluid. Plane burst waves with a center frequency of 7.34 MHz were used to uniformly drive microbubbles with a radius of 1.4 ± 0.3 μm (mean ± standard deviation) in a flow channel. Bubbles were detected using the Doppler method using pulse waves with a center frequency of 5.2 MHz, and the velocities of individual bubbles were analyzed by tracking them in consecutive images. Examinations were conducted at various viscosities from 1 to 3 mPas. The experimentally determined velocity–viscosity relationship qualitatively agreed with numerical simulations. This was written as a power-law dependence and used as a calibration curve to evaluate the local viscosity coefficient for the trajectories of individual bubbles. We succeeded in demonstrating viscosity imaging by multiplying the obtained viscosity coefficient with the bubble trajectories, convoluted with the point spread function of ultrasound imaging.

For applying an alternative to resist removal, we analyzed and confirmed that electronically excited hydroxyl (OH) radical is produced from the reaction of highly concentrated ozone (O₃) gas with ethylene (C₂H₄) gas for the resist removal processing at 10² Pa pressure. Fourier-transform infrared absorption spectroscopy revealed that the products of the initial part of the reaction are H₂O, CO, CO₂, an aldehyde, and an OH-containing species. Mass spectrometry confirmed the aldehyde to be formaldehyde (HCHO) as was reported. Ultraviolet-visible emission spectroscopy confirmed the OH-containing species to be electronically excited OH radical formed as an initial reaction intermediate, with its emission peak at 310 nm in the chemiluminescence emission spectrum. A second alkene molecule, isobutene (i-C₄H₈), was also found to produce the same OH species under the same experimental conditions, albeit at a lesser amount than that produced with C₂H₄. This oxidant can provide a novel resist removal method.

This study explores the plasma-induced graft polymerization of poly(acrylic acid) (PAA) on polytetrafluoroethylene (PTFE) using a helix atmospheric pressure plasma system. While PTFE exhibits excellent chemical resistance and thermal stability, its hydrophobic surface and poor adhesion limit broader applications. Plasma pretreatment was employed to activate the PTFE surface, enhancing the grafting rate of PAA during subsequent immersion in an acrylic acid solution. The effects of plasma power on grafting efficiency and surface properties were systematically analyzed. Optical emission spectroscopy and infrared thermal imaging characterized the plasma, while contact angle measurements and an electronic microbalance assessed changes in wettability and graft density. Scanning electron microscopy, ATR-FTIR, and X-ray photoelectron spectroscopy revealed modifications in surface morphology and chemical composition. The results demonstrated improved hydrophilicity and adhesion of PTFE surfaces, with tunable characteristics achieved by optimizing plasma power, broadening PTFE's applicability in diverse industrial fields.

After quartz glass wafers with PDC-SiO₂ films were bonded using thin Y, Sc, and Zr films, oxidation of these bonded films by oxygen dissociated from the PDC-SiO₂ films was assessed. Optical and structural analyses revealed fully oxidized films formed at the bonded interface, achieved by application of post-bonding annealing at 300 °C using these 0.5 nm thick films. Particularly, Y films were oxidized easily. The surface free energy at the bonded interface γ was evaluated using a blade test, for convenience. The values, found to be higher than 2.6 J m⁻² for as-bonded interfaces, were enhanced further by annealing.

Reported dependence of backward diffusion of Zn in (100) InP on misorientation directions was explained by relating kink velocities to Zn incorporation sites during metalorganic vapor-phase epitaxy. Because of the larger density of kinks per phosphorus-terminated steps (B-steps) compared to the density of kinks per indium-terminated steps (A-steps), we assumed that most of the Zn atoms surface-diffusing toward B-steps should be incorporated into In-sublattice sites, whereas those surface-diffusing toward A-steps should go into tetragonal interstitial positions surrounded by P atoms. This assumption was supported by the resultant reproduction of the reported backward diffusion profiles of Zn in InP.

Physical vapor deposition (PVD) methods for polymer thin films were reviewed with an emphasis on those techniques that use energy beams such as UV light, electron beam, and ion beam. One class of PVD is a direct evaporation of polymer materials, which can produce thin films consisting of small molecular weights. Molecularly oriented thin films can be obtained with this method for some types of polymers. The other class called vapor-deposition polymerization, involves a polymerization reaction in the process of film growth. The vapor-deposition polymerization can be achieved either by the stepwise reaction, such as polycondensation or polyaddition of co-evaporated monomers or by the chain reaction through radical polymerization of single monomer species activated by UV light, electron beam, ion beam, etc. Typical examples of film formation and applications are reviewed for each process. Also, mentioned is a strategy to covalently tether the interface between the polymer films and the substrates.

The bottom-up fabrication technique is one of the key technologies taking place in conventional top-down approaches to create nanoporous (NP) thin film materials with tailorable nanostructures such as film thickness, film density, pore form, and pore size with nanometer (or sub-nanometer)-scale accuracy. This progress review specifically highlights bottom-up fabrication techniques using two-phase interfaces including solid–gas interfaces, solid–liquid interfaces, liquid–liquid interfaces, and gas–liquid interfaces by referring to recent publications. Moreover, experimental techniques to analyze nanostructures of NP thin film materials from well-ordered regular structures to non-periodic structures are introduced. Finally, some emerging potential applications and future perspectives of NP thin film materials are mentioned by using the latest literature.

Thin films of ferroelectric materials have been investigated for various applications because of their high dielectric constants, as well as piezoelectric and ferroelectric properties. Ferroelectricity has been explored for memory applications because of its two stable states after releasing an electric field, depending on the direction. Perovskite-based ferroelectrics have been studied for the last 30 years for these applications and have already been commercialized. However, the degradation of their ferroelectricity with decreasing film thickness (below about 30 nm) makes high-density memory applications difficult. A recent "discovery" of novel ferroelectrics, e.g., fluorite-type structure HfO₂-based films and wurtzite structure AlN-, GaN-, and ZnO-based films, have enabled significant reductions in film thickness without noticeable degradation. In this article, we discuss the status and challenges of these novel non-perovskite-based ferroelectric films mainly for memory device applications.

This paper describes the concepts for achieving n-type and p-type WSe₂ field-effect transistors (FETs) and their complementary metal-oxide-semiconductor (CMOS) inverter operation. First, n-type and p-type WSe₂ FETs were demonstrated using molecular chemistry approaches that offer the manipulation of WSe₂ properties through low-temperature, low-energy processes. Next, the advancement in device technology was explained to achieve symmetric characteristics in n-type and p-type WSe₂ FETs. WSe₂ single-channel CMOS offers a promising pathway for simplifying device integration to suppress variability and fluctuations in FET characteristics, although many challenges remain to be addressed. Further fundamental research holds the potential to advance the development of WSe₂ single-channel CMOS devices.

Ion channels regulate membrane potential by mediating the permeation of specific ion species via their transmembrane pore with gating. Understanding the structural dynamics of ion channels is important for elucidating their functional mechanisms. This review highlights the application of high-speed atomic force microscopy (HS-AFM) in investigating structural dynamics of ion channels and ligands. The use of oriented reconstitution techniques allowed for high-resolution, real-time visualization of ion channel dynamics such as pH-dependent clustering in KcsA potassium channels, induced-fit binding of agitoxin-2 (AgTx2), ligand-induced fluctuations in transient receptor potential vanilloid 1 (TRPV1), and voltage sensor dissociation in voltage-gated sodium channels (Na_v). These studies provide valuable insights into the molecular mechanisms that govern ion channel function and contribute to a deeper understanding of their physiological roles. Additionally, the findings underscore the potential of HS-AFM in exploring ion channel behavior under various conditions.

The ultrasonic viscoelasticity measurement method can evaluate bulk properties and 
surface properties of samples at megahertz frequencies. As an application example, it was 
shown that it is possible to distinguish between samples of different manufacturers and 
compositions in commercially available inkjet inks with small viscosity terms, which was 
said to be difficult to do with previous methods. Since the high-frequency viscoelasticity 
measurement method has a structure that matches well with the ejection principle of the 
inkjet method in terms of stress wave propagation, the results obtained are thought to 
provide useful parameters for inkjet ejection analysis. 
Furthermore, we will introduce a method for obtaining equivalent viscoelasticity 
measurement results to those for a single material and a laminated material by using a 
measurement model that mimics the skin layer on the polymer surface, which is a problem 
when hardening gels and other materials, while also grasping the skin layer thickness and 
density.

Vertically aligned MoS₂ nanotube-based humidity sensors have been fabricated, and the dependence of the sensing performance on electrode positions were investigated. The MoS2 nanotube arrays were prepared by a coating on aluminum oxide (AAO) porous substrates using a decompression filtration technique. The two types of electrodes were formed in the horizontal and vertical positions. It was found that the humidity response for the vertical positions of electrode is about 6.5 times more sensitive than the horizontal positions, resulting in higher sensitivity. In addition, the response of nanotubes with different thicknesses was compared, and it was found that the response of nanotubes with thicker films was about 5 times more sensitive than thicker films. In addition, the application of response detection by the approach of a finger was also carried out and demonstrating the potential of the MoS₂ nanotube humidity sensor and innovative humidity sensing technology.

Floating photovoltaics (FPV) has emerged as a promising solution for renewable energy generation, particularly in land-scarce regions. However, the unique environmental conditions of FPV systems, particularly wave-induced mechanical stresses, pose significant challenges to the performance and long-term reliability of photovoltaic (PV) modules. This study investigates the effects of three specific and non-standard mechanical loads: torsions, vibrations and wave-in-deck impacts. Through a campaign of experimental testing, we propose advanced stress tests and explore their implications, focusing on the risk of degradation and failure modes such as structural collapse, glass and cell cracks and cell microcracks. This study provides essential insights into optimising the design of FPV modules and introducing new type approval strategies for them, aiming to improve their reliability in harsh aquatic environments and pave a pathway for the PV community to rethink the need and redefine specific test protocols for the qualification testing of modules deployed in floating systems.

In this study, to control the N distribution in GaAsN films, GaAsN/GaAs superlattice (SL)-structure films were grown by repeating one cycle of the GaAsN atomic layer growth sequence and n (0–9) cycles of the GaAs growth sequence using atomic layer epitaxy. The effects of n on the incorporation of N atoms into the GaAsN layer and the detailed N distribution in the film were investigated by considering the lattice constants of the GaAsN/GaAs SL and SL periods, as evaluated by X-ray diffraction. The formation of the SL structures was confirmed, although the SL periods deviated slightly from the designed values. The SL periods were not singular for the films and the direction of the SL period was slightly tilted (~0.2°) from the growth direction. This indicates the existence of at least two regions with different tilt directions and periods in the film.

Copper nitride (Cu3N) thin films were prepared using the reactive radio frequency (RF) magnetron sputtering method on MgO (100) and α-Al2O3 (0001) substrates and their physical properties were evaluated. Both x-ray diffraction and hall measurement data showed better crystalline quality of the sample grown on α-Al2O3 (0001) substrates (Cu3N/α-Al2O3 (0001)) than on MgO (100) substrates (Cu3N/MgO (100)). Then, the nitrogen gas fraction (RN2) effect on Cu3N/α-Al2O3 (0001) was studied by changing the Ar and N2 gas mixture ratio during the deposition. The full width at half maximum of (100) diffraction peak was the lowest (0.125˚) at RN2=0.67. The UV-Vis data revealed a large absorption coefficient (> 104 cm-1) for all the samples, with band gaps ranging from 1.90 to 1.98 eV. The lowest resistivity (26 Ωcm) and the highest carrier concentration (6.4×1017 cm-3) were observed at RN2=0.67. Consequently, Cu3N/α-Al2O3 (0001) exhibited promising results, suggesting potential for developing efficient solar cells.

In EUV lithography, residual hydrocarbon gas in a vacuum chamber causes carbon contamination of the mask and optics, resulting in a reflectance drop. To mitigate this issue, several pascals of hydrogen gas are introduced into the EUV scanner. In a hydrogen atmosphere, high-power EUV irradiation generates EUV-induced hydrogen plasma, which might destroy the absorber layer or Mo/Si multilayer of the EUV mask. This damage is called a "blister." To evaluate the damage, a high-power EUV irradiation tool with hydrogen gas was installed at the BL09 beamline of the NewSUBARU synchrotron light facility. The durability of a normal TaBO/TaBN absorber on an EUV mask was evaluated. No blister occurred on this absorber at a high EUV dose of 2600 kJ cm⁻². The hydrogen ion dose was estimated as 1.3 × 10¹⁴ ions s⁻¹ by current and voltage measurements with an EUV intensity of 43 W cm⁻² (89 mW) and hydrogen pressure of 70 Pa.

High power conversion efficiency (PCE) and mechanical robustness are essential for organic solar cells (OSCs) used in wearable electronics. In this paper, we report a polymerized small molecular acceptor, PNH, achieved by incorporating hydrogen-bonding (H-bonding) urea flexible spacers (FS) into a Y5-OD-like polymer backbone. Fourier transform infrared spectroscopy corroborates the formation of strong H-bonding (N-H···O=C) between the carbonyl unit in the donor polymer PBDB-T and the amine group in PNH, as well as within the PNH acceptors. Furthermore, a control Y5-OD polymer (PCO) incorporating a carbonate FS unit, thus incapable of H-bonding with PBDB-T was investigated. Notably, the PBDB-T:PNH blend achieved a power conversion efficiency (PCE) of 12.1% outperforming the PBDB-T:PCO device (10.8%). This improved PCE is attributed to the enhanced molecular aggregation and charge transport induced by H-bonding interactions. Moreover, the introduction of H-bonding via FS incorporation effectively dissipates the strain energy under mechanical deformations. Thus, blend films exhibit an improved crack-onset strain from 12.16% (PBDB-T:PNH) to 18.02% (PBDB-T:PCO). Importantly, intrinsically stretchable OSCs (is-OSCs) based on the PBDB-T:PNH blend retain 70% of its initial PCE under a 25% strain. Our results highlight the role of incorporating H-bonding FS into the PSMA backbone to enhance both PCE and mechanical stretchability.

Selective-area growth of InGaAs nanowires (NWs) and vertical gate-all-around (VGAA) transistors using the vertical InGaAs NWs on Silicon-on-insulator (111) substrates were characterized toward future three-dimensional integrated circuit applications using III-V NW-based VGAA transistors. On an n-type SOI, the VGAA transistor acts as a field-effect transistor (FET), involving carrier transport and the electrostatic modulation inside the InGaAs NW channels. While on a p-type SOI, the transistor exhibited tunnel FET properties, involving tunnel transport at the InGaAs NW/SOI interface. Characterization of the VGAA transistors with the variation of NW diameter revealed that device properties, including off-leakage current and subthreshold slope, was degraded with large NW diameter due to misfit dislocation at NW/Si interface.

Scanning acoustic microscopy is an effective tool for non-invasive observation of living cells' elasticity based on acoustic impedance (AI). This tool allows the visualization of intracellular three-dimensional structures in the depth direction. Here, we investigated the mechanism of the appearance of artifactual AI images in three-dimensional tomography using various cellular conditions. These ghost AI images were derived from prolonged reflection waves in the time domain, and multiple reflections between cell-cell gap structure and intracellular elastic materials were synthesized, causing complex ghost images. Synthesized reflection waves contained information on specific intracellular spaces and the distribution of intracellular elastic components. The ghost images derived from reflection waves were weak in non-biological interactions. Our result suggests complex reflections of AI would not only be a ghost-image maker but also transfer information about invisible delicate structures in cultured cells. This reflection analysis would be useful for detecting artificial organs' differentiation and cell-cell connection.

Wafer-level direct bonding has become a critical process for advanced 3D architectures in logic, memory, and CMOS image sensors. The minimization of the wafer distortion caused by wafer bonding is essential for a precise overlay for the subsequent backside lithography. Although numerous studies have reported a strong connection between distortion and bond wave speed, discussion of the relationship between the pre-bonding surface and the bond wave speed has been inadequate. This study aimed to clarify the latter correlation using 300 mm wafers. Through the application of surface-sensitive techniques, we found that the plasma activation process enhances the amount of Si–OH groups on the surface, thereby enhancing the bond wave speed. Conversely, high-power plasma results in a slight decrease in bond wave speed because of the influence of excessive adsorbed water. In addition, the present study reveals no correlation between bond wave speed and adherence energy.

Using focused helium-ion irradiation by helium-ion microscopy (HIM), we demonstrated the formation of nanosized hole arrays (nanopore arrays) on ultrathin (<3.6 nm) silicon nanosheets. Nanoscale patterning was conducted by setting the helium ion (He⁺) acceleration energy to 30 keV and modulating the ion dose to the irradiated area from 1 × 10¹⁷ to 10¹⁹ cm⁻¹. The He⁺ irradiated area was observed as a bright spot on the HIM image at a low dose, which changed to an etch pit-like shape as the dose increased. Cross-sectional transmission electron microscopy (XTEM) observations indicated that the nanosheet where the He⁺ was irradiated vanished under the increased dose condition, and the area without irradiation was preserved. Simultaneously, blistering was observed over the entire area where the nanopore array was formed. In the XTEM image, a space was formed between the buried oxide film and the Si layer owing to ion implantation.

Secondary electron bremsstrahlung (SEB) has been proposed for range verification in particle therapy. However, the uncertainty in the range-shift estimation attributed to high statistical noise from small numbers of carbon-ion irradiation remains unclear. This simulation study evaluated the uncertainty of SEB-based range-shift estimations under conditions of limited numbers of carbon ions. The simulated SEB images were generated by irradiating an acrylic target with monoenergetic carbon-ion beams and calculating the energy deposited onto a cadmium telluride pixel detector. Estimated range shifts were derived from the SEB images using a proposed method, with uncertainties of 1.4 mm for 10⁸ ions and 4.4 mm for 10⁷ ions. The results suggested that improving the detector sensitivity is effective in reducing the uncertainty.

All-perovskite double- and triple-junction solar modules using monolithically series-interconnected structures provide many advantages including high conversion efficiency, scalability, lightweight, flexibility, etc., However, the wide-bandgap (WBG) top cells currently suffer from insufficiently high efficiency and durability. We proposed module configurations to circumvent these drawbacks of the WBG cells, by introducing an additional design parameter unique to large-sized modules: the subcell-width ratio. The top and bottom modules are designed so that their maximal-power voltages are approximately the same by tuning the subcell widths, and parallel-connected in the voltage-matched (VM) configuration. Another configuration is the series connection of the current-matched (CM) submodules. These configurations yield approximately the same or higher efficiencies as the conventional modules in which all the subcells of the same width are directly series-connected, eliminating the I/Br-phase-segregation problem of the WBG cells. The VM or CM modules are selected depending on the remaining degradation factors of the WBG cells.

Physical vapor deposition (PVD) methods for polymer thin films were reviewed with an emphasis on those techniques that use energy beams such as UV light, electron beam, and ion beam. One class of PVD is a direct evaporation of polymer materials, which can produce thin films consisting of small molecular weights. Molecularly oriented thin films can be obtained with this method for some types of polymers. The other class called vapor-deposition polymerization, involves a polymerization reaction in the process of film growth. The vapor-deposition polymerization can be achieved either by the stepwise reaction, such as polycondensation or polyaddition of co-evaporated monomers or by the chain reaction through radical polymerization of single monomer species activated by UV light, electron beam, ion beam, etc. Typical examples of film formation and applications are reviewed for each process. Also, mentioned is a strategy to covalently tether the interface between the polymer films and the substrates.

In wafer bonding technologies used for MEMS the bonding temperature is becoming an increasingly critical parameter with respect to very different aspects such as device functionality and for the process itself, especially in terms of overall process time. This paper shows that even for classical bonding processes, such as anodic and glass frit bonding, temperatures can be reduced, resulting in functional benefits such as avoiding outgassing of PE-CVD layers allowing the use of temperature sensitive materials. For the standard glass Schott Borofloat®33 it has been shown that anodic wafer bonding can be performed at 200°C. Using a newly available material, AGC TNS-062, glass frit bonding can be done at temperatures as low as 310°C. These significantly lower bonding temperatures, demonstrated in two different wafer bonding processes, enable more economical processing with about 1/3 shorter bonding times, reduced energy requirements and increased wafer bonding tool capacity.

We conducted a fundamental study to elucidate the relationship between acoustic and electrical properties in the context of liver steatosis. The speed of sound, attenuation coefficient, conductivity and relative permittivity were measured in rat livers with varying degrees of fat deposition. Fat deposition results in a decrease in the speed of sound, an increase in the attenuation coefficient and a reduction in conductivity and relative permittivity. However, no linear correlation was observed between these properties and fat content or droplet size individually. However, a notable correlation between changes in acoustic and electrical properties was identified when the structural and organizational effects of fat were considered in combination. In particular, attenuation changes were found to correlate with corresponding changes in electrical properties. These findings underscore the importance of comprehensively considering structural factors, such as fat droplet size and distribution, to better understand the physical mechanisms underlying the relationship between acoustic and electrical properties.

Ga/In alloy, known for its low melting point and liquid state at room temperature, is a promising material for producing fine metal particles. Conventional methods often face challenges in efficiency or particle uniformity, particularly for particle sizes below 10 μm. Ultrasonic processing offers a potential solution, enabling efficient production of microscale and sub-microscale particles. This study examined the effects of ultrasonic frequency and power on the particle size distribution of Ga/In alloy. The effect on particle refinement of adding a second ultrasonic irradiation step was also evaluated. High-speed video imaging was used to capture the dispersion process in real time. The results indicate that particle size depended strongly on ultrasonic frequency and power, with higher frequencies yielding finer particles. The secondary irradiation effectively improved size distribution and dispersion. These findings provide insights into the controlled formation of metal microparticles using ultrasonic techniques.

We evaluated surface activated bonding (SAB), a room temperature bonding, for hybrid surfaces bonding. At first, SAB process was evaluated on copper and silicon oxide full sheet surfaces, in order to separately study the impact of the SAB activation on both types of materials embedded in a hybrid surface layer. Then, 200 mm wafers with 2.5 μm copper pads 2.5 μm apart in a silicon oxide matrix were used to probe the impact of activation with atomic force microscopy. Two test vehicles were then manufactured in order to morphologically and electrically study the bonding interface. Thus, hybrid wafers were aligned and bonded in an EVG^®COMBOND^® equipment. Cross-sectional scanning and transmission electron microscopy characterizations were performed on both test vehicles in order to observe the bonding interface. Electrical tests were also performed at the end of full 3D integration on daisy chain structures to demonstrate a high connectivity through the bonding interface.

We experimentally demonstrate the anti-ferroelectric (AFE) behavior of a Hf_1−xZr_xO₂ (HZO)/Si FET and its potential for high-endurance nonvolatile memory operation. The AFE-HZO FET with Zr content of 75% exhibits a double polarization switching and half-loop switching of its double hysteresis under bipolar and unipolar bias conditions, respectively. The counterclockwise hysteresis in the transfer I_d–V_g characteristics is demonstrated under unipolar V_g sweep through half-loop polarization in AFeFET. The steep subthreshold swing values were observed for both forward and backward V_g sweeps of I_d–V_g curves for AFeFET under unipolar bias condition. The nonvolatile feature of AFeFET is achieved by introducing the optimized hold voltage of 1.3 V during the retention period. The threshold voltage shift can be realized by utilizing the unipolar program/erase V_g pulses. Also, the high-endurance properties of HZO/Si AFeFET are demonstrated under unipolar V_g stress with observable memory window up to 10⁹ cycles without gate insulator breakdown.

We elucidate the role of gallium (Ga) in the structural and electronic properties of amorphous indium gallium oxide (a-IGO) for different Ga concentrations with oxygen interstitial defects using hybrid density functional methods. Ab initio molecular dynamic simulations reveal that Ga substitution significantly affects the structural characteristics, and that Ga–O coordination is particularly sensitive to changes in oxygen stoichiometry. The electronic structure indicates the formation of an O–O dimer in the neutral state. The stability of this dimer upon capturing electrons is influenced by the local atomic structure around the dimer. When the bond breaks, the dimer's antibonding defect level is significantly lowered from the conduction band, approaching the valence band. This makes it more energetically advantageous for the dimer to capture two electrons. We statistically studied the Ga concentration dependence on the impact of O₂ dimer generation in a-IGO. Formation transition energy indicates that O–O bond is broken easily with more Ga, which acts as an electron trap identifying the origin of positive bias stress observed in the transistor behavior.

Dynamic ultrasound scattering methods are becoming established to allow measurements of the dynamics of microparticles in Brownian motion. Using a focused transducer, nanoparticles can be analyzed, but applying strong ultrasound to large submicron particles causes problems with excessive acoustic energy that interferes with the dynamics of the particles. Backscattering is an attractive setup that maximizes spatial resolution, but when the sample thickness is reduced to eliminate the acoustic flow effects, the reflected waves of two cell windows that sandwich the suspension and the weak particle scattering signal interfere with each other. Therefore, a new technique was attempted to remove the reflected waves and extract only the scattered waves. After showing that the acoustic energy does not interfere with the analysis of nanoparticles even in the presence of large particles, we showed that these sizes can be extracted simultaneously, using a mixture of particles with diameters of 50 and 500 nm.

This work presents a comprehensive study on the sensitivity optimization of electrical impedance flow cytometry devices for identifying analytes suspended in a flowing liquid. The optimization is achieved by investigating the influence of various parameters, including applied frequency, electrode geometry dimensions, bacterial properties, and buffer characteristics. The study utilizes COMSOL Multiphysics simulation to analyze the impedance variation based on differential Maxwell's equations solved using finite element methods. The frequency optimization reveals that the sensitivity peak is around 12.6 kHz when considering imaginary impedance due to medium conductivity. Geometry optimization involves electrode dimensions with a length of 30 µm and a gap of 15 μm, as well as a channel width and height of 20 μm. Furthermore, the paper explores the effect of buffer conductivity, showing that it plays a significant role in defining total impedance with or without cells/particles. Higher buffer conductivity leads to dominant changes in real impedance, while lower conductivity affects imaginary impedance more prominently. The study also investigates the impact of variations in bacterial parameters, such as cell membrane permittivity and cytoplasm conductivity. These parameters influence total impedance, with cell radius showing a notable effect on sensitivity. By optimizing these parameters, the sensitivity and performance of impedance-based flow cytometry devices can be enhanced, making them more effective for bacterial analysis and characterization in various applications.

We examined the stability of writing in a magnetic domain wall device from the Oersted field induced by electrical current flowing in an embedded metal line. We found that the Joule heating from the writing current raises the device temperature, leading to destabilization of its magnetization after the pulse ends abruptly. To address this issue, we suggested adding a falling trailing edge to the main writing pulse, providing a stabilizing Oersted magnetic field while the device temperature reduces. We found the adequate trailing edge length fits to the thermal transient obtained from the 3D thermal simulations. This approach improved the writing stability of the device and highlights the importance of writing pulse shape and thermal management for stable writing of domain wall devices.

The current directed self-assembly (DSA) process utilizes a diblock copolymer composed of polystyrene (PS) and polymethylmethacrylate (PMMA) as standard materials. However, domain spacing of the self-assembled PS-b-PMMA is limited to ∼20–30 nm due to weak segregation strength. In this study, we explore a potential to overcome this size limitation through a multiblock approach that has previously been demonstrated with (PS-b-PI)_n. Specifically, we simulate the self-assembled morphology of the linear multiblock copolymer, (PS-b-PMMA)_n, using the so-called theoretically informed coarse-grained model developed for symmetric PS-b-PMMA. The simulation results demonstrate that the lamella pitch of (PS-b-PMMA)_n can be reduced by ∼20%–25% compared to that of diblock copolymer. This reduction is attributed to loop and bridge conformations of the multiblock copolymer chains. These findings indicate that (PS-b-PMMA)_n could be advantageous for DSA, not only by enabling the size reduction, but also by potentially enhancing the guiding effects through physically cross-linked, self-assembled domains via bridged chains.

We developed a systematic measurement method that simultaneously captures pump detuning, the optical spectrum, RF beat noise, and the linewidth of a microresonator frequency comb. This comprehensive measurement approach enables us to investigate and visualize the phase transition between two distinct states within the modulation instability (MI) comb: a low-noise state (MI comb phase 1) and a high-noise state (MI comb phase 2). While phase 2 is typically recognized as the MI comb, our findings suggest that phase 1 represents a transition from the Turing pattern to the MI comb, maintaining a low-noise profile despite exhibiting the spectral characteristics of an MI comb.