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.

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.

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.

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.

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.

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.

This study discusses the fabrication and characterization of optically responsive microfibers with uniaxially ordered nematic liquid crystal molecules at their core. The liquid crystal microfibers were electrospun from a solution of polyvinylpyrrolidone (PVP) and N-(4-methoxybenzylidene)-4-butylaniline (MBBA). A study of phase transition and optical behavior was performed using optical observation by polarized optical microscope, and intermolecular interaction was investigated using Fourier transform infrared (FTIR). The diameter, orientational order of the fibers and light intensity that passed through the fibers depended on the MBBA concentration during the electrospinning process. The nematic–isotropic temperature (T_NI) of PVP–MBBA microfibers shifted lower from the T_NI of MBBA. Meanwhile a reverse correlation between MBBA concentrations and phase transition was found in the isotropic phase; a significant increase in temperature rate and response time was occurred with small weightage of MBBA. FTIR measurement confirmed that the liquid crystal molecules were self-phase separated from the PVP chains in the fibers.

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.

BaSi₂ has suitable optoelectronic properties for solar cells, with a limiting efficiency of over 30% under one sun condition. However, its high reactivity often hinders heterojunction or heterostructure formation with other materials for property analysis and device fabrication. Here, we demonstrate the effectiveness of MgO and Sm₂O₃ interlayers by synthesizing BaSi₂ films on fused silica substrates using two evaporation-based techniques: machine learning-assisted thermal evaporation and close-spaced evaporation. The BaSi₂ films were deposited at 450–500 °C and 800 ^∘C, respectively. High-temperature depositions did not produce secondary phases, except for surface oxidation-induced Si segregation after long in situ annealing at 500 ^∘C for 30 min. These results highlight the effectiveness of the interlayers and machine learning-assisted thermal evaporation. Investigations on close-spaced evaporation on Si layers revealed the benefits of excess Ba deposition for BaSi₂ synthesis and challenges like exfoliation and cracking. These findings are crucial for fabricating BaSi₂-based heterostructures via evaporation-based techniques.

The diffraction limit of light fundamentally limits the spatial resolution of conventional optical microscopy. However, tip-enhanced Raman spectroscopy (TERS) which combines scanning probe microscopy with Raman spectroscopy overcomes this limitation by utilizing near-field technique with a plasmonic tip. This enables the simultaneous acquisition of morphology and optical response of materials present on the surface. As a result, the nanoscale features of surfaces and their optical signals, which are not accessible through far-field signals, can be measured at sub-nanometer resolution. In this review, we first provide a brief introduction followed by an overview of the essential components of TERS, including the working principle of TERS and fabrication methods of plasmonic tips. Subsequently, we will look into the advances in the instrumentation of TERS, such as the operation of TERS in various environments, dynamic control using a tip, and the implementation of adaptive optics in TERS. Finally, we will review very recent TERS studies in selected research areas, including biomaterials, 2D materials, catalytic processes, and single-molecule chemistry.

In the image reconstruction of ultrasound B-mode images, an average speed of sound (SoS) in living tissue is assumed to be a constant value. However, the assumed value may be different with the true values because the SoS varies depending on the properties of the tissue. The error between the true and assumed SoS causes degradation of ultrasound B-mode images. We have proposed a method for estimating an average SoS distribution. In this study, we conducted numerical simulations and evaluated the effects of motion on the average SoS estimation method. Furthermore, we conducted phantom experiments. In both the numerical simulation and phantom experiment, when a B-mode image was reconstructed using the estimated average SoS distribution, the contrast value was improved regardless of the motions.

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.

Two-dimensional (2D) materials offer exceptional properties for microelectronics, yet scaling these technologies from laboratory research to industrial applications remains challenging. Processes for growth, transfer, and fabrication require significant adaptation. Direct bonding and transfer without polymer intermediaries are particularly attractive to avoid organic residues and potential defects. This study demonstrates the transfer of 2D MoS₂ layers onto full 200 mm silicon wafers using direct molecular bonding. Additionally, a water-mediated transfer process from the growth substrate to the target wafer is described. With the use of a hydrophobic silicon wafer, over 95% of the 2D material surface is successfully transferred while preserving MoS₂ quality, as verified through photoluminescence characterization.

In this study, we propose a novel model to predict Al₂O₃ film conformality in different aspect ratio trench structures under various process conditions. This model is grounded on a two-dimensional diffusion-reaction equation integrated with the distance regularized level set evolution method based on edge active contour. The simulation results demonstrate that increasing the gas pressure, the pulse time, and the initial sticking probability of precursor and co-reactant molecules can enhance conformality during the deposition process of the Al₂O₃ film. And the higher deposition temperature and lower initial sticking probability of co-reactant molecules can also lead to better film conformality. By employing our proposed model, both researchers and engineers can refine atomic layer deposition process parameters, thereby ensuring the fabrication of high-quality deposition films for advanced semiconductor structures with high aspect ratio structures.

The diffraction limit of light fundamentally limits the spatial resolution of conventional optical microscopy. However, tip-enhanced Raman spectroscopy (TERS) which combines scanning probe microscopy with Raman spectroscopy overcomes this limitation by utilizing near-field technique with a plasmonic tip. This enables the simultaneous acquisition of morphology and optical response of materials present on the surface. As a result, the nanoscale features of surfaces and their optical signals, which are not accessible through far-field signals, can be measured at sub-nanometer resolution. In this review, we first provide a brief introduction followed by an overview of the essential components of TERS, including the working principle of TERS and fabrication methods of plasmonic tips. Subsequently, we will look into the advances in the instrumentation of TERS, such as the operation of TERS in various environments, dynamic control using a tip, and the implementation of adaptive optics in TERS. Finally, we will review very recent TERS studies in selected research areas, including biomaterials, 2D materials, catalytic processes, and single-molecule chemistry.

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.

Since the liquid/liquid interface is a variety of reaction fields, its high-spatial- resolution analysis is crucial. In this paper, we report the force spectroscopy on a liquid gallium/aqueous solution interface using atomic force microscopy (AFM). For stable analysis of the liquid/liquid interface, a probe-scan-type AFM with a qPlus sensor was developed. By using the frequency modulation technique, conservative and dissipative interactions were separately detected. As a result, a step-like change in resonance frequency corresponding to the conservative interaction was detected on the interface. This was well explained by the conical shape of the tip and the interfacial energy change. The energy dissipation change on the interface was more obscure than the frequency shift change. This result suggests that the detection of conservative interaction is preferable for interfacial analysis of liquids with large surface tension but small viscosity differences, such as liquid Ga and aqueous solutions.

A barometric pressure change sensor utilizing a microelectromechanical system (MEMS) piezoresistive cantilever achieves high sensitivity and robustness. However, its miniaturization is constrained by the trade-off between the cutoff frequency of the mechanical high-pass filter and the air chamber volume. This study investigates the relationship between cantilever dimensions and their frequency characteristics. Experimental and theoretical results confirm that the frequency response varies with cantilever length and thickness. These findings contribute to optimizing these parameters, enabling miniaturization while maintaining high sensitivity and a low cutoff frequency.

We fabricated large-diameter, low-threading dislocation density (TDD) GaN wafers using Na-flux multi-point seed (MPS) and flux-film-coated (FFC) techniques. In the FFC technique, the crystal grows repeatedly inside and outside the melt to planarize the crystal surface. However, regions where the three pyramidal crystals coalesced at regular intervals exhibited a high TDD exceeding 10⁵ cm^-2. Recently, we found that the growth morphology of crystals can be controlled by varying the ratio of the growth time inside and outside the melt using the FFC technique. In this study, we discovered that the TDD above the coalescence region was reduced from 4.4 × 10⁵ cm^-2 to 2.5 × 10⁵ cm^-2 by optimizing growth morphology, such as {10-12} facet growth and increasing the c-plane sector boundary angle. Furthermore, based on the relationship between the dislocation propagation angle and c-plane sector boundary angle, we propose a growth model for effective TDD reduction.

We review our studies to assess charge carrier dynamics inside a perovskite film and interfacial charge transfer dynamics for a perovskite layer sandwiched by an electron transporting layer (ETL) such as TiO2 compact or mesoporous layer and a hole transporting layer (HTL) such as spiro-OMeTAD. Both electron and hole injection occurs faster than electron-hole recombination inside a perovskite film, however both change injection yields decrease with increase in excitation intensity. Since the electron mobility inside methylammonium lead iodide (MAPbI3) perovskite is smaller than the hole mobility, employing a mesoporous ETL structure is suitable to maximise an electron injection yield. Interfacial charge recombination lifetime increases with increase in perovskite film thickness and separated charge carrier density. We therefore conclude that for p-type MAPbI3 solar cells, the perovskite film thickness should be increased to the hole diffusion length while the mesoporous ETL structure should be employed to maximise the electron injection yield.

The resonance properties of A₀- and A₁-mode Lamb waves and SH₁ mode plate waves in a LiNbO₃ (LN) thin plate bonded to a support substrate with periodic voids were simulated using the finite element method. Resonance properties similar to those of the plate waves were obtained by partially bonding the LN thin plate, and the main displacement nodes of the plate waves appeared on the support substrate. For the A₁-mode Lamb wave on 123°YX-LN/4H-SiC with LN thickness h = 0.15 λ (where λ is the wavelength) and void width w to pitch p ratio (w/p) = 0.7, a resonance property with a fractional bandwidth (FBW) of 9.3% was obtained at a phase velocity of 15880 m/s. For the A₀-mode Lamb wave on 141°YX-LN/glass with h = 0.28 λ and w/p = 0.7, a resonance property with FBW of 4.0% was obtained at a phase velocity of 2690 m/s.

This study aims to develop surface modification pretreatment for ultrasonic bonding to optimize aluminum-to-aluminum metal direct bonding for multilayer packaging applications. Vacuum ultraviolet (VUV) irradiations in air or formic acid atmosphere were adopted. Experimental results indicate that VUV pre-treatment could alter the functional group bonding on the aluminum surface, especially the increase in the content of Al–OH bonds. The atmosphere of formic acid vapor gave rise to the formation of formate ligands via monodentate coordination mode. An appropriate amount of Al–OH and formate ligands enhance the strength of aluminum/aluminum joints. However, excessive organic acid treatment resulted in incomplete reaction residues, leading to a deterioration in bonding.

We review our studies to assess charge carrier dynamics inside a perovskite film and interfacial charge transfer dynamics for a perovskite layer sandwiched by an electron transporting layer (ETL) such as TiO2 compact or mesoporous layer and a hole transporting layer (HTL) such as spiro-OMeTAD. Both electron and hole injection occurs faster than electron-hole recombination inside a perovskite film, however both change injection yields decrease with increase in excitation intensity. Since the electron mobility inside methylammonium lead iodide (MAPbI3) perovskite is smaller than the hole mobility, employing a mesoporous ETL structure is suitable to maximise an electron injection yield. Interfacial charge recombination lifetime increases with increase in perovskite film thickness and separated charge carrier density. We therefore conclude that for p-type MAPbI3 solar cells, the perovskite film thickness should be increased to the hole diffusion length while the mesoporous ETL structure should be employed to maximise the electron injection yield.

Ultraviolet-induced degradation (UV-ID) of various PV cell types was analyzed under optical UV filters with different cutoff wavelengths. Cell types studied included interdigitated back contact (IBC), passivated emitter and rear totally diffused (PERT), and heterojunction technology (HJT) based on crystalline Si (c-Si), and metal halide perovskite (MHP) cells. Analyzing degradation rates in two distinct regimes proved beneficial for all cell types. We used empirical linearizing functions ln(t) for c-Si technologies and ²√t for MHP samples where t is time. These were applied to extrapolate UV-induced degradation over the lifetime of PV modules under various levels of optical UV filtering and used to predict the relative economic benefits for PV power plants. Degradation rates for all technologies were generally faster under the long pass optical filters having shorter cutoff wavelengths transmitting more UV irradiation and at elevated temperatures when testing MHP samples in the range between 60 °C and 90 °C.

Secondary electron bremsstrahlung (SEB) has been proposed for range verification in particle therapy. However, the uncertainty in range-shift estimation due to high statistical noise under small numbers of carbon ion irradiation remains unclear. This simulation study evaluated the uncertainty of SEB-based range-shift estimations under conditions with limited numbers of carbon ions. The 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 in simulation. Estimated range shifts were derived from the obtained SEB images using our proposed range-shift estimation method. As a result, the uncertainty was 1.4 mm for 10⁸ ions and 4.4 mm for 10⁷ ions. The results suggested that improving the sensitivity of the detector is effective in reducing the uncertainty.

Atomic force microscopy (AFM) is a powerful tool for topographic imaging and force sensing on solid objects buried in liquid. In the present study, the feasibility of force detection in the frequency-modulation mode has been demonstrated in 1-octanol liquid at temperatures as low as -15 °C. A commercial microscope was cooled within an acoustic enclosure, and topographic images of octanol molecules adsorbed on graphite were obtained with nanometer-scale resolution. The molecules of octanol in the liquid phase exhibited flat layers over the octanol-adsorbed graphite, as evidenced by a series of force–distance curves. This research certified the usability of frequency-modulation AFM operated at sub-zero temperatures, even though the viscosity of the imaging liquid is enhanced.

In order to fabricate multi-layered artificial blood vessels, bubble-surrounded cells were retained on the wall in a flow channel using an interferential acoustic field. We measured the cell retention performance using an interferential acoustic field, investigated the effect of burst waves and phase sweeping on increasing the retained area of the cells. First, we compared the retention area of BSCs under exposure to ultrasound with the simulated results of a theoretical model of retention. Next, we compared the retention performance using burst waves with delay times in an interferential acoustic field. Finally, the effect of phase sweeping was also evaluated by cell retention performance at different sweep velocities and duty ratios.

Ultrathin gold oxide (AuOx) films were patterned on gold surfaces using UV/O3 treatment applied through quartz photomasks with Cr patterns. The formation of AuOx films was confirmed through reflective spectroscopy and X-ray photoelectron spectroscopy. Reflective spectroscopy conducted on antireflective (AR) multilayer substrates demonstrated a minimum reflectance at 535 nm, which shifted by 3.0 nm toward longer wavelengths upon AuOx formation. This shift enabled the imaging of the AuOx patterns by the camera. The maximum contrast of the AuOx patterns reached 9.3% in the images obtained under 530 nm light. Fine patterns, including a 12.7 µm-wide line pattern and numerical designs, were successfully fabricated. This method enabled the real-time imaging of AuOx patterns using standard optical setups and cameras, with AR substrates enhancing the optical sensitivity. These results demonstrate a scalable and precise approach for analyzing ultrathin films and advancing nanofabrication applications.

In wafer bonding technologies used for micro-electro-mechanical systems (MEMS) capping, sealing and system integration, 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, which directly defines both the bonding process cost and the bonding tool capacity. 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 plasma-enhanced chemical vapour deposition layers into the sealed cavities and allowing the use of temperature sensitive materials in wafer bonded MEMS. For the standard glass Schott Borofloat^®33 it has been shown that anodic wafer bonding can be performed at 200 °C if the thermomechanical stress between glass and silicon, which is higher at this process condition, is not critical for the realted application. 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.

Scattering solar concentrators (SSCs) incorporating light scattering layers based on TiO₂ microparticles were fabricated and systematically characterized. The concentration of TiO₂ microparticles in the scattering layer significantly influenced the power output of a silicon solar module mounted on one of the sidewalls of the SSCs. The application of a dichroic mirror as a rear-side reflector, selectively reflecting near-infrared light, substantially enhanced the power output while maintaining a high average visible light transmittance. The light guiding efficiency from the top surface to the sidewall was calculated to be 8.36%, with the conversion efficiency of the sidewall-mounted silicon solar module reaching 1.22%. The SSC demonstrated an average visible light transmittance of 47.7%. Interestingly, the conversion efficiency of the silicon solar module did not decrease monotonically with increasing angle of incidence to the SSC. A maximum conversion efficiency of 1.85% was achieved at an incidence angle of 45°. This angle-dependent behavior highlights the potential of SSCs for use in window-integrated photovoltaic applications.

We investigated the poly-crystallization of catalytic chemical vapor deposited (Cat-CVD) amorphous silicon (a-Si) films using flash lamp annealing (FLA) to obtain polycrystalline silicon (poly-Si) thin films. In this study, a crystalline Si seed layer was first formed by crystallizing Cat-CVD a-Si films through aluminum induced crystallization (AIC). Subsequently, a-Si films deposited on the seed layer received flash pulse with various conditions. The films remained intact without peeling, and the seed layer significantly promoted crystallization. Consequently, the crystallization rate increased dramatically due to the seed layer's influence, demonstrating its effectiveness in enhancing the crystallization of a-Si films.

Ultraviolet-induced degradation (UV-ID) of various PV cell types was analyzed under optical UV filters with different cutoff wavelengths. Cell types studied included interdigitated back contact (IBC), passivated emitter and rear totally diffused (PERT), and heterojunction technology (HJT) based on crystalline Si (c-Si), and metal halide perovskite (MHP) cells. Analyzing degradation rates in two distinct regimes proved beneficial for all cell types. We used empirical linearizing functions ln(t) for c-Si technologies and ²√t for MHP samples where t is time. These were applied to extrapolate UV-induced degradation over the lifetime of PV modules under various levels of optical UV filtering and used to predict the relative economic benefits for PV power plants. Degradation rates for all technologies were generally faster under the long pass optical filters having shorter cutoff wavelengths transmitting more UV irradiation and at elevated temperatures when testing MHP samples in the range between 60 °C and 90 °C.

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.