Spotlights

In this study, precious metal/tungsten trioxide (WO₃) composite particles in which palladium (Pd) and platinum (Pt) were loaded on WO₃ particles were synthesized via the ultrasonic reduction method. The surface observation of the synthesized composite materials was performed and their photocatalytic performance under visible light irradiation was evaluated from the decomposition rate of methylene blue in aqueous solution. From the TEM image, it was found that the Pd/WO₃ composite particles synthesized by the ultrasonic reduction method had a structure in which Pd nanoparticles were supported on WO₃ particles. The photocatalytic performance of Pd/WO₃ and Pt/WO₃ increased with increasing contents of Pd and Pt. When synthesizing Pd(0.5 wt%)/WO₃ particles by ultrasonic reduction method, the photocatalytic activity was improved by feeding Pd equivalent to 0.17 wt% per feed three times at regular time intervals, rather than by feeding 0.5 wt% of Pd at a time.

A 100 nm wide superconducting niobium (Nb) interconnect was fabricated by a 300 mm wafer process for Cryo-CMOS and superconducting digital logic applications. A low pressure and long throw sputtering was adopted for the Nb deposition, resulting in good superconductivity of the 50 nm thick Nb film with a critical temperature (T_c) of 8.3 K. The interconnects had a titanium nitride (TiN)/Nb stack structure, and a double-layer hard mask was used for the dry etching process. The exposed area of Nb film was minimized to decrease the effects of plasma damage during fabrication and atmosphere. The developed 100 nm wide and 50 nm thick Nb interconnect showed good superconductivity with a T_c of 7.8 K and a critical current of 3.2 mA at 4.2 K. These results are promising for Cryo-CMOS and superconducting digital logic applications in the 4 K stage.

Ge-on-Insulator (GOI) is considered to be a necessary structure for novel Ge-based devices. This paper proposes an alternative approach for fabricating GOI based on the Ge-on-Nothing (GeON) template. In this approach, a regular macropore array is formed by lithography and dry etching. These pores close and merge upon annealing, forming a suspended monocrystalline Ge membrane on one buried void. GOI is fabricated by direct bonding of GeON on Si carrier substrates, using an oxide bonding interface, and subsequent detachment. The fabricated GOI shows uniform physical properties as demonstrated using micro-photoluminescence measurements. Its electrical characteristics and cross-sectional structure are superior to those of Smart-Cut^TM GOI. To demonstrate its application potential, back-gate GOI capacitors and MOSFETs are fabricated. Their characteristics nicely agree with the theoretically calculated one and show typical MOSFET operations, respectively, which indicates promising Ge crystallinity. This method, therefore, shows the potential to provide high-quality GOI for advanced Ge application devices.

We developed a compact thermo-optic Mach–Zehnder interferometer switch with a direct heating heater using multimode interference and achieved a sufficiently low thermal crosstalk performance. Large-scale switch systems, such as optical neural networks, require thermo-optical switches with low power consumption, fast switching speed, compact size, and low thermal crosstalk. This switch is equipped with a heater that directly heats the Si core waveguide, which is a structure that connects non-doped Si wires between phase shifters and a heatsink. As a result, a significant miniaturization with a phase shifter length of approximately 7 μm, low π-phase shift power consumption of less than 20 mW, and fast switching in sub-microseconds were achieved. The improved phase shifter showed a very small figure of merit of 8.89 mWμs. Simultaneously, transmission spectrum measurements of nearby ring resonators show that the thermal crosstalk is significantly reduced even at a distance of only 30 μm. This device can contribute to the overall circuit performance and footprint reduction in large-scale optical integrated circuits and optical neural network configurations.

Two metal-induced lateral crystallization (MILC) methods are proposed as candidate techniques to enhance cell current in future ultra-high-density NAND-type 3D flash memory devices. The channel crystallinity differs depending on the MILC method. In a single MILC, the channel is composed of single-crystal Si, whereas in a regional MILC, the channel comprises multiple crystal grains that are larger than those of the conventional polycrystalline Si. Using transmission electron microscopy, the inhibiting factor of MILC was modeled to reveal that the two MILC approaches result in different cell current distributions that are related to their degree of crystallinity. A comparison of these two cell current distributions in a 3D flash memory with over 900 word-line stacks showed that the single MILC delivers a higher median cell current with outliers on the lower side. In contrast, the regional MILC delivers a lower median cell current without outliers on the lower side.

This paper comprehensively analyses dual integration of approximate random weight generator (ARWG) and computation-in-memory for event-based neuromorphic computing. ARWG can generate approximate random weights and perform multiply-accumulate (MAC) operation for reservoir computing (RC) and random weight spiking neural network (SNN). Because of using device variation to generate random weights, ARWG does not require any random number generators (RNGs). Because RC and random weight SNN allow approximate randomness, ARWG only needs to generate approximate random weights, which does not require error-correcting code to correct weights to make the randomness accurate. Moreover, ARWG has a read port for MAC operation. In this paper, the randomness of random weights generated by the proposed ARWG is evaluated by Hamming distance and Hamming weight. As a result, this paper reveals that the randomness required for ARWG is much lower than that for physically unclonable functions and RNGs, and thus the proposed ARWG achieves high recognition accuracy.

By modulating a ζ potential of graphene FET (G-EFT), the sensitivity of G-FET could be enhanced than that without modulation. Therefore, 1 × 10⁷ FFU ml⁻¹ SARS-CoV-2 was detected using G-FET modified with the ζ potential modulator which is the cation polymer with the positive charge. This method is based on the relationship between the surface charge and the sensitivity, in which the highest sensitivity is obtained when the ζ potential is 0 and/or the surface charge is almost 0. In this study, the microfluidic channel was installed on G-FET to get the precise result because it could wash away the free-floating virus and the physical adsorbed virus. 32 G-FETs including the reference FETs were integrated on the silicon substrate and the precise results were obtained by subtracting the noise terms.

Plasmonic color is a structural color generated via preferential light absorption and scattering in dielectric nanostructures. In this study, a large plasmonic color image was successfully fabricated by an electron beam lithography (EBL) system. A software program, referred to as P-color in this study, was developed to facilitate the conversion of a desired color bitmap image to a GDS file composed of multiple nano-patterns to realize plasmonic color. The relationship between the color, width, and pitch of the pattern structures was investigated under different area-dose conditions during EBL as basic data for plasmonic color image design. After establishing conversion techniques for both the large-capacity GDS and EBL files, a plasmonic color image sample with a size of 60 mm × 40 mm area (which is difficult to fabricate using a conventional point-type EBL system) was successfully fabricated.

This paper proposes a design methodology for a compact edge vision transformer (ViT) Computation-in-Memory (CiM). ViT has attracted much attention for its high inference accuracy. However, to achieve high inference accuracy, the conventional ViT requires fine-tuning many parameters with pre-trained models on large datasets and a large number of matrix multiplications in inference. Thus, to map ViT to non-volatile memory (NVM)-based CiM compactly for edge applications (IoT/Mobile devices) in inference, this paper analyses fine-tuning in training, clipping, and quantization in inference. The proposed compact edge ViT CiM can be optimized by three design methods according to use cases considering the required fine-tuning time, ease of setting memory bit precision, and memory error tolerance of ViT CiM. As a result, in CIFAR-10, the most compact type successfully reduces the total memory size of ViT by 85.8% compared with the conventional ViT. Furthermore, the high accuracy type and high error-tolerant type improve inference accuracy by 4.4% and memory-error tolerance by more than four times compared with convolutional neural networks, respectively.

Sc-based contacts to Si:P have shown great potential for NMOS devices. However, the promising properties of this material system are not yet fully understood. This work provides new insights into the crystallinity and composition of annealed TiN/Sc/Si:P stacks. After silicidation, two distinct phases are evidenced, with orthorhombic ScSi lying atop a thin Sc_1−x−ySi_xP_y interfacial layer that shares a commensurate interface with the underlaid Si:P, hypothetically resulting in a low interface defectivity. The formed ScSi phase is observed to be thermally stable between ∼450 °C and 700 °C, which is suitable for most device applications. The impact of additional thermal budgets within this temperature range is investigated, revealing potential origins for thermally induced degradation of the contact properties.

There is a growing demand for physical reservoirs that operate with low power consumption and low computational cost. We have conducted research on the basic properties of Ag₂S reservoirs, which are a type of physical reservoir. However, little research has been conducted on their applications. In this study, as a first step toward the practical application of Ag₂S reservoirs, we implemented two types of rock-paper-scissors judgment systems using Ag₂S reservoirs. In these experiments, we were able to demonstrate fast learning in the reservoir by comparing the results with methods using a single-layer perceptron and a convolutional neural network. In addition, we could obtain a maximum accuracy rate of about 98%.

We proposed a NIR spectroscopy system that measures multiple types of gases using a plasmonic photodetector. We formed a gold diffraction grating on a silicon substrate to create a plasmonic photodetector and conducted gas spectral measurements in the NIR region. As a result, we could measure the transmission spectrum of water vapor gas at a concentration of 2%. Furthermore, we could measure ethanol gas transmittance at different concentrations of 4.5% and 2.7%, and change in transmission depending on concentration. Lastly, the transmission spectrum of 10% NH₃ gas was measured. Since these results are consistent with evaluations using Fourier transform IR spectroscopy, it was confirmed that the proposed gas measurement can be applied to multiple types of gas sensing.

In this study, we try to reduce the temperature range for the large magnitude of dimensionless figure of merit ZT = 20 that was observed for the Ag₂S composite consisting of low- and high-temperature phases under a unique temperature gradient at around 400 K. It reveals that partial substitution of Cu for Ag sites in Ag₂S reduces the phase transition temperature, and subsequently the temperature range for this high ZT down to a temperature of 373 K. This result strongly suggests that our developed Cu-substituted Ag₂S could be one of the best thermoelectric component materials in the generators capable of effectively recovering electric power from heat exchangers using hot water as a working liquid.

Longer wavelength emitters such as green LEDs display a pronounced efficiency drop at higher current densities, resulting in relatively low wall-plug efficiency (WPE). Multi-active region approach can improve the WPE significantly and tackle the "green gap" challenge. This work reports multi-active region p-down LEDs with high external efficiency operating entirely in the green wavelength. Devices were developed using p-down topology, where the PN junction is oriented such that electric fields from depletion and built-in polarization dipoles are aligned. Ga-polar multi-active region green LEDs with excellent voltage and external quantum efficiency scaling, and significantly higher WPE is demonstrated in this work.

Bismuth ferrite (BiFeO₃: BFO) is a multiferroic material that exhibits ferroelectricity, antiferromagnetism, and ferroelasticity simultaneously at RT. BFO holds great promise as a ferroelectric semiconductor because of its ability to alter conductivity by reversing its spontaneous polarization. Moreover, BFO thin films doped with transition metals such as Mn or V can modulate their conductivity. Nevertheless, the mechanism of this conductivity change remains unclear because the effects of dopants on the local atomic structure of BFO are not fully understood. In this study, we investigated the local atomic structure around the Fe site in a V-doped BFO thin film by X-ray fluorescence holography. Reconstructed atomic structures from the Fe Kα hologram patterns revealed that the atomic structure stability of the V-doped BFO thin film differs from that of previously reported Mn-doped BFO thin films. The results provide important insights into the mechanism of controlling the conductivity of BFO thin films by dopants.

Surface-activated direct bonding of diamond (100) and c-plane sapphire substrates is investigated using Ar atom beam irradiation and high-pressure contact at RT. The success probability of bonding strongly depends on the surface properties, i.e, atomic smoothness for the micron-order area and global flatness for the entire substrate. Structural analysis reveals that transformation from sapphire to Al-rich amorphous layer is key to obtaining stable bonding. The beam irradiation time has optimal conditions for sufficiently strong bonding, and strong bonding with a shear strength of more than 14 MPa is successfully realized. Moreover, by evaluating the photoluminescence of nitrogen-vacancy centers in the diamond substrate, the bonding interface is confirmed to have high transparency in the visible wavelength region. These results indicate that the method used in this work is a promising fabrication platform for quantum modules using diamonds.

Distributions of transient and local lattice strains on resonating AT-cut quartz oscillators were measured in situ by scanning time-resolved X-ray diffraction under an alternating electric field to reveal the effects of the crystal shape and electrode thickness on their piezoelectric vibration. The concentration of the lattice vibration amplitude and energy at the electrode center in a plano-convex type oscillator and enhancement of the lattice strain in a plano–plano type oscillator within the electrode area with increasing electrode thickness have been unambiguously demonstrated by the method without any surface modifications.

In this study, a physical reservoir computing system, a hardware-implemented neural network, was demonstrated using a piezoelectric MEMS resonator. The transient response of the resonator was used to incorporate short-term memory characteristics into the system, eliminating commonly used time-delayed feedback. In addition, the short-term memory characteristics were improved by introducing a delayed signal using a capacitance-resistor series circuit. A Pb(Zr,Ti)O₃-based piezoelectric MEMS resonator with a resonance frequency of 193.2 Hz was employed as an actual node, and computational performance was evaluated using a virtual node method. Benchmark tests using random binary data indicated that the system exhibited short-term memory characteristics for two previous data and nonlinearity. To obtain this level of performance, the data bit period must be longer than the time constant of the transient response of the resonator. These outcomes suggest the feasibility of MEMS sensors with machine-learning capability.

The rotation of polarization at 90-degree domain walls in tetragonal BaTiO₃ was directly observed by the STEM-CBED method, which combines scanning transmission electron microscopy and convergent-beam electron diffraction (CBED). The CBED patterns in the domain wall region exhibit continuous changes in intensity distribution within disks and specific features corresponding to the direction of the rotation of polarization. Simulations were performed using hypothetical superstructures created by continuously connecting Ti displacement with a 90-degree rotation and showed good qualitative agreement with the experimental patterns. The quantitative evaluation of the mirror symmetries existing in the tetragonal structure in bulk form revealed the width of the domain wall is approximately 9 nm. While distorted regions with slightly broken symmetry in CBED disks were found to extend further on both sides of the domain wall region in 6–7 nm. This finding can explain the discrepancy in the domain wall widths reported in previous studies.

To investigate the electrical properties and degradation features of dielectric materials during plasma exposure, we developed an in situ impedance spectroscopy (IS) system. We applied the proposed system to monitor SiO₂/Si structures exposed to Ar plasma. By analyzing the measured data based on an equivalent circuit model considering the plasma and SiO₂/Si structures, we obtained the resistance (R) and capacitance (C) values for the SiO₂ film and SiO₂/Si interface. In a cyclic experiment of in situ IS and high-energy ion irradiation, we characterized dielectric degradation by ion irradiation based on the variations in the R and C values of the SiO₂ film. A continuous in situ IS measurement revealed temporal variations in the electrical properties of the film and interface independently. The thickness-dependent degradation observed for the RC variation was analyzed and compared with the results of previous ex situ measurement studies. This study demonstrates that the in situ IS measurement technique is promising for monitoring plasma-assisted dry processes.

Post-treatment of perovskite solar cells with CuSCN hole-transport layers to enhance their photovoltaic performance was investigated. Crystallinity and uniformity of CuSCN layers were improved by recrystallisation caused by oleylamine (OA) treatment. Further, the OA adsorbed on CuSCN tuned the VB edge potential and improved the hole extraction from perovskite materials. Power conversion efficiency of the CuSCN-based perovskite solar cells improved from 8.58% to 11.4%.

29.2%-conversion efficiency of a two-terminal (2T) perovskite/crystalline Si heterojunction tandem solar cell using 145 μm thick industrial Czochralski (CZ) Si wafer is obtained. The structural optimization, such as surface passivation of the perovskite layer and better light management techniques, improved power conversion efficiency (PCE). To our knowledge, this PCE is the best in 2T-tandem solar cells using CZ wafers. Towards industrialization, crucial issues with the 2T tandem solar cells with crystalline Si bottom cell are discussed. Four-terminal (4T) tandem solar cells are evaluated as an approach to avoid the crucial issues. Examining our base technologies which realize 22.2%-conversion efficiency perovskite single junction solar cell module and 26%-heterojunction back-contact solar cells, we clarified that the based technologies were ready to realize 30%-conversion efficiency 4T perovskite/heterojunction crystalline Si tandem solar cells with approximately quarter size of an industrial crystalline Si solar cell (∼64 cm²).

We clarified the design guides for H₂- and CO-producing artificial photosynthetic devices. The combination of a voltage-matched (VM) tandem solar-cell (SC) module and an electrochemical (EC) module was adopted. The parallel-connected top and bottom SC modules, in which multiple organic–inorganic hybrid perovskite (PVK) SCs with a bandgap of 1.7 eV and crystalline-silicon SCs were connected in series, respectively, powered the EC module consisting of series-connected multiple EC reactors. It was found that the design parameters of the series connection numbers must be optimized under slightly greater solar intensity and higher temperature than the average values to minimize the mismatch between the device operating voltage and SC maximal power voltage. This is in contrast to that the annual electricity production of the VM SC module coupled with a power conditioner is not sensitive to the optimization conditions. Increases in the bandgaps of the PVK SCs do not affect the annual production significantly.

Trihalide vapor phase epitaxy (THVPE) is a new type of halide vapor phase epitaxy (HVPE) that uses GaCl₃ as a group III source, enabling Ga₂O₃ growth without particle generation, although the growth rate is low. In this study, β-Ga₂O₃ is grown by THVPE using solid GaCl₃ as a group III precursor. The growth rate increases linearly with increasing partial pressure of the precursor. The dependence of the growth rate on the VI/III ratio is revealed on sapphire substrates, with the growth rate reaching a maximum at a VI/III ratio of 95. We have also obtained a growth rate of 32.2 μm h⁻¹ on β-Ga₂O₃ (001) substrates with no particle generation, crystal quality equivalent to that of the substrate, and high purity equivalent to that of HVPE.

Herein, we have studied the exciton dynamics of a novel fused ring π-conjugated molecule (YS3) in solution and film states by spectroscopic measurements. This molecule incorporates dithienonaphthobisthiadiazole as a core unit that is a two-dimensionally π-extended fused ring. As a result, we found a long exciton lifetime in YS3 films originating from reduced radiative and nonradiative transitions. This is partly because radiative deactivation is effectively suppressed because of the dipole-forbidden transition in H-aggregates and partly because rotational deactivation is effectively suppressed in the crystalline film state.

In metalorganic vapor phase epitaxy of β-Ga₂O₃ using triethylgallium (TEGa) and O₂ as precursors and Ar as the carrier gas, the gases directly above the substrate were sampled and analyzed by time-of-flight mass spectrometry. TEGa was found to decompose at 400 °C–600 °C via β-hydrogen elimination reaction to generate gaseous Ga, hydrocarbons (C₂H₄, C₂H₂, C₂H₆), and H₂. When β-Ga₂O₃ was grown at temperatures greater than 1000 °C and with input VI/III ratios greater than 100, the hydrocarbons and H₂ were combusted and CO₂ and H₂O were generated. The C and H impurity concentrations measured by secondary-ion mass spectrometry in the β-Ga₂O₃(010) homoepitaxial layer grown under these conditions were less than their respective background levels. Thus, to grow β-Ga₂O₃ without C and H contamination, conditions that favor the complete combustion of hydrocarbons and H₂ generated by the decomposition of TEGa should be used.

Radiation tolerance of Cu(In,Ga)Se₂ (CIGS) solar cells has been investigated using high-fluence proton beam irradiation for application to devices in extremely-high-radiation environments. CIGS solar cells deteriorated after high-energy proton irradiation with non-ionizing energy loss of 1 × 10¹⁶ MeVn_eq cm⁻², however, the CIGS solar cells could generate power after high-fluence irradiation. The ideality factors increased from 1.3 to 2.0, and series resistance increased, indicating that the concentration of recombination centers increased in CIGS layers. After heat-light annealing, the conversion efficiencies gradually recovered, and the recombination centers were confirmed to be partly passivated by annealing at 90 °C. The short-circuit currents for 10 μm thick CIGS solar cells were recovered by dark annealing in the same manner as for 2 μm thick CIGS solar cells. Dark annealing on irradiated CIGS solar cells has beneficial effects on passivate the recombination centers, even using thicker CIGS layers.

Improving the accuracy of heart wall motion measurement is essential to realise better cardiac function evaluation. This paper proposed a two-dimensional (2D) displacement estimation method with a high temporal resolution using the 2D complex cross-correlation of element RF signals of an ultrasonic probe between frames returned from the target scatterers. The application of the proposed method to the phantom displacement confirmed its principle. The estimated 2D displacement of the phantom was consistent with the set displacement. Subsequently, the method was applied to two healthy subjects to measure the 2D displacement of the interventricular septum during one cardiac cycle. Consequently, during systole and diastole, the movement of the myocardium was measured, and the results were validated.

We report the growth of α-Ga₂O₃ on m-plane α-Al₂O₃ by conventional plasma-assisted molecular-beam epitaxy and In-mediated metal–oxide-catalyzed epitaxy (MOCATAXY). We report a growth rate diagram for α-Ga₂O₃($10\bar{1}0$), and observe (i) a growth rate increase, (ii) an expanded growth window, and (iii) reduced out-of-plane mosaic spread when MOCATAXY is employed for the growth of α-Ga₂O₃. Through the use of In-mediated catalysis, growth rates over 0.2 μm h⁻¹ and rocking curves with full width at half maxima of Δω ≈ 0.45° are achieved. Faceting is observed along the α-Ga₂O₃ film surface and explored through scanning transmission electron microscopy.

The time dependence of the ion composition in pulse-modulated dual-frequency capacitively coupled plasma with Ar/C₄F₈/O₂ was measured using a quadrupole mass spectrometer with an electrostatic energy analyzer. After turning on the pulse, Ar⁺ ions were preferentially generated, and then, the composition of C_xF_y⁺ ions, such as C₂F₄⁺ and C₃F₅⁺ ions, increased. This phenomenon was discussed on the basis of the time variation of electron temperature and the resultant change in the ratio of the C₄F₈ ionization rate to that of Ar atoms.

A real-time temperature measurement technique with high spatial (≤20 μm) and temporal (≤1 μs) resolutions for SiC wafers during ultra-rapid thermal annealing (URTA) has been developed based on optical-interference contactless thermometry (OICT). This technique consists of hardware (OICT imaging setup) and software (fast temperature extraction program). Under URTA by atmospheric-pressure thermal plasma jet, a clear variation of optical-interference fringes was observed by a high-speed camera and then analyzed by a fast temperature extraction program using image preprocessing and a database. 3.5D (x, y, z and time) temperature distribution in SiC wafer was obtained within 0.43 s.

The growth of large-diameter high-resistivity β-Ga₂O₃ (010) substrates is important for the low-cost production of lateral Ga₂O₃ devices. We grew a 2 inch diameter Fe-doped high-resistivity β-Ga₂O₃ (010) single crystal by using the vertical Bridgman (VB) method, which is expected to grow large-diameter β-Ga₂O₃ crystals with various crystal orientations. Two-inch substrates were prepared from the obtained crystals, and their crystallinity, concentration of Fe dopants, and electrical properties were investigated. Consequently, a 2 inch β-Ga₂O₃ (010) substrate, which is comparable to the largest size of (010) substrate prepared using the Czochralski method, was successfully fabricated with the VB method. The in-plane distribution of the X-ray rocking curve from 020 diffraction of the fabricated 2 inch substrate showed that the full widths at half maximums were less than 35 arcsec at almost all measurement points, indicating high crystallinity and high in-plane uniformity. In addition, the crystals contain Fe concentrations in the range of 3.5 × 10¹⁸–1.9 × 10¹⁹ cm⁻³, indicating that impurity Si donors are sufficiently compensated by the Fe dopants. Therefore, substrates prepared using the VB method exhibited high resistivities of 6 × 10¹¹–9 × 10¹² Ω·cm at room temperature.

In this work, we comprehensively investigate the development of unwanted parasitic particles in the MOVPE chamber while growing μm level films. The density of the parasitic particles is found to be pronounced at film thicknesses starting from >1.5 to 2 μm. These particles seem to induce structural defects such as twin lamellae, thereby harming the electrical properties of the grown film. The origin of the parasitic particle is attributed to the parasitic reactions within the chamber triggered by the promoted gas-phase reactions during the growth process, which can be largely reduced by increasing the total gas flow and decreasing the showerhead distance to the susceptor. A film thickness of up to 4 μm has been achieved after minimizing the density of parasitic particles. Thereby, RT Hall measurements reveal carrier mobilities of 160 cm²V⁻¹s⁻¹ at carrier concentrations of 5.7 × 10¹⁶ cm⁻³.

This paper describes a stacked thin-plate region for focusing the transmitted waves. The region was designed to focus the wave field in the bulk medium by utilizing the dispersion nature of Lamb waves. The first numerical calculation proved that an incident plane wave changes the wavefront in a stacked thin-plate region because of the different phase velocities in plates with different thicknesses, and the resulting transmitted wave was focused at the target. Second, when a delayed longitudinal wave was applied to the edge of the stacked thin-plate region with identical thickness, the numerical calculations showed that the delayed wavefront of the S0 mode was preserved in the stacked plate region, and that the transmitted longitudinal wave was appropriately focused at the target. The focusing devise consisting of a stacked thin-plate structure is useful for the buffer for phased array inspection.

This work comprehensively analyzes the error robustness of hyperdimensional computing (HDC) by using FeFET-based local multiply and global accumulate computation-in-memory. HDC trains and infers with hypervectors (HVs). Symmetric or asymmetric errors, which simulate read-disturb and data-retention errors of FeFET, are injected into Item memory and/or Associative memory before/after or during training in various cases when solving European language classification task. The detailed error injection reveals that HDC is acceptable for both symmetric and asymmetric error rate up to 10⁻¹. Based on the detailed analysis of error robustness, training window slide (TWS) improves the error robustness against memory errors by removing data which contain different amount of errors. TWS shows 10 times higher error robustness. In addition, parallelization of HV encoding in training achieves fast training with up to 10 000 parallelism while maintaining the inference accuracy.

A physical reservoir that accepts direct light irradiation as input was developed using a Ag₂S island network. Short-term memory and nonlinearity required for reservoirs are achieved by the diffusion of Ag⁺ cations in each Ag₂S island and the growth of Ag filaments between Ag₂S islands. We found that direct light irradiation to Ag₂S islands changes local conductivity in a reservoir, which enhances the performance in short-term memory and nonlinearity of the reservoir. Using the effect, we performed a pattern classification of light that was irradiated to a Ag₂S island network reservoir through a rectangular slit, which resulted in the accuracy of over 95%.

In this study, we developed a capacitorless dynamic random-access memory (DRAM) (1T-DRAM) device based on a junctionless (JL) bulk-fin field-effect transistor structure with excellent reliability and negligible variability against work-function variation (WFV). We investigated the variation in the transfer characteristics and memory performance of the memory cell owing to WFV. In particular, to investigate the WFV effect, we analyzed the transfer characteristics and memory performance of 200 samples using four metal-gate materials—TiN, MoN, TaN and WN. Consequently, we discovered that the WFV affected the transfer characteristics of the JL bulk-fin field-effect transistor. However, the proposed 1T-DRAM demonstrated that the sensing margin and retention time produced minimal effect owing to the adoption of a structure storing holes in the fin region. Consequently, the proposed 1T-DRAM exhibited strong WFV immunity and excellent reliability for memory applications.

We have investigated the energetics and electronic structure of monolayer MoS₂ with periodic structural corrugations by density functional theory. The total energy of corrugated MoS₂ slightly increases with increasing corrugation height, which indicates that the MoS₂ sheet intrinsically and extrinsically possesses nanometer scale structural corrugation. The corrugation causes an upward shift of the valence band edge and a downward shift of the conduction band edge owing to the local strain at the wrinkle peak. Accordingly, by injecting holes using the external electric field, the corrugation leads to a one-dimensional conducting channel in the MoS₂ sheet. This indicates that corrugation is a plausible procedure to control the dimensionality of the electrons and holes in two-dimensional materials without implementing one-dimensional boundary conditions.

We propose a III–V metal-oxide-semiconductor (MOS) optical modulator with a graphene gate electrode along with the analysis of the modulation properties. With p-type doped graphene used as a transparent gate electrode, we can fully utilize the electron-induced refractive index change in an n-type InGaAsP waveguide with the reduction of the hole-induced optical absorption observed in a III–V/Si hybrid MOS optical modulator. Numerical analysis displays that up to the phase modulation efficiency of 0.82 V·cm and 0.22 dB optical loss for π phase shift can be achieved when the gate oxide thickness is 100 nm. With the elimination of the unnecessary parasitic capacitance found in the overlapping of graphene on the slab part of the waveguide, in conjunction with the high electron mobility in InGaAsP, the device also enables a modulation bandwidth of greater than 200 GHz.

Ultraviolet photodetectors (UVPDs) based on Si-Zn-SnO (SZTO) thin-film transistors (TFTs) with a stacked dual-channel layer (DCL) structure with different carrier concentration and NiO capping layer (CL) to alleviate the trade-off between dark current (I_dark) and photocurrent (I_ph) are reported. Experimental results show that under 275 nm irradiation, the proposed SZTO TFT UVPD with a 30 nm thick upper layer stacked on a 50 nm thick channel layer and a patterned NiO CL exhibit excellent photoresponsivity and photosensitivity up to 1672 A W⁻¹ and 1.03 × 10⁷ A A⁻¹, which is about 272 and 137 times higher than conventional 30 nm thick single-channel layer SZTO TFT. These improvements are due to the use of a DCL which forms a high-low junction to reduce the effective channel thickness and increasing the space for UV illumination and the use of NiO CL lowers the I_dark and causes a considerable negative threshold voltage shift under UV irradiation to significantly boost the I_ph.

The volumetric thermal expansion coefficient α_V is discussed in relation to the bulk modulus B₀ for transition-metal disilicides (TrSi₂), alkaline-Earth metal disilicides (AeSi₂), Mg₂Si, and Si clathrates. For this purpose, the α_V of CoSi₂ at 300 K is determined to be 3.1 × 10⁻⁵ K⁻¹ using powder X-ray diffraction measurements at temperatures ranging from 300 to 835 K. AeSi₂ and Mg₂Si have B₀ values ranging from 27.9 to 52.9 GPa, while the values for α_V range from 3.2 × 10⁻⁵ to 4.8 × 10⁻⁵ K⁻¹. TrSi₂ including CoSi₂ has larger B₀ values ranging from 148.9 to 243 GPa and smaller α_V values ranging from 2.3 × 10⁻⁵ to 3.3 × 10⁻⁵ K⁻¹ than AeSi₂. Si clathrates have intermediate values of α_V and B₀, which are in between those of TrSi₂ and AeSi₂. Thus, the silicides with small B₀ values tend to have large α_V values.

We experimentally demonstrated electrical detection of all-optical magnetization switching (AOS) induced by a single femtosecond laser pulse irradiation by measuring alternate rapid changes in anomalous Hall voltage and magneto-optic image pulse by pulse in a Hall-cross shape ferrimagnetic GdFeCo alloy thin film. We also demonstrated that the amplitude of the change in anomalous Hall voltage depended on the position of the AOS-created magnetic domain on the Hall cross. Furthermore, the AOS-created magnetic domains were stable against subsequent current applications in the Hall cross circuit, whereas reversed magnetic domains were not created when the laser pulse was irradiated with a high current. We found that the cooperative effect among magnetism, light, and electric current was assumed to have effects on the absence of the AOS. Combining the AOS phenomenon and electrical measurement/control techniques can realize ultrafast, deterministic, and distinguishable applications.