The 50 most-cited articles in Japanese Journal of Applied Physics, 2022

Abstract High-NA extreme ultraviolet (EUV) lithography is currently in development. Fabrication of exposure tools and optics with a numerical aperture (NA) equal to 0.55 has started at ASML and Carl Zeiss. Lenses with such high NA will have very small depths-of-focus, which will require improved focus systems and significant improvements in wafer flatness during processing. Lenses are anamorphic to address mask 3D issues, which results in wafer field sizes of 26 mm × 16.5 mm, half that of lower NA EUV tools and optical scanners. Production of large die will require stitching. Computational infrastructure is being created to support high-NA lithography, including simulators that use Tatian polynomials to characterize the aberrations of lenses with central obscurations. High resolution resists that meet the line-edge roughness and defect requirements for high-volume manufacturing also need to be developed. High power light sources will also be needed to limit photon shot noise.

Abstract The present work reviews some fundamental aspects of scintillators, including the light yield, decay time, emission wavelength, afterglow, timing resolution and energy resolution. Following fundamental aspects, recently developed inorganic ceramic, glass and single crystal scintillators are introduced with some future prospects.

Abstract Recent development of organic scintillators is reviewed from the viewpoint of materials science. Design and crystal growth of organic crystalline scintillators, use of novel solvents and solutes in liquid scintillators, and development of plastic scintillators based on novel polymer hosts or novel fluorescent molecules are introduced. Additionally, development of loaded liquid or plastic scintillators is reviewed on the basis of two approaches of loading: molecules or nanoparticles. A disadvantage of organic scintillators has been their low scintillation light yields. Hence, materials design for improving scintillation light yields is introduced in detail with description on related excited state dynamics. Finally, future prospect for the improvement of scintillation light yield is briefly given.

Abstract The effects of field cycling of Al 0.78 Sc 0.22 N capacitors on ferroelectric properties are investigated. In the first hundreds of switching cycles, the reduction in the switching voltage was observed, possibly due to the formation of nitrogen-vacancy to facilitate the atom displacements. With further switching cycles, fatigue effect was observed, especially for domains with low switching voltage. The leakage current analysis indicates continuous downward band bending with the number of switching cycles, effectively reducing the Schottky barrier height for electrons. The breakdown of Al 0.78 Sc 0.22 N films is triggered by the Joule heat due to excessive leakage current. The mechanism is in contrast to conventional ferroelectric materials, where the breakdown is triggered by Joule heat at the local conductive filaments.

Abstract This paper reviews the status of characterization of defects in β -Ga 2 O 3 crystals grown by edge-defined film-fed growth and hydride vapor phase epitaxy using chemical etching, scanning electron microscopy, focused ion beam scanning ion microscopy, X-ray topography (XRT), and transmission electron microscopy (TEM). The observed defects are classified into four types: dislocations, stacking faults (SFs), twins, and plate-like nanovoids (PNVs). First, we present the detailed characterization of dislocations in the crystal by chemical etching, XRT, and TEM, and discuss possible slip systems. Next, we describe XRT analyses of two types of SFs: SFs 1 lying on the ( 2 ¯ 01 ) plane and SFs 2 on the (111) and ( 1 1 ¯ 1 ) planes. We describe the results for twins found in crystals via high-resolution TEM and electron diffraction analysis, and PNVs corresponding to etch pits on the (010) plane. Finally, we discuss possible generation mechanisms of the defects and their influence on device characteristics.

Abstract This paper exposes Hodgkin–Huxley’s “time-varying conductance” as an ill-conceived conceptual blunder and identifies a fundamental new physical concept dubbed “Edge of Chaos Kernel” as nature’s optimal mechanism for creating an “action potential,” aka “all-or-none” response. As a bonus, it also offers a precise characterization of the heretofore unresolved notion of excitability, which in turn finally resolves Galvani’s 240 year old enigma on the physical mechanism which gives rise to a near-abrupt all-or-none phenomenon, triggered by a global saddle-node bifurcation where a stable and an unstable periodic orbit grows in size while evolving their shape, ever so gently, so as to morph onto each other, until they became a single orbit, in high-dimensional state space. Even more intriguing is the Edge of Chaos Kernel’s humble incarnation from the Chua’s Riddle, and its innate ability to exhibit both Turing instability and the yet unresolved Smale’s paradox.

Abstract Low-temperature plasma-processing technologies are essential for material synthesis and device fabrication. Not only the utilization but also the development of plasma-related products and services requires an understanding of the multiscale hierarchies of complex behaviors of plasma-related phenomena, including plasma generation in physics and chemistry, transport of energy and mass through the sheath region, and morphology- and geometry-dependent surface reactions. Low-temperature plasma science and technology play a pivotal role in the exploration of new applications and in the development and control of plasma-processing methods. Presently, science-based and data-driven approaches to control systems are progressing with the state-of-the-art deep learning, machine learning, and artificial intelligence. In this review, researchers in material science and plasma processing, review and discuss the requirements and challenges of research and development in these fields. In particular, the prediction of plasma parameters and the discovery of processing recipes are asserted by…

Abstract In this paper, the utilization of lithographic materials for semiconductor patterning applications based on optical and EUV radiation sources is reviewed. Photoresist platforms including novolac, chemically amplified, chain scission, molecular and inorganic materials are discussed in relation to their chemistry, design, processing, and performance. If the focus of Moore’s Law 1.0 was on laterally scaling the number of components on a single chip, Moore’s Law 2.0 can be understood as the coming era of 3D scaling, where the improved performance from 2D shrinking is replaced by integrated AI, 3D packaging, 3D transistors and new types of memory, among other enablers. As the historical patterning challenges faced by the lithographic industry to scale down semiconductor devices over multiple technology nodes are reviewed from a materials perspective, insight is given regarding future patterning materials utilization and the importance of back-implementing leading-edge materials for Moore’s Law 2.0 patterning applications.

Abstract Printed electronics have been considered to bring about the ICT (Information Communication Technology) revolution. The high-throughput production of the ultra-low-cost printed devices along with the level of integration of logic gates via an all roll-to-roll (R2R) printing method has been the major axes in the revolution. However, there have been certain concerns related to the integration of logic gates via the R2R printing methods. This review paper focuses on the key issues that must be resolved to maintain a uniform threshold voltage ( V th ) value, which can otherwise impede the commercial viability of such devices. Amongst the various factors contributing to the Δ V th value, the ink rheology, web handling, and the disparity in alignment amongst the drain-source electrodes and the gate electrodes due to the limitations of an overlay printing registration accuracy (OPRA) were reviewed to effectively control the variations during the R2R printing process, without including the material’s intrinsic instability factors. Accordingly, a unique design rule for the R2R…

Abstract This review paper discusses the basics of the optically stimulated luminescence (OSL) phenomenon, phosphors for OSL, functional design of OSL phosphors, and application areas of the OSL phenomenon, such as radiation dose monitoring for individual and environmental, computed radiography for medical and dental diagnosis, dating, security, archaeological dating, and autoradiography for drug discovery. Finally, the future prospects of the OSL phenomenon as passive-type dosimeters are mentioned.

Abstract This paper compares three different piston mode designs for temperature-compensated surface acoustic wave (TC-SAW) resonators using SiO 2 /LiNbO 3 structure. It was shown that in rough approximation, phase shift given by extra elements for the piston mode operation is determined by the total mass of extra elements and SiO 2 which overlaid on piston region. The hammer head design without additional metal layers does not work properly due to the weaker impact of the extra elements when the SiO 2 layer is thick. On the other hand, piston mode designs using metal dots or stripes are effective to suppress the transverse mode resonances even when the SiO 2 layer is thick. Although larger metal thickness is preferable for the wideband operation, it also makes the split of main resonance. Thus, the optimal metal thickness can be found from this trade-off, and then the optimal metal width can be found to achieve good transverse mode suppression.

Abstract The dissolution (including the formation of a transient swelling layer) of a resist polymer is key to realizing ultrafine patterning. However, the details of the dissolution of resist polymers remain unclarified. In this study, the swelling and dissolution kinetics of poly(4-hydroxystyrene) (PHS) films in tetramethylammonium hydroxide (TMAH) and tetrabutylammonium hydroxide (TBAH) aqueous solutions were investigated by a quartz crystal microbalance method. PHS is a typical backbone polymer (a dissolution agent) of chemically amplified resists. The swelling and dissolution kinetics of PHS were observed by changing the protection ratio of the hydroxyl groups of PHS and the alkaline concentration in developers. Not only the dissolution rate but also the mode of dissolution depended on the molecular structure of tetraalkylammonium cations. For polymer matrices with strong hydrogen bond networks such as PHS, the penetration of tetrabutylammonium cations is considered to be strongly suppressed by their long alkyl chains.

Abstract Flexible and stretchable electronics present opportunities for transition from rigid bulky devices to soft and conformal systems. However, such technology requires mechanical design and integration strategies to enhance robustness and form factor. In addition, scalable and reliable fabrication pathways are needed to facilitate the high volume manufacturing required to satisfy a growing market demand. This report describes recent advances in design, manufacture, and reliability of flexible and stretchable electronics technology. Flexible concept devices for physiological monitoring are introduced, before discussion of high throughput fabrication of stretchable electronics, then hybrid integration of conventional rigid components on stretchable carrier substrates with an emphasis on a need for further developments in device reliability testing procedures. Finally, consideration is given to transition options for more eco-conscious device constituents. These cases progress flexible and stretchable electronics towards robust, fully integrated, unobtrusive devices incorporating…

Abstract Dy 3+ :Na 2 O-Al 2 O 3 -Gd 2 O 3 -P 2 O 5 (Dy:NAGP) glasses were fabricated to investigate the capability for radiation responses. The influence of Dy 2 O 3 concentration on glass properties was studied. The density and effective atomic number of glass increased with the addition of Dy 2 O 3 content. The glasses absorbed the photons in the ultraviolet, visible light, and near-infrared region. In photoluminescence (PL) spectra, the obvious yellow emission at 574 nm and blue emission at 482 nm of Dy 3+ were both generated by the direct excitation and the Gd–Dy energy transfer. The PL decay time of glasses was in the millisecond order. There was thermal quenching observed in temperature-dependent luminescence (TDL). The radioluminescence (RL) and protonluminescence (PrL) represented the emission pattern of Dy 3+ similarly to PL spectra. The concentration quenching caused 0.50Dy:NAGP glass with the highest PL and RL emission intensity. The X-ray imaging of developed glass using a synchrotron light source was successfully imaged for the first time.

Abstract Radiophotoluminescence (RPL) is a phenomenon in which a luminescence centre is formed in a medium upon interaction with ionizing radiation. The RPL is observed by a conventional photoluminescence (PL) technique, and the PL intensity is proportional to the dose. With the latter feature, the RPL has found successful applications in personnel and environmental dosimetry. However, the conventional materials considered for radiation measurements may be limited to Ag-doped phosphate glass, LiF, and Al 2 O 3 :C,Mg. The recent research works, however, have found a number of additional RPL materials for luminescence dosimetry. The aim of the present paper is to review the series of newly reported RPL materials and potential applications in dosimetry.

Abstract There is high interest in the synergism of thin-film and flexible electronics with additive manufacturing. This review primarily focuses on the prospective developments in convergence with flexible electronics manufacturing technologies. Specifically, this paper covers the latest 3D printing and hybrid manufacturing technologies, the utility of specific types of materials, their functionalization and characterization, post-processing and testing strategies toward fabricating robust and application-specific flexible electronics. Besides exploring the advances in this area of research—it also highlights the limitations and gaps that have been observed in the previous years that will challenge and offer opportunities for advancing research and development. Lastly, the future of 3D-printed flexible electronics is discussed in the aspects of customizability, scalability, and its game-changing and state-of-the-art potential for intelligent sensing, instrumentation, and wearables for various medical, engineering, and industrial applications.

Abstract A concise overview of ferroelectric ceramics and composites, which constitute the backbone of transducer applications such as actuators, sensors, energy harvesting, and storage are provided. For piezoelectric composites based on ferroelectric ceramics, underlying principles are developed using linear equations of state for piezoelectricity and the concepts of crystalline anisotropy, symmetry, composite connectivity, and form factor engineering as unifying themes. Emphasis is given to diphasic piezoelectric composites which have revolutionized transducer engineering in fields such as sonar and medical ultrasound imaging. It is shown that through judicious selection of a ferroelectric ceramic in conjunction with an inactive material such as a polymer or metal, effective material properties exceeding the performance of single-phase ceramics can be achieved. The application of traditional composite strategies and advances in fabrication technologies to rapidly growing fields such as dielectric energy storage and piezoelectric energy harvesting are also discussed.

Abstract Unconventional Computing (UComp) identifies several data processing paradigms focused on exploiting emergent complexity and collective phenomena from various classes of physical substrates. Among UComp platforms, neuromorphic artificial systems aim at the reproduction of the human brain functions in terms of classification and pattern recognition capabilities, overcoming the limitations of traditional digital computers and closing the gap with the energetic efficiency of biological systems. Here we present a model, the receptron, and its physical implementation via a neuromorphic system which opens the way for the exploitation of complex networks of reconfigurable elements. Recently we have reported that nanostructured Au films, fabricated from gold clusters produced in the gas phase, have non-linear and non-local electric conduction properties caused by the extremely high density of grain boundaries and the resulting complex arrangement of nanojunctions. Exploiting these non-linear and non-local properties we produced and tested a device, based on a generalization of the…

Abstract We report on the epitaxial growth of highly conductive degenerated Ge or Si doped β -Ga 2 O 3 and β -(Al x Ga 1− x ) 2 O 3 films by MOCVD. Highly conductive homoepitaxial β -Ga 2 O 3 layers with record conductivities of 2523 and 1581 S cm −1 were realized using Si and Ge dopants. Highly conductive Si doped β -(Al x Ga 1− x ) 2 O 3 films were also grown. The incorporation of Si decreased with the increase in Al content and layer thickness. Record high conductivity of 612 S cm −1 was attained for coherently strained β -(Al 0.12 Ga 0.88 ) 2 O 3 .

Abstract One of the challenges in underwater acoustic positioning is the occurrence of missing measurements and large errors in multipath environments, such as shallow water and harbor areas. In this paper, we propose a new underwater positioning method for multipath environments by using direct wave arrival time groups and database matching. The proposed method accurately measures baseline length from the impulse response of the underwater channel by calculating time window groups that cover the propagation time from the sound source to each hydrophone in advance and then extracting only the impulse response around the propagation time of the direct waves when the sound source exists in a certain region of the measurement space. The performance of the proposed method was experimentally evaluated in a static environment. The results showed that the proposed method achieved an accuracy of 0.03 m and a precision of 0.02 m in a test tank.

Abstract Bond strength is the most reliable criterion of the wafer bonding quality. Water stress corrosion affects the bond strength, corresponding to the measurement atmosphere and residual moisture at the bonding interface. In this study, we developed a new methodology to measure the wafer bond strength including the water stress corrosion effect under the controlled atmospheres, namely, dry atmosphere, wet atmosphere, and vacuum. The developed method experimentally demonstrates the evaluation of the water stress corrosion by the surrounding air and the interfacial water separately. Furthermore, it is also indicated that the water stress corrosion depends on the bonding methods, such that the surface activated bonding using Si intermediate layer has high durability for corrosion and the hydrophilic bonding has low durability. This study will provide a new understanding of the relation between the bonding process and the water stress corrosion effect, especially for the interfacial water.

Abstract The limitations of von Neumann computing systems in terms of information processing speed and energy consumption were overcome using neuromorphic devices. Among these devices, electrolyte-gated synaptic transistors (EGSTs) operated through the movement of ions in electrolytes are suitable devices for neuromorphic computing owing to their efficient energy consumption and biocompatibility. Herein, we explain the basic operating principle of EGSTs and then classify recent studies into four main characteristics: synaptic plasticity, fast switching speed, low energy consumption, and biocompatibility. Finally, we address additional requirements that should be satisfied and limitations that should be overcome for various and expanded applications of EGSTs.

Abstract Radiophotoluminescence (RPL) is an emission phenomenon induced by the photoexcitation of luminescent centers (RPL centers) formed by ionizing radiation. Ag-doped phosphate glasses exhibiting RPL are applied in glass badge dosimeters used for personal monitoring. In this paper, we discuss the RPL behavior of Ag-doped phosphate glasses and their properties along with RPL center formation and disappearance mechanisms. When Ag-doped phosphate glasses are exposed to ionizing radiation, Ag 0 , Ag 2+ , and Ag m n+ , such as Ag 2 + , clusters are formed because Ag + acts as an electron and hole trap. Ag 2+ is formed by the transfer of holes from PO 4 3− tetrahedra. On the other hand, electrons are trapped by Ag + to form Ag 0 . Subsequently, Ag 2 + is formed by the association between Ag 0 and Ag + owing to the diffusion of Ag + . Ag 0 is attributed to blue RPL center, while Ag 2+ and Ag 2 + are attributed to orange RPL centers. Moreover, Ag 2 + and Ag 2+ disappear upon heating at 500 and 673 K, respectively.

Abstract This article presents the fundamentals and an overview of the optical-fiber-based scintillation detectors, which consist of a scintillator and an optical fiber light guide. This type of detector is preferentially used in special applications. In these applications, only a scintillator probe is placed in a severe environment, while a photodetector stays in a mild environment. Additionally, a detector should not disturb an irradiated field. As examples, applications in nuclear reactor physics experiments, medical uses, such as radiation therapies, and severe radiation conditions are reviewed.

Abstract In this work, we fabricated Ga 2 O 3 (001)/Si(100) and Ga 2 O 3 (010)/Si(100) heterointerfaces by surface activated bonding at room temperature and investigated the effect of Si thickness on the thermal stability of the heterointerfaces by heating the bonding samples at different temperatures. The heterointerface with a thin Si exhibited a good thermal stability at 1000 °C. A 4 nm thick intermediate layer with a uniform thickness was formed at the as-bonded Ga 2 O 3 (001)/Si(100) heterointerface, but for the as-bonded Ga 2 O 3 (010)/Si(100) heterointerface, an intermediate layer with a non-uniform thickness was formed. The thickness of both intermediate layers ranged from 3.6 to 5.4 nm and decreased after annealing at 500 °C, followed by an increase after annealing at 1000 °C. The component of the intermediate layer includes Ga, O, and Si atoms.

Abstract We have fabricated III–V gain region/Si waveguide hybrid lasers with an InP-based two-storied ridge structure using direct bonding technology. Continuous-wave operation at a temperature of 20 °C with a threshold current as low as 30 mA was obtained for a hybrid laser consisting of a Fabry–Perot cavity with facets formed on the Si waveguide, and it was achieved thanks to a high optical coupling efficiency of over 80% at the interface between the III–V gain region and the Si waveguide using a two-storied ridge structure and a taper waveguide. The wavelength tunable laser which is comprised of a Si cavity with a loop mirror and double ring filters and III–V gain regions with laser and semiconductor optical amplifier (SOA) sections was demonstrated by utilizing this hybrid structure. It exhibited a wide wavelength tuning range of 48.6 nm and an optical amplification of 10 dB by SOA.

Abstract In this work we investigated the effects of the addition of guanidinium [C(NH 2 ) 3 ; GA] on CH 3 NH 3 PbI 3 perovskite solar cells fabricated at a high temperature of 190°C in atmospheric air. The addition of GA iodide and the insertion of decaphenylpentasilane between the perovskite and hole transport layer improved the external quantum efficiency and short-circuit current density, and the conversion efficiencies were stable after 1 month. X-ray diffraction showed that the lattice constant of the perovskite crystals was increased by the addition of GA, and addition of GA also improved the surface morphology. First-principles calculations on the density of states and band structures showed reduction of the total energy by the addition of GA and the effectiveness of the nitrogen atoms in GA.

Abstract We present SiO 2 /GaN interfaces with a low interface state density and a high breakdown electric field. The SiO 2 films were deposited by plasma-enhanced atomic layer deposition (ALD) using bis(diethylamino)silane and O 2 plasma at 300 °C on n-type GaN (0001) homoepitaxial layers. An interface state density of less than 10 11 cm −2 eV −1 at 0.3 eV below the conduction band edge was confirmed by the conductance method. The value is much lower than those of previously reported ALD-SiO 2 /GaN interfaces (10 12 –10 13 cm −2 eV −1 ). A low fixed charge density at the SiO 2 /GaN interface of 3.7 × 10 11 cm −2 and a high dielectric breakdown field of ~10 MV cm –1 were obtained. Moreover, the interface state density and current−voltage characteristics were further improved by post-deposition annealing at 400 °C in N 2 ambient. Scanning transmission electron microscopy with energy-dispersive X-ray analysis revealed the existence of a GaO x interlayer between SiO 2 and GaN. The unintentionally formed interlayer could be one of the reasons for the improvement of interface properties…

Abstract In this work, we explore pattern formation dynamics across a diffusively coupled Memristor Cellular Nonlinear Network (MCNN), which is composed of identical cells with locally active memristors. We bias the cells on the edge-of-chaos, introduce a systematic design procedure to induce complexity in the array, and extract the element values analytically in a parametric form. In order to enhance the stability and speed of the numerical simulations, we apply a simple variable transformation to a core memristor model while we include the additional effect of parasitic resistors to investigate the locally active dynamics of a VO2 device. We first take a close look at the effect of the linear coupling resistor on pattern formation, and later study how nonlinearly-resistive coupling, based upon tangent hyperbolic law, affect the emergence of complex patterns. Simulation results reveal that a variety of static patterns with different characteristics can emerge across the proposed MCNN.

Abstract The equilibrium electron velocity distribution function (EVDF) and electron transport coefficient in weakly ionized plasmas under crossed DC uniform electric and magnetic fields are calculated via the Boltzmann equation (BE) using physics-informed neural networks (PINNs). The latent solution of the BE is represented by an artificial neural network, and then the neural network is trained to respect the BE. By leveraging automatic differentiation, no mesh generation in velocity space is required, allowing us to calculate the three-dimensional EVDF properly with 0.01% of memory capacity required for the conventional mesh-based method. The EVDF and electron transport coefficients in SF 6 calculated from the PINNs are benchmarked by comparing with those calculated from the Monte Carlo simulation (MCS). In most cases, the relative difference between the electron transport coefficient calculated from the PINNs and MCS is found to be within 1%.

Abstract Film thickening by aerosol deposition (AD) is effective for the fabrication of self-sustained piezoelectric energy harvesting devices. Here we investigated the properties, microstructure, and residual stresses of BaTiO 3 films deposited by AD at different film thicknesses. The Young’s modulus measured by the nanoindentation test showed no thickness dependence; however, it increased from approximately 130– 160 GPa with annealing. Ferroelectric hysteresis curves showed that the increase in film thickness facilitated polarization switching. The microstructure of the films showed no significant changes with the film thickness, while the results of X-ray diffraction and finite element analysis of thermal stress showed that the residual stress after annealing depended on the film thickness. The energy harvesting performance of the BaTiO 3 films deposited by AD may increase owing to the residual stress, rather than the increase in the film thickness.

Abstract The sputtering power dependence of 40 nm thick Al 0.7 Sc 0.3 N ferroelectric properties was characterized from 200 to 300 W. X-ray rocking curve revealed higher orientated growth into the c -axis with higher sputtering power. Films formed by high power showed reduced leakage current with a higher breakdown field, enabling one to apply the high field for ferroelectric switching. A high remnant polarization ( P r ) of 130 μ C cm −2 was obtained with a coercive field ( E c ) of 6 MV cm −1 . The switching cycle test revealed a wake-up effect for all the films; increasing the leakage current and modifying the E c . We anticipate the change is attributed to the existence and the generation of nitrogen vacancies ( V N ) in the films.

Abstract Extreme ultra-violet lithography lithography resolves features below 11 nm. However, photonic and atomic variations at these photon energies and dimensions lead to less than 1:109 potential stochastic defects causing device failures in stable manufacturing processes. This study investigates a methodology intended to identify root causes of stochastic defects with potential mitigation paths. Simulation techniques using pseudo random numbers are used to identify failing photonic and chemical event or distribution combinations. Failing combinations occurring in many photon-chemical configurations are thought to have potential mitigation methodologies. Photonic effects demonstrated significant impacts on stochastic defect formation with approximately 73% of the photon seeds resulting in a failure in at least 60% of the trials. The material results were mixed with large failure quantities that demonstrated low impacts. The photonic shot noise based failures were dominating in this study and these failures will not be mitigated by material enhancement alone.

Abstract Noncontact acoustic inspection methods using acoustic irradiation-induced vibration and laser Doppler vibrometer that can perform defect exploration from a distance are being studied. This method has the feature that it can measure a wide range of measurement objects such as composite materials used for aerospace as well as concrete structures such as tunnels and bridges without contact. From the experimental results, it was found that the increase in noise level due to the decrease in the return light of the laser due to the condition of the measurement surface causes a decrease in the estimation accuracy of defect exploration. Therefore, it has been clarified that the detection accuracy of the defect position can be improved by devising a resonance judgement process for discriminating the signal and noise due to the resonance of the defect portion.

Abstract We demonstrated a coverage-controllable sidewall protective film by controlling the degree of oxidation during plasma-enhanced SiO2 atomic layer deposition (ALD) as a novel technology to suppress bowing in a high-aspect-ratio-contact (HARC) hole etch process. By depositing SiO2 protective film with atomic order on only the top-local region of patterns, to suppress bowing was achieved during HARC etch without the shrinkage of the bottom critical dimension (CD) and etch-stop. In addition, we investigated the parameters that determine the ALD coverage to estimate the coverage profile of sidewall protective film. By analyzing the relationship between activation time and ALD film thickness at each AR, we confirmed that the coverage is determined by the transport of oxygen radical based on the Knudsen transport model. Furthermore, we developed an ALD simulator from the transport model, and successfully estimated the coverage of protective film during etching to improve the verticality of the HARC profile with small bowing-bottom CD bias.

Abstract Thin films of RE Ba 2 Cu 3 O 7− δ ( RE 123, RE : rare earth) having a high-entropy (HE) RE site were successfully fabricated by the pulsed laser deposition method. Solution various RE elements result in increasing configurational entropy of mixing. Critical current density of the HE films exceeds an order of 1.0 MA cm −2 under conditions of T < 20 K and μ 0 H < 7 T. Since the HE effects have a potential to an improvement of irradiation tolerance, the present results encourage further development of HE RE 123 superconducting materials used in the environment with high magnetic fields and irradiation, for example in fusion reactors.

Abstract High crystal quality of vertical Bridgman (VB)-grown (001) β -Ga 2 O 3 single-crystal was confirmed in comparison with edge-defined film-fed growth (EFG)-grown (001) β -Ga 2 O 3 single-crystal. The FWHMs of VB were lower than FWHMs of EFG from X-ray diffraction rocking curve analysis. VB and EFG crystal curvatures were measured as 232.24 m and 45.83 m, respectively. By using transmission and reflection geometry in synchrotron X-ray topography, we unambiguously determined the Burgers vector ( b ) = [010] and [001]. For the VB crystal, screw dislocations with b = [010] and dislocation direction ( t ) = [010] were observed. For the EFG crystal, edge dislocations with b = [001] and t = [010] were observed. In addition, wandering dislocations on the (001) plane with b = [010] for EFG and b = [001] for both EFG and VB were observed. These phenomena indicate that the wandering dislocations were formed by a slip motion on the (001) slip plane.

Abstract This paper describes a highly sensitive microelectromechanical systems (MEMS) accelerometer sensor module to measure micro muscle sounds. Regarding the drift mechanism, we focus on charged particles based on residual water related to MEMS fabrication. Based on temperature programmed desorption analysis and electrical experiments, it is clarified that the drift is caused by negatively charged OH − and is suppressed by vacuum packaging. The noise floor can be reduced by the improved sensitivity of the MEMS accelerometer. The developed MEMS accelerometer can realize the sensitivity of 1157.0 fF/G and Brownian noise of 149.0 nG/√Hz. The developed sensor module consisting of the developed MEMS accelerometer and the capacitance to digital converter can achieve a noise floor of 26.7 μ G/√Hz without any obvious drifts, establishing the target value of less than 50 μ G/√Hz. Therefore, it is confirmed that the developed sensor module can detect micro muscle sounds without contracting a muscle in the frequency range of 20–40 Hz.

Abstract In this note, we demonstrate direct high-temperature growth of single-crystalline GaN on c-plane ScAlMgO4 substrates by metalorganic chemical vapor deposition, without using low-temperature buffers. We found that a trimethylaluminium preflow was crucial to suppress island growth and to achieve uniform mirror-like Ga-polar GaN layers. The preflow time was found to have a direct impact on the crystalline quality of GaN. We also show that thin GaN layers directly grown at high temperature can be used as buffers for the growth of lattice-matched In0.17Ga0.83N layers on ScAlMgO4. The presented results demonstrate the potential of direct growth of GaN on ScAlMgO4.

Abstract We developed a 16 x 8 quantum dot array and CMOS circuit hybrid chip (Q-CMOS). By optimizing the transistor design of Q-CMOS formed by fully depleted (FD)-SOI, it is possible to selectively control each of 16 x 8 quantum dots, and obtained characteristics of quantum dot variation for the first time. Due to the mesoscopic effect, the variation in the characteristics of the quantum dots is larger than the threshold voltage variation of the transistors. Thus, we have obtained an important finding that it is necessary to suppress the variability in order to realize a large-scale quantum computer. We have also confirmed that the characteristics of the quantum dots change depending on the applied gate voltages.

Abstract Isotropic atomic layer etching (ALE) has become an essential technology for the fabrication of logic transistors beyond 2 nm generation and NAND memory with more than 100 layers of stacking. There are promising etching technologies for isotropic ALE, such as reaction-limiting, modification-limiting and ligand exchange processes. In this work, isotropic ALEs undertaken using dry chemical removal (DCR) tools are discussed. In DCR, radicals from plasma are delivered to enhance the surface modification. In addition, the wafer temperature quickly changed due to infrared light and electric static chuck for adsorption and desorption accelerations. Silicon ALE can be realized by the combination of surface oxidation and removal by HF vapor. SiO2 can be etched by the alternate flows of HF and NH3 followed by wafer heating. SiN, TiN and W can be etched at nanometer precision by using fluorination with hydrofluorocarbon radicals and heating. Co and LaO can be etched with diketone exposure and heating.

Abstract 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%.

Abstract We report on the fabrication of integrated active lithium niobate (LN) photonic devices such as waveguide amplifiers and tunable lasers using the photolithography-assisted chemo-mechanical etching (PLACE) technique. Specifically, a maximum internal net gain exceeding 20 dB is achieved in the LN waveguide amplifier, and an electro-optically tunable single-frequency laser with an ultra-narrow linewidth of 454.7 Hz is demonstrated in a high-Q LN microdisk. An electrically driven microring laser is demonstrated by the monolithic integration of a diode laser with an LN microring resonator. We also realize a hybrid integration of passive and active LN microdevices using a continuous lithographic processing approach. The integrated active LN photonic devices have a broad range of applications in light-wave communication, precision sensing and quantum information science.

Abstract The composition dependence of ferroelectric properties was investigated for (111)-oriented epitaxial HfO 2 -CeO 2 solid solution films. Twenty nanometer thick films with different compositions were prepared on (111)ITO//(111)YSZ substrates at room temperature by pulsed laser deposition and subsequent heat treatment at 1000 °C under atmospheric N 2 or O 2 gas flow. All the films had fluorite structures, and their crystal symmetries changed from monoclinic through orthorhombic to tetragonal/cubic phases as x increased for the (Hf 1− x Ce x )O 2 ( x = 0.12–0.25) films. The orthorhombic phase was confirmed by X-ray diffraction analysis for films with x = 0.15 and 0.17. On the other hand, ferroelectric properties were observed in films with x = 0.15–0.20, suggesting that a field-induced phase transition takes place for films with x = 0.20. The film composition showing ferroelectricity was the widest range of doping concentration for reported epitaxial HfO 2 -based films. Their remanent polarization ( P r ) and coercive field ( E c ) were almost identical, at 17–19 μ C cm −2 and…

Abstract The mechanical and dislocation properties of β -Ga 2 O 3 were investigated. Vickers indentations were used to make fractures on the (010)-, (001)-, and (2̅01)-oriented substrates. Sharp cracks along the (100) and (001) planes were observed near the impressions on the (010)-oriented substrate. The cracks were identified as cleavages on the planes, which were parallel to the indentation load. The Vickers hardness was smaller for the (010)-oriented substrate than for the (001)- and (2̅01)-oriented substrates, indicating that the indentation flow activated the cleavages. The small Vickers hardness for the (010)-substrate suggested that the (010) surface is fragile. Dislocation evolution in the (001)-plane was also caused by heat treatment after the indentations were made. This observation indicated that the dislocations were formed by slips on the (001) plane, which suggested that the (001) plane is a slip plane in this material.

Abstract We investigated the photoluminescence wavelength emitted at room temperature from novel stacking faults with a complicated stacking sequence in the epitaxial layer on p-type 4H-SiC substrate. From analysis of photoluminescence imaging and synchrotron X-ray topography, we consider that these complicated stacking faults originate from p-type substrates. We investigated the relationship between photoluminescence energy and stacking sequence of various stacking faults, and confirmed that the maximum number of layers in complicated stacking faults determines the photoluminescence emission energy. This relationship, which was previously only reported for 3C-type stacking faults, follows simple quantum-well theory. We extended this theory to stacking faults with complex structures, focusing on the maximum number of layers.

Abstract Low-temperature plasma plays various roles in industrial material processing as well as provides a number of scientific targets, both from theoretical and experimental points of view. Such rich features in variety are based on its complexities, arising from diverse parameters in constituent gas-phase species, working gas pressure, input energy density, and spatial boundaries. When we consider causalities in these complexities, direct application of machine-learning methods is not always possible since levels of complexities are so high in comparison with other scientific research targets. To overcome this difficulty, progresses in plasma diagnostics and data acquisition systems are inevitable, and the handling of a large number of data elements is one of the key issues for this purpose. In this topical review, we summarize previous and current achievements of visualization, acquisition, and analysis methods for complex plasma datasets which may open a scientific and technological category mixed with rapid machine-learning advancements and their relevant outcomes. Although…

Abstract This paper compares the degradation of sintered silver (s-Ag) die attach between a thermal shock test (TST) and a mechanical cycling test to correctly understand the mechanism of s-Ag die attach failure in power module products during practical operation. A bar-shaped specimen is subjected to two types of four-point bending tests: a centered bending test for bending moment application and a shifted bending test (SBT) for shear force application. The crack path in the SBT is similar to that in the TST, which suggests that shear force has an important role in imitating the degradation and failure of s-Ag in the TST. The crack propagation speed per cycle in the TST is, however, about 4000 times faster than that in the SBT. The lifetime assessment period of the SBT is approximately 1400 times shorter than that of the TST. The difference in failure mechanism between the TST and SBT is discussed by using scanning electron microscopy of the fractured specimens.

Abstract Understanding the interaction of resist materials with the underlayers is important for the development of highly resolving resist materials. In this study, the effect of the surface free energy of the organic underlayer on the dissolution kinetics of poly(4-hydroxystyrene) (PHS) film in a tetramethylammonium hydroxide (TMAH) aqueous developer was investigated by the quartz crystal microbalance (QCM) method. By using 0.95 wt% TMAH standard developer, we observed the correlation between the polar component of the surface free energy of the underlayer and the interaction area of the QCM chart (impedance) near the end of PHS dissolution. The interaction area was defined by the product of impedance change and time. The interaction of the hydroxyl groups of PHS with the underlayer increased with the polar component of the surface free energy of the underlayer. The analytical method developed in this study is useful for the investigation of the resist-underlayer interaction during development.