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This article reports GaN super-heterojunction Schottky barrier diodes (SHJ-SBDs) with substantially improved performance. Metal-2DEG sidewall n-ohmic contacts were deployed to achieve low contact resistance of $0.75~\Omega ~ \cdot ~mm$ , avoiding the risk of abnormally high contact resistance caused by inaccurate etch depth control. A pGaN notch formed near the cathode successfully eliminated excessive hole conduction caused by the sidewall n-ohmic contact. Isolation was improved by a high-energy Al implantation step. The resulting SHJ-SBD exhibited a breakdown voltage (BV) of ~12.5 kV and a specific resistance of 100.8 $\text{m}\Omega ~ \cdot ~cm^{2}$ .

Background: To compare the sensory change and recovery of infraorbital area associated with zygomaticomaxillary and orbital floor fractures and their recoveries and investigate the factors that affect them.Methods: We retrospectively reviewed 652 patients diagnosed with zygomaticomaxillary (n= 430) or orbital floor (n= 222) fractures in a single center between January 2016 and January 2021. Patient data, including age, sex, medical history, injury mechanism, Knight and North classification (in zygomaticomaxillary fracture cases), injury indication for surgery (in orbital floor cases), combined injury, sensory change, and recovery period, were reviewed. The chi-square test was used for statistical analysis.Results: Orbital floor fractures occurred more frequently in younger patients than zygomaticomaxillary fractures (p< 0.001). High-energy injuries were more likely to be associated with zygomaticomaxillary fractures (p< 0.001), whereas low-energy injuries were more likely to be associated with orbital floor fractures (p< 0.001). The sensory changes associated with orbital floor and zygomaticomaxillary fractures were not significantly different (p= 0.773). Sensory recovery was more rapid and better after orbital floor than after zygomaticomaxillary fractures; however, the difference was not significantly different. Additionally, the low-energy group showed a higher incidence of sensory changes than the high-energy group, but the difference was not statistically significant (p= 0.512). Permanent sensory changes were more frequent in the high-energy group, the difference was statistically significant (p= 0.043).Conclusion: The study found no significant difference in the incidence of sensory changes associated with orbital floor and zygomaticomaxillary fractures. In case of orbital floor fractures and high-energy injuries, the risk of permanent sensory impairment should be considered.

Aminotransferases (ATs) are pyridoxal 5'-phosphate-dependent enzymes that catalyze the transamination reactions between amino acid donor and keto acid acceptor substrates. Modern AT enzymes constitute ∼2% of all classified enzymatic activities, play central roles in nitrogen metabolism, and generate multitude of primary and secondary metabolites. ATs likely diverged into four distinct AT classes before the appearance of the last universal common ancestor and further expanded to a large and diverse enzyme family. Although the AT family underwent an extensive functional specialization, many AT enzymes retained considerable substrate promiscuity and multifunctionality because of their inherent mechanistic, structural, and functional constraints. This review summarizes the evolutionary history, diverse metabolic roles, reaction mechanisms, and structure-function relationships of the AT family enzymes, with a special emphasis on their substrate promiscuity and multifunctionality. Comprehensive characterization of AT substrate specificity is still needed to reveal their true metabolic functions in interconnecting various branches of the nitrogen metabolic network in different organisms.

Varistors are technologically important for their large energy handling capabilities and highly nonlinear electrical behavior when voltages above a characteristic switch field are applied. It is generally accepted that the prototypical ZnO–Bi2O3 varistor system forms electrostatic Schottky barriers at grain boundaries in response to residual Bi and other dopants left at grain surfaces during Bi2O3 segregation. While barrier heights can be modulated with formulation and defect chemistry, mechanisms by which dopant locations, defect compensation, and local phases determine varistor behavior are not completely understood. Bulk studies are challenging due to random grain boundary formation and difficulties studying individual boundaries. To circumvent these challenges in the ZnO–Bi2O3 varistor system, we use as-deposited and post-heat-treated thin film ZnO–Bi2O3 prototypes to simulate bulk varistor grain boundary phase formation and investigate resulting defect chemistry. Characterizing interactions between Bi2O3 films deposited on thin film and single-crystal ZnO by XRD and TEM-EDS revealed primarily Zn-out diffusion, resulting in two (Bi2O3)1−x(ZnO)x, or BZO, phases. Using these results, we present a saturated front model correlating changes in Bi2O3 thickness to phase evolution. We subsequently explore the influence of MnO doping leading to substantial changes in phase evolution for post-heat-treated (Mn:ZnO)–Bi2O3 stacks. Dopant-controlled Bi2O3 phase formations yield a 12 × difference, on average, between nonlinear coefficients for γ*- and β*-BZO.

Aromatic L-amino acid decarboxylases (AADCs) catalyze the conversion of aromatic L-amino acids into aromatic monoamines that play diverse physiological and biosynthetic roles in living organisms. For example, dopamine and serotonin serve as major neurotransmitters in animals, whereas tryptamine and tyramine are essential building blocks for synthesizing a myriad of secondary metabolites in plants. In contrast to the vital biological roles of AADCs in higher organisms, microbial AADCs are found in rather a limited range of microorganisms. For example, lactic acid bacteria are known to employ AADCs to achieve intracellular pH homeostasis and engender accumulation of tyramine, causing a toxic effect in fermented foods. Owing to the crucial pharmaceutical implications of aromatic monoamines and their derivatives, synthetic applications of AADCs have attracted growing attention. Besides, recent studies have uncovered that AADCs of human gut microbes influence host physiology and are involved in drug availability of Parkinson's disease medication. These findings bring the bacterial AADCs into a new arena of extensive research for biomedical applications. Here, we review catalytic features of AADCs and present microbial applications and challenges for biotechnological exploitation of AADCs. KEY POINTS: • Aromatic monoamines and their derivatives are increasingly important in the drug industry. • Aromatic L-amino acid decarboxylases are the only enzyme for synthesizing aromatic monoamines. • Microbial applications of aromatic L-amino acid decarboxylases have drawn growing attention.

This letter reports an experimental demonstration of charge-balanced GaN super-heterojunction Schottky barrier diodes (SHJ-SBDs). Charge balance between the n-type delta-doping and the p-type doping was achieved by adjusting the thickness of the pGaN. This device structure enabled scaling of breakdown voltage to over 3 kV, and dynamic switching up to 2.8 kV without using any field-plate.

NAND flash-based storage devices (NFSDs) have been widely employed in various systems, including cloud servers as well as mobile devices. The core component of NFSDs is NAND flash memory (NFM) which has several advantages over the conventional hard disk drives (HDDs). An NFSD typically adopts a bunch of NFMs which are operated in parallel for maximizing the I/O throughput. However, optimizing for performance may not be desirable from the power budget (PB) perspective. In other words, concurrent operations of NFMs often drain inordinate current, which leads to the violation of the PB allocated for a storage device. In this article, we propose a novel power management scheme which maximizes concurrent operations of NFMs under the given power constraint. The proposed method quantizes the given power constraint of an NFSD. A quantum also called token is the basic unit of power management. The proposed power management scheme allocates tokens to NFMs and only the NFMs having enough tokens can perform their operations. We call this method multitoken-based power management (MTPM). The critical issue of MTPM is a deadlock which is resolved with the key allocation scheme. Furthermore, we enhance MTPM to improve performance. The extended method called keyless MTPM (KMTPM) improves the overall performance by relaxing the key acquisition requirement and allowing subatomic operations. In the experimental results, we confirm that the proposed methods always meet the given power constraint. The proposed KMTPM improves throughput by 22.85% compared to state of the art technique. In addition, KMTPM only incurs 3.8% of performance overhead and 0.015% of area overhead.

Toxin–antitoxin (TA) systems regulate key cellular functions in bacteria. Here, we report a unique structure of the Streptococcus pneumoniae HigBA system and a novel antimicrobial agent that activates HigB toxin, which results in mRNA degradation as an antibacterial strategy. In this study, protein structure‐based peptides were designed and successfully penetrated the S. pneumoniae cell membrane and exerted bactericidal activity. This result represents the time during which inhibitors triggered S. pneumoniae cell death via the TA system. This discovery is a remarkable milestone in the treatment of antibiotic‐resistant S. pneumoniae, and the mechanism of bactericidal activity is completely different from those of current antibiotics. Furthermore, we found that the HigBA complex shows a crossed‐scissor interface with two intermolecular β‐sheets at both the N and C termini of the HigA antitoxin. Our biochemical and structural studies provided valuable information regarding the transcriptional regulation mechanisms associated with the structural variability of HigAs. Our in vivo study also revealed the potential catalytic residues of HigB and their functional relationships. An inhibition study with peptides additionally proved that peptide binding may allosterically inhibit HigB activity. Overall, our results provide insights into the molecular basis of HigBA TA systems in S. pneumoniae, which can be applied for the development of new antibacterial strategies. Databases Structural data are available in the PDB database under the accession number 6AF4., HigBA complex shows a crossed‐scissor interface with two intermolecular β‐sheets at both the N and C termini of the HigA antitoxin. The crossed‐scissor constitutes a new type of interface between HigB and HigA. We report a unique structure of the Streptococcus pneumoniae HigBA system and a novel antimicrobial agent that activates HigB toxin, which results in mRNA degradation as an antibacterial strategy.

We present a systematic study on the design of a novel GaN/AlGaN/GaN super-heterojunction Schottky diode. Through physics-based TCAD simulation, we discuss three important design aspects: 1) how to design a GaN/AlGaN/GaN structure to form a high-density 2-D electron gas and to scale it to multiple vertically stacked channels with less risk in reaching the critical thickness limited by the strain in epitaxy; 2) how to reach charge balance and how sensitive is the breakdown voltage with respect to the doping imbalance; and 3) how to ensure that the processes of depleting and accumulating electrons and holes in the structure are fast enough for practical power switching applications.

Plants benefit from symbiotic relationships with their microbiomes. Modifying these microbiomes to further promote plant growth and improve stress tolerance in crops is a promising strategy. However, such efforts have had limited success, perhaps because the original microbiomes quickly re-establish. Since the complex biological networks involved are little understood, progress through conventional means is time-consuming. Synthetic biology, with its practical successes in multiple industries, could speed up this research considerably. Some fascinating candidates for production by synthetic microbiomes are organic nitrogen metabolites and related pyridoxal-5'-phosphate-dependent enzymes, which have pivotal roles in microbe-microbe and plant-microbe interactions. This review summarizes recent studies of these metabolites and enzymes and discusses prospective synthetic biology platforms for sustainable agriculture.

A computational fluid dynamics (CFD) simulation of the molten pool in laser keyhole welding was utilized to acquire temperature data for further metallurgical and mechanical calculations. For the CFD simulation, the governing equations were solved, and the scattering and absorption of the laser beam in the plume were modeled at both the standard atmospheric condition (101,325 Pa) and a vacuum condition (3,000 Pa). A stochastic ray-tracing algorithm was adopted to effectively implement the transmission and scattering of laser bundles of rays. The temperature data from the CFD simulation were then imported to a finite element method (FEM)-based heat conduction analysis to simulate the thermal-metallurgical-mechanical behavior during the cooling phase of the weldment. The strain, residual stress, and distortion were calculated using an elastoplastic model based on the phase transformation-dependent material properties. An element deactivation scheme was used to take care of the zero-strength condition of the elements in the molten pool and keyhole region. The Vickers hardness and the residual stress were measured to verify the simulation model, and the experimental and simulation results had a similar tendency.

We tried to estimate anthropogenic emission sources, including the contributions of neighboring regions, that affect the fine particle concentration (PM2.5) in Daejeon using positive matrix factorization (PMF), concentration weight trajectory (CWT), and modified concentration weight trajectory (MCWT) models in a manner that might overcome the limitations of widely applied hybrid receptor models. Fractions of ion, carbonaceous compound and elements in PM2.5 were 58%, 17%, and 3.6% during January and 49%, 17%, and 14.9% during May to June, respectively. The fraction of ions was higher during winter season, while the fraction of elements was higher during the other season. From the PMF model, seven factors were determined, including dust/soil, sea salt, secondary nitrate/chloride, secondary sulfate, industry, coal combustion, and vehicle sources. Secondary sulfate showed the highest contribution followed by secondary nitrate/chloride and vehicle sources. The MCWT model significantly improved the performance of regional contributions of the CWT model, which had shown a high contribution from the Yellow Sea where there are no emission sources. According to the MCWT results, regional contributions to PM2.5 in the Daejeon metropolitan region were highest from eastern and southern China, followed by Russia, northeastern China, and Manchuria. We conclude that the MCWT model is more useful than the CWT model to estimate the regional influence of the PM2.5 concentrations. This approach can be used as a reference tool for studies to further improve on the limitations of hybrid receptor models.

Varactors, with its capacitance tunable by the applied voltage, are enabling components for reconfigurable RF systems. The performance of a varactor could be characterized by its ${Q}$ -factor and the capacitance tuning ratio. In this article, we seek to develop a new varactor with very high ${Q}$ -factor and large tuning ratio, enabling reconfigurable RF systems with large bandwidth. There were two main innovations in varactor diode design. One was the use of the fin structure, in which the electrodes were placed on two opposite sidewalls of the mesa structure instead of one on top and the other at the bottom or next to the mesa. This design eliminates the extrinsic series resistance in the conventional varactor diode designs, leading to substantially increased ${Q}$ -factor. The other was the use of a multichannel structure. The structure was composed of multiple AlGaN/GaN heterojunctions with high-mobility 2-D electron gas. The high-mobility electron gas helped lowering the intrinsic series resistance, thereby further improving the ${Q}$ -factor.

Summary By integrating a direct electron detector with ultrafast electron microscopy and controlling the quality of the pulsed electron beam, unprecedented spatiotemporal resolution in real-space imaging was achieved under practical pump-probe measurements. As a proof-of-principle demonstration of this new technique, the acoustic vibrations of plasmonic nanorods that were one nanometer amplitude or less and picosecond period upon femtosecond-pulsed photoexcitation were studied at the frictional interfaces. The subnanometer sensitivity in visualizing individual mechanical movement captures new details about acoustic vibrations such as the initial launching of the vibrations and the suppression and release of the vibration at the interfaces.

Dynamic random access memory (DRAM) reliability has become one of the critical issues in embedded systems, as DRAM process technology advances with the increase in bit error probability. Unfortunately, redundant error-correction code (ECC) chips cannot be applied to embedded systems since cores and DRAMs are tightly coupled without a dual in-line memory module (DIMM) slot to account for the form factor, cost, and limited pin count. Therefore, ECC parities are typically placed in the same physical array where the user and system data reside. This coexistence eventually deteriorates data locality, which could be the critical factor in DRAM performance degradation. To address this issue, we propose an ECC scheme called locality-aware compression (LoComp) which integrates a compression algorithm, DRAM data layout, and memory controller especially optimized for embedded systems. We focus on the locality of the dataset and its corresponding metadata, as well as spatial data locality in the design of DRAM data layout, which reduces the number of row activations. The major feature in a compression algorithm is adjusting the misalignment of data streams caused by the data packing in many embedded systems. Moreover, we specialize the memory controller to reduce DRAM access for ECC parities and compression flags. The core technologies for the memory controller are the adoption of a set of small caches for metadata and the support of partial write operation without changing the DRAM interface. LoComp+, an enhanced version of LoComp, further reduces DRAM access for metadata by placing the metadata close to the corresponding data. In the experiment, previous works increase the DRAM access time from 68% to over twice the value compared to ECC DIMM. Whereas, LoComp and LoComp+ show reduced performance degradation by 33% and 48%, respectively. In other words, LoComp and LoComp+ substantially improved performance from between 13% and 33% compared to previous embedded ECC schemes.

Fine control of the ligand and strain effects of secondary elements on the catalytic function of primary elements is critical for developing high-performance bimetallic catalysts. In this paper, we describe a method for making Pd–Ag bimetallic core–shell nanocatalysts with synergistic ligand and Ag strain effects. (PdAg alloy core)@(ultrathin Pd shell) nanocrystals with regulated core compositions and shell thicknesses, as well as a well-defined octahedral shape, could be achieved through precision core–shell engineering. The produced octahedral PdAg@Pd core–shell nanocrystals showed excellent catalytic activity in the creation of hydrogen from the breakdown of formic acid. The highest catalytic activity was attained using PdAg@Pd nanocrystals made up of PdAg alloy cores with an average Pd/Ag atomic ratio of 3.5:1 and a 1.1 atomic layer of Pd shells, which set a new record for catalytic activity.

To create better fuel cell catalysts, effective approaches to generate hybrid materials comprised of intimately connected metal nanocatalysts and nonstoichiometric metal oxides with finely regulated topologies are very desirable. The production of closely connected metal (PtNi alloy)–metal oxide (CeOx, ceria) hybrid nanostructures is reported here using a simple one-pot synthesis technique. Heating a mixed metal (Pt, Ni, and Ce) precursor solution in oleylamine/oleic acid resulted in well-defined PtNi/ceria hybrids, in which PtNi alloy nanodendrites with multiple branches are evenly spread over small-grained ceria nanosheets. The ceria nanosheets in the hybrids have a large number of oxygen vacancies and a high conductivity due to their small grain size. In comparison to carbon-supported counterparts and a commercial catalyst, the prepared PtNi/ceria hybrids exhibited outstanding electrocatalytic activity and stability for both methanol oxidation and oxygen reduction reactions, which can be attributed to the synergistic effects of the Ni component and ceria on the enhancement of the electrocatalytic function. The current technique will be used to create the best multicomponent catalysts for specific processes.

Herein, gold nanoparticles (Au NPs) were synthesized by pulsed laser ablation (PLA) in a mixed-phase solvent of acetonitrile and water. The size of Au NPs and the number of graphitic carbon (GC) layers were controlled by varying the ratio of the solvent mixture. The surface-enhanced Raman scattering (SERS) of the Au NPs was investigated using 10−3 M 4-aminobenzenethiol and 10−4 M 4-nitrobenzenethiol as probe molecules. The SERS activity strongly depended on the nanogaps between particles owing to the formation of hot spots. In the present work, the nanogaps were controlled by changing the amount of GC layers. No GC layers were produced in water, resulting low SERS intensity. In contrast, Au NPs prepared in 30 vol% of acetonitrile showed significant SERS enhancement, which was attributed to the optimal size of the GC-coated NPs and a reasonable gap between them. The obtained results revealed that Au NPs produced by PLA in liquid could be applied in SERS-based microsensors.

The structure-function relationships of toxin-antitoxin (TA) systems from Mycobacterium tuberculosis have prompted the development of novel and effective antimicrobial agents that selectively target this organism. The artificial activation of toxins by peptide inhibitors can lead to the growth arrest and eventual death of bacterial cells. Optimizing candidate peptides by hydrocarbon α-helix stapling based on structural information from the VapBC TA system and in vitro systematic validation led to V26-SP-8, a VapC26 activator of M. tuberculosis. This compound exhibited highly enhanced activity and cell permeability owing to the stabilizing helical propensity of the peptide. These characteristics will increase its efficacy against multidrug-resistant tuberculosis and extensively drug-resistant tuberculosis. Similar approaches utilizing structural and biochemical information for new antibiotic targets opens a new era for developing TB therapies.

The risk assessment of hazardous substances has become increasingly important for the efficient prevention and management of various diseases or accidents caused by increased amounts of hazardous substances in the workplace. In this study, risk assessment was conducted for 36 kinds of hazardous substances requiring management by using qualitative and quantitative risk assessments. Qualitative risk assessment was performed by multiplying the exposure level class by the hazard class according to the Korea Occupational Safety and Health Agency’s (KOSHA) Chemical Hazard Risk Management (CHARM). The quantitative risk assessment was followed by a four-step risk assessment system presented in the Guidelines for Hazard Risk Assessment of Chemicals (KOSHA GUIDE W-6-2016). In the quantitative assessments, we presented a new method of classifying risk levels into four steps, much like qualitative assessments. In this study, the quantitative risk assessment was considered difficult to predict through qualitative risk assessment. Therefore, it is necessary to perform a quantitative risk assessment after a qualitative risk assessment for a higher level of risk assessment.

A coronavirus disease (COVID-19) outbreak associated with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been spreading widely through person-to-person transmission. Various detection approaches have been developed involving quantitative polymerase chain reaction (qPCR) methods, CRISPR-based systems, and direct targeting of specific coronavirus proteins. However, there have only been a few reports on the detection of RNA-dependent RNA polymerase (RdRP), the primer-independent RNA-replicable protein produced by the RNA genes of coronavirus. Here, we introduce a novel diagnostic methodology for COVID-19 using the RNA-directed and de novo RNA replicable function of RdRP. We devised an RNA platform for RdRP-induced transcription (RPRIT) that includes an RNA template that can be directly transcribed by RdRP. By utilizing RPRIT, the presence of RdRP can be readily confirmed within 30 min using isothermal incubation without PCR. This RdRP detection method can provide a new route for rapid diagnosis of RNA virus-infected patients.

Incorporation of catalytically active materials into plasmonic metal nanostructures can efficiently merge the reactivity and energy harvesting abilities of both types of materials for visible light photocatalysis. Here we explore the influence of electromagnetic hotspots in the ability of plasmonic core-shell colloidal structures to induce chemical transformations. For this study, we developed a synthetic strategy for the fabrication of Au nanoparticle (NP) trimers in aqueous solution through fine controlled galvanic replacement between Ag nanoprisms and Au precursors. Core-shell Au@M NP trimers with catalytically active metals (M = Pd, Pt) were subsequently synthesized using Au NP trimers as templates. Our experimental and computational results highlight the synergy of geometry and composition in plasmonic catalysts for plasmon-driven chemical reactions.

Aromatic L-amino acid decarboxylases (AADCs) are ubiquitously found in higher organisms owing to their physiological role in the synthesis of neurotransmitters and alkaloids. However, bacterial AADC has not attracted much attention because of its rather limited availability and narrow substrate range. Here, we examined the biochemical properties of AADC from Bacillus atrophaeus (AADC-BA) and assessed the synthetic feasibility of the enzyme for the preparation of monoamine neurotransmitters. AADC-BA was expressed in Escherichia coli BL21(DE3) and the purified enzyme showed a specific activity of 2.6 ± 0.4 U/mg for 10 mM L-phenylalanine (L-Phe) at 37 °C. AADC-BA showed optimal pH and temperature ranges at 7-8 and 37-45 °C, respectively. The KM and kcat values for L-Phe were 7.2 mM and 7.4 s-1, respectively, at pH 7.0 and 37 °C. Comparison of the kinetic constants at different temperatures revealed that the temperature dependency of the enzyme was mainly determined by catalytic turnover rather than substrate binding. AADC-BA showed a broad substrate scope for various aromatic amino acids, including L-Phe, L-tryptophan (610% relative to L-Phe), L-tyrosine (12%), 3,4-dihydroxyphenyl-L-alanine (24%), 5-hydroxy-L-tryptophan (L-HTP, 71%), 4-chloro-L-phenylalanine (520%), and 4-nitro-L-phenylalanine (450%). Homology modeling and docking simulations were carried out and were consistent with the observed substrate specificity. To demonstrate the synthetic potential of AADC-BA, we carried out the production of serotonin by decarboxylation of L-HTP. The reaction yield of serotonin reached 98% after 1 h at the reaction conditions of 50 mM L-HTP and 4 U/mL AADC-BA. Moreover, we carried out preparative-scale decarboxylation of L-Phe (100 mM in 40-mL reaction mixture) and isolated the resulting 2-phenylethylamine (51% recovery yield). We expect that the broad substrate specificity of AADC-BA can be exploited to produce various aromatic biogenic amines. KEY POINTS: • AADC-BA showed broad substrate specificity for various aromatic amino acids. • The substrate specificity was elucidated by in silico structural modeling. • The synthetic potential of AADC-BA was demonstrated for the production of biogenic amines.

We demonstrated gallium nitride (GaN) based negative capacitance field-effect transistors (NCFETs) that achieve steep switching operation. Ferroelectric phase characteristics were successfully demonstrated using a 10 nm thick undoped-HfO2 ferroelectric thin film fabricated through atomic layer deposition. The HfO2 metal-ferroelectric-metal (MFM) capacitor was connected in series with the gate electrode of a recessed normally-off AlGaN/GaN MOS-HFET. The forward/reverse subthreshold slopes were dramatically reduced from 104/105 to 22/23 mV/dec.

We introduce a horizontal array capacitor with nine capacitances in a single body using an organic dielectric layer impregnated with glass fiber as a prepreg sheet. An organic solid horizontal array capacitor with a dielectric of prepreg materials of the epoxy type can implement the nine capacitances in a single body via a unique simple lamination and cutting process. We then investigate the basic electrical properties of a horizontal array capacitor. The organic solid array capacitors with five electrodes and four dielectrics are Cu/PPG layer/Cu/PPG layer/Cu/PPG layer/Cu/PPG layer/Cu with a horizontal array structure. The size of a completed array capacitor is 2.85 × 2.85 mm. The height of the fabricated array capacitor in the vertical direction is 0.5 mm, with nine capacitances possessing a series-type structure. The average capacitance value of C1, C2, C3, and C4 is 1.98 nF, and each tolerance has a value within 1% based on the average value. The temperature change rate in the capacitance maintains a nearly linear characteristic, but the rate of change tends to increase finely from 120°C or more. The capacitance values of C5, C6, and C7 with the parallel circuit were measured according to the voltage. Impedance and ESR (equivalent series resistor) of C1 were measured according to frequency and temperature.

We investigated the distributions and the energy levels of defects in SiO2/AlGaN/GaN highelectron-mobility transistors (HEMTs) by using frequency-dependent (F-D) capacitance-voltage (C-V) measurements with resonant optical excitation. A Schottky barrier (SB) and a metal-oxidesemiconductor (MOS) HEMT were prepared to compare the effects of defects in their respective layers. We also investigated the effects of those layers on the threshold voltage (V th ). A drastic voltage shift in the C-V curve at higher frequencies was caused by the large number of defect levels in the SiO2/GaN interface. A significant shift in V th with additional light illumination was observed due to a charging of the defect states in the SiO2/GaN interface. The voltage shifts were attributed to the detrapping of defect states at the SiO2/GaN interface.