Termination Area Research Articles

Expanding the dose window of step-etched space-modulated JTE for ultrahigh voltage 4H-SiC devices

A step-etched space-modulated junction termination extension (SE-SM-JTE) is proposed for ultrahigh voltage (≥10 kV) 4H-SiC devices in this work. The proposed structure creates a stepped effective JTE dose profile by introducing the step etching into space-modulated JTE (SM-JTE), which shows great merits in the compromises of the JTE dose window, termination efficiency, termination area, and the complexity of the fabrication process. According to the TCAD simulation results, the SE-SM-JTE with a length of 300 μm (3 times the drift layer thickness) obtains a wide implantation dose window of ±47 % above 12 kV, achieving a wide tolerance to JTE dose and surface fixed charge. The maximum breakdown voltage (BV) of the proposed SE-SM-JTE is 13.8 kV, exhibiting a termination efficiency of 92 %. Moreover, the proposed JTE structure requires only a single ion implantation and subsequent two etchings, which facilitates the fabrication feasibility in ultrahigh voltage 4H-SiC devices.

Measurements of ear-canal geometry from high-resolution CT scans of human adult ears

Description of the ear canal’s geometry is essential for describing peripheral sound flow, yet physical measurements of the canal’s geometry are lacking and recent measurements suggest that older-adult-canal areas are systematically larger than previously assumed. Methods to measure ear-canal geometry from multi-planar reconstructions of high-resolution CT images were developed and applied to 66 ears from 47 subjects, ages 18–90 years. The canal’s termination, central axis, entrance, and first bend were identified based on objective definitions, and the canal’s cross-sectional area was measured along its canal’s central axis in 1–2 mm increments. In general, left and right ears from a given subject were far more similar than measurements across subjects, where areas varied by factors of 2–3 at many locations. The canal areas varied systematically with age cohort at the first-bend location, where canal-based measurement probes likely sit; young adults (18–30 years) had an average area of 44mm2 whereas older adults (61–90 years) had a significantly larger average area of 69mm2. Across all subjects ages 18–90, measured means ± standard deviations included: canals termination area at the tympanic annulus 56±8mm2; area at the canal’s first bend 53±18mm2; area at the canal’s entrance 97±24mm2; and canal length 31.4±3.1mm2.

Termination area design for reduced leakage current and improved ruggedness of HV IGBTs

Abstract A termination design which efficiently reduces leakage current and improves robustness of very high voltage insulated gate bipolar transistors (IGBTs) (>3.3 kV) without adversely affecting other device characteristics is presented here. Proposed design uses a selectively formed Buried N+ layer in the N-buffer under the termination region. Optimised placement of the N+ buried regions reduces carrier modulation in the termination area thus lowering the leakage current and reducing maximum temperature during the reverse bias safe operating area tests. This improves dynamic ruggedness of the IGBT without deteriorating other device characteristics.

Deep learning-based diagnosis models for onychomycosis in dermoscopy.

Onychomycosis is a common disease. Emerging noninvasive, real-time techniques such as dermoscopy and deep convolutional neural networks have been proposed for the diagnosis of onychomycosis. However, deep learning application in dermoscopic images has not been reported. To explore the establishment of deep learning-based diagnostic models for onychomycosis in dermoscopy to improve the diagnostic efficiency and accuracy. We evaluated the dermoscopic patterns of onychomycosis diagnosed at Sun Yat-sen Memorial Hospital, Guangzhou, China, from May 2019 to February 2021 and included nail psoriasis and traumatic onychodystrophy as control groups. Based on the dermoscopic images and the characteristic dermoscopic patterns of onychomycosis, we gain the faster region-based convolutional neural networks to distinguish between nail disorder and normal nail, onychomycosis and non-mycological nail disorder (nail psoriasis and traumatic onychodystrophy). The diagnostic performance is compared between deep learning-based diagnosis models and dermatologists. All of 1,155 dermoscopic images were collected, including onychomycosis (603 images), nail psoriasis (221 images), traumatic onychodystrophy (104 images) and normal cases (227 images). Statistical analyses revealed subungual keratosis, distal irregular termination, longitudinal striae, jagged edge, and marble-like turbid area, and cone-shaped keratosis were of high specificity (>82%) for onychomycosis diagnosis. The deep learning-based diagnosis models (ensemble model) showed test accuracy /specificity/ sensitivity /Youden index of (95.7%/98.8%/82.1%/0.809) and (87.5%/93.0%/78.5%/0.715) for nail disorder and onychomycosis. The diagnostic performance for onychomycosis using ensemble model was superior to 54 dermatologists. Our study demonstrated that onychomycosis had distinctive dermoscopic patterns, compared with nail psoriasis and traumatic onychodystrophy. The deep learning-based diagnosis models showed a diagnostic accuracy of onychomycosis, superior to dermatologists.

Are work zones and connected automated vehicles ready for a harmonious coexistence? A scoping review and research agenda

The recent advent of connected and automated vehicles (CAVs) is expected to transform the transportation system. CAV technologies are being developed rapidly and they are foreseen to penetrate the market at a rapid pace. On the other hand, work zones (WZs) have become common areas on highway systems as a result of the increasing construction and maintenance activities. The near future will therefore bring the coexistence of CAVs and WZs which makes their interaction inevitable. WZs expose all vehicles to a sudden and complex geometric change in the roadway environment, something that may challenge many of CAV navigation capabilities. WZs however also impose a space contraction resulting in adverse traffic impacts, something that legitimately calls for benefiting from the highly efficient CAV functions. CAVs should be able to reliably traverse WZ geometry and WZs should benefit from CAV intelligent functions. This paper reviews the state-of-the-art and the key concepts, opportunities, and challenges of deploying CAV systems at WZs. The reviewed subjects include traffic performance and behaviour, technologies and infrastructure, and regulatory considerations. Eighteen CAV mobility, safety, and environmental concepts and functions were distributed over the WZ area which was subdivided into five segments: further upstream, approach area, queuing area, WZ activity, and termination area. In addition, among other topics reviewed and discussed are detection of WZ features, smart traffic control devices, various technologies at connected WZs, cross-border harmonization, liability, insurance, and privacy. The paper also provides a research agenda with a list of research needs supported by experts rating and inputs. The paper aims to provide a bird’s eye view, but with necessary details that can benefit researchers, practitioners, and transportation agencies.

Safety Impact of Connected Vehicles on Driver Behavior in Rural Work Zones under Foggy Weather Conditions

Work zone safety is one of the paramount goals of the safety community. Safety in WZs is a particular concern under foggy conditions as they represent an exogenous factor contributing to high variability in driver behavior. In line with the Connected Vehicle (CV) Pilot Deployment Program on Interstate-80 (I-80) in Wyoming, this study investigates the safety benefits of CV Work Zone Warning (WZW) applications on driver behavior during foggy weather conditions. A work zone (WZ) was simulated using VISSIM in four sequential areas, including the advance warning, transition, activity, and termination area. The effect of drivers’ increased situational awareness under the effect of WZW was calibrated in VISSIM based on the results of a high-fidelity driving simulator experiment. Various Surrogate Measures of Safety (SMoS), including Time-To-Collision (TTC), Time Exposed Time-to-collision (TET), Time-Integrated Time-to-collision (TIT), and Modified Deceleration Rate to Avoid Crash (MDRAC), were employed to quantify the safety performance of CVs under varying CV Market Penetration Rates (MPRs). According to the results of TTC and MDRAC, it was found that an increase in CV-MPR enhances the safety performance of the WZ area. Findings showed that, under foggy weather conditions, the advance warning area had the highest TIT and TET values. Furthermore, it was revealed that an increase in MPR of up to 60% on I-80 would reduce mean speeds and the standard deviation of speed at each of the WZ areas, leading to more speed harmonization and minimizing the crash risk in WZs.

Improved HV-H3TRB robustness of a 1700 V IGBT chip set in standard power modules

High Voltage-High Humidity High Temperature Reverse Bias (HV-H3TRB) is the standard to test power modules for humidity driven degradation. This test has contributed significantly to detect and fix weak points in device designs, especially of the junction termination. Thus, the latest junction termination designs offer unprecedented humidity robustness. This work reports on a comparative HV-H3TRB test on 1.7 kV IGBT modules with chips sets of two consecutive generations tested at two different test voltages each. The progress in the chip design and material composition provides more than an order of magnitude better performance in HV-H3TRB. Failure analyses have indicated vastly reduced degrees of aluminium corrosion in the junction termination area, leading to a slowed down failure mechanism.

A Fork Trap in the Chromosomal Termination Area Is Highly Conserved across All Escherichia coli Phylogenetic Groups.

Termination of DNA replication, the final stage of genome duplication, is surprisingly complex, and failures to bring DNA synthesis to an accurate conclusion can impact genome stability and cell viability. In Escherichia coli, termination takes place in a specialised termination area opposite the origin. A ‘replication fork trap’ is formed by unidirectional fork barriers via the binding of Tus protein to genomic ter sites. Such a fork trap system is found in some bacterial species, but it appears not to be a general feature of bacterial chromosomes. The biochemical properties of fork trap systems have been extensively characterised, but little is known about their precise physiological roles. In this study, we compare locations and distributions of ter terminator sites in E. coli genomes across all phylogenetic groups, including Shigella. Our analysis shows that all ter sites are highly conserved in E. coli, with slightly more variability in the Shigella genomes. Our sequence analysis of ter sites and Tus proteins shows that the fork trap is likely to be active in all strains investigated. In addition, our analysis shows that the dif chromosome dimer resolution site is consistently located between the innermost ter sites, even if rearrangements have changed the location of the innermost termination area. Our data further support the idea that the replication fork trap has an important physiological role that provides an evolutionary advantage.

A temporal investigation of crash severity factors in worker-involved work zone crashes: Random parameters and machine learning approaches

In the context of work zone safety, worker presence and its impact on crash severity has been less explored. Moreover, there is a lack of research on contributing factors by time-of-day. To accomplish this, first a mixed logit model was used to determine statistically significant crash severity contributing factors and their effects. Significant factors in both models included work-zone-specific characteristics and crash-specific characteristics, where environmental characteristics were only significant in the daytime model. In addition, results from parameter transferability test provided evidence that daytime and nighttime crashes need to be modeled separately. Further, to explore the nonlinear relationship between crash severity levels and time-of-day, as well as compare the effects of variables to that of the logit model and assess prediction performance, a Support Vector Machines (SVM) model trained by Cuckoo Search (CS) algorithm was utilized. Opening the SVM black-box, a variable impact analysis was also performed. In addition to the characteristics identified in the logit models, the SVM models also included the impacts of vehicle-level characteristics. The variable impact analysis illustrated that the termination area of the work zone is most critical for both daytime and nighttime crashes, as this location has the highest increase in severe injury likelihood. In summary, results of this study demonstrate that work zone crashes need to be modeled separately by time-of-day with a high level of confidence. Furthermore, results show that the CS-SVM models provide better prediction performance compared to the SVM and logit models.

Atomistic Mechanism of 4 H - SiC/SiO2 Interface Carrier-Trapping Effects on Breakdown-Voltage Degradation in Power Devices

The $\mathrm{Si}\mathrm{C}/{\mathrm{Si}\mathrm{O}}_{2}$ interface in the termination area is a crucial component in limiting high-temperature reverse-bias (HTRB) reliability for $\mathrm{Si}\mathrm{C}$-based high-voltage devices. However, the atomic structure and carrier-trapping behavior of the $\mathrm{Si}\mathrm{C}/{\mathrm{Si}\mathrm{O}}_{2}$ interface defects therein and the underlying physical mechanisms of breakdown-voltage (${V}_{\mathrm{BD}}$) variation are still largely unclear. Here, the $\mathrm{Si}\mathrm{C}/{\mathrm{Si}\mathrm{O}}_{2}$ interface defects of 4H-$\mathrm{Si}\mathrm{C}$ gate turn-off (GTO) thyristors before and after HTRB stress are investigated by transient capacitance measurements and density-functional-theory (DFT) calculations. It is found that the bias stress at 4.4 kV enlarges the interface state density at ${E}_{C}\ensuremath{-}0.60$ eV to ${E}_{C}\ensuremath{-}1.33$ eV by electron capturing. As a result, the negative interface charge is generated. As high-resolution transmission electron microscopy reveals the presence of excess carbon near the $\mathrm{Si}\mathrm{C}$ surface, DFT calculations are focused on carbon-related interface defects to clarify the atomic and electronic structures of the $\mathrm{Si}\mathrm{C}/{\mathrm{Si}\mathrm{O}}_{2}$ interface trap and assign them to negatively charged excess split-interstitial carbon at the interface. Furthermore, technical computer-aided-design simulation further proves that the negatively charged $\mathrm{Si}\mathrm{C}/{\mathrm{Si}\mathrm{O}}_{2}$ interface defect is the main cause for the observed ${V}_{\mathrm{BD}}$ degradation after the HTRB test, which leads to a strong electric field crowding effect. These results not only provide deep physical insights underlying ${V}_{\mathrm{BD}}$ degradation in HTRB-stressed high-voltage devices, but are also of significant importance in the optimizations of device structure and oxidation technology for $\mathrm{Si}\mathrm{C}/{\mathrm{Si}\mathrm{O}}_{2}$ interfaces in high-voltage $\mathrm{Si}\mathrm{C}$ devices.

Dependence of humidity-stress impact on passivation film for edge termination area in 4H-SiC diodes

High-temperature reverse bias (HTRB) and high-humidity HTRB (H3TRB) tests were carried out on 4H-SiC diodes to investigate the mechanism of charge accumulation at the SiO2/SiC interface in the edge termination area, which causes breakdown voltage. To analyze the distribution of charge density during these tests, a differentiated capacitance-reverse-voltage method was used. From comparing the results of the HTRB and H3TRB tests, it was clarified that the H3TRB test induces a negative charge at the SiO2/SiC interface but induces a positive charge at the polyimide/SiC interface. We concluded that the origin of the increase in charge density induced by high-humidity stress is the corrosion of the anode metal, which depends on the surface film of the SiC in the termination area, namely, the SiO2/SiC or polyimide/SiC interface. The induced charge mechanism can become a guideline for designing highly reliable SiC power devices against humidity stress.

1200 V / 200 A V-Groove Trench MOSFET Optimized for Low Power Loss and High Reliability

1200 V / 200 A V-groove trench MOSFET optimized to achieve low power loss, high oxide reliability under a drain bias condition and high avalanche ruggedness is shown in this paper. We revealed a relationship between the lifetime under a high temperature reverse bias condition and the oxide electric field. In accordance with the results of the test, the 1200 V / 200 A trench MOSFET showed an improvement in the tradeoff between the on-resistance and oxide electric field with the presence of current spreading layers. In order to obtain low on-resistance and high avalanche ruggedness at the same time, buried guard ring structures, which made the blocking voltage of the edge termination area higher than that of the active area, was developed. The fabricated MOSFETs demonstrated a low specific on-resistance of 3.1 mΩ cm2. A predicted lifetime of 200 years under a high temperature drain bias condition of 1200 V was achieved by the optimized design. A short circuit withstand time of 6 μs and a high avalanche energy of 7.8 J/cm2 were shown.

(Invited) Bio-Inspired High-Performance and Multi-Functional Surfaces Tailored By Atmospheric Pressure Plasmas

This talk will highlight our recent work on the development of atmospheric pressure plasma tools and methods to modify the roughness, surface chemistry, and wettability of dielectric, polymer, and textile surfaces. Dielectric barrier discharges (DBD) at both low (60 Hz) and high frequency (10s kHz, pulsed), along with RF (13.56 MHz) microplasma jets, were used to directly create hydrophobic/philic areas and bio-reactive groups (-COOH, -CFx, -NH2) on surfaces for subsequent immobilization of enzymes and bioactive compounds for sensing, environmental threat detection, and chemical agent destruction. The goal of the work is to provide fundamental understanding of how interfacial properties, namely chemical termination and surface area, roughness geometry and length scale, and incorporation of 2D/3D nanostructures, can impart multi-functionality to different material surfaces. The effect of various plasma operating conditions (e.g., streamer density, frequency, gas atmosphere, power) on wettability contrast, roughness, surface chemistry, and enzyme grafting and viability for different model surfaces will be discussed.

Too Much of a Good Thing: How Ectopic DNA Replication Affects Bacterial Replication Dynamics.

Each cell division requires the complete and accurate duplication of the entire genome. In bacteria, the duplication process of the often-circular chromosomes is initiated at a single origin per chromosome, resulting in two replication forks that traverse the chromosome in opposite directions. DNA synthesis is completed once the two forks fuse in a region diametrically opposite the origin. In some bacteria, such as Escherichia coli, the region where forks fuse forms a specialized termination area. Polar replication fork pause sites flanking this area can pause the progression of replication forks, thereby allowing forks to enter but not to leave. Transcription of all required genes has to take place simultaneously with genome duplication. As both of these genome trafficking processes share the same template, conflicts are unavoidable. In this review, we focus on recent attempts to add additional origins into various ectopic chromosomal locations of the E. coli chromosome. As ectopic origins disturb the native replichore arrangements, the problems resulting from such perturbations can give important insights into how genome trafficking processes are coordinated and the problems that arise if this coordination is disturbed. The data from these studies highlight that head-on replication–transcription conflicts are indeed highly problematic and multiple repair pathways are required to restart replication forks arrested at obstacles. In addition, the existing data also demonstrate that the replication fork trap in E. coli imposes significant constraints to genome duplication if ectopic origins are active. We describe the current models of how replication fork fusion events can cause serious problems for genome duplication, as well as models of how such problems might be alleviated both by a number of repair pathways as well as the replication fork trap system. Considering the problems associated both with head-on replication-transcription conflicts as well as head-on replication fork fusion events might provide clues of how these genome trafficking issues have contributed to shape the distinct architecture of bacterial chromosomes.

Characteristic and Robustness of Trench Floating Limiting Rings for 4H-SiC Junction Barrier Schottky Rectifiers

In this letter, planar floating limiting rings (FLRs) and trench FLRs with different trench depths for the 4H-SiC junction barrier Schottky (JBS) rectifiers are analyzed and compared with simulations and experiments. Compared with the planar FLRs, the experimental results present that the first ring spacing window that termination efficiency exceeds 80% of the parallel plane breakdown voltage (BV) can be widened and termination area can be reduced at the same BV by adopting the trench FLRs. The simulations also indicate that there is an optimal trench depth for the trench FLRs and a smaller sidewall angle can achieve better device performance. Additionally, the repetitive avalanche current stress measurements imply that the trench FLRs has better robustness regarding the BV shift, achieving better device reliability.

Experimental study and characterization of an ultrahigh-voltage Ni/4H–SiC junction barrier Schottky rectifier with near ideal performances

Abstract An ultra-high voltage SiC JBS (silicon carbide junction barrier Schottky) rectifier utilizing a novel area-efficient multi-zone gradient modulated field limiting ring (MGM-FLR) technique have been fabricated, measured, and analysed in this paper. Ni-Schottky metal with a high barrier height is used to achieve a better trade-off between the on-resistance and the breakdown voltage. MGM-FLR, which is implanted simultaneously with the P+ grids within the active area of the device, forms a similar variation of lateral doping to mitigate the electric field crowding caused by junction curvature effect and obtains a maximum blocking voltage with minimally sized edge termination area. The fabricated device is tested to obtain a specific on-resistance is 140 mΩ cm2 and a reverse breakdown voltage of 14 kV with the leakage current of 10 μA, which is quite close to the theoretical value of parallel plane junction calculated using the device parameter of drift region 100 μm and the concentration 5 × 1014 cm−3. The highest Baliga's figure-of-merit (BFOM) 5.6 GW/cm2 was obtained for the proposed devices. Furthermore, the distribution of the extracted barrier height versus ideality factor on the wafer are demonstrated using I–V method. Impacts of ring spacing and zone of MGM-FLR termination on SiC device reverse blocking performance are also investigated in detail.

Multizone Gradient-Modulated Guard Ring Technique for Ultrahigh Voltage 4H-SiC Devices With Increased Tolerances to Implantation Dose and Surface Charges

An area efficient multizone gradient-modulated guard ring (MGM-GR) edge termination technique is proposed, fabricated, and analyzed for 10-kV class silicon carbide devices without extra process steps or masks, which provides a better tradeoff between near ideal blocking capabilities and technological process complexity. The edge termination region is divided into multiple zones by employing MGM-GR technique, which forms a similar linearly graded doping profile to relieve the amount of electric field crowding at the periphery of the active area and achieve a maximum blocking voltage with wide tolerance to implantation dose. The proposed device shows not less than a 35% reduction in edge termination area in comparison with a conventional equally spaced ring at a breakdown voltage of 10 kV. Moreover, MGM-GR shows good tolerances to breakdown voltage for total implant dose and interface charges. With the application of MGM-GR technique to SiC MOSFET with a 100- $\mu \text{m}$ -thick N− epilayer doped to $5 \times 10^{14}$ cm $^{-3}$ , the measured breakdown voltage is 13.6 kV at $10~\mu \text{A}$ . This voltage is nearly 95% of the theoretical value calculated for a 1-D structure. Simulated and measured characteristics show that MGM-GR structure is a candidate for an ultrahigh voltage power device to maximize power density and driving down system complexity.

A role for 3' exonucleases at the final stages of chromosome duplication in Escherichia coli.

Chromosome duplication initiates via the assembly of replication fork complexes at defined origins, from where they proceed in opposite directions until they fuse with a converging fork. Recent work highlights that the completion of DNA replication is highly complex in both pro- and eukaryotic cells. In this study we have investigated how 3′ and 5′ exonucleases contribute towards the successful termination of chromosome duplication in Escherichia coli. We show that the absence of 3′ exonucleases can trigger levels of over-replication in the termination area robust enough to allow successful chromosome duplication in the absence of oriC firing. Over-replication is completely abolished if replication fork complexes are prevented from fusing by chromosome linearization. Our data strongly support the idea that 3′ flaps are generated as replication fork complexes fuse. In the absence of 3′ exonucleases, such as ExoI, these 3′ flaps can be converted into 5′ flaps, which are degraded by 5′ exonucleases, such as ExoVII and RecJ. Our data support the idea that multiple protein activities are required to process fork fusion intermediates. They highlight the complexity of fork fusions and further support the idea that the termination area evolved to contain fork fusion-mediated pathologies.

Replication-transcription conflicts trigger extensive DNA degradation in Escherichia coli cells lacking RecBCD

Bacterial chromosome duplication is initiated at a single origin (oriC). Two forks are assembled and proceed in opposite directions with high speed and processivity until they fuse and terminate in a specialised area opposite to oriC. Proceeding forks are often blocked by tightly-bound protein-DNA complexes, topological strain or various DNA lesions. In Escherichia coli the RecBCD protein complex is a key player in the processing of double-stranded DNA (dsDNA) ends. It has important roles in the repair of dsDNA breaks and the restart of forks stalled at sites of replication-transcription conflicts. In addition, ΔrecB cells show substantial amounts of DNA degradation in the termination area. In this study we show that head-on encounters of replication and transcription at a highly-transcribed rrn operon expose fork structures to degradation by nucleases such as SbcCD. SbcCD is also mostly responsible for the degradation in the termination area of ΔrecB cells. However, additional processes exacerbate degradation specifically in this location. Replication profiles from ΔrecB cells in which the chromosome is linearized at two different locations highlight that the location of replication termination can have some impact on the degradation observed. Our data improve our understanding of the role of RecBCD at sites of replication-transcription conflicts as well as the final stages of chromosome duplication. However, they also highlight that current models are insufficient and cannot explain all the molecular details in cells lacking RecBCD.

Two Mechanisms of Charge Accumulation in Edge Termination of 4H-SiC Diodes Caused by High-Temperature Bias Stress and High-Temperature and High-Humidity Bias Stress

High-temperature reverse bias (HTRB) and high-humidity HTRB (H3TRB) tests were carried out on 4H-SiC diodes to investigate the mechanism of charge accumulation at the SiO2/SiC interface in the edge termination area, which causes breakdown voltage instability. A differentiated capacitance–reverse voltage method was used to analyze the charge distribution. With HTRB, the charge accumulation occurred in the edge termination area with a passivation of O2 oxidation film and the one with a NO oxidation film. In contrast, no charge accumulation occurred in the edge termination area without SiO2 as a passivation film. With H3TRB, however, the charge accumulation took place not only in the edge of termination area with O2 oxidation but also in the edge termination area without SiO2. The results of two tests revealed that the edge termination area without SiO2 has little tolerance to charge accumulation in a high-humidity and high-temperature atmosphere, although it has tolerance in a high-temperature atmosphere. The difference of tolerance depending on stress condition suggests that there are two mechanisms of charge accumulation, one related to the SiO2/SiC interface and triggered by applying temperature and voltage stress without humidity and the other does not related to the interface and triggered by applying temperature and voltage stress with humidity.