Vertical Barrier Research Articles

Systematic Design and Parametric Analysis of GaN Vertical Trench MOS Barrier Schottky Diode With p-GaN Shielding Rings

We report GaN vertical trench MOS barrier Schottky (TMBS) diodes with embedded p-GaN shielding rings (SRs) and systematically investigate the impact of different structural parameters of the p-GaN SRs on the breakdown performance of the GaN-based vertical TMBS diodes by numerical simulation. The charge coupling effect by the embedded p-n junction at the bottom of the trench homogenize the electric field at the trench corner and alleviate the electric field crowding effect at the Schottky contact region, which can effectively avoid the premature breakdown and improve the reverse blocking capability of the TMBS diodes. The p-GaN SRs can also broaden the overlapped depletion region and shift the pinch-off point into the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> -GaN drift region, thus facilitating the 2-D depletion in the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> -GaN drift layer and boosting the breakdown performance of the conventional TMBS diodes. We found that the doping concentration, thickness, and the width of the p-GaN SRs are closely associated with the electric field distribution and the reverse breakdown characteristics of the GaN-based vertical TMBS diodes. The vertical TMBS diodes with optimal p-GaN SR parameters featured a dramatic improvement in the breakdown voltage from 907 to 1281 V, without an obvious degradation in the ON performance. The proposed TMBS diodes with a p-GaN SR structure can pave the way toward a high-performance GaN vertical power device for high-power and high-efficiency power switch applications.

Dilation properties of coherent Nearly-Linear models

Dilation is a puzzling phenomenon within Imprecise Probability theory: when it obtains, our uncertainty evaluation on event A is vaguer after conditioning A on B, whatever is event B in a given partition B. In this paper we investigate dilation with coherent Nearly-Linear (NL) models. These are a family of neighbourhood models, obtaining lower/upper probabilities by linear affine transformations (with barriers) of a given probability, and encompass several well-known models, such as the Pari-Mutuel Model, the ε-contamination model, the Total Variation Model, and others. We first recall results we recently obtained for conditioning NL model with the standard procedure of natural extension and separately discuss the role of the alternative regular extension. Then, we characterise dilation for coherent NL models. For their most relevant subfamily, Vertical Barrier Models (VBM), we study the coarsening property of dilation, the extent of dilation, and constriction. The results generalise existing ones established for special VBMs. As an interesting aside, we discuss in a general framework how logical (in)dependence of A from B or extreme evaluations for A influence dilation.

Effect of anode area on the sensing mechanism of vertical GaN Schottky barrier diode temperature sensor

Effect of anode area on temperature sensing ability is investigated for a vertical GaN Schottky-barrier-diode sensor. The current-voltage-temperature characteristics are comparable to each other for Schottky barrier diodes with different anode areas, excepting the series resistance. In the sub-threshold region, the contribution of series resistance on the sensitivity can be ignored due to the relatively small current. The sensitivity is dominated by the current density. A large anode area is helpful for enhancing the sensitivity at the same current level. In the fully turn-on region, the contribution of series resistance dominates the sensitivity. Unfortunately, a large series resistance degrades the temperature error and linearity, implying that a larger anode area will help to decrease the series resistance and to improve the sensing ability.

Research on noise reduction characteristic of sound barrier on natural draft wet cooling towers

To weaken the noise pollution of wet cooling towers, a large-scale wet cooling tower with a 660 MW unit is used as an example, and the water-splashing noise is measured in a field test. The sound source characteristics are determined based on the field test results, and the sound source surface is specified as the initial parameters of the simulation. Then, the noise propagation model for the wet cooling tower is established based on the ray-tracing method, with a maximum relative error of only 2.22%. Two noise reduction schemes, vertical and curved sound barriers, are proposed based on this model. Furthermore, the noise reduction effects of two different types of sound barriers are investigated. Under identical conditions, the simulation reveals that the vertical sound barrier performs better than the curved sound barrier in terms of noise reduction. In addition, The results also show that a vertical sound barrier with a length of 90 m, a height of 10 m, and a distance of 15 m from the tower is an optimal scenario, with an A-weighted sound pressure level (A-SPL) of just 42.08 dB(A). In summary, the noise problem associated with wet cooling towers may be effectively addressed in this instance.

(Invited) How to Achieve Low Thermal Resistance and High Electrothermal Ruggedness in Ga2O3 Devices?

Ultra-wide-bandgap semiconductor gallium oxide (Ga2O3) has been promoted for years as a promising candidate for power electronics and RF applications, due to its high critical electrical field, controllable n-type doping, and the availability of large-diameter wafers by the melt growth. However, a fundamental limitation of Ga2O3 is its low thermal conductivity (k T = 0.1-0.3 Wcm-1K-1), which is about 1/6 of the k T of Si, 1/10 of GaN, and 1/20 of SiC. The resulting high thermal resistance of Ga2O3 chip has brought serious concerns regarding the current and power scalability of Ga2O3 devices and their electrothermal ruggedness. As a result, questions have persisted on the true viability of Ga2O3 devices in industrial power and RF applications.Despite some simulation and modeling works on the Ga2O3 thermal management, there has been no experimental report on the packaging and thermal management of large-area Ga2O3 devices. The lack of these data makes it difficult to compare Ga2O3 with commercial device technologies (e.g., Si, SiC, GaN) and evaluate the application space of Ga2O3 devices. Some recent works characterized the channel (or junction) temperatures in Ga2O3 devices, but all of these devices have small areas with a current much lower than 1 Amp, and none of these devices are packaged.This work presents the first experimental demonstration of large-area Ga2O3 devices and their thermal management through device-package co-optimization. Vertical Ga2O3 Schottky barrier diodes (SBDs) with a 3×3 mm2 Schottky contact area were fabricated with an on/off ratio over 1010, a forward current over 20 A, and a reverse breakdown voltage over 600 V. These large-area Ga2O3 SBDs were packaged in the bottom-side-cooling and double-side-cooling configurations using the nanosilver sintering as the die attach and the silver plate as the thermal pad.Surge current ruggedness is an essential ruggedness metric listed in any power diode’s datasheet and the most important indicator of a device’s transient electrothermal ruggedness. It measures the device’s capability of temporarily sustaining a current much higher than the rated current. To evaluate the surge current ruggedness of packaged Ga2O3 devices, a surge-current test circuit was prototyped to produce a 10-ms-wide half-sinusoidal current waveform based on the JEDEC standard. The surge-current tests revealed a critical surge current of 37.5 A for the single-side-packaged Ga2O3 SBD and 68 A for the double-side-packaged Ga2O3 SBD. The ratio between the peak surge current and the rated current of the double-side-packaged Ga2O3 SBD was found to be superior to that of similarly-rated commercial SBDs.The key enabling mechanisms for this superior-to-SiC surge current capability are two-fold: first, the fabricated Ga2O3 SBD shows a smaller temperature dependence of on-resistance as compared to the SiC SBDs, which strongly reduces the thermal runaway; second, the double-side-packaging allows the heat to be extracted directly from the Schottky junction without the need for going through the low-k T bulk Ga2O3 chip.To further evaluate the steady-state thermal performance of these Ga2O3 SBDs, the junction-to-case thermal resistance (R θJC) of a double-side-packaged Ga2O3 SBD was measured in the bottom-side- and junction-side-cooling configurations. The R θJC characterization is based on the transient dual interface method, i.e., JEDEC 51-14 standard. The R θJC of the junction- and bottom-cooled Ga2O3 SBD was measured to be 0.5 K/W and 1.43 K/W, respectively, with the former R θJC lower than that of similarly-rated commercial SiC SBDs. This low R θJC is attributable to the heat extraction directly from the Schottky junction instead of through the Ga2O3 chip.The higher surge current ruggedness and lower thermal resistance demonstrated in a large-area, packaged Ga2O3 SBD as compared to the similarly-rated SiC devices proves the viability of Ga2O3 devices for high-power applications. Note that no complex or costly process, such as substrate thinning and layer transfer, has been applied to our Ga2O3 chip. These results manifest that device-packaging co-optimization is an effective and low-cost approach for the thermal management of Ga2O3 devices.

(Invited) Recent Progress on Anisotropic Electrical and Optical Studies in Ultrawide Bandgap β-Ga2O3 Electronics and Photonics

Ultrawide bandgap semiconductor beta-phase gallium oxide (β-Ga2O3) has recently garnered significant research interests in various electronic and photonic devices such as power devices, RF electronics, photodetectors, self-powered sensors, and high temperature and radiation-hardened devices. This is mainly driven by two factors. The first factor is β-Ga2O3’s advantageous material properties, including large bandgap (4.8 eV), high critical electric field (8 MV/cm), high device figure of merits, and excellent material stability in harsh environments. The second factor is that cost-effective bulk β-Ga2O3 substrates are commercially available, and high-quality β-Ga2O3 epilayers can be grown using various methods (e.g., MOCVD, MBE, and HVPE) for electronic and photonic device fabrication. One of the most important aspects to consider for β-Ga2O3 device design and fabrication is crystal orientation. Since β-Ga2O3 crystalizes in a highly asymmetric monoclinic structure, there are many selections available in terms of crystal orientations such as (010), (-201), (001), and (100). These different crystal orientations may lead to anisotropic electrical and optical properties in β-Ga2O3 electronics and photonics, which warrants a systematic study. This talk will discuss our recent studies of electrical and nonlinear optical properties in β-Ga2O3 with different crystal orientations and their effects on β-Ga2O3 devices. In the first part of the talk, a comparative investigation will be presented for vertical (010) and (-201) β-Ga2O3 Schottky barrier diodes, where their temperature-dependent forward and reverse I-V and C-V characteristics are compared. At forward bias, they showed different on-resistances, turn-on voltages, electron mobilities, and Schottky barrier heights. At reverse bias, different leakage currents, breakdown voltages, and leakage mechanisms were observed in the two devices. These discrepancies are ascribed to different atomic configurations and dangling bonds, and distinct surface band bending revealed by x-ray photoelectron spectroscopy (XPS) on the two surfaces of different crystal orientations. In addition, we also examined the deep-level defects in β-Ga2O3 with different crystal orientations using deep level transient spectroscopy (DLTS). The second part of the talk will focus on the nonlinear optical properties of (010) and (-201) β-Ga2O3, including two-photon absorption coefficient, Kerr nonlinear refractive index, and their polarization dependence. (-201) β-Ga2O3 has a smaller two-photon absorption coefficient, a larger Kerr refractive index, and strong in-plane nonlinear optical anisotropy. Interestingly, the two-photon absorption coefficient of β-Ga2O3 is 20x smaller than wide bandgap GaN, indicating its potential for low-loss waveguides, stable resonators, and integrated photonics. We recently demonstrated β-Ga2O3 optical waveguides with a low loss of 3.7 dB/cm in the ultraviolet to near infrared spectral region. More investigations are expected in this area as β-Ga2O3 electronics and photonics research progresses. And the choice of crystal orientations for the mass production of β-Ga2O3 devices rests on applications, device designs, and costs of substrate of a certain crystal orientation.

(Invited) Gallium Oxide Process Development and Integration for Future RF and Power Switching Applications

Beta-phase Gallium Oxide (BGO) is emerging as a high-performance, low-cost electronic device technology for future switching applications. BGO possesses unprecedented critical electric field strength that dominates switch loss figures of merit along with shallow donor energy and large-area native substrates manufactured from the melt. Clear commercial applications exist in vertical Schottky barrier diodes (SBD) offering performance near or surpassing SiC at much lower cost. This commercial pull will mature various BGO transistor applications such as fast-switch power converters made small enough for chip-level process integration.This abstract reviews BGO transistor development progress made by the Air Force Research Laboratory (AFRL) and the community at-large. AFRL has shown record-high transistor critical field strength, low dynamic switch losses surpassing the limit of Si, and early RF small and large signal power performance. Most recently, AFRL has made progress on vertical transistor topologies, self-aligned gate lateral transistors and dielectric optimization. Recent advances for these topics will be discussed and have culminated with large gate periphery BGO power switches and an early demonstration of the first ultra-wide bandgap integrated circuit. The integrated circuit monolithically combines a high-κ capacitor, SBD and power transistor all fabricated on a BGO common substrate.

Stabilisation of compliant floating platforms with sheet barriers under wave action

Excessive surface displacement of a compliant floating platform made of interconnected modular floats due to wave action can cause damage to the utility system (solar power, etc.) or endanger the safety of the service personnel on top. This study examines the use of a vertical tensioned sheet barrier installed in front of the floating platform for its stablisation under incident waves. Two configurations are investigated, namely finite and semi-infinite, representing a medium and large size platform respectively. Analytical analysis is performed without the pre-assumption of the dynamic behavior of the sheet barrier, and solutions are obtained using the eigenfunction expansion together with the least square method. For both configurations, the wave transmission to the floating platform reduces when the dynamic of the sheet barrier shifts from plate-like to membrane-like with increasing tension and also deeper draft and larger viscosity, which in turn reduces the platform displacement and the hydrodynamic pressure force on the platform. Overall, the results in the present study show that the installation of the barrier in front of the platform in the membrane-like hydroelastic regime with a penetration ratio more than ∼0.4 can significantly improve the stability of the compliant floating platform in the coastal environment.

Promoting sustainable consumption in Higher Education Institutions through integrative co-creative processes involving relevant stakeholders

The United Nations proposes to ensure a sustainable future for all through the Sustainable Development Goals, assigning a new role to each individual in all sectors of society. Higher Education Institutions are outstanding agents of change, introducing and implementing sustainability in a holistic way, connecting people, and including social and institutional considerations, with students being a key component of change. This study presents a co-creation model to incorporate sustainability in Higher Education Institutions, integrating all members of the university community with a multidisciplinary approach, seeking to address global needs with development tools for new products and services to facilitate the transition of consumers towards responsible consumption. The model aims to analyze the daily consumption pattern of the community at the university, to identify the degree of commitment to sustainability of its members, and to co-create in search of solutions related to responsible consumption and production. This is achieved through five phases of a model, each with specific tasks and objectives based on co-creation processes and tools. As a result, the model enables stakeholders to understand the needs of their community by actively participating within the five phases for developing more democratic solutions and social involvement regarding sustainability issues that can be solved through a co-creative process. The model combines the benefits through ethnographic techniques to discover habits, tools to involve participation, and co-creation to manage complex problems. Future research will focus on the application of the proposed model to more generalist contexts of society, addressing potential challenges due to vertical collaboration and barriers pre-established by society for the adoption of a sustainable lifestyle.

Oblique water wave scattering by vertical elastic porous barriers

The mixed boundary value problem associated with scattering of obliquely incident water waves by a flexible porous barrier of different barrier configurations is considered here. The originally defined half-plane problem is converted into a quarter-plane problem. Then a novel connection is established between the solution potential of the converted problem and a resolvable potential in the quarter-plane. Further Galerkin approximation is used to obtain close bounds for the reflection and the transmission coefficients. Numerical results are presented for scattering quantities against various parameters in each of the problems under consideration.

Assessment of global wave forces and moments on porous vertical barriers in random wave fields

Experimental investigations were carried out to assess the global wave forces and wave induced moments on slotted vertical barriers (SVB). Fourty two different wave barrier configurations (5%, 10%, 20%, 30%, 40%, 50% and 60% porosities and 1 to 6 number of slotted walls) were tested in random wave fields of JONSWAP spectra for wide range of significant wave heights and peak periods. It is found that the wave force is very sensitive to the change in porosity of the SVB. It is also found that relatively long waves and low porosity on SVB results in the highest wave force and short waves and high porosity on the SVB results in the lowest wave force. For most of the conditions, the wave force on SVB is less than the wave force on a single impervious vertical wall and force reduction to an extent of 20% to 80% is possible for the range of porosity and number of porous walls studied. A predictive equation to estimate the wave induced significant moment is provided with high regression coefficient. The average lever arm for assessing the wave induced moment is 0.6145 times the local water depth.

Highlights of the 1st Latin American Conference of Women in Bioinformatics and Data Science

Highlights of the 1st Latin American Conference of Women in Bioinformatics and Data Science

Noise assessment of elevated rapid transit railway lines and acoustic performance comparison of different noise barriers for mitigation of elevated railway tracks noise

Subways or rapid transit railways can be found in many major cities. These rapid transit railways are typically built above ground whenever possible to avoid the high capital cost of tunneling and also the high running cost of air conditioning and ventilation. However, noise from trains running on elevated tracks or viaducts close to residential and commercial buildings or houses is a problem for many cities. Noise barriers have been used extensively to mitigate noise from motorways, heavy trunk roads, and construction sites. On the other hand, relatively few reported studies on the design and performance of noise barriers for elevated railway tracks or viaducts to mitigate rapid transit train noise. The effectiveness of noise barriers on elevated railway tracks or viaducts for the mitigation of train noise may be different and challenging to predict due to complex street canyons and surrounding buildings beside the barrier designs and construction materials. Riding on the Singapore Railway Noise Barrier Programme, the present research conducted on-site measurements of several housing estates in Singapore to investigate the effect of noise barriers on the mitigation of train noise. Comparisons were also carried out to examine the performance of two different designs, Taiwan's Taipei subway track noise barriers and the vertical noise barriers used by the Singapore Mass Rapid Transit (MRT) system. Acoustic mapping revealed that the simulated noise mitigation barriers led to a 5–12 dB(A) reduction in noise levels reaching the resident apartments.

Numerical study on the effect of excavation dewatering on the contaminant emission in sandy soil

In recent years, construction has increased widely throughout the world, and the need for excavation and dewatering has increased dramatically. The potential for pollutants to enter soil and groundwater including chemical fertilizers, municipal landfill leachate, and hydrocarbons has also increased. The dewatering process used in the excavation can detrimentally affect the spread of contamination in the soil. In this study, the effect of different parameters on the emission of pollutants in different excavation depths has been investigated. Two software products SEEP/W and CTRAN/W are used for numerical modelling. The results show that the physical properties of soil have a significant influence on the contaminant movement. Also, it is indicated that the change in water level depth and the excavation depth have a massive effect on the contaminant migration process. Moreover, the vertical barrier can be an effective way to reduce the migration of contaminants to the excavation zone.

Optimal Design of a U-Shaped Oscillating Water Column Device Using an Artificial Neural Network Model

A U-shaped oscillating water column (U-OWC) device has been investigated to enhance power extraction by placing the bottom-mounted vertical barrier in front of a conventional OWC. Then, the optimal design of a U-OWC device has been attempted by using an artificial neural network (ANN) model. First, the analytical model is developed by a matched eigenfunction expansion method (MEEM) based on linear potential theory. Using the developed analytical model, the input and output features for training an ANN model are identified, and then the database containing input and output features is established by a Latin hypercube sampling (LHS) method. With 200 samples, an ANN model is trained with the training data (70%) and validated with the remaining test data (30%). The predictions on output features are made for 4000 random combinations of input features for given significant wave heights and energy periods in irregular waves. From these predictions, the optimal geometric values of a U-OWC are determined by considering both the conversion efficiency and wave force on the barrier. It is found that a well-trained ANN model shows good prediction accuracy and provides the optimal geometric values of a U-OWC suitable for wave conditions at the installation site.

Origin of low-temperature negative transconductance in multilayer MoS2 transistors

In this paper, negative transconductance (NTC) behavior in molybdenum disulfides (MoS2) field effect transistors (FETs) is investigated. Combining experimental observation and numerical analysis, we demonstrate that positive shift in the device transfer curves results from the electron trapping/de-trapping processes, where the defect densities at the MoS2/SiO2 interface are reduced when the temperature T decreases from 300 to 200 K. Moreover, the main types of defects that affect the device electrical performance are the interface defect and bulk sulfur vacancy VS in which VS induces the p-type doping effect. While decreasing T below 100 K, NTC occurs when their active layer thickness t (=41 and 35 nm) is larger than the Debye length λ (28 nm). Considering the n-type doping effect induced by the interface defects and the p-type doping caused by the bulk S vacancies, these two opposite doping regions are carefully implemented in simulation at T = 70 K. A vertical barrier induced by the inhomogeneous electron distribution enlarges with the increased gate bias VGS and, thereafter, leads to the unconventional increase in the contact and total resistances with t &amp;gt; λ. While t ≦ λ, the barrier and NTC behavior disappear. The current IDS and transconductance g obtained from the simulation confirm the low-temperature NTC mechanism related to the defects as discussed above. The material defects and physical origin of NTC discussed in the multilayer MoS2 transistors provide the theoretical foundation for designing and realizing novel structures of functional devices via defect engineering in the two-dimensional FET.

Dual BEM for wave scattering by an H-type porous barrier with nonlinear pressure drop

In this paper, wave scattering by an H-type porous barrier having nonlinear pressure drop boundary condition is analysed within the framework of small amplitude water wave theory. The H-type barrier is constructed using multiple thin (near zero thickness) rigid porous plates which are termed degenerate boundaries. The boundary value problem is solved using an iterative dual boundary element method. Different barrier configurations are analysed and compared to demonstrate the improved hydrodynamic performance of the H-type barrier. Further, the effect of porosity, relative spacing, the relative depth of submergence of the horizontal plate, wave steepness, and the rotation of the horizontal plate is investigated parametrically. Several results such as scattering coefficients (reflection, transmission, and energy-loss) and force coefficients (horizontal, vertical, and moment) are presented to understand the feasibility of the H-type barrier in real field applications. It is revealed that the increase in the structure porosity consistently increases the wave transmission, but reduces wave reflection, and force coefficients. Further, an increase in the relative spacing between the vertical barriers reduces the wave transmission by 20% without increasing the horizontal wave force but at the expense of increasing the vertical force coefficient in the shallow water regime. The results of this study are expected to be useful for the appropriate selection of different structure parameters to optimize the design.

Development and test-retest reliability assessment of a low-cost, 3D printed tool for assessing different aspects of hand dexterity

Hand dexterity assessments related to fine motor movements are routinely administered in clinical settings to ascertain an individual's hand function. However, to perform a detailed assessment multiple devices are needed which can be time-consuming and costly to administer. We designed and assessed the test-retest reliability of a 3D printed dexterity device in a cohort of healthy young adults and community-dwelling older adults. This study examines the reliability of the device, association between perceived fine motor gripping and manipulation dexterity components, and dominant hand outperformance during both tasks. Test-retest study of a clinical measurement tool. A convenience sample of thirty-six healthy community-dwelling older and young adults was included in our study. The device was used to collect data at two testing sessions to establish test-retest reliability. Fine motor manipulation dexterity was assessed by lifting notched pegs over a vertical barrier and inserting them into randomly oriented holes sequentially. Fine motor gripping dexterity was assessed by taking these notched pegs out of the holes, lifting them over the barrier and dropping them into a large container. Intraclass correlation coefficient (ICC)2,1 showed good to excellent test-retest reliability on the dominant and nondominant hands when using the device. Only modest association was found within-hand for the gripping versus manipulation dexterity tests. The between-hand motor gripping dexterity test demonstrated a strong association; however, between-hand the motor manipulation dexterity test was only moderately associated. The device was reliable, discriminated between the motor gripping and motor manipulating dexterity tasks, and was sensitive to handedness during the motor manipulating dexterity task. It shows promise as a hand dexterity assessment device which may provide efficiency and cost advantages. It is freely available via http://www.rehabtools.org/dexterity.html.

Study on Hydrodynamic Performance of Unsymmetrical Double Vertical Slotted Barriers

Study on Hydrodynamic Performance of Unsymmetrical Double Vertical Slotted Barriers

Study Unconventional Alternatives to Vertical Breakwater

The main objective of the breakwaters is to protect the port, the beach or the beach facilities from strong waves and storms, as they help to establish calm inside the port and thus achieve safety for ships, and ease of operation. This research aims to present study unconventional alternatives to vertical breakwater. In this study, two different models of vertical wave barriers implemented were chosen for their study and evaluation of the hydrodynamic performance. The first model is a vertical wall with circular slots and the second model is a vertical wall with square slots. A comparison was made between the two models it was found that the square slots reduce the transmission of waves more than circular slots by 5 to 20%. The use of two circular slotted walls decreases wave transmission by up to 30% and increases wave energy dissipation by up to 40% as compared to a single wall. With increasing relative length (h/L), the horizontal wave force rises. The relative wave forces (F/Fo), at porosity ( ) =0.25, was greater than at porosity ( ) = 0.50 by 10 to 30%. At the openings, the wave velocity is high, and the wave energy dissipation factor was also high; the higher the wave amplitude, the greater the wave energy dissipation factor.