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1
Evans, Jon, Jash Patel, Ahmed Ben Khaial, Nicholas Burridge, Rhonda Hyndman, Finn Monaghan, Mike Jennings, Huma Ashraf, Rob Harper e Matthew Elwin. "Fabrication of Quasi-Vertical GaN-On-SiC Trench MOSFETs". Key Engineering Materials 945 (19 maggio 2023): 61–66. http://dx.doi.org/10.4028/p-97g365.
Testo completoAbstract (sommario):
We demonstrate quasi-vertical GaN MOSFETs fabricated on SiC substrates. The GaN epitaxial layers were grown via MOCVD on 100 mm 4H-SiC wafers, with the device structure consisting of a 2.5 μm drift layer and a Mg doped p-GaN body. The fabricated transistors exhibit normally-off characteristics, with low off-state leakage behavior and an on/off ratio of over . The specific on-resistance was measured to be which compares favorably to devices fabricated on other foreign substrates. Our results demonstrate an alternative substrate for realizing vertical GaN devices, which potentially offers better material quality and thermal properties compared with other foreign substrate choices.
2
Weikle, Robert M., S. Nadri, C. M. Moore, N. D. Sauber, L. Xie, M. E. Cyberey, N. Scott Barker, A. W. Lichtenberger e M. Zebarjadi. "Thermal Characterization of Quasi-Vertical GaAs Schottky Diodes Integrated on Silicon Using Thermoreflectance and Electrical Transient Measurements". Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2019, DPC (1 gennaio 2019): 001293–310. http://dx.doi.org/10.4071/2380-4491-2019-dpc-presentation_tha3_009.
Testo completoAbstract (sommario):
Thermal management and design have been understood, for many years, as critical factors in the implementation of submillimeter-wave Schottky-diode-based circuits and instruments. Removal of heat is particularly important for frequency multipliers, as these circuits generally exhibit low-to-modest conversion efficiencies, and are usually driven with high-power sources to achieve usable output power in the submillimeter-wave region of the spectrum. Elevated diode junction temperature due to inadequate heat sinking is known to degrade performance, accelerate aging effects (for example, due to electromigration, ohmic contact deterioration, or thermally-induced stress), and can ultimately lead to device failure. The relatively-low thermal conductivity of GaAs (the predominant material technology for submillimeter-wave diodes), coupled with restrictions on diode anode size and geometry needed to minimize parasitics and achieve the device impedances required for high-frequency operation, present significant challenges and trade-offs between electrical and thermal designs of these devices. Recognition that heating is a major factor limiting efficiency and output power has prompted a number of approaches to mitigate excessive temperature rise in the junction of planar Schottky diodes, including the use of AlN or diamond as low-loss substrates that act as heat spreaders. A new diode topology, based on a quasi-vertical geometry that is realized through heterogeneous integration of GaAs with high-resistivity silicon, was recently developed at the University of Virginia for submillimeter-wave applications. Unlike planar diodes, the device structure of the quasi-vertical diode consists of a metal contact that underlies the diode's anode and epitaxial mesa, thus providing a large-area ohmic cathode contact that also serves as an integrated heat sink. Measurement of high-efficiency multipliers based on this technology suggest the quasi-vertical architecture provides an effective approach for heat removal and thermal management in Schottky diodes. This paper presents the first results reporting thermal performances of terahertz quasi-vertical GaAs Schottky diodes integrated on silicon. The devices are characterized using a thermoreflectance measurement technique, a method based on the change in refractive index, and therefore surface reflectivity, with changes in temperature. Heating and cooling temperature profiles and 2-D temperature maps are obtained for 3.5 micron and 5.5 micron diameter diodes. From these measurements, the device thermal resistances, junction temperatures, and thermal time-constants are extracted. Equivalent thermal circuit and finite element models are developed to study the device geometry, and extract material thermal parameters. The devices are also characterized using an electrical transient method, and the temperature and cooling transients found from this technique are found to be comparable to those obtained from thermoreflectance measurements. The quasi-vertical diodes studied in this work are shown to demonstrate a faster transient thermal response compared to flip-chip bonded terahertz diodes reported in the literature.
3
Zhu, Xiaoxiao, Wei Lu, Jing Ning, Jincheng Zhang, Dong Wang, Chi Zhang, Yanbo Wang et al. "A high-performance quasi-vertical MoSe2 photodiode with ultra-low dark current". Applied Physics Letters 121, n. 14 (3 ottobre 2022): 141103. http://dx.doi.org/10.1063/5.0104664.
Testo completoAbstract (sommario):
Van der Waals heterostructure based on 2D materials is a promising technology for high-performance optoelectronic devices because of its tunable bandgaps and optical properties. However, photodetectors with a low dark current and a fast response speed commonly lose their photoresponsivity. The recovery current induced by the Schottky barrier height variation cancels out the device's reverse bias current in this paper, resulting in a quasi-vertical MoSe2 photodiode with ultralow dark current (<1 pA). Simultaneously, rapid electron–hole pair separation occurs at the interface due to the large heterojunction area and the strong interlayer coupling of MoSe2/graphene heterojunction, resulting in a fast response time of 1.5 ms and a high photoresponsivity of 19.72 A/W. Furthermore, the Au/MoSe2 forms a Schottky contact, which is asymmetrical to the Ohmic contact formed by the MoSe2/graphene, enabling the proposed device to achieve high-performance self-powered photodetection. Our work shows an alternative approach to improve the performance of future electronic and optoelectronic applications.
4
Liu, Cheng, Ming Li, Zhang Wen, Zhao-Yuan Gu, Ming-Chao Yang, Wei-Hua Liu, Chuan-Yu Han, Yong Zhang, Li Geng e Yue Hao. "Establishment of composite leakage model and design of GaN Schottky barrier diode with stepped field plate". Acta Physica Sinica 71, n. 5 (2022): 057301. http://dx.doi.org/10.7498/aps.71.20211917.
Testo completoAbstract (sommario):
Quasi-vertical GaN barrier Schottky diodes have attracted much attention due to their low cost and high current transfer capability. The main problem is that the reverse characteristics of the devices may not be well estimated, which affects the design of the diodes. In this paper, the defects of GaN materials and the leakage related tunneling mechanisms accompanied with other mechanisms are considered. Based on the established composite device models, the reverse leakage current is simulated which is well consistent with the recent experimental result. With the assistance of the proposed models, several field plate structures are discussed and simulated to obtain a quasi-vertical GaN barrier Schottky diode with high breakdown voltage. The major leakage mechanisms are also analyzed according to the relation among leakage current, temperature and electric field at various reverse voltages. High BFOM up to 73.81 MW/cm<sup>2</sup> is achieved by adopting the proposed stepped field plate structure.
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Khan, Sahanowaj, Aritra Acharyya, Hiroshi Inokawa, Hiroaki Satoh, Arindam Biswas, Rudra Sankar Dhar, Amit Banerjee e Alexey Y. Seteikin. "Terahertz Radiation from High Electron Mobility Avalanche Transit Time Sources Prospective for Biomedical Spectroscopy". Photonics 10, n. 7 (10 luglio 2023): 800. http://dx.doi.org/10.3390/photonics10070800.
Testo completoAbstract (sommario):
A Schottky barrier high-electron-mobility avalanche transit time (HEM-ATT) structure is proposed for terahertz (THz) wave generation. The structure is laterally oriented and based on AlGaN/GaN two-dimensional electron gas (2-DEG). Trenches are introduced at different positions of the top AlGaN barrier layer for realizing different sheet carrier density profiles at the 2-DEG channel; the resulting devices are equivalent to high–low, low–high and low-high–low quasi-Read structures. The DC, large-signal and noise simulations of the HEM-ATTs were carried out using the Silvaco ATLAS platform, non-sinusoidal-voltage-excited large-signal and double-iterative field-maximum small-signal simulation models, respectively. The breakdown voltages of the devices estimated via simulation were validated by using experimental measurements; they were found to be around 17–18 V. Under large-signal conditions, the series resistance of the device is estimated to be around 20 Ω. The large-signal simulation shows that the HEM-ATT source is capable of delivering nearly 300 mW of continuous-wave peak power with 11% conversion efficiency at 1.0 THz, which is a significant improvement over the achievable THz power output and efficiency from the conventional vertical GaN double-drift region (DDR) IMPATT THz source. The noise performance of the THz source was found to be significantly improved by using the quasi-Read HEM-ATT structures compared to the conventional vertical Schottky barrier IMPATT structure. These devices are compatible with the state-of-the-art medium-scale semiconductor device fabrication processes, with scope for further miniaturization, and may have significant potential for application in compact biomedical spectroscopy systems as THz solid-state sources.
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Yadav, Sugandha, Poornima Mittal e Shubham Negi. "An In-Depth Analysis of Variation in Characteristic Performance of OLED with Respect to Position of Charge Generation Layer". ECS Journal of Solid State Science and Technology 12, n. 10 (1 ottobre 2023): 106001. http://dx.doi.org/10.1149/2162-8777/acfd5f.
Testo completoAbstract (sommario):
In this paper, a high performance blue organic light emitting diode having a charge generation layer (CGL) is proposed and compared with the other five CGL and non-CGL based devices. The utilized CGL layer in the different structure consists of two materials; HAT-CN (hexaazatriphenylene-hexacarbonitrile) and TAPC (1,1-bis[(di-4-tolyamino)phenyl)]cyclohexane,) for electrons and holes generation, correspondingly. In the proposed novel structure, the CGL layer is incorporated outside of the emissive layer (EML) which significantly enhances the device performance in terms of current and luminescence. The device exhibits luminescence and current values as 3636.3 cd m−2 and 0.44 A, respectively. Furthermore, this paper represents in-depth internal analysis of the six devices (D1-D6). This analysis is provided by drawing horizontal and vertical cutlines inside the devices. The proposed device is analysed and compared with other mentioned devices in terms of several parameters such as Langevin recombination rate, electron concentration, hole concentration, band energy, total current density, electron affinity, hole QFL (quasi-Fermi level), conduction current density, potential distribution and electron/hole mobility. In comparison with D1, D2, D3, D4 and D5, the current of the proposed device (D6) is about 16.9, 2.2, 1.7, 3 and 1.6 times improved, correspondingly. Moreover, structural analysis is also included to understand the performance of the devices more precisely.
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Briskin, E. S., L. D. Smirnaya e K. S. Artemyev. "On the Control of Traction Characteristics and Resistance to Movement of Mobile Robots with Walking Propulsion Devices". Mekhatronika, Avtomatizatsiya, Upravlenie 24, n. 2 (6 febbraio 2023): 101–6. http://dx.doi.org/10.17587/mau.24.101-106.
Testo completoAbstract (sommario):
The problem of increasing the traction and dynamic properties of mobile robots with walking propulsion devices is considered. The interdependence of the traction forces developed by the propulsion devices and the forces of resistance to the movement of robots, due to their interaction with the environment, is analyzed. A mathematical model is proposed based on the quasi-static nature of the robot’s movement and taking into account the static uncertainty of the problem. Static indeterminacy is due to the presence of propulsion devices on each of the sides and interacting with the supporting surface in the amount of more than two. A feature of the solution is also taking into account the gait and schedule of the robot’s movement, which characterize the time sequence of the propulsion devices being in the phase of interaction with the supporting surface and in the phase of transfer to a new position. The gait is also characterized by the mode coefficient, which is the ratio of the time the propulsion device is in the stance phase to the total time of the cycle of its movement. An optimality criterion is introduced on the basis of which the design perfection of the propulsion devices and the place of their installation on the robot is evaluated. The optimality criterion consists of two indicators: the value of the maximum traction force and the average force of resistance to movement. The tractive force is assumed to be proportional to the sum of the maximum normal loads acting on each propulsion device unit, and the resistance force to the squares of the same loads. Simulation modeling has been carried out, proving the dependence of the magnitude of traction properties and the forces of resistance to movement on the location of the propulsion devices. Two systems of vertical arrangement of the points of suspension of propulsion devices were compared. It has been established that a sufficiently small change in the vertical coordinate of the suspension point of even one propulsion devices has a noticeable change in the maximum traction forces and movement resistance forces. It is concluded that by adjusting the vertical position of the propulsion devices foot relative to the robot body, it is possible to control the traction properties and movement resistance, as well as the importance of the positioning accuracy of the foot of the propulsion devices walking mechanism during movement.
8
Cristoloveanu, Sorin, Joris Lacord, Sébastien Martinie, Carlos Navarro, Francisco Gamiz, Jing Wan, Hassan Dirani, Kyunghwa Lee e Alexander Zaslavsky. "A Review of Sharp-Switching Band-Modulation Devices". Micromachines 12, n. 12 (11 dicembre 2021): 1540. http://dx.doi.org/10.3390/mi12121540.
Testo completoAbstract (sommario):
This paper reviews the recently-developed class of band-modulation devices, born from the recent progress in fully-depleted silicon-on-insulator (FD-SOI) and other ultrathin-body technologies, which have enabled the concept of gate-controlled electrostatic doping. In a lateral PIN diode, two additional gates can construct a reconfigurable PNPN structure with unrivalled sharp-switching capability. We describe the implementation, operation, and various applications of these band-modulation devices. Physical and compact models are presented to explain the output and transfer characteristics in both steady-state and transient modes. Not only can band-modulation devices be used for quasi-vertical current switching, but they also show promise for compact capacitorless memories, electrostatic discharge (ESD) protection, sensing, and reconfigurable circuits, while retaining full compatibility with modern silicon processing and standard room-temperature low-voltage operation.
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Eyvazian, Arameh, Hozhabr Mozafari, Faris Tarlochan e Abdel Magid S. Hamouda. "Numerical and Experimental Investigation on Corrugation Geometry for Metallic Tubes under Lateral Loading". Materials Science Forum 916 (marzo 2018): 226–31. http://dx.doi.org/10.4028/www.scientific.net/msf.916.226.
Testo completoAbstract (sommario):
Energy absorption devices are being used to protect structures from severe damages and reduce injury to occupants during accidents. The integrated characteristics of crash absorption devices can be classified as high energy absorption capacity, light-weight, and cost-effective. One of the thin-walled structures which has drawn the attention of scientists is corrugated tube structure. In this paper, the effect of corrugation geometry on the crushing parameters of an aluminum corrugated tube is investigated. In this regard, different elliptical corrugation shapes were deemed and the compression response was numerically evaluated under lateral quasi-static loading. Finally, the crashworthiness parameters were extracted and compared to determine the influence of corrugation shape on the crashworthy response. Our results showed that using vertical elliptical corrugation decrease the densification point. Moreover, there is a gradual enhancement of mean crushing load by moving from the horizontal elliptical corrugations to the vertical ones. Also, by modifying of corrugation shape, the stress variation pattern changes, significantly.
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Salgado, Ruben, Amirmahdi Mohammadzadeh, Fariborz Kargar, Adane Geremew, Chun-Yu Huang, Matthew A. Bloodgood, Sergey Rumyantsev, Tina T. Salguero e Alexander A. Balandin. "Low-frequency noise spectroscopy of charge-density-wave phase transitions in vertical quasi-2D 1T-TaS2 devices". Applied Physics Express 12, n. 3 (15 febbraio 2019): 037001. http://dx.doi.org/10.7567/1882-0786/ab0397.
Testo completo
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Jiang, Hongbo, Jian Sun, Hongxing Qiu, Dafu Cao, Wenjie Ge, Qiang Fang, Hengwei Cui e Kongyang Chen. "Cyclic Behavior of Multiple-Stiffness Hardening Precast Concrete Shear Walls". Buildings 12, n. 12 (25 novembre 2022): 2069. http://dx.doi.org/10.3390/buildings12122069.
Testo completoAbstract (sommario):
Precast Concrete (PC) shear walls are becoming popular in building structures. With “wet” connection techniques, PC shear walls often behave like conventional cast-in-place walls, where stiffness hardening occurs after yielding. In this study, two PC shear walls assembled by the “dry” connection technique, and one cast-in-place shear wall, were tested by means of quasi-static cyclic loading. The main purpose of the experiment was to systematically investigate the cyclic response of PC shear walls with varying types of vertical connection in the form of a friction-bearing device. The results showed that vertical bearing in devices, which mainly stems from the longitudinal elongation of PC wall panels, could enlarge the axial force of end column so that it provided an additional resistance moment. The PC shear wall with weak connection achieved ductile failure and second ascending branches on load-displacement relationship, i.e., secondary stiffness hardening, and the wall with strong vertical connection performed great moment capacity as well as tertiary hardening. Compared to cast-in-place walls, the peak load and cumulative hysteretic energy of PC shear walls increased by about 60% and 100%, respectively. A conceptual analysis of the multiple stiffness hardening phenomenon is presented based on experimental results.
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Liu, Dewen, Yang Liu, Dongfa Sheng e Wenyuan Liao. "Seismic Response Analysis of an Isolated Structure with QZS under Near-Fault Vertical Earthquakes". Shock and Vibration 2018 (2018): 1–12. http://dx.doi.org/10.1155/2018/9149721.
Testo completoAbstract (sommario):
Seismic isolation devices are usually designed to protect structures from the strong horizontal component of earthquake ground shaking. However, the effect of near-fault (NF) vertical ground motions on seismic responses of buildings has become an important consideration due to the observed building damage caused by vertical excitation. As the structure needs to maintain its load bearing capacity, using the horizontal isolation strategy in vertical seismic isolation will lead to the problem of larger static displacement. In particular, the bearings may generate large deformation responses of isolators for NF vertical ground motions. A seismic isolation system including quasi-zero stiffness (QZS) and vertical damper (VD) is used to control NF vertical earthquakes. The characteristics of vertical seismic isolated structures incorporating QZS and VD are presented. The formula for the maximum bearing capacity of QZS isolation considering the stiffness of vertical spring components is obtained by theoretical derivation. From the static analysis, it is found that the static capacity of the QZS isolation system with vertical seismic isolation components increases when the configurative parameter reduces. Seismic response analyses of the seismic isolated structure model with QZS and VD subjected to NF vertical earthquakes are conducted. The results show that seismic responses of the structure can be controlled by setting the appropriate static equilibrium position, vertical isolation period, and vertical damping ratio. Adding a damping ratio is effective in controlling the vertical large deformation of the isolator.
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Yeh, Cheng-Hsien, Chuan-Feng Shih, Yuan-Wen Hsiao, Yu-Hui Huang, Hsuan-Ta Wu e Ching-Chich Leu. "2D/3D Heterojunction Perovskite Devices with Controlled Order and Orientation". ECS Meeting Abstracts MA2024-02, n. 39 (22 novembre 2024): 2619. https://doi.org/10.1149/ma2024-02392619mtgabs.
Testo completoAbstract (sommario):
This research demonstrates 2D/3D heterojunction perovskite devices with controlled order and orientation. First, a state-of-the-art vertical-transport photodetector with a n-type three-dimensional (3D) MAPbI3/p-type quasi-two-dimensional (Q-2D) perovskite heterojunction. This structure introduces a built-in electric field at the n-p junction that greatly improves the characteristics of the perovskite photodetector, and the presence of Q-2D perovskite on the surface much improves the life. The electrical polarities of the 3D and the Q-2D perovskite layers are simply controlled by self-constituent doping, making clearly defined n-p characteristics. Doctor-blade coating is used to fabricate the photodetector with a large area. The Q-2D materials with highly oriented (040) Q-2D (n = 2, 3) planes are near the surface, and the (111) preferred planes mixed with high index Q-2D materials (n = 4, 5) are found near the 3D/Q-2D interface. The stacking and interface are beneficial for the carrier extraction and transport, yielding excellent perovskite photodetectors. Secondly, solvent engineering, anti-solvent engineering and annealing process were used here to control the crystal orientation of 2D perovskite, and successfully form a novel vertical/horizontal (2D/2D) stacked bilayer heterogeneous structure by the introduction of a thin BAI layer. The device exhibits significant bipolar switching characteristics, stable resistance distribution, high switching ratio (106), long retention time (104 s) and outstanding endurance (~4,000 cycles).
14
Czyszanowski, Tomasz, Marcin Gębski, Emilia Pruszyńska-Karbownik, Michał Wasiak e James A. Lott. "Monolithic high-contrast grating planar microcavities". Nanophotonics 9, n. 4 (11 marzo 2020): 913–25. http://dx.doi.org/10.1515/nanoph-2019-0520.
Testo completoAbstract (sommario):
AbstractSemiconductor planar microcavities significantly enhance the interaction between light and matter and are thus crucial as a fundamental research platform for investigations of quantum information processing, quantum dynamics, and exciton-polariton observations. Microcavities also serve as a very agile basis for modern resonant-cavity light-emitting and detecting devices now in large-scale production for applications in sensing and communication. The fabrication of microcavity devices composed of both common materials now used in photonics and uncommon or arbitrary materials that are new to photonics offers great freedom in the exploration of the functionalities of novel microcavity device concepts. Here we propose and carefully investigate two unique microcavity designs. The first design uses a monolithic high-index-contrast grating (MHCG) and a distributed Bragg reflector (DBR) as the microcavity mirrors. The second design uses two MHCGs as the microcavity mirrors. We demonstrate by numerical analysis that MHCG-DBR and MHCG-MHCG microcavities, whose lateral radial dimension is 16 μm, reach very large quality factors at the level of 104 and nearly 106, as well as purposely designed wavelength tuning ranges of 8 and 60 nm in both configurations, respectively. Our MHCG-MHCG microcavities with a very small size of 600 nm in the vertical dimension show extremely large quality factors, which can be explained by treating the optical modes as quasi-bound states in a continuum (BICs). Moreover, we verify our theoretical analysis and calibrate our simulation parameters by comparing to the experimental characteristics of an electrically injected MHCG-DBR microcavity vertical-cavity surface-emitting laser (VCSEL) emitting at a peak wavelength of about 980 nm. We use the calibrated parameters to simulate the emission characteristics of electrically injected VCSELs in various MHCG-DBR and MHCG-MHCG microcavity configurations to illustrate the influence of microcavity designs and their quality factors on the predicted lasing properties of the devices.
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Huang, Guoping, Jianhua Hu, Haibo Liu e Xiugui Sun. "Girder Longitudinal Movement and Its Factors of Suspension Bridge under Vehicle Load". Advances in Civil Engineering 2021 (1 ottobre 2021): 1–14. http://dx.doi.org/10.1155/2021/1443996.
Testo completoAbstract (sommario):
Vehicle load may not only cause vertical deformation and vibration of suspension bridge but also lead to longitudinal deformation and vibration. And the longitudinal behavior is closely related to the durability of the girder end devices and the bending fatigue failure of suspenders. In this study, the longitudinal deformation behavior and longitudinal vibration of suspension bridge under vehicles, as well as the related influencing factors, are investigated. The underlying mechanism of girder longitudinal movement under the moving vehicles is revealed. Based on the simplified vehicle model of vertical concentrated force, the characteristics of main cable deformation and girder longitudinal displacement under vertical loads are analyzed first. Then, the longitudinal motion equation of the girder under vertical moving loads is derived. Finally, a single long-span suspension bridge is employed in the case study, and the girder longitudinal response and influencing factors are investigated based on both numerical simulation and field monitoring. Results indicate that the asymmetric vertical load leads to cable longitudinal deflection owing to the geometrically nonlinear characteristic of the main cable, leading to longitudinal movement of the girder. The results of field monitoring and numerical simulation indicate that the girder moves quasi-statically and reciprocates longitudinally with centimeter amplitude under normal operational loads.
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Kaneko, Kentaro, Shizuo Fujita, Takashi Shinohe e Katsuhisa Tanaka. "Progress in α-Ga2O3 for practical device applications". Japanese Journal of Applied Physics 62, SF (1 giugno 2023): SF0803. http://dx.doi.org/10.35848/1347-4065/acd125.
Testo completoAbstract (sommario):
Abstract Recent progress in α-phase gallium oxide (α-Ga2O3) grown on sapphire for low-cost and practical device applications is reviewed. This review focuses on (i) dislocations formed by heteroepitaxy, (ii) p-type conductivity (a common issue with β-Ga2O3), and (iii) thermal instability due to the metastable phase of α-Ga2O3, and discusses efforts aimed at overcoming these issues. The results reveal guidelines for the dislocation density (<1 × 108 cm−2) so that the dislocation scattering is veiled in the electron transport, and for this purpose we mentioned buffer layers and epitaxial lateral overgrowth. Quasi-vertical Schottky barrier diodes (SBDs) show defect-insensitive behavior in current–voltage characteristics under a low current density. We also demonstrate the heterojunction pn diodes with α-phase iridium oxide (α-Ir2O3) or α-(Ir,Ga)2O3 and the ways to improve thermal stability of α-Ga2O3. The up-to-date device characteristics, that is, low on-resistance and large current SBDs, and high reverse voltage of 1400 V of a pn junction suggest promising development in α-Ga2O3-based devices.
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Talich, Milan, Jan Havrlant, Lubomír Soukup, Tomáš Plachý, Michal Polák, Filip Antoš, Pavel Ryjáček e Vojtěch Stančík. "Accuracy Analysis and Appropriate Strategy for Determining Dynamic and Quasi-Static Bridge Structural Response Using Simultaneous Measurements with Two Real Aperture Ground-Based Radars". Remote Sensing 15, n. 3 (2 febbraio 2023): 837. http://dx.doi.org/10.3390/rs15030837.
Testo completoAbstract (sommario):
Over the past 10 years, ground-based radar interferometry has become a frequently used technology for determining dynamic deflections of bridge structures induced by vehicle passages. When measuring with only one radar device, the so-called Interpretation Error (EI) considerably rises. When using two radars, it is possible to simultaneously determine, for example, vertical and longitudinal displacements and to eliminate the Interpretation Error. The aim of the article is to establish a suitable strategy for determining dynamic and quasi-static response of bridge structures based on the accuracy analysis of measurement by two radars. The necessary theory for displacements determination by means of two radar devices is presented. This is followed by an analysis of errors when measuring with only one radar. For the first time in the literature, mathematical formulas are derived here for determining the accuracy of the resulting displacements by simultaneous measurement with two radars. The practical examples of bridge structures displacements determination by measuring with two radar devices in the field are presented. The key contribution of the paper is the possibility to estimate and plan in advance the achievable accuracy of the resulting displacements for the given radar configurations in relation to the bridge structure.
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Abd-alla, Abo-el-nour N., Fatimah Alshaikh, Idir Mechai e I. A. Abbas. "Influence of Initial Stresses and Piezoelectric Constants on the Propagation Bulk Acoustic Waves in an Anisotropic Smart Material (Aluminum Nitrite)". Journal of Computational and Theoretical Nanoscience 13, n. 10 (1 ottobre 2016): 6488–94. http://dx.doi.org/10.1166/jctn.2016.5591.
Testo completoAbstract (sommario):
The aim of this paper is to illustrate the effect of initial stresses on the propagation of plane waves in a general anisotropic elastic medium. Therefore, an analytical analysis supported by numerical tests to calculate the bulk acoustic wave propagation in Aluminum Nitrite (AlN) as piezoelectric hexagonal elastic material has been presented. In addition, the Christoffel’s equation has been solved and the corresponding eigenvalues and eigenvectors have been obtained. Then, an explicit expressions of the waves propagation with three distinct phase velocities in anisotropic piezoelectric material including the effect of the initial stresses have been derived. The three velocities of bulk acoustic waves (BAW) which are called quasi-longitudinal, quasi-shear vertical and quasi-shear horizontal for Aluminum Nitrite are numerically calculated. The numerical examples are considered to illustrate graphically the effect of initial stresses on the variations of velocities of the BAW versus the angle of the propagation. The velocities of BAW change significantly with initial stresses as well as piezoelectric constants. This research is theoretically useful in signal processing, sound system, wireless communication and for the design of surface acoustic wave (SAW) devices with high performance.
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Lee, Sein, Taehoon Sung, Min-Kyu Song e J. Y. Kwon. "Vertical Oxide Channel Thin Film Transistor for Ultra-High-Resolution Display". ECS Meeting Abstracts MA2022-01, n. 31 (7 luglio 2022): 1334. http://dx.doi.org/10.1149/ma2022-01311334mtgabs.
Testo completoAbstract (sommario):
The significance of backplane devices for ultra-high-resolution (UHR) display has increased with the recent development of augmented reality (AR) and virtual reality (VR) devices. Since the human visual resolution can distinguish up to 60 pixels per degree (PPD), the AR/VR device panel needs at least 3000 pixels per inch (PPI) to exceed the human retina resolution limit for clear display without screen effect. As a results, the unit pixel pitch of thin film transistor (TFT) for UHR display should be not only smaller than a few micrometers (~3 μm), TFT channel length should also be sub-micrometers level. In active matrix organic light emitting diode (AMOLED) display type, self-aligned top gate (SATG) TFT has been widely used as a planar backplane device structure because of its low parasitic capacitance and tolerance of illumination degradation caused by the light from emitting layer [1-2]. However, SATG TFT has fundamental disadvantages for device miniaturization due to its essentially required area of metallization region for reducing contact resistance and scaling limit of channel induced by carrier diffusion shrinking effective channel length. For this reason, we suggested a size tunable oxide channel VTFT structure that can achieve a high pixel density on account of structural benefit on device footprint. In this work, we fabricated amorphous indium gallium zinc oxide (a-IGZO) based VTFT. The previously published VTFT structure, channel length is determined by the thickness of spacer between source and drain electrodes [3]. Owing to spacer etching process, uneven backchannel roughness and high off current has become well-known issues of VTFT. On the contrary, the proposed VTFT structure has a controllability of effective channel aspect ratio because source and drain electrodes are able to be patterned by photolithography process. Furthermore, the parasitic capacitance is also relatively less than the formerly reported VTFTs controlled by inevitable thickness limit structurally due to the electrodes. To sum up, we not only realized the oxide channel VTFT that meets high performance for AR/VR display, but opened new application possibility to UHR electronic devices platform. Figure 1. (a) Schematic of the proposed VTFT (b) Transfer characteristic of VTFT Acknowledgement This work was supported by the Korea Evaluation Institute of Industrial Technology(KEIT) grant funded by the Korea government (MOTIE) (No. 2021-11-1283) References Kang, Dong Han, et al. "Self-aligned coplanar a-IGZO TFTs and application to high-speed circuits." IEEE electron device letters 32.10 (2011): 1385-1387. Wang, Guoying, et al. "8.3: High Stability Against Light and Heat Based on the Top Gate Self‐Aligned a‐IGZO TFTs under OLED Dislplay." SID Symposium Digest of Technical Papers. Vol. 49. 2018. Petti, Luisa, et al. "Flexible quasi-vertical In-Ga-Zn-O thin-film transistor with 300-nm channel length." IEEE Electron Device Letters36.5 (2015): 475-477. Figure 1
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Li, Haizeng, Jinmin Wang, Qiuwei Shi, Minwei Zhang, Chengyi Hou, Guoying Shi, Hongzhi Wang, Qinghong Zhang, Yaogang Li e Qijin Chi. "Constructing three-dimensional quasi-vertical nanosheet architectures from self-assemble two-dimensional WO 3 ·2H 2 O for efficient electrochromic devices". Applied Surface Science 380 (settembre 2016): 281–87. http://dx.doi.org/10.1016/j.apsusc.2016.01.009.
Testo completo
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Laging, G., e H. Rothert. "Numerical Results of Tire-Test Drum Interaction". Tire Science and Technology 14, n. 3 (1 luglio 1986): 160–75. http://dx.doi.org/10.2346/1.2148772.
Testo completoAbstract (sommario):
Abstract Inflated tires without grooves have been examined both numerically and experimentally for behavior under vertical and horizontal loads. Complete load-deformation analysis of the contact area was emphasized. Both two-dimensional and three-dimensional models were investigated. The three-dimensional approach includes geometrical non-linearities, hyperelastic material properties, deformation-dependent load components, and a contact problem with friction. Any contact surface contour can be included in the computation by introducing local coordinates for each node in the footprint area. Test drum experiments can thus be used for comparison. Extensive experimental and numerical studies were done on tires quasi-statically loaded against convex and concave drums. Results seem to confirm the need for plane-surface test devices. The main reason for this is the nonlinear relation of the size of the contact area to the stress distribution or to the maximum stress values.
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Bonnaud, Olivier, Peng Zhang, Emmanuel Jacques e Regis Rogel. "Vertical Conduction in the New Field Effect Transistors: p-Type and n-Type Vertical Channel Thin Film Transistors". International Journal of High Speed Electronics and Systems 23, n. 03n04 (settembre 2014): 1450023. http://dx.doi.org/10.1142/s0129156414500232.
Testo completoAbstract (sommario):
In order to pursue the integration, the research activities were oriented during the last years towards channel conduction in a plan perpendicular to the substrate surface while in the traditional architectures the conduction is parallel to the surface, under the gate. In the integrated technologies, this approach led to the FinFET. But in this case, even though the conduction plan is perpendicular to the substrate surface, the direction of the drain currents remains parallel to the substrate. New electronics devices were designed with the channels vertically oriented. In the monolithic technologies, many drawbacks have stopped this trend. However, in the case of thin film technologies, the approach appeared more suitable. The channel conduction is thus vertically oriented. But a drawback comes from the leakage current flowing between source and drain. The introduction of an insulating barrier in-between and the decrease of the thickness of the channel active layer, led to electrical behavior much more suitable for applications. After an overview of the different approaches developed as well in monolithic technologies as in thin film technologies, this presentation will give details on the concept and on the fabrication process of quasi-vertical thin film transistors. The associated electrical results will be described, analyzed and commented.
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Slonov, Mykhailo, e Oleksandr Maryliv. "A method of quasi-continuous image formation in observation devices with discrete receivers". Ukrainian journal of remote sensing 8, n. 2 (12 giugno 2021): 4–11. http://dx.doi.org/10.36023/ujrs.2021.8.2.192.
Testo completoAbstract (sommario):
The article proposes a new method of quasi-continuous image formation in observation devices with discrete receivers. The increase in the number of spatial sampling points in the object image is provided by intraframe scanning. Scanning is carried out by a photosensitive matrix with a regularly changed (controlled) density of the elementary receivers (CDR-matrix). The CDR-matrix contains identical elementary receivers. They are regularly distributed over the matrix surface. The vertical and horizontal distance between adjacent receivers is a multiple of the size of the elementary receiver. The CDR-matrix becomes equivalent in pixel dimensions to a larger photosensitive matrix. The magnitude of the multiplicity placement of the receivers is chosen by the developer when designing the light-sensitive matrix. The image of the object by the CDR-matrix (a separate frame) is composed of a series of snapshots. Each snapshot is formed by signals coming from all elementary receivers of the CDR-matrix. The number of snapshots in the frame is set by the multiplicity of the size of the elementary receivers vertically and horizontally. While using intraframe scanning, the CDR-matrix with a pixel size of the video format can operate in the mode of a photosensitive matrix with a pixel size of 2.5 MP. A CDR-matrix with a pixel size of 6 MP can operate as a 48 MP matrix of a conventional design. A mechanism for storing a frame with observation results when using a CDR-matrix is proposed. It assumes the use of the matrix addition operation. The signal matrix of the observed frame is considered as the sum of the signal matrices of all the snapshots in the frame. Application of the developed method will make it possible to multiply the pixel size of the image relative to the pixel size of the controllable photosensitive matrix. The advantages of the proposed method also include the absence of a mandatory decrease in the effective area of an elementary receiver with an increase in their number in the photosensitive matrix; simplification of hardware measures to reduce the effect of image shift on its quality; absence of information losses in the intervals between adjacent elementary receivers.
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Labutkina, Tetiana, e Ruslan Ananko. "«Горизонтальні» спостереження орбітальних об’єктів пристроями орбітального базування: супутникове угруповання тотального покриття заданої області висот". Aerospace Technic and Technology, n. 5 (3 ottobre 2023): 21–49. http://dx.doi.org/10.32620/aktt.2023.5.02.
Testo completoAbstract (sommario):
Promising approaches to updating multi-faceted information about space vehicles and objects of space debris involve the addition of networks of ground-based surveillance tools using satellite systems for observing near-Earth space, built on several orbital groups (segments). The purpose of the research is to develop the task of building a satellite system that provides total coverage of a given area of heights above the Earth's surface by the application zones of orbital-based devices that carry out "horizontal observations" (the axis of symmetry of the instantaneous zone of possible application of the "horizontal" observation device lies in the plane of the instantaneous local horizon space vehicle-device carrier). Results: 1) two "symmetrical" methods of solving the problem of choosing the parameters of the grouping of one of the segments of the satellite observation system, which has a well-known, often used structure based on the "rings" of spacecraft in symmetrically spaced orbital planes, have been developed (the grouping should ensure total coverage of the spherical layer in the altitude area of near-Earth space in its environment with the given parameters of the instantaneous cone-shaped zone of application of the observation device; the "width" of the covered spherical layer is chosen as a part of the layer that would be covered using observation devices with the given characteristics with an infinite number of spacecraft based on them); 2) the proposed approach to the construction of a satellite system of "horizontal" observations on several orbital groups of different heights, quasi-optimal according to the criterion of minimizing the number of spacecraft; 3) calculated examples of the application of the developed methods are given, and several approximate estimates are made regarding the implementation of systems based on "horizontal" observations. Conclusions: satellite systems for observing orbital objects based on "vertical" (in the radial direction) observations can be supplemented with the implementation of "horizontal" observations.
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Ho, Johnny C. "(Invited) From Bulk to Nanostructured Perovskites". ECS Meeting Abstracts MA2022-02, n. 36 (9 ottobre 2022): 1307. http://dx.doi.org/10.1149/ma2022-02361307mtgabs.
Testo completoAbstract (sommario):
The dimensionality of semiconductors has a crucial role in determining their properties. Recently, metal halide perovskites have been demonstrated with many exciting applications, attracting wide attention to further their development for advanced optoelectronics, such as photovoltaics, photodetectors, light-emitting diodes, and lasers. At length scales down to nanoscale regimes, surface features as well as quantum confinement effects become dominant in regulating the material properties of perovskite materials. In past years, our group focus on the synthesis and characterization of metal halide perovskites with different configurations, ranging from bulk films, microplates, nanosheets, to nanowires. The corresponding physical properties and device applications were also systematically studied based on their widely tunable dimensionality, morphologies, and compositions. Specifically, for perovskite bulk films, surface defects and bulk structural order significantly affect their device performance. Through optimizing processing techniques, self-assembled quasi-2D perovskite films with graded phase distribution were successfully prepared. Gradient type-II band alignments along the out-of-plane direction of perovskites with spontaneous separation of photo-generated electrons and holes are obtained, which is later employed to construct self-powered vertical-structure photodetectors for the first time. Without any driving voltage, the device exhibited impressive performance with the responsivity up to 444 mA/W and ultrashort response time down to 52 µs. In addition, to assess the intrinsic material properties of crystalline perovskites, freestanding MAPbI3 nanosheets and lead-free Cs3Sb2I9 microplates were fabricated by two-step chemical vapor deposition method, in which excellent optoelectronic performance (e.g., responsively of MAPbI3 nanosheet is measured to be 40 A/W) together with ultra-fast response speed (down to 58 µs) and superior thermal stability were obtained. For nanostructured perovskites, understanding the dimensional features and their impact on the materials and devices is becoming increasingly important. Lately, we reported the direct vapor-liquid-solid growth of single-crystalline all-inorganic lead halide perovskite (i.e., CsPbX3; X = Cl, Br, or I) NWs. These NWs exhibited high-performance photodetection with the responsivity exceeding 4489 A/W and detectivity over 7.9 × 1012 Jones toward the visible light regime. Field-effect transistors based on individual CsPbX3 NWs were also fabricated to show the impressive carrier mobility of 3.05 cm2/Vs, being higher than other all-inorganic perovskite devices. Besides, the realization of high-mobility CsPbBr3 NW devices is reported via a simple surface charge transfer doping strategy. After MoO3 decoration and device fabrication, the hole mobility of CsPbBr3/MoO3 core-shell NW device is significantly enhanced to 23.3 cm2/Vs. All these results provide important guidelines for the further improvement of these perovskite nanostructures for practical utilization.
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Ezekiel, Anyebe. "Investigation of Indium droplet assisted nucleation of InAs nanowires on graphite". Dutse Journal of Pure and Applied Sciences 10, n. 2a (18 luglio 2024): 118–25. http://dx.doi.org/10.4314/dujopas.v10i2a.11.
Testo completoAbstract (sommario):
An investigation of the Indium (In) droplet assisted nucleation of InAs nanowires (NWs) on graphite based on the quasi-van-der-Waals epitaxy method is reported. The surface morphology of as-grown NWs was studied using FEI XL30 SFEG scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDX) used for composition determination. Clear evidence is presented to demonstrate that the uniaxial growth of the InAs NWs directly on the underlying graphitic substrate is driven by the Indium droplets which etch nanoholes in the graphitic substrate and promote the formation of InAs seed particles underneath the NWs facilitating their vertical directionality. A high yield of InAs NWs exclusively in the [111]/[0001] growth direction on graphite is attributed to the InAs seeding particle. This report not only provides a better understanding of the InAs NWs nucleation on graphite but also unravels a cost-effective technique for obtaining a high yield of vertically oriented NWs on graphite with enormous potential for applications in highly efficient and flexible nano devices.
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Freitas, Jaime A., James C. Culbertson, Jennifer K. Hite, James Gallangher, Mona Ebrish, Michael Mastro e Travis J. Anderson. "(Invited) Optical Characterization of Bulk GaN Substrates and Homoepitaxial Films". ECS Meeting Abstracts MA2022-02, n. 37 (9 ottobre 2022): 1359. http://dx.doi.org/10.1149/ma2022-02371359mtgabs.
Testo completoAbstract (sommario):
Low ON-resistance and high breakdown voltage, made possible by improved critical electric field and mobility, has promoted GaN from a potential to the most promising semiconductor material for use in the next-generation of medium- and high voltage-power converters. The commercial availability of large area substrates, produced by HVPE (Hydride Vapor Phase Epitaxial, a quasi-bulk deposition technique) and ammonothermal bulk growth method, provides wafers with reduce concentrations of extended defect, allows the deposition of electronic grade epitaxial films and the realization of high performance electronic devices. Despite that, many steps of substrate preparation, such as miss-cut orientation and surface finishing, must be improved and standardized to yield reproducible epitaxial film growth. To verify the importance of substrate characteristics on the intrinsic properties of homoepitaxial MOCVD films, we initially evaluated substrate provided by various commercial supplies. The substrate effects on epi morphology, uniformity, and impurity incorporation were substantiated by growing simultaneously on wafers from different vendors. The goal of this work is to detect and identify defects in GaN substrates with a series of quick, non-destructive, inexpensive techniques with capabilities of mapping whole wafers. All evaluated substrates had nominally similar as-received specifications (resistivity, thickness, off-cut angle, bow, surface finish). The substrates were evaluated with a variety of techniques including Raman spectroscopy, photoluminescence, white light interferometry, and Nomarski imaging, enabling the detection of different concentrations of grain boundaries, impurities, point defects, v-shaped pits, polishing defects, crystal stress damage, and non-uniform insulating and conductive regions. The substrates can be grouped in two different categories: those with uniform characteristics, including carrier concentration, and those without. Comparing these results to those from homoepitaxial growth on the same wafers, the effects are both subtle and overt. Macroscopic surface morphology, which has shown a direct correlation to leakage current, copies and exaggerates that of the underlying substrate. Photoluminescence of the homoepitaxial surface along with Raman spectroscopy show that non-uniformities in the substrate carrier concentration can continue into the epitaxy. If time permits, results from vertical Schottky diodes, fabricated to quickly evaluate device performance, will presented. While most of the films showed the ability to withstand high electric fields, more uniform electrical properties were observed for those grown on substrates having more uniform properties. These results show that improving bulk substrates is the path to high voltage vertical devices, and that such substrates have a significant influence on device performance. Acknowledgments: Work at NRL is supported by the Office of Naval Research
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Cortis, D., E. Mancini, S. Nisi, D. Orlandi, P. Di Stefano, M. Utzeri e M. Sasso. "Compression Tests at High Strain Rate on 3D-Printed CuCrZr Alloy Specimens - Material Model Calibration". Journal of Physics: Conference Series 2444, n. 1 (1 febbraio 2023): 012001. http://dx.doi.org/10.1088/1742-6596/2444/1/012001.
Testo completoAbstract (sommario):
Abstract CuCrZr alloy is used to produce actively cooled components for high heat flux elements of beamlines and for heat sink of plasma facing components in nuclear fusion devices such as ITER and DEMO. It has an excellent thermal conductivity and specific mechanical strength, together with a high electrical conductivity that is giving high push to its use. Recently, CuCrZr alloy was also considered as an attractive material for Additive Manufacturing, leading to extend its application in the field of strain rate studies. As a matter of fact, its strain rate dependency is playing an important role for vertical target plasma-facing units components uses as heat sink in the ITER divertor or as structural material for actively cooled plasma facing components. This paper describes the results obtained by quasi-static and dynamic compression tests carried out on CuCrZr specimens produced by laser Powder Bed Fusion (PBF), with Selective Laser Melting (SLM) technology. Quasi-static tests have been conducted by means a servo-hydraulic tensile machine, while a direct tension-compression split Hopkinson bar has been used to perform the tests at high strain rate. Since dedicated heat treatments are required to obtain optimal combination of strength, ductility, and conductivity, some of the specimens have been heated up to 560 – 580 °C for 4 – 5 h and then cooled in air. Eventually, the calibration of the most appropriate constitutive models for 3D-printed CuCrZr alloy deformed at high strain rate has been carried out by means an inverse analytical procedure.
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Leblouba, Moussa, Palani Selvaraj Balaji e Muhammad Ekhlasur Rahman. "Wire Rope Isolators for the Vibration Protection of Heavy Equipment: Exploratory Research". Buildings 12, n. 12 (13 dicembre 2022): 2212. http://dx.doi.org/10.3390/buildings12122212.
Testo completoAbstract (sommario):
Wire rope isolators (WRI) are devices that dissipate vibrational energy. They are used in various industrial applications to protect equipment and machinery. Heavy machinery and limited space are still some of the constraints engineers face when designing the WRI system. Heavy equipment requires increased vertical stiffness; however, using larger WRIs decreases their lateral flexibility, which is the target property in the first place. Using several small-sized WRIs is not possible in the case of limited space. Therefore, the present study proposes two improvements to WRIs to overcome the challenges caused by heavy-weight equipment and a lack of the space required to insert the appropriate number and size of WRIs. Two new configurations for WRIs are proposed, Spring-WRI (S-WRI) and Double-WRI (D-WRI), to improve the stiffness and damping properties in order to expand their applications. Monotonic and quasi-static cyclic loading tests were performed on the conventional and proposed WRI variants. Exploratory tests showed that the WRI’s stiffness greatly depends on the wire rope diameter. Adding springs inside a conventional WRI (S-WRI) can improve vertical stiffness while maintaining the required lateral flexibility. The D-WRI was found to preserve the necessary flexibility and to be capable of solving the problem of limited space. The hysteresis behavior of the D-WRI can be expressed as the sum of the hysteresis of each WRI. The proposed configurations effectively improve the stiffness and damping properties of WRIs and expand their applicability for the vibration isolation of heavy equipment and in limited space.
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Weikle, Robert M., C. Zhang, S. Hawasli, S. Nadri, L. Xie, N. Scott Barker e A. W. Lichtenberger. "Terahertz Diode Arrays and Differential Probes based on Heterogeneous Integration and Silicon Micromachining". Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2016, DPC (1 gennaio 2016): 000924–62. http://dx.doi.org/10.4071/2016dpc-tp36.
Testo completoAbstract (sommario):
Due to the technological needs of the radio astronomy and remote sensing scientific communities, as well as emerging applications in the areas of imaging, security, and broadband communications, terahertz and submillimeter-wave electronics continues to be an area of growth and increasing interest for academic researchers, government laboratories, and industry. The recent establishment of a commercial infrastructure for test and measurement instrumentation in this spectral region has fueled this growth and the emergence of CMOS as a submillimeter-wave technology has greatly expanded access to this spectral region by providing circuit designers with a platform for realizing terahertz circuits without need for specialized fabrication facilities or processes. The continued emergence of new terahertz devices has created a need for improved approaches to packaging, integration, and measurement tools for diagnostics and characterization in this portion of the spectrum. This paper focuses on progress in two parallel efforts aimed at addressing these needs: (1) the development of a direct-contact probe technology for on-wafer measurement of differential scattering-parameters in the WR-5.1 (140—220 GHz) and WR-3.4 (220—330 GHz) frequency bands, and (2) the development of processing technologies for realizing highly-integrated submillimeter-wave diode-based quasi-optical arrays, including phase modulators and sideband generators, that are based on heterogeneous integration of III-V semiconductors onto thin silicon membranes as a support substrate. The foundation for these efforts is micromachining and processing of silicon, allowing the fabrication of mechanically-robust and low-loss membrane carriers that can support and interconnect terahertz devices as well as directly interface them to surrounding circuitry. Examples of heterogeneous integration onto silicon as an approach to packaging and interfacing terahertz components that are detailed in this paper include development of differential micromachined wafer probes for in situ measurements of devices and circuits in the 140—330 GHz region. The probe design concept includes an integrated on-chip balun and matching network for terminating common-mode signals that may be generated by the DUT. The design methodology and initial measurement results for this probe will be presented. In addition, an example of heterogeneous integration/packaging of a submillimeter-wave frequency sideband generator array for phase modulation at 1.6 THz will be discussed. The sideband generator design incorporates 100 planar varactor diodes integrated into an array of bowtie antennas on a common substrate. Performance of the array as a phase shifter is described and the application of a new quasi-vertical diode fabrication process that consists of transfer of GaAs epitaxy to thin silicon support substrates will be discussed as an approach for implementing optimized arrays in the terahertz frequency range.
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Wirapraja, Agung Yanuar, Handaru Bowo Cahyono e Mohamad Marhaendra Ali. "Shielding Elektromagnetik Tembaga dari Proses Elektrolisis Air Limbah Industri Printed Circuit Board". Jurnal Teknologi Bahan dan Barang Teknik 10, n. 1 (30 giugno 2020): 9. http://dx.doi.org/10.37209/jtbbt.v10i1.162.
Testo completoAbstract (sommario):
Some electronic products have high electromagnetic interference so that it gives a negative impact on the electronic devices around it. The use of electromagnetic shielding is a solution to reduce the value of electromagnetic radiation interference from electronic products. The research conducted includes the manufacture of electromagnetic shielding from copper material resulting from the electrolysis process of PCB (Printed Circuit Board) industrial wastewater and analyzing the effect of electromagnetic shielding from copper waste on the value of radiation emission. Electromagnetic shielding is made of vinyl which is coated with copper as a result of the electrolysis of PCB industrial wastewater. The measurement results show that electromagnetic shielding from copper waste can reduce radiation emissions. The use of electromagnetic shielding from copper waste is effective at frequencies from 250 to 350 MHz with a decrease in the quasi-peak value of 38.02 dB. The measurements with horizontal antenna polarization show that the margin of radiation emission value is higher comparated to vertical antenna polarization.Sebagian produk elektronika memiliki gangguan interferensi elektromagnetik yang tinggi, sehingga berdampak kurang baik terhadap perangkat elektronika di sekitarnya. Pemanfaatan shielding elektromagnetik menjadi solusi untuk mengurangi nilai gangguan radiasi elektromagnetik yang dimiliki oleh produk elektronika. Penelitian yang dilakukan meliputi pembuatan shielding elektromagnetik dari bahan tembaga hasil dari proses elektrolisis limbah industri PCB (Printed Circuit Board) dan melakukan analisa pengaruh shielding elektromagnetik dari limbah tembaga terhadap nilai emisi radiasi. Shielding elektromagnetik terbuat dari bahan vinyl yang dilapisi dengan tembaga hasil elektrolisis limbah cair industri PCB. Hasil pengukuran menunjukkan bahwa shielding elektromagnetik dari limbah tembaga dapat menurunkan emisi radiasi. Penggunaan shielding elektromagnetik dari limbah tembaga efektif di frekuensi 250 – 350 MHz dengan penurunan nilai quasi-peak sebesar 38,02 dB. Pada pengukuran dengan polarisasi antena horisontal, margin nilai emisi radiasi lebih tinggi jika dibandingkan dengan polarisasi antena vertikal. Kata Kunci: Shielding elektromagnetik, Emisi radiasi, Tembaga, PCB
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Weikle, Robert M., N. Scott Barker, Arthur W. Lichtenberger, Matthew F. Bauwens e Naser Alijabbari. "Heterogeneous Integration and Micromachining Technologies for Terahertz Devices and Components". Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2015, DPC (1 gennaio 2015): 002041–81. http://dx.doi.org/10.4071/2015dpc-tha31.
Testo completoAbstract (sommario):
Terahertz electronics has been a topic of research and development for many years, motivated largely by the technological needs of the radio astronomy and remote sensing scientific communities. Over the past decade, however, this field has experienced dramatic growth and intense, renewed interest from academic researchers and federal agencies, as well as from industry. This interest has arisen, in part, from recent funding initiatives from the federal government (such as DARPA's Terahertz Electronics Program), but is also largely due to the establishment of a commercial infrastructure that has made test and measurement instrumentation available to the engineers and scientists working at these frequencies. Moreover, the emergence of CMOS as a potential submillimeter-wave device technology has greatly expanded access to this spectral region by providing circuit designers with a platform for realizing terahertz circuits without need for specialized fabrication facilities or processes. The recent and rapid progress in terahertz electronics has created a demand for improved approaches to packaging and integration, as well as a need for new measurement instrumentation for characterizing emerging terahertz devices. This paper focuses on two recent research developments aimed at addressing these needs and broadening the technology base for both terahertz system implementation and terahertz metrology. These developments include (1) the development of a direct-contact probe technology that permits on-wafer scattering-parameter characterization and measurement of planar integrated devices at frequencies to 1 THz and beyond, and (2) the establishment of processing technologies that permit fabrication of highly-integrated submillimeter-wave diode-based circuits, such as heterodyne receivers and frequency multipliers, that are based on heterogeneous integration of III-V semiconductor devices with thin silicon membranes as a support and integration substrate. The technical foundation for each of these efforts is micromachining of silicon that allow the formation of mechanically-robust and low-loss membrane carriers to support terahertz devices and circuitry. Two examples of heterogeneous integration with silicon as an approach to packaging terahertz components are detailed in this paper. These include development of micromachined probes for on-wafer measurements of devices and circuits in the WR-1.0 waveguide band (0.75 – 1.1 THz). The probe design concept will be presented and methods for characterizing the probe described. Measurements demonstrate that the probes exhibit an insertion loss of less than 7 dB and return loss of greater than 15 dB over 750—1100 GHz band, yielding the first demonstration of on-wafer probe operating above 1 THz. In addition, an example of heterogeneous integration/packaging of a submillimeter-wave frequency quadrupler operating at 160 GHz with efficiency of 30% and corresponding output power of 70 mW will be discussed. The quadrupler design includes two frequency doubler stages in cascade and is based on a balanced circuit architecture that addresses degradation issues often arising from impedance mismatches between multiplier stages. A unique quasi-vertical diode fabrication process consisting of transfer of GaAs epitaxy to the thin silicon support substrate is used to implement the quadrupler, resulting in an integrated drop-in chip module that incorporates 18 varactors, matching networks and beamleads for mounting.
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Wiedmann, Stephen, e Bob Sturges. "Spatial Kinematic Analysis of Threaded Fastener Assembly". Journal of Mechanical Design 128, n. 1 (26 aprile 2005): 116–27. http://dx.doi.org/10.1115/1.2114909.
Testo completoAbstract (sommario):
Compliant mechanisms for rigid part mating exist for prismatic geometries. A few instances are known of mechanisms to assemble screw threads. A comprehensive solution to this essentially geometric problem comprises at least three parts: parametric equations for nut and bolt contact in the critical starting phase of assembly, the possible space of motions between these parts during this phase, and the design space of compliant devices which accomplish the desired motions in the presence of friction and positional uncertainty. This work concentrates on the second part in which the threaded pair is modeled numerically, and contact tests are automated through software. Tessellated solid models were used during three-dimensional collision analysis to enumerate the approximate location of the initial contact point. The advent of a second contact point presented a more constrained contact state. Thus, the bolt is rotated about a vector defined by the initial two contact points until a third contact location was found. By analyzing the depth of intersection of the bolt into the nut as well as the vertical movement of the origin of the bolt reference frame, we determined that there are three types of contacts states present: unstable two-point, quasi-stable two-point, stable three point. The space of possible motions is bounded by these end conditions which will differ in detail depending upon the starting orientations. We investigated all potential orientations which obtain from a discretization of the roll, pitch, and yaw uncertainties, each of which has its own set of contact points. From this exhaustive examination, a full contact state history was determined, which lays the foundation for the design space of either compliant mechanisms or intelligent sensor-rich controls.
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Ho, Johnny C. "(Invited) Design of Perovskites for High-Performance Electronics and Optoelectronics". ECS Meeting Abstracts MA2023-01, n. 14 (28 agosto 2023): 1335. http://dx.doi.org/10.1149/ma2023-01141335mtgabs.
Testo completoAbstract (sommario):
The success of lead halide perovskites as active materials in optoelectronic technologies is often associated with the unique properties of their optical excitations. Specifically, the photo-generated excitons in perovskites are responsible for the large absorption coefficients close to their band gap, reaching as high as 105 cm-1. Due to the advent of nanotechnology, perovskite materials can be readily fabricated into nanoscale configurations with different dimensionalities, and more importantly, the corresponding excitonic effects could be further enhanced. On the other hand, at length scales down to the nanoscale regime, surface features as well as quantum confinement effects, become dominant in regulating the advanced material properties of perovskite materials. [1, 2] In recent years, our group focused on the synthesis and characterization of metal halide perovskites with different forms, ranging from bulk film, microplate, and nanosheet, to nanowire. The corresponding physical properties and device applications were also systematically studied based on their widely tunable dimensionality, morphologies, and compositions. For perovskite bulk films, surface defects and bulk structural order significantly affect device performance. Through optimizing processing techniques, self-assemble quasi-2D perovskite films with graded phase distribution were successfully prepared by our group. [3] Gradient type-II band alignments along the out-of-plane direction of perovskites with spontaneous separation of photo-generated electrons and holes are obtained, which is further employed to construct self-powered vertical-structure photodetectors for the first time. Without any driving voltage, the device exhibited impressive performance with responsivity up to 444 mA/W and ultrashort response time down to 52 µs. In addition, to probe the intrinsic material properties of crystalline perovskites, freestanding MAPbI3 nanosheets, and lead-free Cs3Sb2I9 microplates were fabricated by two-step chemical vapor deposition method, in which excellent optoelectronic performance (e.g., responsively of MAPbI3 nanosheet is measured to be 40 A/W) together with ultra-fast response speed (down to 58 µs) and superior thermal stability were obtained. [4, 5] For nanostructured perovskites, understanding the dimensional features and their impact on the materials and devices is becoming increasingly important. For the first time, we reported the direct vapor-liquid-solid growth of single-crystalline all-inorganic lead halide perovskite (i.e., CsPbX3; X = Cl, Br, or I) NWs using Sn as catalyst seeds. [6] These NWs exhibited high-performance photodetection with the responsivity exceeding 4489 A/W and detectivity over 7.9 × 1012 Jones toward the visible light regime. Field-effect transistors based on individual CsPbX3 NWs were also fabricated to show the impressive carrier mobility of 3.05 cm2/Vs, being higher than other all-inorganic perovskite devices. After that, the Au catalyst seeds were used to avoid the Sn-related impurity doping, by which lower dark current and higher detectivity were achieved in Au-seeded CsPbI3 NWs. Besides, the realization of high-mobility CsPbBr3 NW devices is reported via a simple surface charge transfer doping strategy. [7] After MoO3 decoration and device fabrication, the hole mobility of CsPbBr3/MoO3 core-shell NW device is significantly enhanced to 23.3 cm2/Vs. All these results provide important guidelines for the further improvement of these perovskite nanostructures for practical utilization. References [1] Meng Y.†, Li F.†, Lan C., Bu X., Kang X., Wei R., Yip S., Li D., Wang F., Takahashi T., Hosomi T., Nagashima K., Yanagida T., Ho J.C.*, Science Advances, 6, eabc6389, 2020. [2] Li D., Lan C., Manikandan A., Yip S.P., Zhou Z., Liang X., Shu L., Chueh Y.L., Han N.,* Ho J.C.*, Nature Communications, 10, 1664, 2019. [3] Lai Z., Meng Y., Zhu Q., Wang F., Bu X., Li F., Wang W., Liu C., Wang F., Ho J.C.*, Small, 17, 2100442, 2021. [4] Lan C., Dong R., Zhou Z., Shu L., Li D., Yip S.P., Ho J.C.*, Advanced Materials, 29, 1702759, 2017. [5] Shil S.K.†, Wang F.†,*, Lai Z., Meng Y., Wang Y., Zhao D., Hossain M.K., Egdo K.O., Wang Y., Yu K.M.*, Ho J.C.*, Nano Research, 14, 4116-4124, 2021. [6] Meng Y., Lan C., Li F., Yip S.P., Wei R., Kang X., Bu X., Dong R., Zhang H., Ho J.C.*, ACS Nano, 13, 6060-6070, 2019. [7] Meng Y., Lai Z., Li F., Wang W., Yip S.P., Quan Q., Bu X., Wang F., Bao Y., Hosomi T., Takahashi T., Nagashima K., Yanagida T., Lu J., Ho J.C.*, ACS Nano, 14, 12749-12760, 2020.
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Roizin, Gregory, Ofer Beeri, Mor Mordechai Peretz e Yaniv Gelbstein. "Vertical power MOS transistor as a thermoelectric quasi-nanowire device". Journal of Applied Physics 120, n. 24 (28 dicembre 2016): 244903. http://dx.doi.org/10.1063/1.4973275.
Testo completo
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Hoshii, Takuya, Tatsuro Toyoda, Hitoshi Wakabayashi, Kazuo Tsutsui e Kuniyuki Kakushima. "Threshold Voltage Shift of P-Ch GaN Misfets with Charge Trapping Insulator". ECS Meeting Abstracts MA2024-02, n. 20 (22 novembre 2024): 1819. https://doi.org/10.1149/ma2024-02201819mtgabs.
Testo completoAbstract (sommario):
The realization of high-performance p-channel devices and threshold voltage control are desired to achieve GaN CMOS circuits. Recess-gate devices on polarized junction substrates have been reported as candidates for p-channel devices that can be integrated with n-channel devices, including HEMTs [1]. In addition, we have reported that the use of a quasi-atomic layer etching process with nitrogen plasma to fabricate the recessed gate structure improves the MIS interface characteristics and increases the drive current [2]. However, regarding threshold voltage control, the recessed gate structure may not be sufficient. Although control by the back gate is a candidate, other control methods are worth considering for circuit simplicity. In this study, we investigated the threshold control by introducing a charge trapping layer into the gate insulator. Figure 1 shows the schematic structure of p-channel GaN MISFETs with a charge-trapping layer fabricated on a polarization junction substrate. The insulator, Al2O3/HfO2/Al2O3 layer, was formed by atomic layer deposition. A negative threshold voltage shift could be expected when positive charges are trapped in the HfO2 layer or at the HfO2/Al2O3 interfaces. Figure 2 shows the I d-V g characteristics of a p-channel MISFET. V d was set to -3 V, and two consecutive double-sweep measurements were performed. Figure 2(a) shows the results of measurements with a V g range of +5 to -6 V. It shows a large hysteresis, with a negative sweep changing to the on state at a positive voltage and a positive sweep to the off state at a negative voltage. The second sweep also reproduces the first sweep's characteristics. This result can be attributed to the fact that the negative gate voltage introduces positive charges into the charge-trapping layer, resulting in a negative threshold voltage, and that the positive gate voltage completely removes the positive charge from the charge-capture layer, resulting in a positive threshold voltage again. On the other hand, Fig. 2(b) shows that, using the V g range of +2 to -6 V, the threshold voltage of the negative sweep in the second sweep shifts to negative. This result indicates that only partial charge was released from the charge trapping layer, and the remaining charge caused the shift. Also, Fig. 2(c) shows the results of the V g range of 0 to -6 V. The hysteresis at the second sweep is significantly reduced, indicating normally-off operation. This is considered to be a result of the positive charge captured in the charge-trapping layer being retained in the negative gate voltage range. Furthermore, Figs. 2(d), (e), and (f) present the vertical axes of Figs. 2(a), (b), and (c)c in logarithmic form, respectively, and in addition, I g is also shown. The gate leakage current is kept low compared to the drain current, and an on-off ratio of more than five orders of magnitude is obtained. Additionally, there is no significant change in the subthreshold slope due to threshold voltage variation, indicating that the charging and discharging of the charge trapping layer does not significantly affect the carrier transport properties in channel region. In this study, the threshold voltage shift and resulting normally-off operation of p-channel GaN MOSFETs is demonstrated by using a charge trapping layer. The same effect is promising for threshold voltage control of n-channel devices, and this technique is expected to be used for power-saving GaN CMOS circuits with two-dimensional carrier gases. Acknowledgments This work was supported by JSPS KAKENHI Grant Number 21K04172. References [1] A. Nakajima, et al., IET Power Electron. 11, 689 (2018). [2] S. Kimura, et al., in The International Workshop on Nitride Semiconductors 2022,p. 126. Figure 1
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Lin, Feng, Tuanzhuang Wu, Weidong Wang, Zhengxuan Wang, Yi Zhang, Sheng Li, Ran Ye et al. "Demonstration of Integrated Quasi-Vertical DMOS Compatible with the Bipolar-CMOS-DMOS Process Achieving Ultralow RON,sp". Nanomaterials 15, n. 3 (23 gennaio 2025): 172. https://doi.org/10.3390/nano15030172.
Testo completoAbstract (sommario):
An integrated quasi-vertical double-diffused MOSFET (DMOS) with split-gate trench (SGT) structure (SGT-QVDMOS), whose specific ON-state resistance (RON,sp) breaks the traditional Si limit significantly, is proposed and fabricated. The measured data of the latest manufactured device is presented. By introducing the vertical gate poly, the split grounded source poly, and the asymmetric thick oxide in the gate trench, the traditional lateral drift region is folded in the SGT-QVDMOS. In this way, the device voltage withstanding mode transforms from one dimension to two dimensions, including the horizontal and the vertical directions. Combining the electric field modulation effect and the reduced lateral area, which benefit from the quasi-vertical structure, the forward conducting characteristic of the SGT-QVDMOS is effectively improved. According to the measured results from the SGT-QVDMOS manufactured by the 180 nm Bipolar-CMOS-DMOS (BCD) process, the ultralow ON-state resistance is obtained. The device achieves 1.9 V VTH, 11.07 mΩ∙mm2 RON,sp, and 48.6 V BV, which is 39.0% lower than the traditional Si limit.
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Pandey, Shyam S., Shubham Sharma, Kumar Vivek Gaurav e Shuichi Nagamatsu. "Synergistic Control of Molecular Self-Assembly and Orientation to Enhance the Performance of Organic Field-Effect Transistors Utilizing Solution-Processable Organic Semiconductors". ECS Meeting Abstracts MA2024-02, n. 34 (22 novembre 2024): 2402. https://doi.org/10.1149/ma2024-02342402mtgabs.
Testo completoAbstract (sommario):
Introduction: Fast development of solution-processable organic semiconductors and their utilization as active components of organic electronic devices has gained momentum in the recent past aiming towards the practical realization of low-cost flexible and printable electronics. The past decade has witnessed significant scientific efforts to improve the charge transport characteristics of organic semiconductors by tuning their chemical structure or by varying the film fabrication techniques to enhance the macromolecular ordering. Due to the quasi-one-dimensional nature of organic conjugated polymers (CPs), their backbone orientation and self-assembly have been extensively explored to improve the optoelectronic characteristics of organic electronic devices. Organic electronic devices quite often need multilayer fabrication of devise components, where control of their morphology along with the various interfaces critically controls the overall performance of the devices. Therefore, there is an urge for the facile fabrication of large-area uniform films with controllable film morphology and minimal interference to the underlying layers. Our group has developed and improvised a novel method of thin film fabrication known as the floating-film transfer method (FTM), which provides not only large-area uniform thin films but also these films exhibit directional molecular orientation. Control of molecular orientation is highly desired to control the extent and directionality (vertical or in-plane) of the charge transport, which needs to be amicably utilized to harness the full potentiality of the device performance under investigation. Results and Discussion: The uniqueness of the FTM lies in 1st of all the fabrication of floating films of solution-processable CPs on an orthogonal liquid substrate followed by its transfer on any desired substrate by stamping, which has been schematically represented in Fig.1(a). Thanks to the isolation of film fabrication and transfer, it is possible to fabricate multilayers of the same or different CPs without having any adverse effect on the underlying layers, which is one of the intriguing issues for thin film fabrication using solution processing. We have demonstrated that controlling the parameters for thin film fabrication using NR-P3HT under FTM led to not only macroscopically oriented thin films but also there was a remarkable enhancement in the field effect mobility (>100 times) of organic field-effect transistors (OFETs) as compared to their spin-coated thin film device counterparts. One of the well-studied CPs, PBTTT-C14 possesses a rigid-rod-like polymeric backbone with liquid-crystalline behaviour, which is rather difficult to orient, and has been reported to impart enhanced carrier mobility when its thin film was annealed at its liquid-crystalline temperature of 180oC. Utilizing highly edge-on oriented thin films of this CP processed by FTM, we have not only demonstrated a very high optical dichroism of >10 but also an OFET mobility of 1.24 cm2/Vs, which is one of the highest reported mobility for this class of CPs as shown in Fig. 1(b). Despite the enhancement in solubility as a function of increasing alkyl-chain length in the P3AT class of CPs, there is a drastic fall in carrier mobility up to 4-5 orders of magnitude. We have recently demonstrated that FTM is capable of solving this issue amicably, where the detrimental influence of alkyl chain length for planer charge carrier transport was not observed making the freedom for the selection of any of P3ATs for OFET applications. Fabrication of a large-area ≈40 cm2 film with uniform orientation was recently reported for poly(3,3‴-dialkylquaterthiophene) (PQT) using FTM. An array of bottom-gate top contact OFETs fabricated along the length of a single large-area (≈15 × 2.5 cm2) thin film demonstrated the average field-effect mobility of 0.03 cm2/V s with a very narrow standard deviation of 12%. It has been found that the pre-conceived notion of the orientation of the FTM thin films is perpendicular to the direction of the flow of thin films is not completely true and the viscous force of not only the liquid substrate but also the CP solution plays a vital role in determining the direction of orientation as shown schematically in Fig. 1(c). Based on combined theoretical and experimental approaches, we have demonstrated the control of the extent and direction of molecular orientation using DPP-TTT, a rigid rod-like donor-acceptor type CP, which is rather difficult to orient owing to its molecular rigidity. Harnessing the synergy of orientation and molecular orientation under FTM using DPP-TTT, a very high field-effect mobility of 12.4 cm2V-1s-1 was recently demonstrated, which is one of the highest values reported for solution-processable organic semiconducting polymers. Results pertaining to the film fabrication by FTM, orientation mechanism, film uniformity and anisotropy along with the application of FTM-processed films towards their suitability of OFETs will be discussed in detail. Figure 1
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Pfeiffer, Franz, Tim Salditt e Christian David. "Reflection of waveguided X-rays in two-dimensional nanostructures". Journal of Applied Crystallography 35, n. 4 (18 luglio 2002): 430–33. http://dx.doi.org/10.1107/s0021889802006817.
Testo completoAbstract (sommario):
The internal reflection of an excited X-ray waveguide mode in a synthetic nanostructure, defined by electron-beam lithography, has been measured. In this device, the X-ray beam is first coupled into a conventional vertical thin-film waveguide structure and then reflected laterally at the quasi-one-dimensional edge of the waveguiding layer. The reflectivity of the quasi-one-dimensional interface has been recorded under simultaneous excitation of the (vertical) waveguide mode. The experiment constitutes an important step towards the production of a coherent nanometre-sized X-ray point source by two-dimensionally defined waveguide structures.
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Jia, Fuchun, Qingyuan Chang, Mengdi Li, Yungang Liu, Ziyan Lu, Jifan Zhang, Jinming Lai et al. "A Study of Reverse Characteristics of GaN-on-Si Quasi-Vertical PiN Diode with Beveled Sidewall and Fluorine Plasma Treatment". Micromachines 15, n. 12 (29 novembre 2024): 1448. http://dx.doi.org/10.3390/mi15121448.
Testo completoAbstract (sommario):
In this work, we show a high-performance GaN-on-Si quasi-vertical PiN diode based on the combination of beveled sidewall and fluorine plasma treatment (BSFP) by an inductively coupled plasma (ICP) system. The leakage current and breakdown voltage of the diode are systematically studied. Due to the beveled sidewall treated by the fluorine plasma, the diodes achieve an excellent breakdown voltage (VBR) of 790 V and a low reverse leakage current. In addition, the GaN-on-Si quasi-vertical PiN diode achieves a low specific on-resistance (Ron,sp) of 0.51 mΩ·cm2 and a high Baliga’s figure of merit (BFOM) of 1.22 GW/cm2. The relationship between the total leakage current and the device diameter shows that the sidewall leakage is the main leakage path of the device. Afterwards, the TCAD simulations based on electric field and electric potential reveal that the fluorine plasma treatment is a major factor in suppressing the leakage current and increasing the VBR for a diode with BSFP. This work systematically analyzes the effects of beveled sidewall and fluorine plasma treatment based on the reverse characteristics of the GaN-on-Si quasi-vertical PiN diode and highlights the great potential of the GaN-on-Si PiN diode for various power applications.
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Sun, Yue, Xuanwu Kang, Yingkui Zheng, Ke Wei, Pengfei Li, Wenbo Wang, Xinyu Liu e Guoqi Zhang. "Optimization of Mesa Etch for a Quasi-Vertical GaN Schottky Barrier Diode (SBD) by Inductively Coupled Plasma (ICP) and Device Characteristics". Nanomaterials 10, n. 4 (1 aprile 2020): 657. http://dx.doi.org/10.3390/nano10040657.
Testo completoAbstract (sommario):
The optimization of mesa etch for a quasi-vertical gallium nitride (GaN) Schottky barrier diode (SBD) by inductively coupled plasma (ICP) etching was comprehensively investigated in this work, including selection of the etching mask, ICP power, radio frequency (RF) power, ratio of mixed gas, flow rate, and chamber pressure, etc. In particular, the microtrench at the bottom corner of the mesa sidewall was eliminated by a combination of ICP dry etching and tetramethylammonium hydroxide (TMAH) wet treatment. Finally, a highly anisotropic profile of the mesa sidewall was realized by using the optimized etch recipe, and a quasi-vertical GaN SBD was demonstrated, achieving a low reverse current density of 10−8 A/cm2 at −10 V.
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Liu, Tao, Aiqun Li e Hengyuan Zhang. "Optimal Design and Dynamic Analysis of a New Quasi-Zero-Stiffness Isolation Device". Structural Control and Health Monitoring 2023 (18 luglio 2023): 1–17. http://dx.doi.org/10.1155/2023/9756226.
Testo completoAbstract (sommario):
Compared with the linear isolation system, the quasi-zero-stiffness (QZS) nonlinear isolation system has the characteristics of high static stiffness and low dynamic stiffness, which has better low-frequency vibration isolation performance. However, most of the existing QZS isolators only consider the quasi-zero-stiffness characteristic at the static equilibrium position achieved by the parallel connection of positive and negative stiffness structures. To optimize the isolation performance of the QZS system, a new isolation device based on the parallel connection of oblique springs and vertical springs was proposed. The device can not only achieve quasi-zero-stiffness at the static equilibrium position but also expand the interval of quasi-zero-stiffness through parameter optimization design to optimize the stiffness characteristics of the QZS system, thus effectively improving the vibration isolation performance. The QZS nonlinear systems with the optimal parameters were analyzed dynamically, and the nonlinear motion equations were approximately solved based on the fifth-order polynomials fitted by the restoring force curves. A prototype was further designed and fabricated to compare and analyze the vibration isolation performance of the QZS system and the equivalent linear system through a shaking table test.
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Rathkanthiwar, Shashwat, Pegah Bagheri, Dolar Khachariya, Seiji Mita, Spyridon Pavlidis, Pramod Reddy, Ronny Kirste, James Tweedie, Zlatko Sitar e Ramón Collazo. "Point-defect management in homoepitaxially grown Si-doped GaN by MOCVD for vertical power devices". Applied Physics Express 15, n. 5 (14 aprile 2022): 051003. http://dx.doi.org/10.35848/1882-0786/ac6566.
Testo completoAbstract (sommario):
Abstract We demonstrate controlled Si doping in the low doping range of 5 × 1015–2.5 × 1016 cm−3 with mobility >1000 cm2 V−1 s−1 in GaN films grown by metalorganic chemical vapor deposition. The carbon-related compensation and mobility collapse were prevented by controlling the electrochemical potential near the growth surface via chemical potential control (CPC) and defect quasi-Fermi level (dQFL) point-defect management techniques. While the CPC was targeted to reduce the net CN concentration, the dQFL control was used to reduce the fraction of C atoms with the compensating configuration, i.e. C N − 1 . The low compensating acceptor concentration was confirmed via temperature-dependent Hall effect analysis and capacitance–voltage measurements.
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El Amrani, Mohammed, Julien Buckley, Thomas Kaltsounis, David Plaza Arguello, Hala El Rammouz, Daniel Alquier e Matthew Charles. "Study of Leakage Current Transport Mechanisms in Pseudo-Vertical GaN-on-Silicon Schottky Diode Grown by Localized Epitaxy". Crystals 14, n. 6 (14 giugno 2024): 553. http://dx.doi.org/10.3390/cryst14060553.
Testo completoAbstract (sommario):
In this work, a GaN-on-Si quasi-vertical Schottky diode was demonstrated on a locally grown n-GaN drift layer using Selective Area Growth (SAG). The diode achieved a current density of 2.5 kA/cm2, a specific on-resistance RON,sp of 1.9 mΩ cm2 despite the current crowding effect in quasi-vertical structures, and an on/off current ratio (Ion/Ioff) of 1010. Temperature-dependent current–voltage characteristics were measured in the range of 313–433 K to investigate the mechanisms of leakage conduction in the device. At near-zero bias, thermionic emission (TE) was found to dominate. By increasing up to 10 V, electrons gained enough energy to excite into trap states, leading to the dominance of Frenkel–Poole emission (FPE). For a higher voltage range (−10 V to −40 V), the increased electric field facilitated the hopping of electrons along the continuum threading dislocations in the “bulk” GaN layers, and thus, variable range hopping became the main mechanism for the whole temperature range. This work provides an in-depth insight into the leakage conduction transport on pseudo-vertical GaN-on-Si Schottky barrier diodes (SBDs) grown by localized epitaxy.
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Zhang, Xin, Da Ming Wu, Ying Liu e Guang Jun Song. "The Mechanism of Quasi-Dynamic Expansion Method and the Design of the Equipment for Manufacturing Biaxial Oriented PVC Pipes". Applied Mechanics and Materials 372 (agosto 2013): 410–15. http://dx.doi.org/10.4028/www.scientific.net/amm.372.410.
Testo completoAbstract (sommario):
Due to the biaxial oriented PVC (PVC-O) pipes have a great improvement in the strength, heat resistance, modulus, and impact resistance, etc. So the new products can be used in many situations. Referring to the foreign Mouth die drawing method, the mechanism of quasi-dynamic expansion method is proposed in the paper. We chose the hard polyvinyl chloride (PVC-U) pipes for raw materials, through the forward movement of the pipe match with the vertical reciprocating movement of the expansion parts, improve the design of a whole package of biaxial oriented self-reinforced pipe continuous production device. The device has great advanced properties: small expansion friction resistance, high hoop extension ratio, simple production device, production line is easy to start etc.
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Zhao, Wen, e Ming Li. "Study of Nonlinear Dynamics of Rotor-Bearing System Coupled with a Floating Raft Isolation Device". Applied Mechanics and Materials 598 (luglio 2014): 202–5. http://dx.doi.org/10.4028/www.scientific.net/amm.598.202.
Testo completoAbstract (sommario):
The mathematic model of rotor-bearing system coupled with floating raft isolation device is developed and its nonlinear dynamic characteristics are mainly discussed in this paper. First, on the basic assumption theory of short bearing, the nonlinear dynamic motions of the system with 4 DOF is deduced after considering the vertical and horizontal deformation and the nonlinear vibrating behaviors are analyzed such as the steady state response and its spectrum, orbit and its Poincaré map. The results show that the responses at a low speed appear single periodic motion, with increasing the speed it indicates the doubling and quasi periodic motion, etc.
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Kamal, Shahanawaz, Mohd Fadzil Bin Ain, Ubaid Ullah, Abdullahi S. B. Mohammed, Roslina Hussin, Mohamad Faiz Bin Mohamed Omar, Fathul Najmi et al. "A Low-Profile Quasi-Loop Magneto-Electric Dipole Antenna Featuring a Wide Bandwidth and Circular Polarization for 5G mmWave Device-to-Device Communication". Journal of Electromagnetic Engineering and Science 22, n. 4 (31 luglio 2022): 459–71. http://dx.doi.org/10.26866/jees.2022.4.r.110.
Testo completoAbstract (sommario):
The deployment of the millimeter (mmWave) frequency spectrum by fifth-generation (5G) device-to-device (D2D) wireless networks is anticipated to meet the growing demands for increased capacity. The antenna is regarded of as an important determinant that guarantees the maximum performance of wireless communication. This paper presents a low-profile magneto-electric (ME) dipole antenna for 5G mmWave D2D communication. A single-element quasi-loop radiator was designed to excite horizontal polarization, and a coaxial probe was used to produce vertical polarization. Subsequently, the structure of the radiator was transformed into a two-element quasi-loop antenna to achieve an omnidirectional radiation pattern with relatively enhanced gain. A coaxially fed T-junction microstrip element was implemented to equally distribute the signal between the two quasi-loop radiators and attain proper impedance matching. Furthermore, a pair of shorting pins was introduced into the two-element design to maintain the circularly polarized (CP) radiation. The finest values of the axial ratio and |S<sub>11</sub>| were derived by rigorously optimizing all the geometry parameters. Both single-element and two-element quasiloop antennas were fabricated and characterized experimentally on the air substrate. The advantage of avoiding a physical substrate is to realize a wide bandwidth, circumvent dielectric losses, and ascertain the maximum gain. The measured and simulated results agree thoroughly with each other. Stable in-band CP radiation were accomplished, thus confirming an appropriate field vector combination from the coaxial probe and the radiator. The finalized antenna engaged an area of ~7.6λ<sup>2</sup><sub>0</sub> for operation at 23.9–30.0 GHz with an axial ratio <3 dB, radiation efficiency ~80%, and gain >5 dBic.
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Zhang, Runzhe, Siyuan Qiao, Yixiong Luo, Yinghui Guo, Xiaoyin Li, Qi Zhang, Yulong Fan, Zeyu Zhao e Xiangang Luo. "Structured-Light 3D Imaging Based on Vector Iterative Fourier Transform Algorithm". Nanomaterials 14, n. 11 (25 maggio 2024): 929. http://dx.doi.org/10.3390/nano14110929.
Testo completoAbstract (sommario):
Quasi-continuous-phase metasurfaces overcome the side effects imposed by high-order diffraction on imaging and can impart optical parameters such as amplitude, phase, polarization, and frequency to incident light at sub-wavelength scales with high efficiency. Structured-light three-dimensional (3D) imaging is a hot topic in the field of 3D imaging because of its advantages of low computation cost, high imaging accuracy, fast imaging speed, and cost-effectiveness. Structured-light 3D imaging requires uniform diffractive optical elements (DOEs), which could be realized by quasi-continuous-phase metasurfaces. In this paper, we design a quasi-continuous-phase metasurface beam splitter through a vector iterative Fourier transform algorithm and utilize this device to realize structured-light 3D imaging of a target object with subsequent target reconstruction. A structured-light 3D imaging system is then experimentally implemented by combining the fabricated quasi-continuous-phase metasurface illuminated by the vertical-cavity surface-emitting laser and a binocular recognition system, which eventually provides a new technological path for the 3D imaging field.
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Hwang, Jeong-Yeon, Lena Wysocki, Erdem Yarar, Gunnar Wille, Fin Röhr, Jörg Albers e Shanshan Gu-Stoppel. "Low Power Compact 3D-Constructed AlScN Piezoelectric MEMS Mirrors for Various Scanning Strategies". Micromachines 14, n. 9 (19 settembre 2023): 1789. http://dx.doi.org/10.3390/mi14091789.
Testo completoAbstract (sommario):
In this paper, the newly developed 3D-constructed AlScN piezoelectric MEMS mirror is presented. This paper describes the structure and driving mechanism of the proposed mirror device, covering its driving characteristics in both quasi-static and resonant scan modes. Particularly, this paper deals with various achievable scan patterns including 1D line scan and 2D area scan capabilities and driving methods to realize each scanning strategy. Bidirectional quasi-static actuation along horizontal, vertical, and diagonal scanning directions was experimentally characterized and even under a low voltage level of ±20 V, a total optical scan angle of 10.4° was achieved. In addition, 1D line scanning methods using both resonant and non-resonant frequencies were included and a total optical scan angle of 14° was obtained with 100 mVpp under out-of-phase actuation condition. Furthermore, 2D scan patterns including Lissajous, circular and spiral, and raster scans were realized. Diverse scan patterns were realized with the presented AlScN-based MEMS mirror device even under a low level of applied voltage. Further experiments using high voltage up to ±120 V to achieve an enhanced quasi-static scan angle of more than 20° are ongoing to ensure repeatability. This multi-functional MEMS mirror possesses the potential to implement multiple scanning strategies suitable for various application purposes.
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Zhang, Rong. "Reection and refraction of plane waves at the interface between magnetoelectroelastic and liquid media". Theoretical and Applied Mechanics 40, n. 3 (2013): 427–39. http://dx.doi.org/10.2298/tam1303427z.
Testo completoAbstract (sommario):
This paper analyzes the reflection and refraction of plane wave incidences at the interface between magnetoelectroelastic (MEE) and liquid media. The MEE medium is assumed to be transversely isotropic and the liquid medium to be nonviscous. Three cases, i.e., the coupled quasipressure wave incidence from the MEE medium, the coupled quasi-shear vertical wave incidence from the MEE medium, and the pressure wave incidence from the liquid medium, are discussed. The expressions of reflection and transmission coefficients varying with the incident angle are obtained. This investigation would be useful to the MEE acoustic device field.