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SSRN 2024年

作者： Zebarjadi, Mona Tonni, Farjana Ferdous Yazawa, Kazuaki Shakouri, Ali Department of Electrical and Computer Engineering University of Virginia CharlottesvilleVA22904 United States Department of Materials Science and Engineering University of Virginia CharlottesvilleVA22904 United States Purdue University 1205 W State St. West LafayetteIN47907 United States

We demonstrate enhanced Peltier cooling at the nanoscale using geometrical constriction. This nozzle structure leads to electron expansion under an applied bias, which in turn results in additional cooling. This extra cooling enhances the overall Peltier effect when the electrons are out of equilibrium with the lattice. An ensemble Monte Carlo simulation is used to demonstrate the non-equilibrium expansion of an electron gas using nanoscale trapezoidal geometric confinement. The proposed device operates under steady-state conditions, providing enhanced cooling compared to a one-dimensional flat geometry. We observe a five-fold increase in both the maximum cooling temperature and cooling power density, reaching more than 5 kW/cm2, when comparing the trapezoidal geometry to the regular flat geometry. © 2024, The Authors. All rights reserved.

关键词： Solid state device structures

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Broken Symmetry Effects due to Polarization on Resonant Tunneling Transport in Double-Barrier Nitride Heterostructures

arXiv

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arXiv 2023年

作者： Encomendero, Jimy Protasenko, Vladimir Sensale-Rodriguez, Berardi Fay, Patrick Rana, Farhan Jena, Debdeep Xing, Huili Grace School of Electrical and Computer Engineering Cornell University IthacaNY14853 United States Department of Electrical and Computer Engineering The University of Utah Salt Lake CityUT84112 United States Department of Electrical Engineering University of Notre Dame Notre DameIN46556 United States Department of Materials Science and Engineering Cornell University IthacaNY14853 United States Kavli Institute Cornell for Nanoscale Science Cornell University IthacaNY14853 United States

The phenomenon of resonant tunneling transport through polar double-barrier heterostructures is systematically investigated using a combined experimental and theoretical approach. On the experimental side, GaN/AlN resonant tunneling diodes (RTDs) are grown by molecular beam epitaxy. In-situ electron diffraction is used to monitor the number of monolayers incorporated into each tunneling barrier of the RTD active region. Using this precise epitaxial control at the monolayer level, we demonstrate exponential modulation of the resonant tunneling current density as a function of barrier thickness. At the same time, both the peak voltage and characteristic threshold bias exhibit a dependence on barrier thickness as a result of the intense electric fields present within the polar heterostructures. To get further insight into the asymmetric tunneling injection originating from the polar active region, we present an analytical theory for tunneling transport across polar heterostructures. A general expression for the resonant tunneling current which includes contributions from coherent and sequential tunneling processes is introduced. After the application of this theory to the case of GaN/AlN RTDs, their experimental current-voltage characteristics are reproduced over both bias polarities, with tunneling currents spanning several orders of magnitude. This agreement allows us to elucidate the effect of the internal polarization fields on the magnitude of the tunneling current and broadening of the resonant tunneling line shape. Under reverse bias, we identify new tunneling features originating from highly attenuated resonant tunneling phenomena, which are completely captured by our model. The analytical form of our model, provides a simple expression that reveals the connection between the design parameters of a general polar RTD and its current-voltage characteristics. This new theory paves the way for the design of polar resonant tunneling devices exhibiting efficient reso

关键词： Resonant tunneling

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Investigation on Structures of Axial Gap Type Magnetic Multiple Spur Gear for In-Wheel Motor System of Electric Vehicle

Investigation on Structures of Axial Gap Type Magnetic Multi...

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IEEE Conference and Expo Transportation Electrification Asia-Pacific (ITEC Asia-Pacific)

作者： Taiga Kamijo Kohei Aiso Kan Akatsu Yasuaki Aoyama Electrical Engineering and Computer Science Shibaura Institute of Technology Tokyo Japan Department of Electrical Engineering Shibaura Institute of Technology Tokyo Japan Department of Faculty of Engineering Division of Intelligent Systems Engineering Yokohama National University Yokohama Japan Center for Technology Innovation - Materials Hitachi Ltd. Research & Development Group Ibaraki Japan

A novel drive system using Magnetic Multiple Spur Gear (MMSG) and multiple high-speed motors is characterized by small size, lightweight, and high efficiency even at high-speed region, it is expected to apply to in-wheel motor systems. However, there is a risk of contact between the rotors when applied to in-wheel motor system. In this study, a novel axial-gap MMSG is proposed to solve this problem, stabilize the air gap between the high-speed and low-speed rotors, and effectively utilize the magnets, and its performance is evaluated by finite element analysis.

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Proposal of Axial-gap type Magnetic Multiple Spur Gear for In-wheel Motor System of Electric Vehicle

Proposal of Axial-gap type Magnetic Multiple Spur Gear for I...

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IEEE International Conference on Electric Machines and Drives (IEMDC)

Magnetic gears have the characteristics of maintenance-free, low noise, and low vibration due to non-contact power transmission. By taking advantage of the non-contact power transmission, the motor system can be made smaller and lighter by further increasing the motor speed. Magnetic Multiple Spur Gear (MMSG) has been proposed, the drive system of MMSG and multiple high-speed motors can reduce the size and weight of the drive system by converting the total power of multiple high-speed motors. Applying this drive system to in-wheel motors will increase the available interior space in electric vehicles. However, there is a risk that the high-speed rotor and low-speed rotor contact with each other due to the radial structure in the in-wheel motor system. In this research, an axial-gap MMSG is proposed to solve the problem and to obtain higher torque density, the performances such as torque density and efficiency are evaluated by finite element analysis.

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Heterogeneous Freeform Metasurfaces: A Platform for Advanced Broadband Dispersion engineering

arXiv

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arXiv 2024年

作者： Li, Zhaoyi Campell, Sawyer D. Park, Joon-Suh Jenkins, Ronald P. Lim, Soon Wei Daniel Werner, Douglas H. Capasso, Federico Department of Materials Science and Engineering Massachusetts Institute of Technology CambridgeMA02139 United States Harvard John A. Paulson School of Engineering and Applied Sciences Harvard University CambridgeMA02138 United States School of Electrical Engineering and Computer Science The Pennsylvania State University University ParkPA16802 United States

Metasurfaces, with their ability to control electromagnetic waves, hold immense potential in optical device design, especially for applications requiring precise control over dispersion. This work introduces an approach to dispersion engineering using heterogeneous freeform metasurfaces, which overcomes the limitations of conventional metasurfaces that often suffer from poor transmission, narrow bandwidth, and restricted polarization responses. By transitioning from single-layer, canonical meta-atoms to bilayer architectures with non-intuitive geometries, our design decouples intrinsic material properties (refractive index and group index), enabling independent engineering of phase and group delays as well as higher-order dispersion properties, while achieving high-efficiency under arbitrary polarization states. We implement a two-stage multi-objective optimization process to generate libraries of meta-atoms, which are then utilized for the rapid design of dispersion-engineered metasurfaces. Additionally, we present a bilayer metasurface stacking technique, paving the way for the realization of high-performance, dispersion-engineered optical devices. Our approach is validated through the demonstration of metasurfaces exhibiting superior chromatic aberration correction and broadband performance, with over 81% averaged efficiency across the 420-nm visible-to-near-infrared bandwidth. Our synergistic combination of advanced design physics, powerful freeform optimization methods, and bi-layer nanofabrication techniques represents a significant breakthrough compared to the state-of-the-art while opening new possibilities for broadband metasurface applications. Copyright © 2024, The Authors. All rights reserved.

关键词： Chromatic dispersion

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Switching between topological edge states using phase-change materials

Switching between topological edge states using phase-change...

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2023 Active Photonic Platforms, APP 2023

作者： Veronis, Georgios Huang, Yin Shen, Yuecheng School of Electrical Engineering and Computer Science Louisiana State University Baton RougeLA70803 United States Center for Computation and Technology Louisiana State University Baton RougeLA70803 United States Department of Optoelectrics Information Science and Engineering School of Physics and Electronics Central South University Hunan Changsha410012 China State Key Laboratory of Optoelectronic Materials and Technologies School of Electronics and Information Technology Sun Yat-Sen University Guangdong Guangzhou510275 China

ISBN: (纸本)9781510665088

We introduce non-Hermitian plasmonic waveguide-cavity structures based on the Aubry-Andre-Harper model to realize switching between right and left topological edge states using the phase-change material germanium-antimony-tellurium (GST). The structure unit cells consist of a metal-dielectric-metal (MDM) waveguide side-coupled to MDM stub resonators with modulated distances between adjacent stubs. In such structures the modulated distances introduce an effective gauge magnetic field. We show that switching between the crystalline and amorphous phases of GST leads to a shift of the dispersion relation of the optimized structure so that a right topological edge state for the crystalline phase, and a left topological edge state for the amorphous phase occur at the same frequency. Thus, we realize switching between right and left topological edge states at that frequency by switching between the crystalline and amorphous phases of GST. Our results could be potentially important for developing compact reconfigurable topological photonic devices. © 2023 SPIE.

关键词： Gages

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Strong Damping-Like Torques in Wafer-Scale MoTe2 Grown by MOCVD

arXiv

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arXiv 2024年

作者： Chyczewski, Stasiu T. Lee, Hanwool Li, Shuchen Eladl, Marwan Zheng, Jun-Fei Hoffmann, Axel Zhu, Wenjuan Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign UrbanaIL61801 United States Department of Materials Science and Engineering University of Illinois at Urbana-Champaign UrbanaIL61801 United States Entegris Inc. DanburyCT06810 United States

The scalable synthesis of strong spin orbit coupling (SOC) materials such as 1T’ phase MoTe2 is crucial for spintronics development. Here, we demonstrate wafer-scale growth of 1T’ MoTe2 using metal-organic chemical vapor deposition (MOCVD) with sputtered Mo and (C4H9)2Te. The synthesized films show uniform coverage across the entire sample surface. By adjusting the growth parameters, a synthesis process capable of producing 1T’/2H MoTe2 mixed phase films was achieved. Notably, the developed process is compatible with back-end-of-line (BEOL) applications. The strong spin-orbit coupling of the grown 1T’ MoTe2 films was demonstrated through spin torque ferromagnetic resonance (ST-FMR) measurements conducted on a 1T’ MoTe2/permalloy bilayer RF waveguide. These measurements revealed a significant damping-like torque in the wafer-scale 1T’ MoTe2 film and indicated high spin-charge conversion efficiency. The BEOL compatible process and potent spin orbit torque demonstrate promise in advanced device applications. © 2024, CC BY.

关键词： Damping

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Interferometry Among Strongly Driven Quasiparticles with Distinct Dynamical and Geometrical Phases

Interferometry Among Strongly Driven Quasiparticles with Dis...

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CLEO: Fundamental science, CLEO:FS 2024 - Part of Conference on Lasers and Electro-Optics, CLEO 2024

作者： O'Hara, Seamus Costello, Joe Tian, Qi Wu, Qile West, Ken Pfeiffer, Loren Sherwin, Mark Wu, Liang Department of Physics Institute of Terahertz Science and Technology University of California Santa Barbara Santa BarbaraCA93106 United States Intelligence Community Post-Doctoral Research Fellowship Program PhiladelphiaPA19104 United States Department of Physics University of Pennsylvania PhiladelphiaPA19104 United States Department of Electrical and Computer Engineering Princeton University PrincetonNJ08542 United States

ISBN: (纸本)9781957171395

In this proceeding, we present polarization data of sidebands emitted from strongly driven quasiparticles, demonstrate the dependence of these data on various parameters of the external driving field, and describe the data using an analytical expression, dependent on driving field parameters and the effective Hamiltonian of the system. We propose using this method on spin-momentum locked systems, such as altermagnets, to observe and reconstruct sidebands which are influenced by the topology of individual bands. © Optica Publishing Group 2024, © 2024 The Author(s)

关键词： Hamiltonians

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Top-Down Fabrication of Diamond Nanostructures

SSRN

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SSRN 2024年

作者： Biswas, Abhijit Li, Chenxi Pieshkov, Tymofii Mei, Zhaobo Xu, Mingfei Li, Tao Murukeshan, Jishnu Vajtai, Robert Zhao, Yuji Ajayan, Pulickel M. Department of Materials Science and NanoEngineering Rice University HoustonTX77005 United States Applied Physics Graduate Program Smalley-Curl Institute Rice University HoustonTX77005 United States Department of Electrical and Computer Engineering Rice University HoustonTX77005 United States

Diamond nanostructures can have exciting applications in electronics and thermal management, but their controlled fabrication can be challenging. Here, we present a top-down approach for the fabrication of diamond nanorod (DNR) clusters, via use of metal masks (Al, Ag, Au, and Cr) and reactive-ion etching (RIE). Prolonged RIE on Ag and Cr masks yields distinct etching profiles, and DNR clusters are selectively formed from Ag masks, with individual nanorods having dimensions of ~100 nm diameter and ~1.5 µm length. Detailed electron microscopy shows thin layer of amorphous carbon (a-C) around single crystalline DNR cores. Chemical analyses also show presence of oxygen on the surface of the DNRs. Fabrication of the DNR clusters with scalable top-down approach could lead to new nanodiamond-based applications. © 2024, The Authors. All rights reserved.

关键词： Nanorods

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Thermo-Mechanical Analysis of a 650 V/150 A e-GaN HEMT Sandwiched Between a PCB and DBC Substrate

Thermo-Mechanical Analysis of a 650 V/150 A e-GaN HEMT Sandw...

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IEEE Workshop on Wide Bandgap Power Devices and Applications (WiPDA)

作者： Carl Nicholas Filip Boshkovski Emmanuel Arriola Zichen Zhang Guo-Quan Lu Bradley Department of Electrical and Computer Engineering Virginia Tech Blacksburg VA USA Center for Power Electronics Systems Virginia Tech Blacksburg VA USA Department of Materials Science and Engineering Virginia Tech Blacksburg VA USA

Following successful packaging of a 650 V/150 A e-GaN HEMT between a printed-circuit board and a direct-bond-copper substrate, this study evaluates the thermo-mechanical reliability of the sandwich-style package. Thermo-mechanical fatigue of both soldered and silver-sintered bonds in the package under temperature cycling was studied using ANSYS Mechanical. Deformation properties of eutectic lead-tin solder and sintered silver were modeled after Anand viscoplastic behavior. The inelastic volume-averaged strain energy density accumulated per thermal cycle at each bond was used as a metric of bond fatigue. Simulation results showed that the silver-sintered bond at the gate pad and the solder bond closest to the package center have the highest per-cycle strain energy density. Simulations also evaluated the effect of encapsulation materials on bond fatigue. It was found that using rigid encapsulants, such as one with a coefficient of thermal expansion of 14.9 ppm/°C and an elastic modulus of 17.5 GPa, instead of a commonly used silicone gel reduced the per-cycle bond fatigue by 97%. Findings of this study would help guide the development of high performing and high reliability packaging technology for the 650V/150A GaN HEMT.

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