High Power Applications Research Articles

Achieving ultrahigh hole mobility in hydrogen-terminated diamond via boron nitride modifications

Wide-bandgap semiconductors with high carrier mobility are in great demand for high-power radio-frequency applications. In the past decades, extensive efforts have been devoted to investigating the carrier transport properties of hydrogen-terminated diamond (H-diamond), however, achieving its high hole mobility remains a challenge, thereby limiting the development of diamond electronic devices. Herein, we propose a novel strategy to increase the hole mobility of H-diamond by boron nitride (BN) clusters modifications. Amorphous BN clusters were deposited on high-quality H-diamond surfaces using magnetron sputtering. The modified H-diamond exhibits an ultrahigh hole mobility of 1100 cm2 V−1 s−1, over 10-fold higher than that of H-diamond prior to BN modification. Moreover, the BN-modified H-diamond also exhibits outstanding high-temperature tolerance and excellent thermal stability benefitting from the passivation effect of BN. At 380 K, it still maintains a hole mobility of 385 cm2 V−1 s−1. Even after annealing at 350 K for over 8 h, there are no noticeable variations in its carrier transport properties. The hole mobility enhancing mechanism and the factors influencing carrier transport properties of the BN-modified H-diamond are discussed using first principles calculations analysis. The developed BN-modified H-diamond opens up new possibilities for diamond-based radio-frequency electronic devices operating in challenging temperature environments.

Heterogeneous integration of thick GaN and polycrystalline diamond at room temperature through dynamic plasma polishing and surface-activated bonding

Direct heterogeneous integration of GaN on diamond enhances device performance and reliability for high-power applications, while the implementation on thick GaN films and polycrystalline diamond (p-diamond) substrates remains challenging. In this study, the direct bonding between thick GaN films (∼370 μm) and p-diamond substrates was achieved. A dynamic plasma polishing (DPP) technique was adopted on the diamond to flatten surficial spikes from maximum 15 nm to 1.2 nm, obtaining a smooth surface with 0.29 nm Ra, achieving a robust GaN/diamond bonding with high bonding rate of ∼92% at room temperature combining the surface-activated bonding (SAB) method. The chemical status, thermal stress, and interfacial microstructures of GaN/diamond heterostructures were analyzed, revealing a residual stress of ∼200 MPa at the GaN/diamond interface, and the asymmetric increase of interfacial stress at rising temperature demonstrates the effectiveness of amorphous interlayer to release the stress.

Efficient broad-band NIR-II emitting phosphor Mg4Ta2O9: Ni2+ with satisfactory thermal stability of luminescence

The applications of near-infrared (NIR) spectroscopy in the fields of medicine and food safety require efficient and compact NIR light sources, for example, NIR phosphor converted light-emitting diodes (pc-LEDs). In recent years, Ni2+ has become one of the main activators for its broadband NIR-II (1000–1700 nm) emission under ultraviolet or visible light excitation. However, two important effects (Concentration quenching which decreases the emission intensity and temperature quenching which decreases the adaptability of phosphor in high-power applications) seriously hinder the development of Ni2+ doped NIR-II emitting phosphors. It is an urgent and important task to restrain both concentration and thermal quenching of the Ni2+ luminescence to develop an efficient NIR-II emitting phosphor. Here, novel NIR-II emitting Mg4Ta2O9: Ni2+ phosphors with perovskite-like structure were synthesized and investigated. In Mg4Ta2O9, the quenching concentration of Ni2+ is as high as 0.045. This is a relatively high value for Ni2+ activated NIR-II emitting phosphors. Mg4Ta2O9: 0.045Ni2+ presents broadband emission (1100–1700 nm, the full width at half maximum (FWHM) = 218 nm) with internal and external quantum efficiency of 64.2% (IQE) and 7.2% (EQE), respectively. The phosphor exhibits excellent luminous thermal stability (at 423 K, it keeps 84.85% of initial intensity at room temperature). High structure stiffness of Mg4Ta2O9 is responsible for the high quenching concentration and desirable luminous thermal stability. This work developed an efficient NIR-II emitting phosphor which exhibits desirable thermal stability of luminescence. Theoretically, this work points out a direction for future development of efficient NIR-II emitting phosphors, selecting an inorganic compound with high structural rigidity as the host for Ni2+ doping.

An Overview of BMS Technologies in Electric Vehicles

Batteries are used extensively in high-power applications, including hybrid and electric vehicles (EVs), where the proper battery management system (BMS) is essential to the batteries' dependable and safe performance. The purpose of this study is to provide a quick overview of several important BMS technologies, such as battery charging, state estimation, and battery modelling. The most common battery types utilized in EVs are first examined, and then important BMS technologies are introduced. The most crucial step in determining the energetic range of an EV is the valuation of the electrical properties of batteries. It’s vital to apprehend the variability of battery performance characteristics in order to understand battery behavior in several environments. Finally, the performance characteristics of EV charging and batteries are analyzed to raise the demand for electric vehicles globally.

Unlocking superior safety, rate capability, and low-temperature performances in LiFePO4 power batteries

The safety concerns associated with lithium-ion batteries (LIBs) have sparked renewed interest in lithium iron phosphate (LiFePO4) batteries. It is noteworthy that commercially used ester-based electrolytes, although widely adopted, are flammable and fail to fully exploit the high safety potential of LiFePO4. Additionally, the slow Li+ ion diffusion and low electronic conductivity of LiFePO4 batteries limit their utility in high-power applications. Despite the crucial role played by liquid electrolytes in LIBs, achieving simultaneous improvements in safety, rate capability, and low-temperature performance remains a formidable challenge. In this study, we addressed these challenges by innovatively applying a single solvent ethyl vinyl sulfone (EVS) electrolyte to graphite/LiFePO4 batteries. While renowned for its broad electrochemical window, low freezing point and superior safety performance, the EVS electrolyte exhibited compatibility issues with the graphite anode. To overcome this hurdle effectively, we utilized vinylene carbonate as an additive with lower reductive reactivity than EVS to modify the interphase formed by EVS successfully. Simultaneously, the EVS-based electrolyte was found to create a sulfone-rich interphase on the LiFePO4 cathode surface, significantly enhancing Li+ ion diffusion both across the interphase and within the material. These modifications culminated in a conspicuous improvement in the performance of graphite/LiFePO4 batteries. Our study illuminates the potential of EVS-based electrolytes in boosting the rate capability, low-temperature performance, and safety of LiFePO4 power lithium-ion batteries. It yields valuable insights for the design of safer, high-output, and durable LiFePO4 power batteries, marking an important stride in battery technology research.

Design and characterization of cell topology effect on SiC VDMOSFETs for high power and frequency applications

In this paper, we present a comprehensive investigation of the impact of cell topology and pitch reduction on the DC and AC characteristics of 1200V-rated 4H-SiC planar VDMOSFETs. We have designed and fabricated four different cell topologies, namely linear, square, hexagonal, and staggered cell, in order to characterize their performance. Among the various cell types, the hexagonal cell exhibits the most favorable specific on-state resistance (Ron,sp) value. However, it is worth noting that the breakdown values of both the hexagonal and staggered square cells fall significantly below the simulated values. This is attributed to the interaction between the irregular cell boundaries and the edge cell termination region. Furthermore, we observed that the linear cell has the highest gate resistance compared to the other cell types. Additionally, the linear cell also demonstrates a lower input capacitance than the other cells. This can be attributed to its longer gate trasmission line and smaller area. Lastly, we performed dynamic double pulse tests on the fabricated VDMOSFETs to compare their switching characteristics. It was concluded that linear cell VDMOS is suitable for high switching applications, while square, hexagonal and S.S cell VDMOS are better suited for lower switching applications that require a high output current.

Dual Volts-per-Hertz Control of Double-Inverter-Fed Wound Rotor Induction Machine

Double-inverter-fed wound rotor induction machine (DI-WRIM) is a two-port machine capable of maintaining rated torque even at twice the rated speed. Such machines are gaining popularity in high-speed and high-power applications for their versatility and degrees of freedom in control. The existing control methods for DI-WRIM are all based on the dynamic model of the machine and the associated controller structures are complex with multiple controllers. This article proposes a novel control scheme for DI-WRIM based on the steady-state model which requires only one controller. The proposed control scheme has the capability to operate the machine in both sub and super-synchronous modes in all the four quadrants in torque-speed plane. The simplicity of the proposed dual volts-per-hertz control method can be compared to the very popular scalar control used in cage-rotor induction machine drives. Mathematical derivation of the control law with appropriate approximations is discussed. Experimental results are presented from a 5-hp, 8-pole wound rotor induction machine drive.

Study of lithium transport in Li2O component of the solid electrolyte interphase in lithium-ion batteries

In lithium-ion batteries (LIBs), as a promising energy storage device, materials with fast lithium (Li) transport are required for high-power applications such as electric vehicles. Thus, a deeper understanding of Li transport in components of LIBs is crucial for improving their rate capability. In this study, the Li transport in lithium oxide (Li2O), as one of the key components of the solid electrolyte interphase (SEI) layer, was examined by a multiscale computational approach ranging from density functional theory (DFT) to Monte Carlo simulations. The DFT calculations were used to investigate the recombination of Frenkel pairs, their first-principles total energies, and the Li diffusion mechanisms. The effect of atomic configurations on both first-principles total energies and diffusion barrier energies was formulated by periodic and local cluster expansions. These formalisms were then incorporated into the Monte Carlo and Kinetic Monte Carlo (KMC) simulations to calculate the diffusion coefficient of Li. Our calculations revealed that the vacancy-mediated jump along the 〈100〉 direction in the antifluorite structure of Li2O possesses the lowest barrier energy compared to other diffusion mechanisms. The KMC simulations indicated that the diffusion coefficient of Li better converged with the direct experimental measurement when the recombination of Frenkel pairs was integrated into the simulations. At a temperature of 300 K, the KMC simulation yielded a Li diffusion coefficient of 3.8×10-12cm2/s in Li2O. This is only one order of magnitude larger than indirect experimental measurement, suggesting the accuracy of our formalism. Thus, our formalism for studying Li transport in Li2O will pave the path to a rational design of inorganic SEI in the future development of LIBs.

Advanced Fabrication of 3D Micro/Nanostructures of Gallium Oxide with a Tuned Band Gap and Optical Properties.

Gallium oxide (Ga2O3) is a promising material for high-power semiconductor applications due to its wide band gap and high breakdown voltage. However, the current methods for fabricating Ga2O3 nanostructures have several disadvantages, including their complex manufacturing processes and high costs. In this study, we report a novel approach for synthesizing β-Ga2O3 nanostructures on gallium phosphide (GaP) using ultra-short laser pulses for in situ nanostructure generation (ULPING). We varied the process parameters to optimize the nanostructure formation, finding that the ULPING method produces high-quality β-Ga2O3 nanostructures with a simpler and more cost-effective process when compared with existing methods. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to characterize the samples, which indicated the presence of phosphorous. X-ray photoelectron spectroscopy (XPS) confirmed the formation of gallium oxide, along with a minor amount of phosphorus-containing compounds. Structural analysis using X-ray diffraction (XRD) revealed the formation of a monoclinic β-polymorph of Ga2O3. We also measured the band gap of the materials using reflection electron energy loss spectroscopy (REELS), and found that the band gap increased with higher nanostructure formation, reaching 6.2 eV for the optimized sample. Furthermore, we observed a change in the heterojunction alignment, which we attribute to the change in the oxidation of the samples. Our results demonstrate the potential of ULPING as a novel, simple, and cost-effective method for fabricating Ga2O3 nanostructures with tunable optical properties. The ULPING method offers a green alternative to existing fabrication methods, making it a promising technology for future research in the field of Ga2O3 nanostructure fabrication.

Performance Investigation of HFR Full-bridge Inverter in Resonant Inductive Coupled Power Transfer System for an Electric Vehicle

Inductive WPT of the resonant category is generally employed for medium and high-power transmission applications like electric vehicle charging due to it contributes excellent efficiency. The high-frequency resonant full-bridge inverter using series-series resonant topology is proposed. The design of the high-frequency resonant inverter is simulated and verified by MATLAB/SIMULINK software. The charging scheme which is available in the AC-DC as well as in the DC-DC converter should operate with the two steps to achieve a duty cycle-based voltage control and hysteresis current control. The resonant frequency of the proposed system has a frequency range of 65 kHz with a DC voltage of 12V. The simulation has been carried out successfully and transmitted a 5KW power load of constant current and voltage control. The Performance chart of with the existing method is carried out in terms of parameters and the efficiency can be achieved by 95%.

Complementary negative capacitance field-effect transistors based on vertically stacked van der Waals heterostructures

Complementary field-effect transistors (CFETs) with a vertically stacked n-FET/p-FET configuration can provide a promising solution to boost area efficiency. However, the substantial power dissipation exhibited by these CFET devices poses a notable challenge to the energy efficiency. By combining a negative-capacitance field-effect transistor (NCFET) and a CFET, the problem of excessive power consumption can be solved. By using a negative-capacitance gate stack, the supply voltage (Vdd) applied to the gate of the CFET is increased, resulting in a reduction in power consumption. Here, we experimentally demonstrate a vertically integrated complementary negative capacitance field-effect transistor (NC-CFET) that combines tungsten diselenide (WSe2) p-NCFET and molybdenum disulfide (MoS2) n-NCFET. With the hexagonal boron nitride/copper indium thiophosphate CuInP2S6 (CIPS) dielectric stack, both n-type and p-type van der Waals (vdW) NCFETs exhibit sub-60 mV/decade switching characteristics. The vdW NC-CFET exhibits a voltage gain of 78.34 and a power consumption of 129.7 pW at a supply voltage of 1 V. These device characteristics demonstrate the great potential of the vdW NC-CFET for high density and low power applications.

Improved energy storage performance achieved in (Bi0.5Na0.5)TiO3-based relaxor ferroelectrics via composition engineering

The utilization of relaxor-ferroelectrics is considered to become a feasible scheme to achieve high energy storage performance owing to their high polarization and low hysteresis loss. Herein, the (1-x)(Bi0.5Na0.5)TiO3-x(Sr0.7La0.2)(Ti0.9Zr0.1)O3 ((1-x)BNT-xSLTZ) ceramics were synthesized by using the traditional solid-state reaction method. A favorable recoverable energy density (Wrec) of 4.0 J cm−3 could be obtained at 295 kV cm−1 by combining composition-driven intensive relaxation behaviors and fine grains. Further, the high stabilities for temperature and frequency, with energy density of 1.56–1.41 J cm−3 over a range of 25–150 °C at 150 kV cm−1 and energy density of 1.48–1.67 J cm−3 at 150 kV cm−1 ranging from 1 Hz to 200 Hz, are achieved in 0.6BNT-0.4SLTZ. These results suggest that the BNT-SLTZ relaxor ferroelectric ceramics have capacity of becoming a promising candidate for high-power energy storage applications.

COMPARATIVE STUDY OF TRADITIONAL PWM INVERTERS AND MULTILEVELS INVERTERS

The need of higher powers in electrical drives has forced the researchers to develop new power source possibilities. Multilevel inverters have been presented as a cost effective solution for various high voltage and high power applications including power quality and motor drive problems. The traditional pulse width modulated (PWM) Inverter does not completely eliminate the unwanted harmonics in the output waveform. Using the multilevel inverter as an alternative to traditional PWM inverters for electric motor drive applications is investigated. The concept of the Optimized Harmonic Elimination Stepped-Waveform (OHESW) technique for a multilevel inverter is presented. The effectiveness of this technique in minimizing the inverter switching losses and its output voltage harmonic content which cause reducing harmonic losses and torque pulsations of an induction motor fed form is investigated analytically. Comparison between the Selective Harmonic Eliminated PWM (SHEPWM) as a traditional PWM technique for three-level inverter and the OHESW technique for multilevel inverter with regard to the switching losses, harmonic distortion, additional harmonic losses in the motor and the pulsating torques is also presented.

Cascaded H–Bridge Multilevel Inverter: Review of Topologies and Pulse Width Modulation

Multilevel inverters (MLIs) have become more popular for medium-voltage and high-power applications. The cascaded H-bridge multilevel inverter (CHBMLI) is one of the three most popular topologies of MLIs. It was more reliable due to its fewer components per level. The number of possible output voltage levels is more than twice the number of DC sources, the most suitable topology for integration with renewable energy sources, easy to design, and has good performance with modularity. The main disadvantage of CHBMLI is the need for separate DC sources for each H-bridge. However, this can be considered as an advantage to be employed in renewable energy applications. This paper provides a review of CHBMLI topologies and pulse width modulation (PWM) techniques, including fundamental and high switching frequency techniques, such as selective harmonic elimination (SHE), space vector modulation (SVM), nearest level modulation (NLM), and Carrier-Based PWM.

RF magnetron sputtering of [formula omitted] thin films: Analysis of thermal annealing induced tuning of structural, optical characteristics, and energy band alignments

This correspondence showcases the deposition of ultra-wide bandgap β−Ga2O3 thin films via the utilization of RF magnetron sputtering at an elevated deposition temperature of 400 °C, followed by a comprehensive analysis of their structural, surface and optical properties using X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Raman, Ultraviolet–Visible Spectroscopy (UV–Vis), and Atomic Force Microscopy (AFM) at 800 °C, 900 °C, and 1000 °C annealed sample. Annealing up to 1000 °C led to a significant enhancement in the film’s crystallinity by 10%, accompanied by a remarkable decrease in dislocation density of up to 93.5%. The study also observed several key trends upon annealing, including a decreasing lattice constant from 12 to 11.97 Å, and an increase in the bandgap from 4.8 to 5.3 eV. Concurrently, crystallite size was consistently increased from 4.07 to 15.77 nm. The conduction band offset (CBO) decreased with higher annealing temperatures. Additionally, the increase in bandgap led to an enhancement in the critical electric field from 8.9 to 11.2 MV/cm. The Electron Density Mapping (EDM) results depicted a covalent bond between the atoms for different annealing processes along with the fundamental structural change in atomic coordinates and unit cell parameters, which has not been reported yet. These findings underline the remarkable material properties of β−Ga2O3 at 1000 °C temperatures. This establishes it as a compelling substitute for materials like SiC and GaN, showcasing its potential across various high-power applications due to a superior Baliga figure of merit and robust sensitivity even under elevated temperatures, positioning it as a promising candidate for optoelectronic applications.

Electronic properties of c-BN/diamond heterostructures for high-frequency high-power applications

Using first principles calculations, this work investigates the suitability of diamond/c-BN heterojunctions for high frequency, high power device applications. The key quantities of band offsets and interface charge polarization are examined for different crystallographic orientations [(110), (111), or (100)], bond terminations (CB or CN), and substrates (diamond or c-BN). The results indicate that both the (111) and (100) structures with polar interfaces are likely to be a type-I alignment with the diamond conduction and valence band extrema nested within the c-BN bandgap, whereas the non-polar (110) counterpart may form type II as the valence band of c-BN is shifted down substantially lower. The valence band offsets are estimated to be around 0.2–0.55 eV and 1.2–1.3 eV for types I and II, respectively, with only a modest dependence on the order of layer stacking and bond termination. The (111) and (100) structures also show net charge polarization in a narrow region at the interface. The electron-deficient and electron-rich nature of the CB and CN bonding are found to induce charge redistribution leading to an essentially 2D sheet of negative and positive polarization, respectively, with a density on the order of 1012−1013q/cm2 (q=1.6×10−19 C). With the predicted band alignments suitable for carrier confinement as well as the possibility of the modulation and polarization doping, the diamond/c-BN heterostructures are a promising candidate for high-performance electronic devices with a highly conductive 2D channel. Both p-type and n-type devices appear possible with a judicious choice of the heterojunction configuration.

Millimeter-wave 3D-printed filtering power divider with high frequency selectivity and enhanced heat dispersion

In this paper, a 3D-printed filtering power divider with high frequency selectivity and enhanced heat dispersion is proposed in the Ka-band. Based on filter synthesis theory, a meticulous design is implemented for 32 rectangular resonators and their adjacent inductive irises, enabling the simultaneous realization of a 1-to-8 power divider function and an integrated 11th-order filtering response. To enhance heat dispersion performance for high power applications, cooling fins, and cooling slots are strategically incorporated into the filtering power divider. The selective laser melting (SLM) 3D printing fabrication technology is employed for the cost-effective monolithic fabrication of the prototype. The measured results demonstrate that the return loss of the input port is over 12 dB within the frequency range of 27.0–31.4 GHz. The phase and amplitude difference between outputs are less than ±8° and ±0.6 dB. The transmission coefficient is approximately 9.7 dB, indicating an excellent low-loss performance of the 1-to-8 power divider. Beyond the operating bands, the transmission coefficient experiences a decline of over 55 dB/GHz, demonstrating an 11th-order filtering response. The proposed filtering power divider excels in low loss, superior frequency selectivity, and enhanced heat dispersion, promising advancements in high-power millimeter-wave systems.

Materials adopted for particle beam windows in relevant experimental facilities

A beam vacuum window is a thin interface of separation between a volume under vacuum and a volume at a higher pressure traversed by particle beams. Their application is not only limited to particle accelerators, where they are typically installed inside the beamline to separate vacuum sectors, but also extends to other fields of nuclear research and to high-power hadron beam applications, such as spallation neutron sources and accelerator-driven systems. The main issue concerning the beam window technology resides intrinsically in the dual role of these components: the thickness of the window is supposed to be as thin as possible to allow the passage of the particles through matter with minimal interaction but, at the same time, enough resistant to maintain the required differential pressure between the two environments. Published by the American Physical Society 2024

Integrated 2T1C pixel circuit with a-Si TFT and NMOS for active matrix mini-LED displays

The 2T1C pixel driver circuit for mini-LED direct display has been proposed, which separates the switching transistor and the driver transistor from the same display substrate, replaces the driver transistor with n-metal oxide semiconductor (NMOS), and combines printed circuit board substrate and thin-film transistor (TFT) substrate to improve the driving capability of the circuit. The NMOS was soldered with mini-LEDs simultaneously onto a substrate which connects to the a-Si TFT array. Two driving modes for a 32-level gray-scale display panel were investigated to compare the voltage-current and optical characteristics. The results demonstrated that the drain-driving mode is better suited for high brightness and high-power display application scenarios as it supports higher-driven currents, but the source-driving mode is more appropriate for precision gray-scale applications due to the higher current linearity of the mode.

Optimization of 150 nm GaN HEMT for Ku-band applications using field plate engineering

This work presents a systematic study to achieve the best result of having high breakdown voltage with high-frequency operation for a 150 nm GaN HEMT device (fabricated) using different field plate engineering techniques. The device breakdown voltage, cut-off frequency and maximum frequency should be high for high power and high frequency applications. The conventional device has a lower breakdown voltage but good cut-off and maximum frequency ranges. Field plate engineering has been done for breakdown improvement. However, the device's frequency operation is hampered by the typical source and gate field plate. As a result, an Air bridge source connected field plate and floating gate field plate architectures are explored and investigated. The best outcome is obtained with air bridge source connected field plate with VBOff = 100 V maintaining the cut-off frequency and maximum frequency at 29.8 GHz and 50.3 GHz respectively which is suitable for high power and high frequency applications.