High Power Electronic Applications Research Articles

Physico-chemical characterization of polyimide passivation layers for high power electronics applications

Silicon carbide (SiC) is a wide bandgap semiconductor suitable for high-voltage, high-power and high-temperature applications. However, the production of advanced SiC power devices still remains limited due to some shortcomings of the dielectric properties of the passivation layer. Thanks to their high operating temperature and dielectric strength, spin coated polyimide (PI) layers are considered ideal candidates for SiC devices passivation and insulation. In this view, a robust methodology for the physico-chemical characterization of such PI layers is required. Thanks to the use of time of flight-secondary ion mass spectrometry (ToF-SIMS), a SIMS-based surface-sensitive technique that provides specific identification of molecules, it was possible to distinguish different types of PIs employed in commercial SiC devices and postulate their molecular structure. This was obtained after careful selection of the analytical conditions used for the characterization of the specimens.The results attained in this study open the way for further improvements in one of the most key issues in the development of higher SiC power devices.

Investigating the Corrosion Resistance of Different SiC Crystal Types: From Energy Sectors to Advanced Applications.

Silicon carbide, as a third-generation semiconductor material, plays a pivotal role in various advanced technological applications. Its exceptional stability under extreme conditions has garnered a significant amount of attention. These superior characteristics make silicon carbide an ideal candidate material for high-frequency, high-power electronic devices and applications in harsh environments. In particular, corrosion resistance in natural or artificially acidic and alkaline environments limits the practical application of many other materials. In fields such as chemical engineering, energy conversion, and environmental engineering, materials often face severe chemical erosion, necessitating materials with excellent chemical stability as foundational materials, carriers, or reaction media. Silicon carbide exhibits outstanding performance under these conditions, demonstrating significant resistance to corrosive substances such as hydrochloric acid, sulfuric acid, nitric acid, and alkaline substances such as potassium hydroxide and sodium hydroxide. Despite the well-known chemical stability of silicon carbide, the stability conditions of its different types (such as 3C-, 4H-, and 6H-SiC polycrystals) in acidic and alkaline environments, as well as the specific corrosion mechanisms and differences, warrant further investigation. This Review not only delves deeply into the detailed studies related to this topic but also highlights the current applications of different silicon carbide polycrystals in chemical reaction systems, energy conversion equipment, and recycling processes. Through a comprehensive analysis, this Review aims to bridge research gaps, offering a comparative analysis of the advantages and disadvantages between different polymorphs. It provides material scientists, engineers, and developers with a thorough understanding of silicon carbide's behavior in various chemical environments. This work will propel the research and development of silicon carbide materials under extreme conditions, especially in areas where chemical stability is crucial for device performance and durability. It lays a solid foundation for ultra-high-power, high-integration, high-reliability module architectures, supercomputing chips, and highly safe long-life batteries.

Design of a Compact Log Periodic Dipole Array Antenna for Broadband and High-Power Beam Synthesis Using Superposition

This paper investigates various array beam shapes for high-power electronic warfare applications using an actual broadband array antenna. For use in a limited mounting space, a compact printed log periodic dipole array (LPDA) operating over a wide bandwidth is designed. The LPDA is then extended to an 8 × 1 array, with active element patterns (AEPs) obtained through simulation and measurement. Beam synthesis is performed by the superposition of several array patterns, which involves adjusting the weight of each AEP. To derive a synthesized array beam shape that is similar to the guided mask, the Taylor window weighting method is applied to each array pattern. Finally, beam synthesis for the flat-top beam, cosecant-squared beam, and iso-flux beam is performed using Taylor window-weighted AEPs, and the results are compared with those of beam shapes using ideal isotropic patterns. The results demonstrate that various beam shapes can be achieved for high-power electronic warfare applications using the AEPs of an actual array antenna.

Epitaxial trench refill of 4H-SiC by chlorinated chemistry

Trench epitaxy of 4H-SiC is investigated with the supersaturation of chlorinated chemistry at a growth temperature of 1550 °C. Coupled with a lower growth temperature than has been previously reported, the integrity of the 4H-SiC trenches is retained and minimal rounding effects of H2 annealing prior to growth are observed. The system gives different growth rates of materials on the various crystal faces of the trenches and can be used to improve the refilling process, resulting in the reduced void formation. The addition of excessive levels of HCl can suppress trench epitaxy by reducing the growth rate on the sidewalls of trenches in favor of growth on the surface. The processes demonstrated offer a scalable and reproducible method to fabricate SiC-based superjunction device structures for applications in high voltage power electronics.

Thermal management of high-powered short-duration electronics aided by a phase change material thermal energy storage

Quantifying the performance of phase change materials (PCMs) for thermal energy storage in high-power short-duration electronics applications requires performing tests that push the material to its limit. This involves designing experiments to test solid-liquid PCMs in near real-world thermal load conditions to test its performance. Conventional cooling methods are sized to manage the maximum loading the cooling system will be subjected to in its operation, even if this loading occurs for a short period of time. This design ethos is inefficient and results in heavy and expensive equipment being used in an application where it will be underutilized most of its useful life. In this work, a PCM thermal energy storage (TES) device was built using a plate-and-frame heat exchanger and investigated to determine the suitability of this system to manage the temperature of high-power electronics with a low duty cycle. These experiments showed how a PCM-TES can be used in conjunction with conventional temperature management equipment to create a reliable cooling solution while allowing the conventional cooling components to be decreased in size and capacity. This work shows that, for a given application, a cooling system can be more efficiently designed with the use of a PCM-TES and opens the door to additional research on this topic.

Anisotropic dielectric dispersions and thermal behaviors in highly textured BN thin films for heat self-dissipating electronics

Mainstream high-k gate materials, such as SiO2, Al2O3, and HfZrO2, are in demand for modern electronics. However, these dielectrics possess lower thermal conductivity, significantly limiting thermal dissipation in electronic devices. Herein, we propose the utilization of complementary metal-oxide semiconductor- (CMOS) compatible high power impulse magnetron sputtering (HiPIMS) for the mass production of highly textured hexagonal boron nitride (h-BN) on (100)-, (110)-, and (111)-oriented SrTiO3 substrates. The as-prepared films exhibit distinct vertical alignments, as evidenced by HRTEM and FTIR analysis. Notably, the R value, ranging from 0.46 to 0.50, is associated with the stress in the film. Importantly, distinct anisotropies in thermal conductivity, dielectric constant, and optical band gap are observed. Furthermore, the values of thermal conductivity in these highly textured h-BN films are 4.5, 5.7, and 5.3 Wm−1K−1, which is almost three times larger than those of SiO2 (1.4 Wm−1K−1) and Al2O3 (1.35 Wm−1K−1), and even an order of magnitude larger than that of HfZrO2 (0.67 Wm−1K−1). The combination of excellent dielectric characteristics, favorable thermal conductivity, and superior stability over a broad temperature range makes this novel material outperform conventional dielectric gate materials in high-power electronics applications.

Identifying the charge states of carbon vacancies in 4H-SiC by ab initio metadynamics

4H Silicon carbide (4H-SiC) is widely recognized as a highly promising material for high-voltage and high-power electronic applications due to its exceptional properties. The performance of devices based on 4H-SiC is often weakened by the presence of carbon-related point defects, particularly carbon vacancies (VC). The defects of VC introduce deep-level traps (e.g., Z1/2 and EH6/7) that deteriorate device functionality. Experimental and theoretical studies on VC have led to some conflicting results about the charge states of VC, especially for the charge state ordering of EH6/7. We now employ ab initio metadynamics (META) to systematically investigate configuration space including the direction and magnitude of bond distortion and identify the most stable structures of VC. Eventually, the charge states of VC in 4H-SiC are identified. The Z1 (EH6) and Z2 (EH7) indicate transitions from acceptor (donor) levels of VC, located on the h and k sublattice sites, respectively. Z1 and Z2 demonstrate negative-U ordering, characterized by U values of −0.16 and −0.37 eV, respectively. Conversely, EH6 and EH7 display positive-U ordering, with U values of 0.16 and 0.08 eV, respectively. The current results provide insights into the properties of VC in 4H-SiC, highlighting the effectiveness of META in the exploration of complex potential energy surfaces associated with point defects in solids.

Growth optimization, optical, and dielectric properties of heteroepitaxially grown ultrawide-bandgap ZnGa2O4 (111) thin film

Ultrawide bandgap ZnGa2O4 (ZGO) thin films were grown on sapphire (0001) substrates at various growth temperatures with a perspective to investigate the electrical and optical characteristics required for high-power electronic applications. Due to the variation in the vapor pressure of Zn and Ga, severe loss of Zn was observed during pulsed laser deposition, which was solved by using a zinc-rich Zn0.98Ga0.02O target. A pure phase single-crystalline ZGO thin film was obtained at a deposition temperature of 750 °C and an oxygen pressure of 1 × 10−2 Torr. The out-of-plane epitaxial relationship between the sapphire and ZGO thin film was obtained from φ-scan. The x-ray rocking curve of the ZGO thin film grown at 750 °C exhibits a full width at half maximum of ∼0.098°, which indicates a good crystalline phase and quality of the thin film. Core-level x-ray photoelectron spectroscopy of ZGO grown at 750 °C indicated that Zn and Ga were in the 2+ and 3+ oxidation states, respectively, and the atomic ratio of Zn/Ga was estimated to be ∼0.48 from the fitted values of Zn-2p3/2 and Ga-2p3/2. The high-resolution transmission electron microscopy images revealed a sharp interface with the thickness of the ZGO film of ∼265 nm, and the signature of minor secondary phases was observed. The bandgap of the ZGO film at different growth temperatures was calculated from the ultraviolet-diffuse reflectance spectroscopy spectra, and its value was obtained to be ∼5.08 eV for the 750 °C grown sample. The refractive index (n) and the extinction coefficient (k) were determined to be ∼1.94 and 0.023 from the ellipsometric data, respectively, and the real dielectric function (ɛr) was estimated to be ∼6.8 at energy 5 eV. The ultrawide bandgap and dielectric function of ZGO recommend its possible potential applications in deep-ultraviolet optoelectronic devices and high-power electronics.

Surface Transfer Doping in MoO3-x/Hydrogenated Diamond Heterostructure.

Surface transfer doping is proposed to be a potential solution for doping diamond, which is hard to dope for applications in high-power electronics. While MoO3 is found to be an effective surface electron acceptor for hydrogen-terminated diamond with a negative electron affinity, the effects of commonly existing oxygen vacancies remain elusive. We have performed reactive molecular dynamics simulations to study the deposition of MoO3-x on a hydrogenated diamond (111) surface and used first-principles calculations based on density functional theory to investigate the electronic structures and charge transfer mechanisms. We find that MoO3-x is an effective surface electron acceptor and the spatial extent of doped holes in hydrogenated diamond is extended, promoting excellent transport properties. Charge transfer is found to monotonically decrease with the level of oxygen vacancy, providing guidance for engineering of the surface transfer doping process.

Modularized Inductive Power Transfer Systems With Inherent Impedance Decoupling for High-Power Applications

Due to the capacity and costs of single power electronic devices, the modularized inductive power transfer systems (MIPT) are widely used in high-power electronic applications. To achieve safe and efficient operation of high-power IPT technology, this paper proposes a modularized topology design method with inherent impedance decoupling feature. When the module number changes, the current and voltage stresses of the devices in the proposed system remain unchanged inside modules at the rated power. Moreover, the impedance of any module will not be affected by neighboring modules, especially in cases where the module number may change abruptly. Such a desired feature significantly improves the reliability of high power IPT systems. A 15 kW MIPT prototype with 3 modules connected in parallel is implemented to verify the validity of the proposed method. The result clearly shows that both the impedance and device stress are decoupled with the module number. The system exhibits peak efficiency of 95.1% and over 92.4% when the power is between 2kW and 15kW.

Improved capacitive energy storage performance in hybrid films with ultralow aminated molybdenum trioxide integration for high-temperature applications.

Dielectric capacitors play a pivotal role in advanced high-power electrical and electronic applications, acting as essential components for electrical energy storage. The current trend towards miniaturization in electronic devices and power systems highlights the increasing demand for scalable, high-performance ultra-thin dielectric films with a high-temperature stability. While significant progress has been made in enhancing the discharged energy density (Ue) of dielectric polymers at elevated temperatures, such advancements have faced certain challenges. Herein, an innovative molecular engineering approach for the bonding of amine-functionalized molybdenum trioxide (A-MoO3) with the dianhydride monomer of polyetherimide (PEI) is presented, leading to a reduction in conduction loss and the substantial enhancement in storage energy density under high-temperature and high-field conditions. It is revealed that charge redistribution at the bonding sites induces a subtle variation in the potential energy, creating an in-built electric field between the PEI matrix and A-MoO3 based on density functional theory (DFT) analyses. The observed phenomenon leads to an increase in the electron barrier, effectively inhibiting the release of trapped electrons. Notably, at conditions of 200 °C and 100 Hz, the PEI/A-MoO3 hybrid film demonstrates a notable Ue at η > 90%, reaching up to 5.53 J cm-3, surpassing the performance of many current dielectric polymers and composites. Furthermore, the hybrid film's exceptional cycling durability, coupled with its ability to be fabricated into large-area, uniform-quality films, underscores its potential in the development of dielectric energy storage devices tailored for extreme environments.

A novel 4H-SiC multiple stepped SGT MOSFET with improved high frequency figure of merit

A novel 4H-SiC Multiple Stepped SGT MOSFET (MSGT-MOSFET) is presented and investigated utilizing TCAD simulations in this paper. We have quantitatively studied the characteristics of the device through simulation modeling and physical model calculations, and comparatively analyzed the performance and application prospects of this novel device. The gate-to-drain capacitance (Cgd) and gate-to-drain charge (Qgd) of the MSGT-MOSFET are significantly reduced in comparison with the double trench MOSFET (DT-MOSFET) and the conventional SGT MOSFET (CSGT-MOSFET), due to the reduction of the overlapping area of the split gate (SG) structure and drift region. Therefore, the obtained high frequency figure of merit (HF-FOM) defined as [Ron × Cgd] reduced by 23.9% compared with DT-MOSFET and CSGT-MOSFET. And the HF-FOM [Ron × Qgd] for the MSGT-MOSFET significantly decreased by 71% and 50%, respectively, compared to that of the DT-MOSFET and CSGT-MOSFET. Furthermore, the switching loss is also simulated and calculated. And the total switching loss of the proposed MSGT-MOSFET realizes 42.9% and 21.7% reduction in comparison with the DT-MOSFET and CSGT-MOSFET. The overall enhanced performances suggest that the MSGT-MOSFET is an excellent choice for high frequency power electronic applications.

Rapid preparation of sintered Ag nanoparticles pastes for high-power electronic packaging

This study developed a low-temperature pressureless sintered Ag nanoparticles (AgNPs) paste with high thermal conductivity (TC), which can be produced on a large scale through rapid pre-treatment. Commercially available unmodified AgNPs were coated with polyvinylpyrrolidone (PVP), and subsequently, citric acid (CA) was used to remove the native oxide layer from the AgNPs surface and improve sintering activity. Compared to the treatment strategy of CA activation followed by PVP coating, applying PVP coating prior to CA activation could prevent their spontaneous bonding that will significantly promote the formation of large grains and strong sintering necks, reducing the interface scattering and leading to an ultra-high TC (≥200 W/mK), thereby meeting the packaging requirements of high-power electronic applications.

Structural, optical, and electrical characterization and performance comparison of AlGaN/GaN HEMT structures with different buffer layers

AlGaN/GaN high electron mobility transistor (HEMT) structures are promising for high power and high speed electronic applications. The selection of a good buffer structure is crucial for the achievement of high quality HEMT devices. Here, we present a comparative analysis of structural, optical, and electrical properties of AlGaN/GAN HEMT structures with three different buffer configurations: step-graded AlGaN and superlattice-based buffers on Si, and no buffer on SiC substrates. The analysis of structural properties showed that the structure on SiC has better crystal quality. The Analysis also provided an insight of the role superlattice buffer to cut-off the dislocations and enhance the GaN channel crystallinity. Optical and electrical characterizations showed the enhanced 2DEG quality in the superlattice-based structure, due to the better stress management in the top layers. The electronic and optoelectronic quality of the structures were studied by fabricating HEMT and metal-semiconductor-metal photodetector devices. The devices analysis showed that the superlattice based structure outperformed the other two structures with drain current and transconductance of 406.3 mA/mm and 81.5 mS/mm, respectively, as well as photo-to-dark current ratio that is 2–3 orders of magnitude higher than the other two structures, under 325 nm light illumination. The results provide insights into the impact of different buffer configurations on the performance of AlGaN/GaN HEMT structures, suggesting that the superlattice buffer structure is the optimal choice for fabricating high-performance AlGaN/GaN HEMT-based electronics.

A novel stepped AlGaN hybrid buffer GaN HEMT for power electronics applications

In this paper, a novel p-type gallium nitride (p-GaN) high electron mobility transistor (HEMT) is proposed and investigated for high power electronic applications. In the proposed device, a stepped hybrid Aluminium GaN (AlGaN) buffer layer with low Al content has been introduced to improve the performance of the device. The low aluminium mole concentration decreases the surface defects which reduces the leakage current, thereby increasing the breakdown voltage of the device. To validate the simulation results, calibration of the device models has been performed with experimental results. Results present that the proposed device exhibits high breakdown voltage, high transconductance and low small signal capacitances. The proposed device achieves improvement in breakdown voltage, transconductance and small signal capacitances as compared to the conventional hybrid buffer high electron mobility transistor (HB-HEMT). Furthermore, the processing steps have been proposed for the possible fabrication of the proposed device. Also, the optimization is performed to achieve the optimal device performance with respect to breakdown voltage. Finally, the performance of the proposed device has been compared with the state-of-the-art devices.

Temperature dependent characteristics of β -Ga2O3 FinFETs by MacEtch

Understanding the thermal stability and degradation mechanism of β-Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) is crucial for their high-power electronics applications. This work examines the high temperature performance of the junctionless lateral β-Ga2O3 FinFET grown on a native β-Ga2O3 substrate, fabricated by metal-assisted chemical etching with Al2O3 gate oxide and Ti/Au gate metal. The thermal exposure effect on threshold voltage (Vth), subthreshold swing (SS), hysteresis, and specific on-resistance (Ron,sp), as a function of temperature up to 298 °C, is measured and analyzed. SS and Ron,sp increased with increasing temperatures, similar to the planar MOSFETs, while a more severe negative shift of Vth was observed for the high aspect-ratio FinFETs here. Despite employing a much thicker epilayer (∼2 μm) for the channel, the high temperature performance of Ion/Ioff ratios and SS of the FinFET in this work remains comparable to that of the planar β-Ga2O3 MOSFETs reported using epilayers ∼10–30× thinner. This work paves the way for further investigation into the stability and promise of β-Ga2O3 FinFETs compared to their planar counterparts.

Tutorial: Metalorganic chemical vapor deposition of β-Ga2O3 thin films, alloys, and heterostructures

β-phase gallium oxide (Ga2O3) is an emerging ultrawide bandgap (UWBG) semiconductor with a bandgap energy of ∼ 4.8 eV and a predicted high critical electric field strength of ∼8 MV/cm, enabling promising applications in next generation high power electronics and deep ultraviolet optoelectronics. The advantages of Ga2O3 also stem from its availability of single crystal bulk native substrates synthesized from melt, and its well-controllable n-type doping from both bulk growth and thin film epitaxy. Among several thin film growth methods, metalorganic chemical vapor deposition (MOCVD) has been demonstrated as an enabling technology for developing high-quality epitaxy of Ga2O3 thin films, (AlxGa1−x)2O3 alloys, and heterostructures along various crystal orientations and with different phases. This tutorial summarizes the recent progresses in the epitaxial growth of β-Ga2O3 thin films via different growth methods, with a focus on the growth of Ga2O3 and its compositional alloys by MOCVD. The challenges for the epitaxial development of β-Ga2O3 are discussed, along with the opportunities of future works to enhance the state-of-the-art device performance based on this emerging UWBG semiconductor material system.

Iridium and gold alloy beta gallium oxide expected to achieve p-type conductivity

The beta monoclinic gallium oxide (β-Ga2O3) is a wide-bandgap material with promising applications in high-power electronics, but bottleneck problem of p-type conductivity has become the biggest obstacle to device performance improvement. The effective p-type doping can be achieved in β-(Ir x Au y Ga1-x-y )2O3 alloys, promising to be synthesised in the laboratory, from an energy perspective. The β-(Ir x Ga1-x )2O3 exhibits an extended valence band with a maximum of 1.94 eV at the edge of the valence band. The location and bandwidth of the extended valence band can be changed with the Ir concentration. The Au substitution at the Ga(2) site actually creates a relatively shallow level, contrary to the expected deep acceptors. The 2p orbital of the O atom easily coupling with the doped atomic orbital to appear as a hole-polaronic state, while the higher energy of the Au-doped hole state avoids coupling with the valence band maximum of the host material. Theoretical feasibility of p-type doping of β-(Ir x Au y Ga1-x-y )2O3 is achieved.

A novel p-GaN HEMT with AlInN/AlN/GaN double heterostructure and InAlGaN back-barrier

In this paper, a novel p-type gallium nitride (p-GaN) high electron mobility transistor (HEMT) is proposed and investigated for high power electronics applications. In the proposed device, an AlInN/AlN/GaN double heterostructure has been used. In addition, InAlGaN back-barrier has also been employed to improve the DC performance of the device. The double AlInN/GaN heterostructures offer low resistance, resulting to a high two-dimensional electron gas (2DEG) density. As a result the current drive efficiency of the device is significantly improved. On the other hand, an inserted InAlGaN back-barrier confines the electrons in the channel which further enhances the performance of the device. To validate the simulation results, calibration of the device models has been performed with experimental results. Results show that the proposed device exhibits low on-resistance (Ron), high drain current (Ids) and high transconductance (gm) as compared to the state-of-the-art devices. Also, the processing steps have been proposed for the possible fabrication of the proposed device. Finally, the optimization of the device design parameter is performed to achieve the optimal device performance with respect to Ron.

Epitaxial growth of AlGaN/GaN HEMTs on patterned Si substrate for high voltage power switching applications

In this work, a series of AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on patterned (Al)GaN-on-Si seed layers by metalorganic chemical vapor deposition (MOCVD) to study the effect of the (Al)GaN buffer thickness and its aluminum content on the vertical breakdown voltage. The atomic force microscopy (AFM) analysis performed on the GaN seed layers shows a perfectly smooth, MOCVD-like morphology with a threading dislocation density (TDD) around 2 × 109 cm−2. We succeeded to regrow up to 10 μm and 5 μm crack-free GaN + HEMT and Al0.30G0.70N + HEMT structures, respectively and scanning electron microscopy (SEM) revealed limited lateral growth on mesas with few microscopic defects while AFM show the same surface morphology of HEMT structures as ones grown on planar substrates. NiAu Schottky contacts were deposited on the regrown (Al)GaN HEMTs as well as on (Al)GaN seed layer structures. No breakdown was noticed up to 200 V for the regrown Al0.30Ga0.70N (3 μm) HEMT and the GaN seed layer structures and the leakage current remained in the range of 1 nA. However, the leakage current in the regrown GaN (5 μm) structure reached rapidly 1 mA. Such a high leakage was not noticed for non-patterned devices. Thus, it is possibly attributed to silicon contamination in the regrown GaN layer. On the other hand, the absence of noticeable leakage in the regrown 3 μm thick Al-rich AlGaN buffer HEMT opens the way to a new competitive solution for high power electronics applications on silicon substrate.