High Power Semiconductor Devices Research Articles

Linear stability analysis of micropolar nanofluid flow across the accelerated surface with inclined magnetic field

PurposeThe purpose of this paper is to study the two-dimensional micropolar fluid flow with conjugate heat transfer and mass transpiration. The considered nanofluid has graphene nanoparticles.Design/methodology/approachGoverning nonlinear partial differential equations are converted to nonlinear ordinary differential equations by similarity transformation. Then, to analyze the flow, the authors derive the dual solutions to the flow problem. Biot number and radiation effect are included in the energy equation. The momentum equation was solved by using boundary conditions, and the temperature equation solved by using hypergeometric series solutions. Nusselt numbers and skin friction coefficients are calculated as functions of the Reynolds number. Further, the problem is governed by other parameters, namely, the magnetic parameter, radiation parameter, Prandtl number and mass transpiration. Graphene nanofluids have shown promising thermal conductivity enhancements due to the high thermal conductivity of graphene and have a wide range of applications affecting the thermal boundary layer and serve as coolants and thermal management systems in electronics or as heat transfer fluids in various industrial processes.FindingsResults show that increasing the magnetic field decreases the momentum and increases thermal radiation. The heat source/sink parameter increases the thermal boundary layer. Increasing the volume fraction decreases the velocity profile and increases the temperature. Increasing the Eringen parameter increases the momentum of the fluid flow. Applications are found in the extrusion of polymer sheets, films and sheets, the manufacturing of plastic wires, the fabrication of fibers and the growth of crystals, among others. Heat sources/sinks are commonly used in electronic devices to transfer the heat generated by high-power semiconductor devices such as power transistors and optoelectronics such as lasers and light-emitting diodes to a fluid medium, thermal radiation on the fluid flow used in spectroscopy to study the properties of materials and also used in thermal imaging to capture and display the infrared radiation emitted by objects.Originality/valueMicropolar fluid flow across stretching/shrinking surfaces is examined. Biot number and radiation effects are included in the energy equation. An increase in the volume fraction decreases the momentum boundary layer thickness. Nusselt numbers and skin friction coefficients are presented versus Reynolds numbers. A dual solution is obtained for a shrinking surface.

Diamond/cubic boron nitride (111) heterojunction interface: Rational regulation of high two-dimonsional electron gas

Wide-bandgap diamond exhibits excellent physical and chemical properties, making it an ideal substrate material for developing high-temperature and high-power semiconductor devices and broadening its application prospects in the field of microelectronics and optoelectronic devices. However, because of the Fermi pinning effect, it is difficult to achieve n-type diamond with excellent transport properties. Cubic boron nitride (cBN) has similar structural properties and a smaller lattice mismatch with diamond. Thus, making the two-dimensional electron gas of the diamond/cBN heterojunction provides a new idea to solve the problem of diamond n-incorporation difficulty and small bandgap regulation range. The diamond/cBN heterojunction is applied to study the law of influence factors on the heterojunction band structure, band alignment, and polarization strength. Further, a regulation mechanism for two-dimensional electron gas density is established at heterojunction interfaces, which can help solve the core difficulties of diamond n-type doping, small bandgap regulation range, and high impedance, providing a theoretical basis for realizing diamond power devices with high power density and low power consumption.

MODELING THERMAL BEHAVIOR IN HIGH-POWER SEMICONDUCTOR DEVICES USING THE MODIFIED OHM’S LAW

This paper addresses the challenge of thermal management in high-power semiconductor devices, where increasing power densities and complex operating environments demand more accurate thermal prediction methods. Traditional approaches often rely on simplified models that do not account for the crucial factor of temperature-dependent resistance variations. This limitation leads to inaccurate device temperature predictions, potentially compromising device reliability. This work proposes a novel approach for thermal management by introducing the first empirical application of a Modified Ohm’s Law. This modified law incorporates an exponential term to account for the non-linear relationship between temperature, current, and resistance. The paper demonstrates through simulations and empirical validation that the Modified Ohm’s Law offers a more accurate representation of thermal behavior compared to the standard version. This translates to more precise predictions of device temperature, especially during periods of rapid temperature changes. The validation process goes beyond simply establishing the Modified Ohm’s Law. It provides valuable insights into the thermal dynamics of the device, allowing for the refinement of simulation parameters used to assess various cooling strategies. These strategies include simulating different heat sink geometries and materials, modifying airflow rates over the device’s surface, and exploring the impact of Thermal Interface Materials (TIMs) between the device and the heat sink. By incorporating these elements, the simulations provide a more comprehensive picture of the device’s thermal behavior under various operating conditions and cooling configurations. Ultimately, this paper not only advances the theoretical understanding of thermal management but also offers practical benefits. Through enabling more accurate thermal predictions, the Modified Ohm’s Law model paves the way for informed decision-making in device design and optimization.

CHBMLI based DSTATCOM for power quality improvemt in a three-phase three-wire distribution system with PI controller

This paper presents a cascaded h-bridge (CHB) multilevel inverter (MLI) based MLI based distribution static synchronous compensator (DSTATCOM). The main objective of this paper is to reduce source current harmonics in the distribution system by using a cascade H-bridge multilevel inverter (CHBMLI) as DSTATCOM with a proportional-integral (PI) controller. The PI controller compensates reactive power, reduces source current harmonics, and maintains the unity power factor in the distribution system. The conventional two-level inverter-based DSTATCOM has many disadvantages such as high total harmonic distortion (THD), and high switching stress power semi-conductor devices, suitable for only low-power applications. This paper to overcome these drawbacks by using MLI-based DSTATCOM. The proposed system simulations are verified in MATLAB/Simulink software. The verified results are source current, load current, and compensating current.

Diamond for High-Power, High-Frequency, and Terahertz Plasma Wave Electronics.

High thermal conductivity and a high breakdown field make diamond a promising candidate for high-power and high-temperature semiconductor devices. Diamond also has a higher radiation hardness than silicon. Recent studies show that diamond has exceptionally large electron and hole momentum relaxation times, facilitating compact THz and sub-THz plasmonic sources and detectors working at room temperature and elevated temperatures. The plasmonic resonance quality factor in diamond TeraFETs could be larger than unity for the 240-600 GHz atmospheric window, which could make them viable for 6G communications applications. This paper reviews the potential and challenges of diamond technology, showing that diamond might augment silicon for high-power and high-frequency compact devices with special advantages for extreme environments and high-frequency applications.

Optimization and Mechanism of SiO2-Based Slurry Components for Atomically Smooth Gallium Nitride Surface Obtained Using Chemical Mechanical Polishing Technique

With the ongoing progress of mobile communication and new energy technologies, the market interest in high-frequency and high-power semiconductor devices has risen. Gallium nitride (GaN), a wide bandgap semiconductor material, has become a popular area of research in relevant fields. A sufficiently flat material surface can significantly enhance the device’s performance. Therefore, this paper explores the effect of oxidants on the quality of GaN surface during chemical mechanical polishing (CMP). Atomic force microscopy (AFM) was employed to examine the surface morphology of GaN after each CMP experiment. The aim was to evaluate the effect of specific slurry components on GaN surface quality. The results revealed that the introduction of oxidizers, particularly the potent oxidizer potassium persulfate (K2S2O8), was advantageous in reducing the surface roughness Sq and thus, enhancing the surface quality of GaN. The surface roughness (Sq) of GaN was reduced from 7.7 nm to 0.78 nm after the CMP process with the optimal components. AFM tests were conducted on different areas of the GaN surface within a range of 1 μm2, which revealed that clear images of the GaN atomic steps can be obtained, and the Sq can reach as low as 0.26 nm.

Voltage Source Converter based High Voltage Direct Current Transmission: A Comprehensive Review of Control Strategies, Developments and Trends

The continuous increasing progress in high power and high voltage semiconductor devices leads to have a substantial impact on optimization and effective management of electric grids. These developments have great influence on High Voltage Direct Current (HVDC) and flexible ac controller technologies. This article gives an outline of the innovations in Voltage source Converter (VSC) based HVDC technology. VSC based HVDC technology offers decent advantages which includes interconnection of asynchronous networks, bulk power transmission and voltage stability support. VSC based HVDC technology niche utilities to grab opportunities in incorporating large scale renewable energy sources to the grid, especially on shore /offshore wind energy to the grid. Furthermore, VSC-based HVDC technology is essential for maintaining voltage stability in networks of interconnected grids. In the face of changing loads and the incorporation of renewable energy, these systems help to maintain grid dependability and resilience by offering dynamic voltage management and wattless power support.This article highlights the transformative potential of VSC-based HVDC technology in modernizing and future-proofing electric grids. By leveraging the latest innovations in semiconductor devices and control technologies, VSC-based HVDC systems empower grid operators to overcome existing challenges and embrace the opportunities presented by the evolving energy landscape.

High-Temperature Reliability of Nano-Ag Sintered Joints on Ag-Plated Cu Substrates

As an emerging lead-free packaging interconnect material, Nano-Ag paste exhibits superior high-temperature mechanical, electrical, and thermal properties. It can meet the stringent high-temperature and high-density packaging requirements of future high-power semiconductor devices and is garnering widespread attention. However, research on the high-temperature reliability of sintered joints remains rather limited. In this study, we fabricated high-strength hot-press sintered nano-Ag joints using a hot-press sintering process. These joints underwent aging at high temperatures of 200°C and 300°C, yielding insights into the variations in mechanical properties at different temperatures. The reasons behind joint failure were analyzed by investigating the evolution of joint microstructures and fracture surfaces. The results indicate that even after extended aging at 200°C, the joint strength can still be maintained at 176 MPa. However, after aging for over 100 hours at 300°C, the joint fails. The growth of Cu oxides was observed within the joint microstructure, which constitutes the primary cause of joint failure at 300°C.

A Study on Electrical Performance of SiC-based Self-switching Diode (SSD) as a High Voltage High Power Device

The Self-switching Diodes (SSDs) have been primarily researched and used in low-power device applications for RF detection and harvesting applications. In this paper, we explore the potential of SSDs in high-voltage applications with the usage of Silicon Carbide (SiC) as substrate materials which offers improved efficiency and reduced energy consumption. Optimization in terms of the variation in the interface charges, metal work function, and doping concentration values has been performed by means of a 2D TCAD device simulator. The results showed that the SSD can block up to 600 V of voltage with an optimum interface charge value of 1013 cm-2, making them suitable for higher voltage applications. Furthermore, it also found that the work function of the metal contact affected the forward voltage value, impacting the current flow in the device. Variation in doping concentrations also resulted in higher breakdown voltages and significantly increased forward current, leading to an increased power rating of 27 kW. In conclusion, the usage of 4H-SiC-based SSDs shows a usable potential for high-voltage applications with optimized parameters. The results from this research can facilitate the implementation of SSD in the development of high-power semiconductor devices for various industrial applications.

Simulation study on total ionizing dose effect of IGBT gamma irradiation

The insulated gate bipolar transistor (IGBT) has emerged as a prominent high-power semiconductor device due to its excellent overall performance. It is widely utilized in various fields, including aerospace. Due to prolonged operation in complex irradiation environments, the performance of IGBTs is susceptible to degradation and damage. Therefore, conducting research on the variation of IGBT characteristics under irradiation environments is crucial to ensuring their long-term functionality in extended space missions. To evaluate and analyze the total ionizing dose (TID) effect of IGBTs during operation, this study adopts a trench IGBT as the device model. Utilizing the finite element method, technology computer-aided design (TCAD) is employed to simulate and analyze the electrical characteristic changes of IGBTs under different total radiation doses. The simulation results are subsequently validated through theoretical analysis. The simulation results indicate that gamma radiation significantly affects the overall electrical characteristics of IGBTs.

Photo-Enhanced Inverse Metal-Assisted Chemical Etching of α-Ga2O3 grown on Al2O3

Si-based semiconductor devices are not suitable for stable operations in the aerospace environments. Among the ultra-wide bandgap semiconductor materials, gallium oxide (Ga2O3) is attracting attention as the next-generation material for high-power semiconductor devices in extreme condition beyond Si, owing to its large band gap of 4.5-5.3 eV, high breakdown electric fields of 7-10 MV/cm, excellent chemical and thermal stability and radiation hardness. Alpha gallium oxide (α-Ga2O3) has the largest bandgap (4.8-5.3 eV) and the highest breakdown electric fields (~10 MV/cm) among the five Ga2O3 polymorphs, which facilitates the application of α-Ga2O3 as a high power device. However, the research on etching technology for α-Ga2O3 is rare. Etching technology is a crucial step of device fabrication. Chemical etching is free from plasma-induced damage which leads to superior device performance compared with dry etching, and high throughput with low cost is beneficial to industrial implementations. Chemical stability of Ga2O3 hinders the effective reaction with most chemical etchants. However, the photo-enhanced inverse metal assisted chemical (I-MAC) etching, where a noble metal with a high work function is utilized as a catalyst under UV irradiation, has emerged as a candidate for the chemical etching of Ga2O3. Deep-UV irradiation generates electron-hole pairs (EHPs) in the uncovered region of Ga2O3, and the metal electrode withdraws carriers from the photo-generated EHPs. The holes that are accumulated in the uncovered region of Ga2O3 react with gallium ions which produce gallium fluoride (GaF3) in a reaction with Hydrofluoric acid (HF). The etching process continues as the oxidant re-oxidizes the metal. The etch rate can be controlled by various parameter, including concentration and temperature of the etchant. In this work, for the I-MAC etch of α-Ga2O3 on sapphire substrate grown by halide vapor phase epitaxy, Pt was deposited on α-Ga2O3. Etch rate and surface roughness were characterized by atomic force microscopy after each step of the I-MAC etch. The I-MAC etch using HF and potassium persulfate (K2S2O8) solution with 185-nm UV irradiation was performed at constant durations under different etchant temperature conditions. The etch rates obtained at each temperature condition were fitted with the Arrhenius plot to estimate the activation energy of 0.898 eV. The etch depth showed a linear increase with time and the etch rate exhibits a direct dependency on the temperature of the etchant, indicating that the I-MAC etching of α-Ga2O3 is an activation-controlled reaction. As the I-MAC etching proceeded, surface roughness of α-Ga2O3 showed a tendency to increase. The rate at which the surface roughness increased increased with raising the etchant temperature. In the case of Pt there was no significant difference in the surface roughness after etching. After the completion of the I-MAC etch, the remaining Pt can be removed using aqua regia. The I-MAC etch process of α-Ga2O3 can allow us to fabricate α-Ga2O3 without plasma-damage. Figure 1

A Review of Select Patented Technologies for Cooling of High Heat Flux Power Semiconductor Devices

The development of wide band-gap power electronics over the last two decades has stimulated a tremendous amount of research into high performance liquid cooling solutions for high heat flux (200-1000 W/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> ) power semiconductor devices. A patent literature search for electronics cooling technologies was conducted in the late-2000 time frame and promising technologies for high performance thermal management were identified, at that time, for research and development. These promising technologies were separated into four categories classified as single-phase (i.e., liquid) jet impingement cooling, microchannel cooling, phase change or two-phase cooling, and near-junction including direct chip cooling. In this Letter, a perspective is provided on select patents from our group that stem from research into these technology areas from 2010 to 2022. Additionally, the thermal-fluid performance capability of each technology is briefly summarized. As a whole, the Letter provides a demonstration of the historical significance of power electronics cooling technology on the mobility industry and briefly outlines future directions for research and development.

Investigation of failure mechanism of aluminum-scandium wire bond contact under active power cycle test

The failure mechanism of aluminum-scandium (Al-Sc) wire bond in comparison with pure Al wire bond under active power cycle (APC) test was investigated. To monitor the degradation of the bond quality, bond shear forces (shear force) were measured over the testing cycles at different level of temperature swing (ΔT). The results show that the Al-Sc wire bond was much more robust than the pure Al wire bond when the ΔT (Tmax) was mild. On the other hand, as the ΔT was increased, the shear force reduction in the Al-Sc wire bond became more and more remarkable. In the cross-sectional analysis of bond contact after the APC tests, a significant crack propagation was observed even for low ΔT conditions for the pure Al wire, and the crack progressed primarily on the wire side of the bond area. As for the Al-Sc wire, while the bond crack was efficiently suppressed for low ΔT conditions, a significant progress of crack was observed at high ΔT conditions, and the crack grew mainly through the Al pad side of the bond area. A detailed analysis at the bond interface after the APC test at high ΔT condition revealed three phenomena at the Al pad side of the bond area: grain coarsening, precipitation of Cu particles, and large void formation. As the material strength is compromised by these effects, the crack grew more easily through the Al pad side of the contact area, resulting in a rapid reduction of shear force at high ΔT. The bond failure mechanism obtained in this study will provide a valuable insight for the future development of high reliability power semiconductor device.

100 kA/10 kV thyristor stack design for the quench protection system in CRAFT

Thyristors have longer lifetimes, higher reliability, and very high voltage and current ratings and they require less maintenance than other high-power semiconductor devices. As a result, they are particularly suitable for quench protection systems (QPSs), which protect the superconducting magnets in large fusion devices from damage. In this paper, we propose a design for a 100 kA/10 kV thyristor stack supported by both theoretical and simulation-based analyses as well as experimental verification. Due to the ultrahigh electrical performance requirements imposed on the QPS by the Comprehensive Research Facility for Fusion Technology (CRAFT), three main issues must be considered: the voltage-balancing problem caused by multiple thyristors in a series structure, the increased junction temperature problem caused by extremely high currents, and the reverse recovery phenomenon that arises from the thyristor’s physical structure. Hence, a series of detailed theoretical analyses, simulations, and experiments, including a thyristor junction temperature prediction method and reverse recovery process modeling, were carried out to optimize the design. Finally, the reliability and stability of the thyristor stack were verified by a series of prototype experiments. The results confirmed the correctness and accuracy of the proposed thyristor stack design method and also indicated that the proposed thyristor stack can meet the application conditions of a 100 kA QPS in the CRAFT project.

Bottom-Up Cu Filling of High-Aspect-Ratio through-Diamond vias for 3D Integration in Thermal Management.

Three-dimensional integrated packaging with through-silicon vias (TSV) can meet the requirements of high-speed computation, high-density storage, low power consumption, and compactness. However, higher power density increases heat dissipation problems, such as severe internal heat storage and prominent local hot spots. Among bulk materials, diamond has the highest thermal conductivity (≥2000 W/mK), thereby prompting its application in high-power semiconductor devices for heat dissipation. In this paper, we report an innovative bottom-up Cu electroplating technique with a high-aspect-ratio (10:1) through-diamond vias (TDV). The TDV structure was fabricated by laser processing. The electrolyte wettability of the diamond and metallization surface was improved by Ar/O plasma treatment. Finally, a Cu-filled high-aspect-ratio TDV was realized based on the bottom-up Cu electroplating process at a current density of 0.3 ASD. The average single-via resistance was ≤50 mΩ, which demonstrates the promising application of the fabricated TDV in the thermal management of advanced packaging systems.

Study on the Surface Structure of N-Doped 4H-SiC Homoepitaxial Layer Dependence on the Growth Temperature and C/Si Ratio Deposited by CVD

The quality of the N-doped 4H-SiC homoepitaxial layers grown via hot-wall horizontal chemical vapor deposition (CVD) was evaluated at various C/Si ratios (1.0–1.2) and growth temperatures (1570–1630 °C). The microstructure and morphology of the epilayers were studied through a comparative analysis of the AFM patterns under different growth conditions. X-ray photoelectron spectroscopy and Raman spectroscopy revealed the quality of the 4H-SiC epilayers and the amount of N-doping. It was found that an increase in the C/Si ratio enabled obtaining a quite smooth epitaxial layer surface. Moreover, only the 4H-SiC crystal type was distinguished in the epilayers. In addition, the epitaxial quality was gradually improved, and the amount of defect-related C-C bonds significantly dropped from 38.7% to 17.4% as the N doping content decreased from 35.3% to 28.0%. An increase in the growth temperature made the epitaxial layer surface smoother (the corresponding RMS value was ~0.186 nm). According to the Raman spectroscopy data, the 4H-SiC forbidden mode E1(TO) in the epilayers was curbed at a higher C/Si ratio and growth temperature, obtaining a significant enhancement in epitaxial quality. At the same time, more N dopants were inserted into the epilayers with increasing temperature, which was opposite to increasing the C/Si ratio. This work definitively shows that the increase in the C/Si ratio and growth temperature can directly enhance the quality of the 4H-SiC epilayers and pave the way for their large-scale fabrication in high-power semiconductor devices.

Electric field induced migration of native point defects in Ga2O3 devices

While the properties of β-Ga2O3 continue to be extensively studied for high-power applications, the effects of strong electric fields on the Ga2O3 microstructure and, in particular, the impact of electrically active native point defects have been relatively unexplored. We used cathodoluminescence point spectra and hyperspectral imaging to explore possible nanoscale movements of electrically charged defects in Ga2O3 vertical trench power diodes and observed the spatial rearrangement of optically active defects under strong reverse bias. These observations suggest an unequal migration of donor-related defects in β-Ga2O3 due to the applied electric field. The atomic rearrangement and possible local doping changes under extreme electric fields in β-Ga2O3 demonstrate the potential impact of nanoscale device geometry in other high-power semiconductor devices.

Fault Management Techniques to Enhance the Reliability of Power Electronic Converters: An Overview

The reliability of power electronic converters is a major concern in industrial applications because of using prone-to-failure elements such as high-power semiconductor devices and electronic capacitors. Hence, designing fault-tolerant inverters has been of great interest among researchers in both academia and industry over the last decade. Among the three stages of fault management, compensating the fault is the most important and challenging part. The techniques for fault compensation can be classified into three groups: hardware redundancy methods which use extra switches, legs, or modules to replace the faulty parts directly or indirectly, switching states redundancy methods which are about omitting and replacing the impossible switching states, and unbalance compensation including the techniques to compensate for the unbalances in the system caused by a fault. In this paper, an overview of fault-tolerant inverters is presented. A classification of fault-tolerant inverters is demonstrated and major cases in each of its categories are explained.

Graphene and 2D Hexagonal Boron Nitride Heterostructure for Thermal Management in Actively Tunable Manner.

Thermal management is a critical task for highly integrated or high-power semiconductor devices. Low dimensional materials including graphene and single-layer hexagonal boron nitride (BN) are attractive candidates for this task because of their high thermal conductivity, semi-conductivity and other excellent physical properties. The similarities in crystal structure and chemistry between graphene and boron nitride provide the possibility of constructing graphene/BN heterostructures bearing unique functions. In this paper, we investigated the interfacial thermal transport properties of graphene/BN nanosheets via non-equilibrium molecular dynamics (NEMD) simulations. We observed a significant thermal rectification behavior of these graphene/BN nanosheets, and the rectification ratio increased with the system length increases up to 117%. This phenomenon is attributed to the mismatch of out-of-plane phonon vibration modes in two directions at the interface. In addition, we explored the underlying mechanism of the length dependence of the thermal transport properties. The results show promise for the thermal management of this two-dimensional heterostructure in an actively tunable manner.

Research on gold film-assisted ultraviolet nanosecond laser machining of diamond microgrooves

Diamond microgrooves have great application prospects in biomedicine, high-power semiconductor devices, optical imaging, chip thermal management, and cutting tools. In this work, the effect of gold film on ultraviolet nanosecond laser machining of single-crystal diamond microgrooves was investigated through simulation and experimental research. The simulation results show that the ablation width and depth gradually increase with the increase of gold film thickness, and the ablation depth reaches a maximum value when the thickness of gold film increases to 100 nm. The surface morphology and elemental analysis show that the gold film was first melted and then re-solidified around the microgrooves under ultraviolet nanosecond laser irradiation. The ablation threshold of Au-coated diamond is 4.05 J/cm2, 24 % smaller than that of uncoated diamond. The material removal rate of Au-coated microgrooves is always higher than that of uncoated microgrooves at the same laser intensity. At laser intensity of 8.5 J/cm2, it is 1.1 times higher than that of uncoated diamond microgrooves. Moreover, the physical mechanism of gold film during laser machining of diamond microgroove is analyzed. This study provides a new method for efficient machining of diamond microgrooves.