Wide Bandgap Devices Research Articles

Bonding with brazing alloys as high-temperature interconnection filler through self-propagating exothermic reaction

There has been growing interest in wide bandgap (WBG) semiconductors including SiC and GaN due to the increasing demands for electronic devices serving at high temperatures. However, to maximise the potential capacity of WBG devices, new high-temperature interconnection materials and processes are indispensable as the current existing Sn-based solder alloys and bonding processes developed for Si devices are unable to meet the reliability requirements. In the present work, reactive brazing alloys including Cu-15Ag-5P and Incusil (Ag-27.25Cu-12.5In-1.25Ti) with melting points above 600°C have been utilized as the interconnection materials which offer excellent properties under high operation temperature. The self-propagating exothermic reaction (SPER) was applied for the bonding process via an intense rapid local heating and cooling at a millisecond scale. The strong Cu/Cu-15Ag-5P/Cu and Cu/Incusil/Cu sandwich bonded structures have been created with the assistance of SPER, where the nanofoil was applied from the outside of stacked structures as an external heat source and the bonding process was conducted in the ambient atmosphere without using flux. It has been found that the P element in Cu-15Ag-P alloy has the self-flux effect, which is beneficial for the ultra-fast interfacial reaction process. The experiments where the nanofoil was placed inside of stacked structures between two sheets of brazing alloys have also been conducted, which exhibited the well-bonded interface microstructures between nanofoil and brazing alloys. The outlook on the design for practicality and industrial uses for SPER-assisted bonding with brazing alloys has also been discussed, as a potential viable assembly route for the high-temperature and high-power electronics packaging.

Transmission Line Rogowski Coil: Isolated Current Sensor With Bandwidth Exceeding 3 GHz for Wide-Bandgap Device

Transmission Line Rogowski Coil: Isolated Current Sensor With Bandwidth Exceeding 3 GHz for Wide-Bandgap Device

Power Electronics Revolutionized: A Comprehensive Analysis of Emerging Wide and Ultrawide Bandgap Devices.

This article provides a comprehensive review of wide and ultrawide bandgap power electronic semiconductor devices, comparing silicon (Si), silicon carbide (SiC), gallium nitride (GaN), and the emerging device diamond technology. Key parameters examined include bandgap, critical electric field, electron mobility, voltage/current ratings, switching frequency, and device packaging. The historical evolution of each material is traced from early research devices to current commercial offerings. Significant focus is given to SiC and GaN as they are now actively competing with Si devices in the market, enabled by their higher bandgaps. The paper details advancements in material growth, device architectures, reliability, and manufacturing that have allowed SiC and GaN adoption in electric vehicles, renewable energy, aerospace, and other applications requiring high power density, efficiency, and frequency operation. Performance enhancements over Si are quantified. However, the challenges associated with the advancements of these devices are also elaborately described: material availability, thermal management, gate drive design, electrical insulation, and electromagnetic interference. Alongside the cost reduction through improved manufacturing, material availability, thermal management, gate drive design, electrical insulation, and electromagnetic interference are critical hurdles of this technology. The review analyzes these issues and emerging solutions using advanced packaging, circuit integration, novel cooling techniques, and modeling. Overall, the manuscript provides a timely, rigorous examination of the state of the art in wide bandgap power semiconductors. It balances theoretical potential and practical limitations while assessing commercial readiness and mapping trajectories for further innovation. This article will benefit researchers and professionals advancing power electronic systems.

Oxygen-vacancy defect in 4H-SiC as a near-infrared emitter: An ab initio study

Optically active spin defects in semiconductors can serve as spin-to-photon interfaces, key components in quantum technologies. Silicon carbide (SiC) is a promising host of spin defects thanks to its wide bandgap and well-established crystal growth and device technologies. In this study, we investigated the oxygen-vacancy complexes as potential spin defects in SiC by means of ab initio calculations. We found that the OCVSi defect has a substantially low formation energy compared with its counterpart, OSiVC, regardless of the Fermi level position. The OCVSi defect is stable in its neutral charge state with a high-spin ground state (S = 1) within a wide energy range near the midgap energy. The zero-phonon line (ZPL) of the OCVSi0 defect lies in the near-infrared regime, 1.11–1.24 eV (1004–1117 nm). The radiative lifetime for the ZPL transition of the defect in kk configuration is fairly short (12.5 ns). Furthermore, the estimated Debye–Waller factor for the optical transition is 13.4%, indicating a large weight of ZPL in the photoluminescence spectrum. All together, we conclude that the OCVSi0 defect possesses desirable spin and optical properties and thus is potentially attractive as a quantum bit.

Sources of error and methods to improve accuracy in interface state density analysis using quasi-static capacitance–voltage measurements in wide bandgap semiconductors

Characterizing interface trap states in commercial wide bandgap devices using frequency-based measurements requires unconventionally high probing frequencies to account for both fast and slow traps associated with wide bandgap materials. The C−ψS technique has been suggested as a viable quasi-static method for determining the interface trap state densities in wide bandgap systems, but the results are shown to be susceptible to errors in the analysis procedure. This work explores the primary sources of errors present in the C−ψS technique using an analytical model that describes the apparent response for wide bandgap MOS capacitor devices. Measurement noise is shown to greatly impact the linear fitting routine of the 1/CS∗2 vs ψS plot to calibrate the additive constant in the surface potential/gate voltage relationship, and an inexact knowledge of the oxide capacitance is also shown to impede interface trap state analysis near the band edge. In addition, a slight nonlinearity that is typically present throughout the 1/CS∗2 vs ψS plot hinders the accurate estimation of interface trap densities, which is demonstrated for a fabricated n-SiC MOS capacitor device. Methods are suggested to improve quasi-static analysis, including a novel method to determine an approximate integration constant without relying on a linear fitting routine.

A Review on Modular Converter Topologies Based on WBG Semiconductor Devices in Wind Energy Conversion Systems

This paper presents a comprehensive review on the employment of wide bandgap (WBG) semiconductor power devices in wind energy conversion systems (WECSs). Silicon-carbide- (SiC) and gallium-nitride (GaN)-based power devices are highlighted and studied in this review, focusing on their application in the wind energy system. This is due to their premium characteristics such as the operation at high switching frequency, which can reduce the switching losses, and the capability to operate at high temperatures compared with silicon (Si)-based devices. These advantages promote the replacement of the conventional Si-based devices with the WBG semiconductor devices in the new modular converter topologies due to the persistent demand for a more-efficient power converter topology with lower losses and smaller sizes. The main objective of this paper was to provide a comprehensive overview of the WBG power devices commercially available on the market and employed in the modular converter topologies for renewable energy systems. The paper also provides a comparison between the WBG power technologies and the traditional ones based on the Si devices. The paper starts from the conventional modular power converter topology circuits, and then, it discusses the opportunities for integrating the SiC and WBG devices in the modular power converters to improve and enhance the system’s performance.

Modeling and Operation of Series-Parallel Resonant Load in Industrial RF Dielectric Heating Application

Radio Frequency (RF) based heating application is used in multiple industries like drying cross-laminated woods, food and packaging, melting silicon etc. These industrial RF heating plants operate at frequencies of 6.78 MHz, 13.56 MHz, or 27.12 MHz (ISM band). Historically, the high frequency requirement has forced the industry to rely on vacuum tube based RF generator, which are only 60% efficient. Modern semiconductors like wide bandgap (WBG) devices have achieved the high frequency operation that is required to replace the inefficient vacuum tubes. However, a comprehensive study of load network for an industrial RF heating plant has not been undertaken such that an existing plant can be retrofitted with semiconductor based turn-key solution. In this paper the authors present design equations for an industrial RF dielectric heating load structure and suggest necessary modifications required to replace vacuum tube RF generator with voltage source converter (VSC). A new figure of merit (FOM) is defined that impacts the load structure efficiency. Finally, a small-scale prototype load is manufactured as a case study. The prototype demonstrated an output power of 750 W at 6.76 MHz with an overall efficiency of 90% from DC input to RF load which can not be achieved with a vacuum tube technology.

High-Temperature Partial Discharge Characteristics of Power Module Packaging Insulation Under Square Pulse With High Dv/Dt Based on Down-Mixing Method

Partial discharge (PD) in the high voltage packaging insulation under square pulse with a high slew rate (SR or dV/dt) is one of the main causes of the power module failure, especially for wide bandgap (WBG) devices. But PD under fast square pulse at high temperatures is rarely studied and one of the critical reasons is the lack of an effective PD detection method under fast square pulses. In addition, the existing PD standard defines the PD criterion under sinusoidal alternating current (AC) situations, which is not the actual working condition of the power module. To address that, this paper proposes a down-mixing PD detection method and explores the influence of temperature on the PD characteristics of the power module packaging insulation. The results show that the partial discharge inception voltage (PDIV) decreases as the temperature increases. The PDIV under square pulse is always higher than that under AC voltage. The less the SR and the greater the pulse width (PW) of the square pulse, the lower the PDIV. Physical-based models for PDIV estimation concerning SR, PW, and temperature are proposed for industrial reference. Moreover, statistical analysis of PD magnitude, number, and occurrence phase under square pulse indicates that PD number decreases but PD magnitude increases with the increase in temperature. Higher temperature leads to PDs with large magnitudes, which may accelerate the degradation of packaging insulation.

A PWM Method for Reducing dv/dt and Switching Losses in Two-Stage Power Converters

Today's semiconductor devices are accompanied by high switching frequencies (> kilo-hertz) and small transition times (< micro-seconds). Such fast transition times are accompanied by undesirable effects such as voltage overshoots at the load terminals, ground leakage currents, wide-band electromagnetic noise, etc. With the advent of wide band-gap devices, several applications are moving towards higher switching frequency operation with at-least an order of magnitude reduction in transition times. While these characteristics are considered necessary to break the next-generation barriers in power density, efficiency and applicability, the undesirable effects due to faster transitions are expected to present obstacles. This work proposes a PWM approach to modify the shape of the switching voltages to overcome the disadvantages of the fast transition times without any increase in switching losses. In fact, several of the switching transitions feature ZVS operation, resulting in reduced switching losses. The paper discusses the analytical details of the approach using a simple DC-DC boost-buck converter and extends it to a DC to three-phase AC converter using the principles of space vector modulation. The paper presents detailed simulation and comparative results in terms of voltage over-shoots over long cables, loss calculations and electromagnetic noise. Results from a laboratory-scale working prototype confirm the benefits of the proposed approach in terms of EMI and loss reduction.

A survey of conductive and radiated EMI reduction techniques in power electronics converters across wide‐bandgap devices

AbstractNowadays, wide‐bandgap (WBG) devices, primarily made from silicon carbide (SiC) and gallium nitride (GaN), are widely applied in power generation, transmission, and conversion. Moreover, the application of WBG devices has had a transformative impact in the field of energy conversion. Compared with Si counterparts, SiC and GaN can remarkably improve the power conversion system efficiency and power density while generating higher electromagnetic interference (EMI) emissions. There are many studies on WBG devices and their behaviour in power systems. However, methods of mitigating EMI/electromagnetic compatibility (EMC) still lack scientific guidance. This article reviews the characteristics of WBG devices, and the significant EMI problems are discussed. Then, the EMI types, EMI causes, and methods of EMI reduction are summarized, and the advantages and disadvantages of these methods are presented as well. Based on the reviewed studies, future research, and the conclusions of this article on EMI/EMC are discussed to help relevant researchers deepen their understanding of the new challenges of EMI brought by the applications of WBG devices, which are useful in engineering.

High Efficiency Isolated 5-Level Dual Active DC–DC Converter Using Wide Band Gap Devices

In this paper a bidirectional isolated dc-dc converter is proposed for application in shipboard power systems. In this topology, an active 5-level T-type converter is used on the primary and secondary sides of a high-frequency transformer. The operation of the proposed converter is optimized based on minimizing power losses. For the optimization, the transformer core loss, reactive power, and rms current are considered. Wide band gap devices are used for minimization of semiconductor switching losses. A control method based on the Fourier series and decomposition theorem is proposed. The proposed converter features higher efficiency, fault tolerant capability and smaller filter size compared to the common dual active bridge dc-dc converters. To reduce voltage overshoot, a laminated dc-link is designed and a two-level turn-off method is used for operating frequencies around 75 kHz. Finally, the step-up and step-down operations of the proposed structure are verified through experiments.

A Unified Differential Mode Noise Estimation Method and Filter Size Comparison in Single-Phase Multileg and Multilevel Totem-Pole PFC Converters

Wide band-gap power devices have enabled single-phase totem-pole (TP) power factor correction (PFC) converter designs to be switched at several tens of kHz under hard-switching and hundreds of kHz under soft-switching. It is straight-forward to analyze and compare the volume of boost inductor for TP PFC converters having multi-leg and multi-level configurations operating under continuous-conduction-mode (CCM) and critical-conduction-mode (CrM) at various switching frequencies; however, the impact of topology and switching frequency selections remains unchallenged for generated differential mode (DM) noise. This paper proposes a unified and generalized DM noise estimation method for multi-leg, and multi-level TP PFC converters operated under both CCM and CrM operation modes. The method has been verified with simulation results obtained from various TP PFC topologies, as well as experimental results obtained from single-leg CCM and 4-Level CCM TP PFC converters. The empirically determined boxed sizes of DM filters have been compared among various TP PFC topologies, and the best switching frequency for each topology has been determined with the integration of boost inductor volume comparison.

A Review of High-Speed GaN Power Modules: State of the Art, Challenges, and Solutions

Wide bandgap (WBG) devices are a desirable choice for high-density energy conversion systems. In high-speed hard-switching applications, voltage overshoot across device terminals, oscillations at gate loop and Electro-magnetic Interference (EMI) becomes harder to mitigate and overall system reliability is reduced. To address the key challenges and harness the benefits offered by these latest generations of devices, improved and advanced packaging structures are required, as packaging technology often has a critical impact on module performance and reliability. This paper summarizes the design procedure for power modules, essential parts, and available materials for the fabrication of a power module package. Moreover, it provides a review of commercially available gallium nitride based high electron mobility transistors (GaN HEMTs) and state-of-the-art module packaging technologies adopted for them with a focus on module layout, module integration trends, and identifying their impacts on the GaN HEMT’s performance. Through this review, the paper also discusses major challenges faced by designers with GaN HEMTs in power electronics applications and their potential solutions, which is critical for the mainstream adoptions of GaN HEMTs and defining the future technology roadmap.

Integrated Common-Mode Filter for GaN Power Module With Improved High-Frequency EMI Performance

While the employment of wide bandgap (WBG) devices in high-frequency and high-voltage applications brings benefits such as reduced system size and improved efficiency, it aggravates the electromagnetic interference (EMI) issue due to fast switching. High-frequency EMI noise suppression relies mainly on the filter design, where the filter's performance is strongly affected by parasitics. Through analyzing the common-mode (CM) equivalent circuit of a half-bridge power module, this letter identifies the key parasitics that dominate the performance of a common-mode filter (CMF) at high frequencies. To minimize the parasitics, the concept of integrating the CMF inside the WBG power module package is developed to improve the noise attenuation. A π-type CMF is integrated with a half-bridge GaN-based power module as a prototype to validate the concept. Experiments are conducted by measuring the CM noise spectrum received by the line impedance stabilization networks (LISNs) from the hard switching of the designed power module under 70 V and 80 kHz. Comparing the measured results of the integrated CMF to the externally-added CMF, up to 50 dBμV more attenuation is achieved by the integrated CMF in the frequency range of 10 MHz to 100 MHz, verifying the theoretical analysis and the established CM equivalent circuit.

Picosecond magneto-optic thermometry measurements of nanoscale thermal transport in AlN thin films

The thermal conductivity Λ of wide bandgap semiconductor thin films, such as AlN, affects the performance of high-frequency devices, power devices, and optoelectronics. However, accurate measurements of Λ in thin films with sub-micrometer thicknesses and Λ &amp;gt; 100 W m−1 K−1 is challenging. Widely used pump/probe metrologies, such as time–domain thermoreflectance (TDTR) and frequency–domain thermoreflectance, lack the spatiotemporal resolution necessary to accurately quantify thermal properties of sub-micrometer thin films with high Λ. In this work, we use a combination of magneto-optic thermometry and TiN interfacial layers to significantly enhance the spatiotemporal resolution of pump/probe thermal transport measurements. We use our approach to measure Λ of 100, 400, and 1000 nm AlN thin films. We coat AlN thin films with a ferromagnetic thin-film transducer with the geometry of (1 nm-Pt/0.4 nm-Co)x3/(2 nm-TiN). This PtCo/TiN transducer has a fast thermal response time of &amp;lt;50 ps, which allows us to differentiate between the thermal response of the transducer, AlN thin film, and substrate. For the 100, 400, and 1000 nm thick AlN films, we determine Λ to be 200 ± 80, 165 ± 35, and 300 ± 70 W m−1 K−1, respectively. We conclude with an uncertainty analysis that quantifies the errors associated with pump/probe measurements of thermal conductivity, as a function of transducer type, thin-film thermal conductivity, and thin-film thickness. Time resolved magneto-optic Kerr effect experiments can measure films that are three to five times thinner than is possible with standard pump/probe metrologies, such as TDTR. This advance in metrology will enable better characterization of nanoscale heat transfer in high thermal conductivity material systems like wide bandgap semiconductor heterostructures and devices.

GaN-Based Matrix Resonant Power Converter for Domestic Induction Heating

Flexible-surface induction cooktops must operate with a variety of induction heating loads with different behavior and power setpoints to be heated simultaneously. In this context, multi-output inverter topologies aim at achieving independent power management while featuring low power-device count and high power density. However, they suffer from limitations when applying classical modulation strategies to ensure soft switching, which is required to reduce transistor losses and achieve efficient operation. In this scenario, wide band-gap devices reduce switching losses, opening a new paradigm in power conversion where soft switching is not mandatory in order to achieve high efficiency. This paper proposes an implementation of a multi-output resonant inverter based on GaN HEMTs and evaluates various modulation strategies in terms of efficiency under different switching modes. The proposed approach is designed and experimentally validated by means of a 2-coil 2000 W prototype implementation.

A Nonlinear-Model-Based High-Bandwidth Current Sensor Design for Switching Current Measurement of Wide Bandgap Devices.

With the growing adoption of wide bandgap devices in power electronic applications, current sensor design for switching current measurement has become more important. The demands for high accuracy, high bandwidth, low cost, compact size, and galvanic isolation pose significant design challenges. The conventional modeling approach for bandwidth analysis of current transformer sensors assumes that the magnetizing inductance remains constant, which does not always hold true in high-frequency operations. This can result in inaccurate bandwidth estimation and affect the overall performance of the current sensor. To address this limitation, this paper provides a comprehensive analysis of nonlinear modeling and bandwidth, considering the varying magnetizing inductance in a wide frequency range. A precise and straightforward arctangent-based fitting algorithm was proposed to accurately emulate the nonlinear feature, and the fitting results were compared with the magnetic core's datasheet to confirm its accuracy. This approach contributes to more accurate bandwidth prediction in field applications. In addition, the droop phenomenon of the current transformer and saturation effects are analyzed in detail. For high-voltage applications, different insulation methods are compared and an optimized insulation process is proposed. Finally, the design process is experimentally validated. The bandwidth of the proposed current transformer is around 100 MHz and the cost is around $20, making it a low-cost and high-bandwidth solution for switching current measurements in power electronic applications.

Gallium Nitride Power Devices in Power Electronics Applications: State of Art and Perspectives

High-electron-mobility transistors based on gallium nitride technology are the most recently developed power electronics devices involved in power electronics applications. This article critically overviews the advantages and drawbacks of these enhanced, wide-bandgap devices compared with the silicon and silicon carbide MOSFETs used in power converters. High-voltage and low-voltage device applications are discussed to indicate the most suitable area of use for these innovative power switches and to provide perspective for the future. A general survey on the applications of gallium nitride technology in DC-DC and DC-AC converters is carried out, considering the improvements and the issues expected for the higher switching transient speed achievable.

A DPWM-Based Quasi-Constant Switching Frequency Control for Full ZVS Range Three-Phase Inverter With Reactive Power Transfer Capability

In this paper, a quasi-constant switching frequency zero voltage switching (ZVS) control strategy is proposed for three-phase grid-connected inverters. Full ZVS range can be achieved for all the switches at any load, modulation index, and power factor using discontinuous pulse width modulation (DPWM). No additional high- frequency sensor or auxiliary circuit is needed. The switching frequency is constant at steady-state. It does not change with the phase angle or the power factor, but it varies with the modulation index, grid RMS voltage and current. The frequency can be easily calculated in a digital controller based on current ripple prediction (CRP) instead of current zero-crossing detection (ZCD). The turn-on loss is eliminated so the inverter can operate at a high switching frequency, especially by using wide band-gap devices. The conversion efficiency, power density, cost, and dynamic response of the inverter can all be improved. A 3.3 kVA experimental prototype using SiC MOSFETs interfacing 400 V DC link with three-phase 110 V AC grid is developed to verify the effectiveness of the proposed control strategy.

Double Sided Integrated GaN Power Module with Double Pulse Test (DPT) Verification

Wide Bandgap devices (WBG) have led to an era of high speed and high voltage operations that were not previously achievable with silicon devices. However, packaging of these devices in the power module has been a challenge due to higher switching rates which can cause several amperes of displacement current to flow through the parasitic capacitance of the package thus impacting the gate driver operation and the switching ability of the device. The severity of this current increases in thin packaging substrates unlike the traditional inorganic substrates e.g. DBC and thus a thorough investigation is needed before it can be used with WBG semiconductors. The objective of this paper is to discuss ways to reduce as well as manipulate the parasitic capacitance at different locations in the power modules to reduce the magnitude of the peak and RMS value of the displacement current and have a better gate drive signal and power waveform. To study this, a Double Pulse Test (DPT) simulation study has been conducted to show how an intelligent distribution of parasitic capacitance benefits the device functioning. This has been validated through experimental fabrication and DPT of dense power module following proposed guidelines. A detailed description of the design of a high-speed capable DPT circuit and measurement setup has been specified to show the steps needed for reliable testing and measurement.