Showing papers on "Power semiconductor device published in 2021"

GaN-based power devices: Physics, reliability, and perspectives

Abstract: Over the last decade, gallium nitride (GaN) has emerged as an excellent material for the fabrication of power devices. Among the semiconductors for which power devices are already available in the market, GaN has the widest energy gap, the largest critical field, and the highest saturation velocity, thus representing an excellent material for the fabrication of high-speed/high-voltage components. The presence of spontaneous and piezoelectric polarization allows us to create a two-dimensional electron gas, with high mobility and large channel density, in the absence of any doping, thanks to the use of AlGaN/GaN heterostructures. This contributes to minimize resistive losses; at the same time, for GaN transistors, switching losses are very low, thanks to the small parasitic capacitances and switching charges. Device scaling and monolithic integration enable a high-frequency operation, with consequent advantages in terms of miniaturization. For high power/high-voltage operation, vertical device architectures are being proposed and investigated, and three-dimensional structures—fin-shaped, trench-structured, nanowire-based—are demonstrating great potential. Contrary to Si, GaN is a relatively young material: trapping and degradation processes must be understood and described in detail, with the aim of optimizing device stability and reliability. This Tutorial describes the physics, technology, and reliability of GaN-based power devices: in the first part of the article, starting from a discussion of the main properties of the material, the characteristics of lateral and vertical GaN transistors are discussed in detail to provide guidance in this complex and interesting field. The second part of the paper focuses on trapping and reliability aspects: the physical origin of traps in GaN and the main degradation mechanisms are discussed in detail. The wide set of referenced papers and the insight into the most relevant aspects gives the reader a comprehensive overview on the present and next-generation GaN electronics.

A Review of Switching Slew Rate Control for Silicon Carbide Devices Using Active Gate Drivers

Abstract: Driving solutions for power semiconductor devices are experiencing new challenges since the emerging wide bandgap power devices, such as silicon carbide (SiC), with superior performance become commercially available. Generally, high switching speed is desired due to the lower switching loss, yet high $dv/dt$ and $di/dt$ can result in elevated electromagnetic interference (EMI) emission, false-triggering, and other detrimental effects during switching transients. Active gate drivers (AGDs) have been proposed to balance the switching losses and the switching speed of each switching transient. The review of the in-existence AGD methodologies for SiC devices has not been reported yet. This review starts with the essence of the slew rate control and its significance. Then, a comprehensive review categorizing the state-of-the-art AGD methodologies is presented. It is followed by a summary of the AGDs control and timing strategies. In this work, using AGD to reduce the EMI noise of a 10-kV SiC MOSFET system is reported. This work also highlights other capabilities of AGDs, including reliability enhancement of power devices and rebalancing the mismatched electrical parameters of parallel- and series-connected devices. These application scenarios of AGDs are validated via simulation and experimental results.

A Review of SiC IGBT: Models, Fabrications, Characteristics, and Applications

Abstract: Along with the increasing maturity for the material and process of the wide bandgap semiconductor silicon carbide (SiC), the insulated gate bipolar transistor (IGBT) representing the top level of power devices could be fabricated by SiC successfully This article presents a thorough review of development of SiC IGBT in the past 30 years The progresses of models, structure design, and performance in SiC IGBT are summarized The challenges resulting from fabrication process and switching characteristics are discussed and analyzed in detail The experimental results and existing problems in SiC IGBT-based applications are summarized in the end

Three Levels Are Not Enough: Scaling Laws for Multilevel Converters in AC/DC Applications

Abstract: Single-phase inverters and rectifiers in 230 V $_{\text{rms}}$ applications, with a dc-side voltage of 400 V, achieve ultrahigh efficiency with a simple two-level topology. These single-phase designs typically utilize a line-frequency unfolder stage, which has very low losses and essentially doubles the peak-to-peak voltage that can be generated on the ac side for a given dc-link voltage. For certain applications, however, such as higher power grid-connected photovoltaic inverters, electric vehicle chargers, and machine drives, three-phase converters are needed. Because of the three-phase characteristic of the system, unfolders cannot be similarly used, leading to a higher minimum dc-link voltage of the three-phase line-to-line voltage amplitude, which is typically set to 800 V for 230 V $_{\text{rms}}$ phase voltage systems. Previous demonstrations indicate that significantly more levels—and the associated higher cost and complexity—are required for ultrahigh-efficiency three-phase converters relative to their single-phase counterparts. In this article, we seek to determine the fundamental reason for the performance difference between three-phase 800 V dc-link converters and single-phase 400 V converters. First, we build a 2.2 kW dc/ac hardware demonstrator to confirm the necessity of higher complexity converters, showing a simultaneous reduction in efficiency and power density between a two-level 400 V benchmark (99.2% peak efficiency at 18.0 kW/L) and a three-level 800 V inverter phase-leg (98.8%, 9.1 kW/L). With the motivation confirmed, we derive general scaling laws for bridge-leg losses across the number of levels and dc-link voltage, finding the efficiency-optimal chip area and the minimum semiconductor losses. With commercially available Si or GaN power semiconductors, the scaling laws indicate that six or more levels would be required for an 800 V three-phase ac/dc converter to meet or exceed the bridge-leg efficiency of a two-level 400 V GaN benchmark for a fixed output filter. With a complete Pareto optimization, we find that at least seven levels are necessary to recover the efficiency of the two-level 400 V benchmark, and we validate this theory with a seven-level 800 V 2.2 kW hardware prototype with a power density of 15.8 kW/L and a peak efficiency of 99.03%. Finally, two practical solutions that make use of the benefits of unfolder bridges familiar in single-phase systems are identified for three-phase systems.

A Single-Source Nine-Level Boost Inverter with A Low Switch Count

Abstract: Switched-capacitor-based multilevel inverters for boost-type dc-ac power conversions usually exhibit a trade-off between the switch count and switch-voltage rating, i.e., a reduction of one necessitating an increase of the other. Such a dilemma is well addressed in this paper by proposing a novel single-phase nine-level inverter based on a switched-capacitor network with a single switch. The proposed inverter then reduces the number of switches while generating a boosted dc-link voltage. A unique six-switch full-bridge cooperating with a low-frequency half-bridge further steps-up the output voltage with a quadruple gain. The voltage stresses on the power devices are, however, maintained low even under the boosted high output voltage, as all the switches/diodes can be clamped to any of the low-voltage capacitors. Consequently, low-voltage power devices can be utilized, reducing the overall power loss. Detailed theoretical analysis, calculations, and design considerations of the proposed inverter are provided. Comparisons with the prior-art inverters illustrate its advantages. Simulations and experimental tests on a 1-kVA inverter prototype verify the above-claimed benefits.

β-Ga2O3 vertical heterojunction barrier Schottky diodes terminated with p-NiO field limiting rings

Abstract: In this Letter, high-performance β-Ga2O3 vertical heterojunction barrier Schottky (HJBS) diodes have been demonstrated together with the investigation of reverse leakage mechanisms. In HJBS configurations, NiO/β-Ga2O3 p-n heterojunctions and p-NiO field limiting rings (FLRs) are implemented by using a reactive sputtering technique at room temperature without intentional etching damages. Determined from the temperature-dependent current-voltage characteristics, the reverse leakage mechanism of the HJBS diode is identified to be Poole-Frenkel emission through localized trap sates with an energy level of EC-0.72 eV. With an uniform FLR width/spacing of 2 μm in HJBS, a maximum breakdown voltage (BV) of 1.89 kV and a specific on-resistance (Ron,sp) of 7.7 mΩ·cm2 are achieved, yielding a high Baliga's figure-of-merit (FOM, BV2/Ron,sp) of 0.46 GW/cm2. The electric field simulation and statistical experimental facts indicate that the electric field crowding effect at device edges is greatly suppressed by the shrinkage of p-NiO FLR spacing, and the capability of sustaining high BV is enhanced by the NiO/β-Ga2O3 bipolar structure, both of which contribute to the improved device performance. This work makes a significant step to achieve high performance β-Ga2O3 power devices by implementing alternative bipolar structures to overcome the difficulty in p-type β-Ga2O3.

Performance of GaN Power Devices for Cryogenic Applications Down to 4.2 K

Abstract: Gallium nitride (GaN) power devices are employed in an increasing number of applications thanks to their excellent performance. Nevertheless, their potential for cryogenic applications, such as space, aviation, and superconducting systems, has not yet been fully explored. In particular, little is known on the device performance below liquid nitrogen temperature (77 K) and the behavior of popular GaN architectures such as gate injection transistor and Cascode below room temperature has not yet been reported. Most importantly, it is still unclear how the different device loss contributions, i.e., conduction, soft- and hard-switching losses, change at cryogenic temperatures. In this letter, we investigate and compare the performance of four GaN commercial power devices in a wide temperature range between 400 and 4.2 K. All of the tested devices can successfully operate at cryogenic temperatures with an overall performance improvement. However, different GaN HEMT technologies lead to significant variations in device gate control and loss mechanisms, which are discussed based on the device structure. The presented results prove the promising potential of the GaN technology for low-temperature applications and provide precious insights to properly design power systems operating under cryogenic temperatures and maximize their efficiency.

An Optimized Hybrid Modulation Scheme for Reducing Conduction Losses in Dual Active Bridge Converters

Abstract: A linearized hybrid modulation scheme for the dual active bridge (DAB) converter is proposed in this article. For the purpose of minimizing the conduction losses dissipated on the transformer and the power transistors, an optimal relationship function between the two control variables employed in extended phase shift (EPS) modulation can be derived. However, the obtained relationship function is a complex expression, which is not good for simple on-line control. Hence, a linearized modulation scheme is proposed in this article. This modulation scheme can achieve a quasi-minimum root-mean-square (rms) value of the leakage inductance current for the same output power. Meanwhile, the zero-voltage switching (ZVS) of the power transistors can be achieved over the whole power range. The power transfer capability is also kept the same as the optimal EPS scheme. Finally, experiments are conducted on a laboratory prototype to validate the effect of the linearized modulation scheme on the reduction of conduction losses. The experimental results present an improved converter efficiency and the realization of ZVS.

Medium Voltage Soft-Switching DC/DC Converter With Series-Connected SiC MOSFETs

Abstract: Nowadays, due to the growing demands of data centers, the traditional line frequency transformer based data center power distribution system (DC-PDS) is becoming bulky and inefficient Although SST-based DC-PDS dramatically improves the system efficiency, the traditional multicell SST with input-series output-parallel architectures has limitations Using high-voltage devices to develop single-cell SST improves system performance, however, its application is limited by high-voltage power devices As an alternative solution, achieving high blocking voltage through the series connection of low-voltage devices brings several advantages Nevertheless, the series connection brings about two main problems, namely the voltage imbalance among devices and the increment of switching loss This article proposes a medium voltage series resonant converter (MVSRC) with series-connected SiC MOSFETs By adding snubber capacitor to each SiC MOSFET and working at LLC resonant soft-switching mode, the voltage imbalance is reduced and switching loss is decreased Due to snubber capacitors, there are differences between MVSRC and traditional LLC converter, hence the analytical model of MVSRC is established Moreover, the voltage imbalance model is established and the voltage imbalance sensitivity is defined to guide the snubber parameter selections Then, a design example of the 99% efficient 5-kV/400-V prototype is presented Last, the experimental results show that the voltage imbalance is reduced effectively and the switching loss is decreased dramatically, verifying the validity of proposed methods and the accuracy of analysis

Modeling and Characterization of Frequency-Domain Thermal Impedance for IGBT Module Through Heat Flow Information

Abstract: Frequency-domain modeling is a relatively new approach for thermal impedance description of power semiconductor devices, and it has shown promising advantages to analyze the multitimescale thermal dynamics of power semiconductor devices under complex mission profiles. However, parameters in the frequency-domain thermal model are still difficult to be accurately extracted, and sometimes the extraction process would be complicated and ambiguous depending on the construction of power devices and heat sink. This article proposes a new method to identify these key parameters of the frequency-domain thermal model for power semiconductors. The proposed approach utilizes the information of heat flowing out of device and only requires temperature responses of three different locations in the heat path of insulated-gate bipolar transistor (IGBT) module under a step power-loss. By the proposed approach, the critical frequencies in the frequency-domain thermal model of IGBT module can be extracted more easily and accurately. The effectiveness of the proposed method is also validated by simulations and experiments.

6.78-MHz Wireless Power Transfer With Self-Resonant Coils at 95% DC–DC Efficiency

Abstract: Megahertz-frequency inductive wireless power transfer holds the promise of compact and efficient wireless power transfer. Unfortunately, due to high-frequency losses in wide-bandgap semiconductors and low- $Q$ high-frequency coil designs, these systems are universally less efficient, on a dc–dc basis, than wireless power systems operating at conventional frequency regimes. This letter describes the design considerations for inductive wireless power transfer systems operating at 6.78 MHz. With a novel high-frequency resonant amplifier topology, a high- $Q$ self-resonant coil structure, and a better understanding of $C_{oss}$ losses in wide-bandgap power semiconductors, we demonstrate 6.78- MHz wireless power transfer systems that achieve 95% dc–dc efficiency at power levels up to and beyond 1 kW.

Multiphase Interleaved Bidirectional DC/DC Converter With Coupled Inductor for Electrified-Vehicle Applications

Abstract: A nonisolated high-power-density bidirectional dc/dc converter named multiphase interleaved with a coupled inductor is described. The proposed converter allows low current and voltage ripple, lower power losses, reduction on power component stress, and magnetic volume. Moreover, the coupled inductor is applied to achieve current sharing between each leg in a simple manner, which is helpful to simplify the structure and meaningfully improve performance. Auxiliary clamp circuits are not required and can operate over a wide voltage and power range, achieve a better dynamic response and low ripple while maintaining high efficiency. This article illustrates the steady-state operating principle under the inductor current continuous, discontinuous conduction modes and their boundary conditions in detail, the voltage and current stress of the power devices are shown, parameter design guideline, mathematical derivations, and a comparison between the proposed converter and previous dc/dc converters were conducted. Finally, a 4.5-kW proof-of-concept laboratory prototype has been designed, developed, and tested to demonstrate the performance of the proposed converter for wide load variation. The measured efficiency for the rated load was over 98% for maximum input voltage. This article is accompanied by a video file demonstrating the operation of the converter.

Next Generation of Power Supplies-Design for Manufacturability

Abstract: In today’s market, quality and reliability in power electronics products are a given Greater emphases are placed on high efficiency, high power density, and low cost Most products are custom designed with significant non-recurrent engineering and manufacturing processes that are labor intensive In certain isolated areas, we have witnessed improvements by integrating power devices, drivers, sensing and control, in the forms of standard power modules, such as the “Intelligent Power Module” (IPM) in small motor drives and “DrMOS” in power supplies for point-of load applications The major road blocks for wide spread applications using these more integrated solutions hinge on the ability to integrate large and bulky passive components with power semiconductors in a form suitable for automation Suffice it to say that the design practice for magnetic components has remained largely the same for the past five decades With recent advances in wide-band-gap (WBG) power semiconductor devices, namely, SiC and GaN, we have witnessed significant improvements in efficiency and power density, compared to the current practice using silicon counterparts Furthermore, with significant higher operating frequency, the integration of magnetic components with embedded windings in the PCB is feasible for a wide range of applications Design trade-offs, previously considered neither practical nor conceivable, can be realized, not only with significant gain in efficiency and power density, but also with drastic improvements of EMI/EMC and manufacturability Several examples are given to illustrate the new design paradigm

Online Junction Temperature Measurement for SiC MOSFET Based on Dynamic Threshold Voltage Extraction

Abstract: The online junction temperature monitoring of power devices is a viable technique to ensure the reliable operation of mission-critical power electronic converters. This article provides a potential approach for the junction temperature estimation of SiC MOSFET s based on the dynamic threshold voltage. The proposed method is independent of load current variation, which eliminates the complicated calibration procedure with load current. First, the physical mechanism and the temperature dependence of the dynamic threshold voltage are analyzed. An analytical model for the dynamic threshold voltage is built to investigate the effects of gate loop parameters on the temperature sensitivity and measurement accuracy. Then, the principle of the dynamic threshold voltage measurement circuit is introduced. Finally, the proposed dynamic threshold voltage measurement circuit is experimentally evaluated through the double-pulse tests. The experimental results show that the dynamic threshold voltage of SiC MOSFET has a good linear relationship with junction temperature. The temperature sensitivity of the dynamic threshold voltage of two SiC MOSFET s is approximately 5.2 mV/°C and 19.6 mV/°C, respectively.

An On-Board Charger Integrated Power Converter for EV Switched Reluctance Motor Drives

Abstract: This article presents a power converter topology with integrated driving and charging capability of switched reluctance motor (SRM) drive for electric vehicle (EV) application. In the driving mode, the bus voltage can be adjusted flexibly by the front-end buck converter, which meets the requirements of the speed open-loop and closed-loop control. Besides, higher voltage demagnetization can be achieved by connecting the upper freewheeling diodes of the asymmetric half-bridge converter to the battery bank, thus can accelerate the demagnetization process, extend the dwell angle, and enhance the output of the motor. In battery charging mode, a bridgeless rectifier converter is constructed by utilizing two-phase windings of the SRM and the existing power devices of integrated power converter, without additional inductors and charging units. The battery charging and power factor correction control can be realized by closed-loop control of charging current. Detailed analysis and experiments on a 1 kW 12/8 structure prototype SRM validate the effectiveness of the proposed technologies.

Design and Control of Power Fluctuation Delivery for Cell Capacitance Optimization in Multiport Modular Solid-State Transformers

Abstract: Modular multilevel converter (MMC)-based solid-state transformers (SSTs) have gained increasing interest lately. Topologies consisting of cells made of directly coupled MMC submodules (SMs) and dual-active-bridge (DAB) modules have been introduced to form multiport SSTs to interface different grid entities. Designated as modular SSTs (M-SSTs), such devices can interconnect hybrid ac–dc distribution systems and enable flexible power flow control among participating grids with different voltage forms and levels. However, the large capacitors needed to suppress power fluctuations in the power cells are a major contributor to the SST's poor power density. This article first proposes a power fluctuation delivery (PFD) control strategy for M-SST cell capacitance optimization. Through a modified phase-shift control, the low-frequency fluctuating power in the MMC SMs is transferred to the DAB's secondary side and is automatically canceled there. As a result, the cell capacitance requirement is significantly reduced. Considering the modified ripple power path, both power semiconductors and the high-frequency transformers in DABs are affected. Therefore, the design considerations of a single M-SST cell (1 MMC SM + 1 DAB) with/without PFD control are elaborated for a 2-MVA M-SST example. It is shown that the cell capacitance can be reduced to 10% of its original value, and the power density of the whole cell is increased by 50% with only 0.22% drop in the overall efficiency. The feasibility and effectiveness of the proposed method are verified by simulation results in this 2-MVA case and experimental results obtained from a 4.8-kVA scaled-down M-SST prototype.

Multi-channel nanowire devices for efficient power conversion

Abstract: Nanowire-based devices can potentially be of use in a variety of electronic applications, from ultrascaled digital circuits to 5G communication networks. However, the devices are typically restricted to low-power applications due to the relatively low electrical conductivity and limited voltage capability of the nanowires. Here, we show that wide-band-gap AlGaN/GaN nanowires containing multiple two-dimensional electron gas channels can be used to create high-electron-mobility tri-gate transistors for power-conversion applications. The multiple channels lead to improved conductivity in the nanowires, and a three-dimensional field-plate design is used to manage the high electric field. Power devices made with 15-nm-wide nanowires are shown to exhibit low specific on resistances of 0.46 mΩ cm−2, enhancement-mode operation, improved dynamic behaviour and breakdown voltages as high as 1,300 V. AlGaN/GaN nanowires containing multiple two-dimensional electron gas channels can be used to create tri-gate power transistors that overcome trade-offs between carried density and mobility.

Novel Hybrid DC Circuit Breaker Based on Series Connection of Thyristors and IGBT Half-Bridge Submodules

Abstract: Hybrid dc circuit breakers (HCBs) are vital equipment in dc grid systems. However, HCBs are usually costly since massive full-controlled power semiconductors are required to withstand high surge voltage and current stresses during current interrupting. Thyristors are good alternatives in realizing HCBs in view of their low cost and high current carrying capability; however, turning off the thyristor fast and reliably is a challenging task. In this article, a novel HCB topology is proposed, of which the solid-state part is realized by hybrid connection of thyristors and insulated gate bipolar transistor (IGBT) half-bridge submodules. The use of IGBT half-bridges provides a negative voltage across the thyristors to turn them off ; accordingly, thyristors withstand a major of turn- off surge voltage instead of IGBTs. By this means, a low-cost HCB can be established while maintaining a high breaking speed. Besides, fast reclose and rebreak function is provided by the proposed topology. Operation principle and design consideration of the novel HCB topology are analyzed in detail, and the effectiveness of the proposed HCB is verified by both software simulation and downscaled experimental results.

Vertical GaN Power Devices: Device Principles and Fabrication Technologies—Part II

Abstract: Vertical gallium nitride (GaN) power devices are enabling next-generation power electronic devices and systems with higher energy efficiency, higher power density, faster switching, and smaller form factor. In Part I of this review, we have reviewed the basic design principles and physics of building blocks of vertical GaN power devices, i.e., Schottky barrier diodes and p-n diodes. Key topics such as materials engineering, device engineering, avalanche breakdown, and leakage mechanisms are discussed. In Part II of this review, several more advanced power rectifiers are discussed, including junction barrier Schottky (JBS) rectifiers, merged p-n/Schottky (MPS) rectifiers, and trench metal–insulator–semiconductor barrier Schottky (TMBS) rectifiers. Normally- OFF GaN power transistors have been realized in various advanced device structures, including current aperture vertical electron transistors (CAVETs), junction field-effect transistors (JFETs), metal–oxide–semiconductor field-effect transistors (MOSFETs), and fin field-effect transistors (FinFETs). A detailed analysis on their performance metrics is provided, with special emphasis on the impacts of key fabrication processes such as etching, ion implantation, and surface treatment. Lastly, exciting progress has been made on selective area doping and regrowth, a critical process for the fabrication of vertical GaN power devices. Various materials characterization techniques and surface treatments have proven to be beneficial in aiding this rapid development. This timely and comprehensive review summarizes the current progress, understanding, and challenges in vertical GaN power devices, which can serve as not only a gateway for those interested in the field but also a critical reference for researchers in the wide bandgap semiconductor and power electronics community.

Incorporating the Dynamic Threshold Voltage Into the SPICE Model of Schottky-Type p -GaN Gate Power HEMTs

Abstract: The threshold voltage ( V TH) of an enhancement-mode Schottky-type p -GaN gate high-electron-mobility transistor (HEMT) is found to have a special dependence on the drain bias. The device commonly requires higher gate voltage to switch on the transistor from a high-drain-voltage off -state than what is expected from the static device characteristics. The reason behind the dynamic V TH has been proved to be the floating p -GaN layer, where charges could be stored and further influence V TH under different drain bias. In this article, a SPICE-compatible equivalent circuit model is presented according to the structure of Schottky-type p -GaN gate HEMTs. It features a floating node to imitate the charge storage process within the gate stack. Compared to conventional models, the proposed model could accurately predict the dynamic V TH characteristics and switching behaviors of power electronics circuits, where Schottky-type p -GaN gate HEMTs are deployed as power transistors. The phenomena related to the dynamic V TH, including the disappearance of Miller plateau, the overestimated false-turn- on problem, and the higher reverse conduction loss are evaluated with a half-bridge circuit and the merits of the proposed model are verified.

Ga2O3-on-SiC Composite Wafer for Thermal Management of Ultrawide Bandgap Electronics.

Abstract: β-phase gallium oxide (Ga2O3) is an emerging ultrawide bandgap (UWBG) semiconductor (EG ∼ 4.8 eV), which promises generational improvements in the performance and manufacturing cost over today's commercial wide bandgap power electronics based on GaN and SiC. However, overheating has been identified as a major bottleneck to the performance and commercialization of Ga2O3 device technologies. In this work, a novel Ga2O3/4H-SiC composite wafer with high heat transfer performance and an epi-ready surface finish has been developed using a fusion-bonding method. By taking advantage of low-temperature metalorganic vapor phase epitaxy, a Ga2O3 epitaxial layer was successfully grown on the composite wafer while maintaining the structural integrity of the composite wafer without causing interface damage. An atomically smooth homoepitaxial film with a room-temperature Hall mobility of ∼94 cm2/Vs and a volume charge of ∼3 × 1017 cm-3 was achieved at a growth temperature of 600 °C. Phonon transport across the Ga2O3/4H-SiC interface has been studied using frequency-domain thermoreflectance and a differential steady-state thermoreflectance approach. Scanning transmission electron microscopy analysis suggests that phonon transport across the Ga2O3/4H-SiC interface is dominated by the thickness of the SiNx bonding layer and an unintentionally formed SiOx interlayer. Extrinsic effects that impact the thermal conductivity of the 6.5 μm thick Ga2O3 layer were studied via time-domain thermoreflectance. Thermal simulation was performed to estimate the improvement of the thermal performance of a hypothetical single-finger Ga2O3 metal-semiconductor field-effect transistor fabricated on the composite substrate. This novel power transistor topology resulted in a ∼4.3× reduction in the junction-to-package device thermal resistance. Furthermore, an even more pronounced cooling effect is demonstrated when the composite wafer is implemented into the device design of practical multifinger devices. These innovations in device-level thermal management give promise to the full exploitation of the promising benefits of the UWBG material, which will lead to significant improvements in the power density and efficiency of power electronics over current state-of-the-art commercial devices.

A New Configuration of Paralleled Modular ANPC Multilevel Converter Controlled by an Improved Modulation Method for 1 MHz, 1 MW EV Charger

Abstract: In this article, a new configuration of the modular multilevel converter (MLC) based on the parallel connection of three-level active-neutral-point-clamped (3L-ANPC) cells as well as its improved modulation method is proposed for 1 MHz, 1 MW electric vehicle (EV) megacharger. In the proposed paralleled modular ANPC-MLC, only six high-frequency silicon carbide (SiC) power switches operating at 333 kHz are required to generate 1 MHz switching frequency spectrum. Moreover, the operating voltage of all power devices is halved, the magnitude of the first switching frequency harmonic cluster is decreased by the factor of five, and the load current is equally distributed between the 3L-ANPC legs by employing the proposed improved modulation method. Hence, the modularity, efficiency, and power density of the proposed converter are notably increased, whereas the value of passive components and the overall switching loss are remarkably decreased. In addition, an optimized design of the one 3L-ANPC cell of the proposed paralleled modular ANPC-MLC for 1 MHz, 1 MW EV megacharger using Ansys SIwave, Icepak, and Q3D finite element method platforms is presented and analyzed in detail. The provided experimental results of the down-scaled setup verify the feasibility and viability of the proposed configuration as well as its improved switching pattern.

Graphite-Embedded High-Performance Insulated Metal Substrate for Wide-Bandgap Power Modules

Abstract: Emerging wide-bandgap (WBG) semiconductor devices such as silicon carbide (SiC) metal–oxide semiconductor field-effect transistors (MOSFETs) and gallium nitride high-electron-mobility transistors can handle high power in reduced semiconductor areas better than conventional Si-based devices owing to superior material properties. With increased power loss density in a WBG-based converter and reduced die size in power modules, thermal management of power devices must be optimized for high performance. This article presents a graphite-embedded insulated metal substrate (thermally-annealed-pyrolytic-graphite-embedded insulated metal substrate—IMSwTPG) designed for WBG power modules. Theoretical thermal performance analysis of graphite-embedded metal cores is presented, with design details for IMSwTPG with embedded graphite to replace a direct-bonded copper (DBC) substrate. The proposed IMSwTPG is compared with an aluminum nitride-based DBC substrate using finite-element thermal analysis for steady-state and transient thermal performance. The solutions’ thermal performances are compared under different coolant temperature and thermal loading conditions, and the proposed substrate's electrical performance is validated with static and dynamic characterization. Using graphite-embedded substrates, junction-to-case thermal resistance of SiC MOSFETs can be reduced up to 17%, and device current density can be increased by 10%, regardless of the thermal management strategy used to cool the substrate. Reduced transient thermal impedance of up to 40% of dies owing to increased heat capacity is validated in transient thermal simulations and experiments. The half-bridge power module's electrical performance is evaluated for on -state resistance, switching performance, and switching loss at three junction temperature conditions. The proposed substrate solution has minimal impact on conduction and switching performance of SiC MOSFETs.

Isolated Gate Driver for Medium-Voltage SiC Power Devices Using High-Frequency Wireless Power Transfer for a Small Coupling Capacitance

Abstract: A high-voltage operation and breakneck switching speed of medium-voltage (MV) silicon carbide (SiC) devices demand gate drivers (GDs) with high voltage withstanding capability, high common-mode (CM) transient immunity and a reliable short-circuit protection. An isolated GD to meet these challenging requirements is presented in this article. A novel isolated gate driver power supply using high-frequency wireless power transfer (WPT) with a nonoverlapped winding arrangement for a small coupling capacitance is proposed. Moreover, a grounded shield is added to further reduce the effective coupling capacitance and the CM current. The receiver (Rx) coil of the WPT system along with its power processing circuit have been epoxy encapsulated to achieve a very high breakdown voltage and an extremely small form factor without violating very demanding clearance and creepage distance requirements. The impact of epoxy, winding arrangement, Rx circuits, and the grounded shield on the coupling capacitance is analyzed in details. In addition, a sophisticated overcurrent protection (OCP) scheme with soft-turn- off capability for MV SiC devices is developed. The designed OCP scheme achieves fast protection and simultaneously avoids false tripping due to very high current overshoot associated with the MV SiC devices during turn- on transitions. An experimental prototype is developed and the performance of the proposed GD under various operating conditions is evaluated experimentally.

Space Radiation Effects on SiC Power Device Reliability

Abstract: Heavy-ion radiation can result in silicon carbide power device degradation and/or catastrophic failure. Test procedures and data interpretation must consider the impact that heavy-ion induced off-state leakage current increases will have on subsequent single-event effect susceptibility and testability. On orbit, reliable performance in the presence of increased off-state leakage currents due to cumulative ion-induced non-catastrophic single-event effects must be assured over the mission lifetime. This work presents a large body of heavy-ion test data for different diode, power MOSFET, and JFET devices. Susceptibility to single-event effects is compared between SiC and Si power devices. Initial recommendations on heavy-ion radiation test methods for silicon carbide power devices are made and radiation hardness assurance is discussed with the goal of moving one step closer to reliably getting this technology off the ground into a broad array of spacecraft and instruments that will benefit from its unique capabilities.

Component-Level Reliability Assessment of a Direct-Drive PMSG Wind Power Converter Considering Two Terms of Thermal Cycles and the Parameter Sensitivity Analysis

Abstract: The availability and efficiency of a wind power system are highly affected by the failure or the unreliable operation of its power converter. This article investigates the failure rate and annual consumed lifetime for a 2-MW direct-drive permanent magnet synchronous generator based full-scale converter in a wind power generation system. The reliability assessment mainly focuses on the component level, namely, diodes and IGBTs, in both of the machine-side converter and the grid-side converter. Annual damages and power cycles for semiconductors are calculated separately under long-term thermal cycles (several seconds to hours) and short-term thermal cycles (dozens to hundreds of milliseconds). Experiments regarding thermal stress measuring for different semiconductors under short-term thermal cycles are affiliated. A comparison between different thermal cycles is given and discussed in detail. To ensure a visualized time-to-failure evaluation, a Monte Carlo method is used to generate the lifetime distributions and entire unreliability functions for power semiconductors. Final B10 and B1 lifetimes can easily be observed from the cumulative distribution functions. Moreover, different standard deviations are assumed for parameters in the Bayerer's lifetime model, and by using several parallel Monte Carlo algorithms, parameter sensitivity to the final lifetime evaluation is analyzed.

Control of MW-Scale High-Frequency “SiC+Si” Multilevel ANPC Inverter in Pump-Back Test for Aircraft Hybrid-Electric Propulsion Applications

Abstract: High-power-density high-speed electric motors for aircraft hybrid-electric propulsion (HEP) applications require high fundamental output frequency from power inverters. Conventional silicon (Si)-based megawatt (MW)-scale power inverters typically have low switching frequency that is not sufficient to meet the dynamic and harmonic requirements for such applications. An MW-scale medium-voltage three-level active neutral-point-clamped (ANPC) inverter based on a hybrid utilization of silicon carbide (SiC) and Si power devices (i.e., “SiC+Si”) has been developed for high-speed HEP drive applications, which has a rated output frequency of 1.4 kHz at 1-MW active power. To evaluate the power capability and efficiency of this ANPC inverter in the laboratory, power pump-back tests need to be carried out. In this article, control methods for single- and three-phase inverter pump-back tests have been developed to evaluate the performance of such high-frequency propulsion drives. The implementation and experimental results are presented to verify the efficacy of the control methods and the performance of the MW-scale “SiC+Si” ANPC inverters.

Wide Bandgap DC–DC Converter Topologies for Power Applications

Abstract: Over the last decade, dc–dc power converters have attracted significant attention due to their increased use in a number of applications from aerospace to renewable energy. The interest in wide bandgap (WBG) power semiconductor devices stems from outstanding features of WBG materials, power device operation at higher temperatures, larger breakdown voltages, and the ability to sustain larger switching transients than silicon (Si) devices. As a result, recent progress and development of converter topologies, based on WBG power devices, are well-established for power conversion applications in which classical Si-based power devices show limited operation. Currently, Si carbide (SiC) and gallium nitride (GaN) are the most promising semiconductor materials that are being considered for the new generation of power devices. The use of new power semiconductor devices, such as GaN high electron mobility transistors (GaN HEMTs), leads to minimization of switching losses, allowing high switching frequencies (from kHz to MHz) for realizing compact power converters. Finally, design recommendations and future research trends are also presented.

Ion-Induced Mesoplasma Formation and Thermal Destruction in 4H-SiC Power MOSFET Devices

Abstract: Both experiments and simulations have shown that single-event burnout (SEB), a catastrophic event, occurs at less than half of the rated blocking voltage in commercial 4H-SiC power devices under a heavy-ion strike. The failure was shown to be due to significant impact ionization near the epi/substrate interface. Adding a buffer layer between the drift epi and substrate layers reduces the impact ionization effect and changes the thermal failure location. In this article, the SEB phenomenon in a 4H-SiC power MOSFET utilizing a buffer layer is investigated. Heavy-ion transport and 3-D electro-thermal transient simulations were performed to study the device response to a heavy-ion strike. In examining the time evolution of electric field profile, charge carrier dynamics, and thermal heat transfer, it is determined that the failure mode for this design is the location shift of the mesoplasma (or hot spot) to within the drift epi region, away from the high field area. A sensitivity analysis was conducted to identify the dominant electrical or thermal factors contributing to device failure due to second breakdown. From these simulations, it is found that the semiconductor thermal conductivity is the primary material parameter that influences the mesoplasma formation.

Degradation of SiC MOSFETs under High-Bias Switching Events

Abstract: Evaluating the robustness of power semiconductor devices is key for their adoption into power electronics applications. Recent static acceleration tests have revealed that SiC MOSFETs can safely operate for thousands of hours at a blocking voltage higher than the rated voltage and near the avalanche boundary. This work evaluates the high-bias robustness of SiC MOSFETs under continuous, hard-switched, turn-off stresses with a dc-bias higher than the device rated voltage. Under this high-bias switching condition, SiC MOSFETs show degradation in merely tens of hours at 25°C and tens of minutes at 100°C. Two independent degradation and failure mechanisms are unveiled, one present in the gate-oxide and the other in the bulk-semiconductor regions, featured by the increase in gate leakage current and drain leakage current, respectively. The second degradation mechanism has not been previously reported in the literature; it is found to be related to the electron hopping along the defects in semiconductors generated in the switching tests. The comparison with the static acceleration tests reveals that both degradation mechanisms correlate to the high-bias switching transients rather than the high-bias blocking states. These results suggest the insufficient robustness of SiC MOSFETs under high-bias, hard switching conditions and the significance of using switching-based tests to evaluate the device robustness.