WBG Devices Research Articles

High-Bandwidth Differential Voltage Probe for Accurate Switching Characterization of WBG Devices

High-Bandwidth Differential Voltage Probe for Accurate Switching Characterization of WBG Devices

Review of cryogenic power conversion and its potential in future all electric transportation systems: from silicon age to WBG era

Cryogenic power electronic conversion (< 123 K) is expected to offer higher efficiencies for future all-electric transportation platforms. Low temperature operation of converters together with integration of wide bandgap devices (WBG) can enable higher switching frequencies with reduced filtering components. This paper briefly reviews the passive components involved in the development of a cryogenic converter. The paper also reviews in detail the converter development with WBG devices by far, and provides a discussion on benefits achieved, and challenges in terms of auxiliary components and measurements. The last part of the paper gives a discussion on envisioned challenges, and different research directions for future superconducting power conversion systems.

Resonant step-down DC-DC converter based on GaN power integrated circuits and SiC diodes

In the paper results of the operation and efficiency of a DC-DC resonant converter with a switched capacitor topology, equipped with GaN transistors and SiC diodes are presented. Investigated problems are related to the optimization of the DC- DC power electronic converter in order to achieve miniaturization, a simplified design and high efficiency. The proposed system operates at a high frequency with low switching losses. The proposed design helps to achieve uniform heating of the transistors and diodes, as demonstrated by the results of the thermal imaging measurements. The GaN transistors are integrated in one package with dedicated gate drivers and used to simplify the drivers circuitry and increase the power density factor of the proposed device. In the high-frequency design presented in the paper, the converter is implemented without electrolytic capacitors. The results included in the paper contain waveforms recorded in the power circuit at ZVS operation when switching on the transistors. It occurs when the system operates above the frequency of current oscillations in the resonant circuit of the switched capacitor. Efficiency characteristics and a voltage gain curve of the converter versus its output power are presented as well. Results of efficiency and quality of waveforms are important because they allow to characterize the tested system for the implementation using WBG devices. The use of integrated GaN modules to minimize elements in the physical system is also unique to this model and it allows for very short dead-time use, operation in ZVS mode at low reverse-conduction losses.

Influence of Wide-Bandgap Semiconductors in Interleaved Converters Sizing for a Fuel-Cell Power Architecture

This study presents a decision-support methodology to design and optimize modular Boost converters in the context of fuel-cell electric vehicles. It involves the utilization of interleaved techniques to reduce fuel-cell current ripple, enhance system efficiency, tackle issues related to weight and size concerns, and offer better flexibility and modularity within the converter. The methodology incorporates emerging technologies by wide-bandgap semiconductors, providing better efficiency and higher temperature tolerance. It employs a multiphysical approach, considering electrical, thermal, and efficiency constraints to achieve an optimal power architecture for FCHEVs. Results demonstrate the advantages of wide-bandgap semiconductor utilization in terms of volume reduction and efficiency enhancements for different power levels. Results from one of the considered power levels highlight the feasibility of certain architectures through the utilization of WBG devices. These architectures reveal improvements in both efficiency and volume reduction as a result of incorporating WBG devices. Additionally, the analysis presents a comparison of manufacturing cost between standard and wide-bandgap semiconductors to demonstrate the market penetration potential.

Reliable WBG Devices Packaging by Forming Nano-gradient Structures on Silver-plated Substrates

Reliable WBG Devices Packaging by Forming Nano-gradient Structures on Silver-plated Substrates

Regulating Crystal Orientation via Ligand Anchoring Enables Efficient Wide-Bandgap Perovskite Solar Cells and Tandems.

Wide-bandgap (WBG) perovskite solar cells have attracted considerable interest for their potential applications in tandem solar cells. However, the predominant obstacles impeding their widespread adoption are substantial open-circuit voltage (VOC ) deficit and severe photo-induced halide segregation. To tackle these challenges, a crystal orientation regulation strategy by introducing dodecyl-benzene-sulfonic-acid as an additive in perovskite precursors is proposed. This method significantly promotes the desired crystal orientation, passivates defects, and mitigates photo-induced halide phase segregation in perovskite films, leading to substantially reduced nonradiative recombination, minimized VOC deficits, and enhanced operational stability of the devices. The resulting 1.66eV bandgap methylamine-free perovskite solar cells achieve a remarkable power conversion efficiency (PCE) of 22.40% (certified at 21.97%), with the smallest VOC deficit recorded at 0.39V. Furthermore, the fabricated semitransparent WBG devices exhibit a competitive PCE of 20.13%. Consequently, four-terminal tandem cells comprising WBG perovskite top cells and 1.25eV bandgap perovskite bottom cells showcase an impressive PCE of 28.06% (stabilized 27.92%), demonstrating great potential for efficient multijunction tandem solar cell applications.

APEC 2023 Returns to Orlando to Display Latest Advances in WBG and Si Devices

APEC 2023 Returns to Orlando to Display Latest Advances in WBG and Si Devices

Emerging Monolithic Bidirectional Switches Bring New Energy to WBG Devices [From the Editor

<fig orientation="portrait" position="float" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <graphic orientation="portrait" position="float" xlink:href="bindr-3239979.tif"/> </fig> In last ten years or so, wide bandgap (WBG) devices, such as silicon carbide (SiC) and gallium nitride (GaN) power transistors, have made significant progress in reliability, performance, and cost, driving adoption of these devices in a wide range of applications. As a result, the GaN market is projected to be worth about US <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\$ $ </tex-math></inline-formula> 2 billion in revenues by 2027, according to market research firm Yole Développement. In 2021, the GaN market was valued at US <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\$ $ </tex-math></inline-formula> 126 million by Yole. Likewise, Yole expects SiC device market to grow beyond US <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\$ $ </tex-math></inline-formula> 6 billion by 2027 at a CAGR of 34%.

Real-Time HIL Emulation of DRM With Machine Learning Accelerated WBG Device Models

Real-Time HIL Emulation of DRM With Machine Learning Accelerated WBG Device Models

Comparative evaluation and analysis of GaN-based VSIs and CSIs

In this paper, a SPICE-based assessment platform for fast-switching Gallium Nitride (GaN) devices-based voltage source inverters (VSIs) and current source inverters (CSIs) is presented. VSI has long been the dominant topology for motor drive systems. The previous research found enormous problems caused by the direct replacement of WBG switches in VSIs. As a viable alternative, the intrinsic properties of CSI topology make it suitable for WBG-based devices. The GaN device is selected in this paper as one of the most promising candidates among all WBG devices. Tailored double pulse test (DPT) is used to characterize the GaN switch in VSI and CSI topologies. VSI-DPT and CSI-DPT printed circuit boards (PCBs) are fabricated to experimentally evaluate the GaN switch, and to further modify the SPICE model. Moreover, the way to realize a dedicated SVPWM modulation scheme for three-phase CSI is introduced. The parasitic elements associated with the DPT-PCB layout are considered for the purpose of accuracy. VSI and CSI circuits are built in LTspice with a modified SPICE model of the GaN switch, enabling more precise analysis of GaN-based VSI and CSI under a wide range of operating conditions.

Overview of Power Electronic Devices &amp; its Application Specifically Wide Band Gap and GaN HEMTs

The review paper presents a prologue of power electronics devices and its industrial applications including wide band gap semiconductor devices in range of 600V to 1700V and latest evaluation of Gallium Nitride High Electron Mobility Transistor technology (GaN HEMT) in range of 30V to 650V with applications. The study emphasizes advance power electronic applications in renewable energy system, smart grid power system, power saving, electric vehicles and energy storage system. Similarly, comparison of latest WBG semiconductors as SiC, SiC JFETs, SJ MOSFETs and GaN-HEMTs discussed in terms of different parameters e.g static losses, dynamic losses and temperature impact, thus further signify latest GaN technology evolution and its related challenges with detailed static as well as dynamic characterization. This paper demonstrates all types of electronics devices in power sector and its practical usage mentioned in detail, it includes tradeoff between different WBG devices and also explain GaN functions and applications in various circuits of high efficiency and density.

Comparative Evaluation of the Two Multilevel Concepts With Full ZVS Operation Employing WBG Devices for Use in 1500-V PV Systems

A multi-level boost topology based on a flying capacitor is compared in this work with the hybrid, multi-level, partial power processing topology already presented in the literature for use as a highly efficient and compact dc/dc stage in 1500-V, two-stage, grid-connected PV systems. Different variations of the resonant stage of the hybrid topology are analyzed and compared in terms of losses, volume and complexity. Full multivariable optimization is conducted for the multi-level boost topology with different number of levels and for all the analyzed variations of the resonant stage of the hybrid topology. Appropriately rated new classes of 650-V and 900-V WBG devices are included in the optimization algorithm. It is concluded that due to the dominant conduction losses and gap in the voltage rating of the commercially available WBG devices between 650V and 200V, increase of the number of levels over 4 leads to the deteriorated loss and volume performances. All the analysis related to the resonant stage of the hybrid topology is confirmed by detailed and comprehensive measurements of two prototypes of 4kW of nominal and 7kW of maximal power. Additionally, all the loss models applied in the optimization algorithms presented in this paper are confirmed by detailed measurements, thermal calibration and finite element thermal simulations of the wide bandgap devices and inductor designs employed in this work.

A High-Efficiency Isolated Wide Voltage Range DC-DC Converter Using WBG Devices

The recent release of the standard USB-PD 3.1 [1] specifies variable output voltages from 5 V to 48 V featuring a step forward towards a universal adaptor but rising new challenges for the converter topologies used up to now. In such applications, a first AC-DC stage is followed by a DC-DC stage. In this paper, emerging WBG technologies are applied to the asymmetrical half-bridge flyback topology, demonstrating the potential of such combination as a wide voltage range DC-DC stage. Its suitability for high-density and high-efficiency USB-PD Extended Power Range (EPR) and battery charger applications is discussed. The impact of different switching technologies, silicon and wide band gap, is analyzed. A general method to dimension the converter is presented and an iterative process is used to evaluate the theoretical efficiency under different conditions and switching devices. Finally, the advantages of the presented converter using Gallium Nitride (GaN) devices are demonstrated in a 240 W DC-DC prototype. It achieves a full load efficiency of 98%, and it is able to deliver an output voltage from 5 V to 48 V with input voltage range from 120 V to 420 V, as well an outstanding power density of 112 W/inch³ uncased.

A wide band gap devices based switched-capacitor circuits for photovoltaic applications

A two-stage power converter for PV applications is developed in this paper. In the first stage, a multiple-input high step-up dc/dc converter is proposed. The second stage is the five-level dc/dc inverter with boosting functionality. The proposed two-stage converter harnesses the superior features of WBG devices to build a converter with high efficiency and high-power density. The high switching speed of WBG power devices allow both stages operating at high switching frequency, hence, large size film capacitors can be replaced by small size multilayer ceramic capacitors, furthermore, the high operating temperature of WBG devices will help to shrink the cooling size. In additions, a zero current-switching technique is implemented in order to reduce the switching loss and electromagnetic interferences. Prototype with 300 W is built and experimental results are presented with a peak efficiency of 98.3%.

Low temperature sintering of MOD assisted Ag paste for die-attach application

In this paper, we have developed a novel Ag paste containing MOD (metal organic decomposition) for assisting the sintering of nanoparticles. Based on the prepared Ag paste, the bonding joint can reach a maximum shear strength of 42.7 MPa at 175 °C. The effect of different amines on the performance of bonded joints was studied to elucidate the mechanism of MOD assisted sintering. Due to the advantage of high sintering performance, the new MOD assisted Ag paste is promising to be applied in the field of WBG device packaging.

Thermal and Reliability Characterization of an Epoxy Resin-Based Double-Side Cooled Power Module

Abstract Wide-Band Gap (WBG) power devices have become a promising option for high-power applications due to the superior material properties over traditional Silicon. To not limit WBG devices’ mother nature, a rugged and high-performance power device packaging solution is necessary. This study proposes a Double-Side Cooled (DSC) 1.2 kV half-bridge power module having dual epoxy resin insulated metal substrate (eIMS) for solving convectional power module challenges and providing a cost-effective solution. The thermal performance outperforms traditional Alumina (Al2O3) Direct Bonded Copper (DBC) DSC power module due to moderate thermal conductivity (10 W/mK) and thin (120 mm) epoxy resin composite dielectric working as the IMS insulation layer. This novel organic dielectric can withstand high voltage (5 kVAC @ 120 μm) and has a Glass Transition Temperature (Tg) of 300°C, which is suitable for high-power applications. In the thermal-mechanical modeling, the organic DSC power module can pass the thermal cycling test over 1,000 cycles by optimizing the mechanical properties of the encapsulant material. In conclusion, this article not only proposes a competitive organic-based power module but also a methodology of evaluation for thermal and mechanical performance.

(Invited) Advances in Ag Sinter Joining for WBG Power Device Assembly and High Temperature Reliability

SiC and GaN, wide bandgap semiconductors (WBGs), providing great benefits such as excellent energy saving, high power density, size reduction of power module, and long-life time, have been attracting many researchers for decades. Actually, there are several new products in the world market. At this moment, one of the technology demands for expanding the market of SiC/GaN is on power packaging technology, which can open these great functions. The increasing power density leads to high operation temperature beyond 200 °C at semiconductor junctions. Not only SiC/GaN devices themselves, insulating ceramic substrates such DBC and DBA must possess good heat-conductivity, heat-resistance and heat-shock resistance. Temperature swing range in operation will be from -50 °C to 250 °C, which is quite severe for the conventional packaging materials including not only insulating substrates, but also solders, wiring, molding compounds, and others. In our group, new assembly materials have been demonstrated and new design rules of die-attach and insulating substrates have been explored to realize reliable SiC/GaN power devices.Sinter joining technology is one of the most promising bonding methods for realizing both high performance and high reliability for WBG devices. The author has developed Ag micron-particles sinter joining with a hybrid of Ag micron/submicron size particles providing excellent heat-resistance beyond 200 °C without any assisting pressure. Ag reacts with oxygen in air resulting in low temperature sintering around 200 °C. The microporous joining structure provides high strength as well as excellent heat/electric conductivity. The die-attached devices are stable even up to 250 °C in thermal shock and in power cycling. For joining Ag sinter materials to various metallization faces such as Au, Ni, Cu or Al, has another critical factor to influence device performance. Ag sinter paste to Ag metallization face is the most recommended one. However, from the various requirements in the market, Ag sinter joining must be also applicable to these dissimilar surfaces. The latest sinter paste enables joining Ag sinter paste even to Al as shown in Fig. 1, which has been recognized as one of the most difficult combination. In this example, the bonding strength reached 35 MPa when bonded at 200 °C.Metal bonded ceramic substrates are the other key materials for WBG power modules. DBAs of AIN, Si3N4 and Al2O3 can survive even in severe thermal shock test between -50 °C to 250 °C. However, significant deformation of metal plates bonded on rigid ceramic insulators results in serious degradation of the WBG assembly. It was found that the properties of surface plating have a key to suppress this surface deformation.Operation monitoring in real service environment will be one of the useful technology for power devices. A nondestructive inspection method by using AE monitoring has been proposed to understand the degradation of module during thermal cycling. During power cycling, abrupt stepwise increases in AE occur showing crack extension in a die-attach layer. Figure 1

Device-Level Thermal Management of Gallium Oxide Field-Effect Transistors

The ultrawide bandgap (UWBG) (~4.8 eV) and melt-grown substrate availability of $\beta $ -Ga2O3 give promise to the development of next-generation power electronic devices with dramatically improved size, weight, power, and efficiency over current state-of-the-art WBG devices based on 4H-SiC and GaN. Also, with recent advancements made in gigahertz frequency radio frequency (RF) applications, the potential for monolithic or heterogenous integration of RF and power switches has attracted researchers’ attention. However, it is expected that Ga2O3 devices will suffer from self-heating due to the poor thermal conductivity of the material. Thermoreflectance thermal imaging and infrared thermography were used to understand the thermal characteristics of a MOSFET fabricated via homoepitaxy. A 3-D coupled electrothermal model was constructed based on the electrical and thermal characterization results. The device model shows that a homoepitaxial device suffers from an unacceptable junction temperature rise of ~1500 °C under a targeted power density of 10 W/mm, indicating the importance of employing device-level thermal managements to individual Ga2O3 transistors. The effectiveness of various active and passive cooling solutions was tested to achieve a goal of reducing the device operating temperature below 200 °C at a power density of 10 W/mm. Results show that flip-chip heterointegration is a viable option to enhance both the steady-state and transient thermal characteristics of Ga2O3 devices without sacrificing the intrinsic advantage of high-quality native substrates. Also, it is not an active thermal management solution that entails peripherals requiring additional size and cost implications.

A Novel Switched-Capacitor Converter With High Voltage Gain

In this paper, a novel topology of switched-capacitor converter is proposed. Compared with the existing switched-capacitor topologies, such as the Dickson-based switched-capacitor converter or the ladder switched-capacitor converter, it limits both voltage stress and current stress of components under lower level, which reduces the volume of capacitor banks and the conduction loss. These characteristics can help high-power density and high-efficiency design, especially in high-voltage-gain applications. The phase shift modulation strategy corresponding to the proposed switched-capacitor converter is also presented in this paper. With phase shift modulation, voltage gain can be adjusted as continuous value. The voltage regulation ability makes up the defect of conventional switched-capacitor converters, and the ZVS operation of all the switching devices is also achieved with the proposed modulation method so that the WBG devices can play more strength in the converter with higher switching frequency. The derivation of the circuit topology and phase shift modulation will be introduced in this paper. The steady analysis and performance comparison will prove the advantage of the proposed converter. A 600-W prototype is built, and the experiment results are presented to validate the proposed converter.

(Invited) Packaging Material Technology for Wide Band Gap Power Devices and Its Performance/Reliability Evaluation

Wide band gap semiconductors such as SiC and GaN have been expected to be established as the next generation power semiconductors, which are capable to reduce huge energy-loss in electric power conversion. The application of them will increase power density resulting in operation temperature rise beyond 200 °C. In addition, both increase of current and of frequency will also increase stress on devices. In general, power devices must possess robustness and high reliability for safe control of power conversion. Heat dissipation from the hot die in operation is one of the essential key factors for establishing high performance WBG devices. Here we report the current status of high temperature packaging materials including die-attach, wiring, substrates, molding compounds, and, in addition, reliability issues including thermal shock, power cycling and transient thermal properties.