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Incorporating nonlinear resistive field grading materials (FGMs) onto metal-brazed substrates has been widely investigated as an efficient electric field reduction strategy at triple points (TPs) within ultrawide bandgap [(U)WBG] power modules. However, most investigations have been carried out using either dc or sinusoidal ac voltages despite actual (U)WBG power modules operating with high-frequency square voltages featuring high-slew rate ( dv/dt ). Thus, this study introduces a field-dependent conductivity (FDC) layer to analyze electric field reduction under high-frequency, high-slew-rate square voltages. Using COMSOL Multiphysics, both coated and uncoated structures were modeled to evaluate electric field reduction. When employing nonlinear FDC coating, the findings demonstrate a notable decrease in field stress, even under square voltages with rapid rise times and high frequencies. However, relying solely on the nonlinear FDC layer may not adequately address the electric field concerns, particularly when factoring in protrusions on metallization layers and reducing layer coverage. In response to this challenge, protrusions at the metal ends are incorporated into a protruding substrate configuration. This entire structure is then coated with a nonlinear FDC layer. The combined impact of the protruding substrate and nonlinear FDC layer effectively reduces the electric field. However, when the rise time is shortened to 75 ns and the frequency is raised to 500 kHz, the electric field stress around TPs exceeds the insulation’s withstand strength. This finding underscores the need for further research into alternative strategies as the prevalent strategies are unable to effectively mitigate electric fields in real-world operating conditions of (U)WBG power modules. 

Most research involving resistive field grading materials or nonlinear field-dependent conductivity (FDC) layers has predominantly concentrated on DC or sinusoidal AC voltages, even though (U)WBG power electronic modules typically operate under high-frequency square wave voltages. To bridge this existing research gap, the present study systematically investigates the efficacy of an FDC coating in alleviating electric field stress when subjected to high-frequency, high-slew-rate square wave voltages. The findings indicate that applying a nonlinear FDC layer significantly reduces electric field stress, even under stringent conditions involving elevated operating frequencies. Furthermore, the influence of the square wave voltage type—the distinction between unipolar and bipolar square waveforms—on electric field stress remains inadequately understood despite substantial progress in breakdown and PD experiments related to these phenomena. Consequently, this study undertakes a comparative analysis of nonlinear FDC layers' performance under unipolar (+27.5 kV) and bipolar (±27.5 kV) square wave voltages. In doing so, this investigation contributes valuable insights into the interplay between high-frequency operation, the polarity of square waveforms, and the efficacy of nonlinear FDC layers in mitigating electric field stress within (U)WBG power module packages. 

The escalating adoption of wide-bandgap (WBG) semiconductor devices in power electronics has led to the generation of high-frequency, high-slew-rate voltage waveforms, which exert significant stress on encapsulating materials such as silicone gel (SG). This study systematically investigates the breakdown performance of SG under DC,60 HzAC, and highfrequency square wave excitations. Breakdown voltage assessments were performed across a frequency range of 10 to 50 kHz for square pulses with 100 ns rise time, revealing a pronounced decline in dielectric strength as frequency increased. Specifically, the breakdown voltage measured under DC conditions, which was 20.6 kV, diminished by 84.9 % when subjected to a square wave excitation at 50 kHz. Furthermore, electric field simulations elucidated the phenomenon of localized field intensification occurring near the needle tip, which corresponded with the identified breakdown locations. The key revelations from this research underscore the limitations inherent in conventional testing methodologies, which fail to adequately characterize the degradation behavior of SG under realistic high-frequency fast-rise square voltage stress conditions. 

In the ever-growing landscape of electrical power demand, the future of power electronics module packaging lies in the realm of wide-bandgap (WBG) materials, including silicon carbide (SiC), gallium nitride (GaN), and cutting-edge ultra WBG (UWBG) materials like diamond, aluminum nitride (AlN), and hexagonal-boron nitride (h-BN). These materials offer superior properties to traditional silicon-based devices, promising higher power density, reduced weight, and increased operating temperature, voltage, and frequency. However, pushing the boundaries for power electronics modules presents challenges in insulation systems as the encapsulation material and the ceramic substrate may not withstand the functional parameters, potentially leading to unfavorable conditions like high field stress and partial discharge (PD), ultimately resulting in insulation failure. This paper presents a thorough analysis of the characteristics of the electrical insulation materials used in power electronics devices based on the research in WBG packaging conducted in recent years. The significance of maximum electric field stress at triple points (TPs) is examined. Furthermore, the paper reviews the strategies and techniques employed to mitigate the challenges related to maximum field stress and PDs in both encapsulation and substrate materials. It is concluded that the mitigation strategies are promising in improving insulation systems for packaging, but the studies lack their implementation under actual operating conditions of WBG power modules. 

In the ever-growing landscape of electrical power demand, the future of power electronics module packaging lies in the realm of wide-bandgap (WBG) materials, including silicon carbide (SiC), gallium nitride (GaN), and cutting-edge ultra WBG (UWBG) materials like diamond, aluminum nitride (AlN), and hexagonal-boron nitride (h-BN). These materials offer superior properties to traditional silicon-based devices, promising higher power density, reduced weight, and increased operating temperature, voltage, and frequency. However, pushing the boundaries for power electronics modules presents challenges in insulation systems as the encapsulation material and the ceramic substrate may not withstand the functional parameters, potentially leading to unfavorable conditions like high field stress and partial discharge (PD), ultimately resulting in insulation failure. This paper presents a thorough analysis of the characteristics of the electrical insulation materials used in power electronics devices based on the research in WBG packaging conducted in recent years. The significance of maximum electric field stress at triple points (TPs) is examined. Furthermore, the paper reviews the strategies and techniques employed to mitigate the challenges related to maximum field stress and PDs in both encapsulation and substrate materials. It is concluded that the mitigation strategies are promising in improving insulation systems for packaging, but the studies lack their implementation under actual operating conditions of WBG power modules. 

A vast majority of research on (U)WBG power modules has been going on to implement nonlinear resistive field grading material on metal-brazed substrates in reducing the electric field that is maximum at triple points (TPs). However, nearly all investigations have been conducted under either DC or 50/60 HZ sinusoidal AC voltages, even though the actual operation of envisioned (U)WBG power modules involves high-frequency square voltages with high slew rates. It has been validated by several studies that fast rise times of square voltages rapidly degrade the breakdown strength of insulation materials, leading to premature failure. Therefore, this paper introduces a nonlinear resistive field grading material or field-dependent conductivity (FDC) layer around the TP and metal edges to evaluate the electric field mitigation under a high frequency and high slew rate square voltage. The modeling and simulation of both coated and uncoated (U)WBG substrates were performed in COMSOL Multiphysics to assess the electric field reduction with the nonlinear FDC layer. The improvement of reduction in electric field under 100 kHz high slew rate square voltage is compared with that of 60 Hz. The results reveal a significant decrease in field stress at the TP, even under square voltages with fast rise times and high frequencies, when applying a nonlinear FDC coating, as opposed to the uncoated substrate. The influence of switching field (Eb) and nonlinearity coefficient (α) of nonlinear FDC layer is studied under 100 kHz square voltage, and it is concluded that α and Eb should be more than 10 and less than 8 kV/mm, respectively to achieve effective performance of resistive field grading material. 

Within the expanding domain of electrical power demand, the future of power module packaging is entwined with the progress of (ultra) wide bandgap (UWBG) materials. These materials, like silicon carbide (SiC), aluminum nitride (AlN), and diamond, offer advantages with higher power density, decreased weight, and expanded operational abilities regarding temperature, voltage, and frequency. However, the pursuit of pushing these limits confronts challenges within insulation systems, which may struggle to endure the demands of these parameters, potentially resulting in unfavorable conditions like high electric field, space charge accumulation, electrical treeing, and partial discharge (PD), leading to insulation failure. The emphasis of this paper is to review the insulation challenges within (U)WBG power modules and recent research in mitigating the electric field stress at triple points (TPs) and resolving the PD issues. The manuscript first discusses the high electric field stress issue at triple points. Then, ceramic substrate materials, encapsulation materials, and the influence of harsh weather conditions on them are reviewed. The space charge, electrical treeing, and PD issues within encapsulation materials are analyzed under practical operation conditions of (U)WBG power modules like high frequency, temperature, and square wave pulses. Finally, the various strategies to alleviate the associated insulation challenges are meticulously discussed. While the identified mitigation strategies are able to strengthen insulation systems for packaging, their validation under actual operational conditions of (U)WBG power modules remains relatively unexplored, representing a potential avenue for further investigation. This review offers a valuable framework by providing the constraints of the current studies and recommendations for the future that can be utilized as a reference point for future research endeavors.