Dielectric Breakdown Characteristics of Silicone Gel for (U)WBG Power Modules Under AC, DC, and High-Frequency Square Wave Stress

As the adoption of (ultra) wide bandgap ((U)WBG) power modules accelerate, ensuring reliable dielectric performance in soft encapsulation materials such as silicone gel (SG) has become a pressing challenge. Existing studies on SG have primarily focused on partial discharge (PD) and electrical treeing under DC or low-frequency AC excitation, with limited attention to dielectric breakdown—despite its critical role in defining insulation failure thresholds. Moreover, few efforts have explored the effects of high-frequency waveforms that closely mirror the fast-switching transients typical of practical (U)WBG applications. This study investigates the dielectric breakdown characteristics of SG under three voltage stress conditions: DC, 60 Hz sinusoidal AC, and high-frequency bipolar square waveforms (10–50 kHz) with a fixed 50 ns rise time. Experimental results reveal a significant, frequency-dependent reduction in breakdown voltage under square wave stress, underscoring the vulnerability of SG to rapid voltage reversals. A two-parameter Weibull statistical analysis further quantifies this degradation, showing increasingly clustered failure distributions at higher frequencies. The breakdown behavior is interpreted through the interplay of space charge dynamics and the time-dependent self-healing response of SG. These findings highlight the importance of accounting for waveform characteristics—not just field strength—when evaluating insulation reliability in UWBG power modules and provide a data-driven basis for future encapsulation design strategies.