Silicon Carbide power devices have gained prominence in high-power, high-temperature, and high-frequency applications due to their superior material properties, including wide bandgap, high thermal conductivity, and high critical electric field. However, reliability challenges remain a critical concern for widespread adoption. Key issues include gate oxide degradation, bipolar degradation in PiN diodes, and cosmic ray-induced failures. Understanding these mechanisms, along with accelerated aging tests, failure analysis techniques, and mitigation strategies, is essential for improving device longevity and performance.

Gate oxide degradation is a significant reliability challenge in SiC power MOSFETs. The interface between silicon dioxide and SiC exhibits higher defect densities compared to silicon-based devices, leading to threshold voltage instability and reduced channel mobility. Negative bias temperature instability (NBTI) and positive bias temperature instability (PBTI) are commonly observed under high electric fields and elevated temperatures. Studies indicate that charge trapping at the SiC-SiO2 interface is a dominant mechanism, with interface states and near-interface oxide traps contributing to threshold voltage shifts. Accelerated aging tests under high gate bias and temperature stress reveal that devices subjected to 175°C and 20 V gate bias exhibit significant threshold voltage drift within 1000 hours. To mitigate these effects, improved oxidation processes, such as nitridation and post-oxidation annealing, have been shown to reduce interface trap densities. Additionally, alternative gate dielectric materials, including aluminum oxide and hafnium oxide, are being investigated for enhanced stability.

Bipolar degradation in SiC PiN diodes is another critical reliability issue caused by the expansion of stacking faults in the basal plane during forward conduction. These faults originate from pre-existing defects in the SiC crystal lattice and propagate under minority carrier injection, leading to increased forward voltage drop and reduced device lifetime. Research demonstrates that basal plane dislocations in 4H-SiC substrates act as nucleation sites for stacking fault formation. Accelerated aging tests under high current density conditions reveal that forward voltage drift can exceed 20% after 1000 hours of operation at 200 A/cm². Mitigation strategies include the use of dislocation-free substrates and optimized epitaxial growth techniques to minimize defect densities. Additionally, advanced device designs, such as the implementation of carrier lifetime enhancement processes, have been shown to suppress bipolar degradation.

Cosmic ray-induced failures pose a unique reliability challenge for SiC power devices, particularly in high-voltage applications. Unlike silicon devices, SiC's higher critical electric field allows for thinner drift layers, but this also increases susceptibility to single-event burnout (SEB) caused by cosmic ray strikes. When high-energy particles interact with the device, they generate dense electron-hole pairs, leading to localized current filaments and thermal runaway. Experimental data indicate that cosmic ray failure rates for 10 kV SiC MOSFETs can be as high as 100 FIT at sea level, increasing with altitude and blocking voltage. To address this issue, improved edge termination designs, such as junction termination extensions and field-limiting rings, are employed to reduce electric field crowding. Additionally, device-level simulations and radiation-hardening techniques, including optimized doping profiles and reduced cell pitch, have been shown to enhance cosmic ray robustness.

Accelerated aging tests are essential for evaluating the long-term reliability of SiC power devices. High-temperature reverse bias (HTRB), high-temperature gate bias (HTGB), and temperature cycling tests are commonly used to assess device stability under stress conditions. HTRB tests at 80% of rated voltage and 175°C for 1000 hours are standard for evaluating leakage current and breakdown voltage stability. HTGB tests focus on gate oxide integrity by applying high gate voltages at elevated temperatures. Temperature cycling tests between -55°C and 175°C assess mechanical stress-induced failures, such as bond wire fatigue and solder joint degradation. These tests provide critical data for predicting device lifetime under real-world operating conditions.

Failure analysis techniques play a crucial role in identifying root causes of reliability issues in SiC devices. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to examine structural defects, such as dislocations and stacking faults. Deep-level transient spectroscopy (DLTS) and capacitance-voltage (C-V) measurements provide insights into trap states and interface defects. Electroluminescence imaging and infrared thermography are employed to detect hot spots and current crowding effects. These techniques enable precise characterization of failure mechanisms, guiding improvements in material quality and device design.

Mitigation strategies for enhancing SiC device reliability focus on material optimization, advanced processing techniques, and innovative device architectures. Improved passivation layers, such as silicon nitride and polyimide, reduce surface leakage and enhance moisture resistance. Edge termination designs, including mesa structures and guard rings, minimize electric field crowding at device peripheries. Furthermore, the adoption of double-trench MOSFET designs and superjunction architectures has demonstrated improved ruggedness and reduced on-resistance. Ongoing research into defect engineering and wafer bonding techniques aims to further enhance the reliability of SiC power devices.

In conclusion, while SiC power devices offer significant advantages over traditional silicon-based technologies, addressing reliability challenges is critical for their successful deployment in demanding applications. Gate oxide degradation, bipolar degradation, and cosmic ray-induced failures remain key concerns, but advances in material science, device design, and failure analysis are driving continuous improvements. Accelerated aging tests and mitigation strategies provide a pathway toward achieving the long-term reliability required for next-generation power electronics systems.