E-Mobility Engineering | November/December 2023 63 demonstrated very high reliability in both laboratory testing and high-volume customer applications,” says Dr Alex Lidow, CEO and co-founder of EPC. “The release of EPC’s 11th reliability report represents the cumulative experience of using millions of devices over a 10-year period and five generations of technology. These tests have been undertaken to continue our understanding of the behaviour of GaN devices over a wide range of stress conditions. “The results of our studies show that GaN is an extremely robust technology that continues to improve at a rapid pace. EPC is committed to subjecting GaN devices to rigid reliability standards and sharing the results with the power conversion industry,” he says. The report shows that the key mechanisms impacting dynamic on-resistance have been identified and are used to create more robust designs. The result is that dynamic changes to on-resistance are not an issue for eGaN FETs. Several eGaN products were tested over the data sheet safe operating area (SOA) and then taken to failure to probe the safety margins. The result showed that eGaN FETs will not fail when operated within the data sheet SOA. eGaN devices are tested to destruction under short-circuit conditions to determine how long and what energy density they can withstand before catastrophic failure. The failures are thermally limited, and withstand time exceeds 10 µs at the recommended gate drive. Conclusion Different technologies are jostling for position in the development of power electronics for e-mobility applications. While silicon remains a stalwart for design engineers, with continuing development the wide bandgap alternative of SiC and GaN are increasing the efficiency and performance of designs. SiC is an easier alternative to silicon and provides higher efficiencies with a limited boost in the switching frequencies achievable. GaN offers the promise of far higher switching frequencies that could drive smaller sizes and even higher efficiencies, but the devices are extremely hard to design at this point. Emerging technology is allowing the full advantage of GaN in e-mobility, with the potential of switching beyond 2 MHz and as high as 20 MHz. This will enable very different power electronics designs to boost the performance and efficiency of e-mobility platforms in the future. GaN transistors on an SiC wafer for higher thermal performance. “GaN on SiC would be awesome but there is no multi-project wafer for that,” says Gwynne. GaN reliability The 11th report on GaN reliability from EPC in 2020 focused on reliability in automotive applications and found the transistors are more rugged than silicon devices. The Phase Eleven Reliability Report covered field experience of 123 billion device-hours over the previous 10 years for EPC’s enhanced GaN (eGaN) technology. The field test strategy used in the report relied on tests forcing devices to fail under various conditions. This approach to GaN reliability creates an understanding of the margin between data sheet limits and products in application; more important, it identifies intrinsic failure mechanisms. This knowledge of the intrinsic failure mechanisms is used to determine the root cause of failures. Knowledge of the behaviour of a device over time, temperature, electrical or mechanical stress can provide users with an accurate representation of the safe operating life of a product over a more general set of operating conditions. “eGaN devices have been in volume production for over 10 years, and have Improving power electronics | Deep insight High-speed switching for GaN (Courtesy of QPT)
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