Reliability Testing of Mitsubishi Electric SiC MOSFETs

SiC and Si each possess different physical characteristics and performance; therefore, different strategies are required for quality assurance. Si devices achieve stable quality based on mature technology, whereas SiC requires stricter quality control and reliability testing to fully utilize its characteristics as a high-performance device.

In recent years, SiC (Silicon Carbide) power semiconductors have attracted widespread attention due to their potential to achieve high performance and high efficiency in power electronics systems. Compared with Si, the advantages of SiC are its unipolar device structure and superior physical properties, and the losses of power modules can be significantly reduced. Table 1 compares the material properties of Si and SiC. Due to the wide bandgap of SiC material, it has high breakdown electric field strength and is suitable for high-temperature operation. In addition, its thermal conductivity is higher than that of Si, resulting in better heat dissipation performance.

Table 1: Comparison of physical properties between Si and SiC materials

As shown in Table 1, although SiC outperforms Si in performance, it also has issues such as crystal defects and gate oxide reliability that Si does not have. Figure 1 shows the failure rate vs. time curves (bathtub curves) for SiC and Si respectively. Since SiC wafers have more crystal defects and higher internal electric field strength, the failure rate of SiC in the early failure stage inevitably shows a higher trend compared to Si.

Figure 1: Failure rate vs. time curves for Si and SiC

To ensure SiC achieves the same level of quality and reliability as Si, we improve its quality through unique Burn-in tests. This burn-in test mainly focuses on the quality of the gate oxide film and the SiC substrate. Failure modes caused by the gate oxide film include abnormal gate leakage current caused by abnormal oxide film formation, and gate threshold voltage (VGS(th)) fluctuations caused by carrier traps at the oxide film interface; therefore, ensuring gate oxide film quality is considered the most important issue. Addressing this issue, based on a large amount of accumulated data—such as voltage acceleration characteristics of gate oxide film life, detection technologies for faults and characteristic changes—and advanced probability statistical distribution calculation results, our company has optimized the burn-in test conditions. This ensures that our SiC power semiconductors achieve quality standards that allow customers to use them with peace of mind. Figure 2 shows the comparison of failure rate vs. time for Si and SiC after implementing the burn-in test. After the burn-in test, the quality reaches a level comparable to Si. Therefore, our SiC power devices have taken the lead globally in being applied to main converter units of railway vehicles, which have strict quality requirements, and have achieved good market performance.

Figure 2: Failure rate vs. time curves for Si and SiC (after accelerated burn-in test)

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<About Mitsubishi Electric>

Mitsubishi Electric was founded in 1921 and is a globally renowned comprehensive enterprise. For the fiscal year ending March 31, 2025, the group's revenue was 5,521.7 billion yen (approximately US$36.8 billion). As a technology-driven company, Mitsubishi Electric holds numerous patented technologies. Relying on strong technical strength and a good corporate reputation, it occupies an important position in global markets such as power equipment, communication equipment, industrial automation, electronic components, and home appliances. Especially in the electronic components market, Mitsubishi Electric has been engaged in the development and production of semiconductors for 69 years. Its semiconductor products are widely used in fields such as inverter home appliances, railway traction, industrial and new energy, electric vehicles, analog/digital communications, and wired/wireless communications.