Dynamic Safe Operating Area (SOA) of Power Semiconductor Devices

This paper investigates the effect of aging on the safe operating area (SOA) of a semiconductor device. SOA is a wellknown device parameter, which indicates the device’s ridethrough-capability against over-voltage and over-current situations. The mean time to failure (MTTF) represents the expected lifespan of the device although it cannot adequately predict the failures. When designing a power converter, we assume a fixed SOA value, and the overall reliability of the circuit simply becomes the probability of an abnormal condition to occur, and the probability of other device failures. However, our experimental results reveal that SOA of any semiconductor device is age-dependent rather than static as considered in reported literature to-date, and this age-dependent SOA is the underlying reason for device failure especially when the device is subjected to accidental over-voltage/current. When a device undergoes aging, it suffers from reduced SOA, which decreases the mean time to failure (MTTF) of the device as well as the overall converter reliability. Therefore, by knowing the aging level, it is possible to estimate the dynamic or real-time SOA of a device, and thus, the overall reliability of the circuit can be determined. By doing this, the scheduled maintenance can be performed more accurately, which is expected to reduce unwanted downtime.