PhD student Furkan Karakaya with Advisor A. Banerjee

Silicon Carbide (SiC) MOSFETs are being widely adopted in the industry as a viable substitute for conventional power transistors, due to their superior figure-of-merit and compact, efficient power conversion. However, the relatively novel manufacturing technology of these devices raises further questions regarding long-term reliability, as SiC devices have been known to suffer from degradation over time, manifesting in an increased on-state resistance or a spike in gate leakage current. In order to identify the remaining useful lifetime of a SiC MOSFET, measuring the on-state resistance periodically is essential, though the operating voltage and current levels in kilovolts and kiloamperes presents a challenge, due to the resistance values typically falling in the range of several dozen milliohms.
Our recent design, as depicted in Figure 6, successfully addresses this challenge and enables reliable on-state resistance characterization, even during an active converter operation, with an estimated resistance error of less than 5%. As shown in Figure 7, the key idea behind the proposed design involves injecting a sinusoidal current in the MHz range, with the resultant voltage being filtered out by custom-engineered analog circuitry. Then, necessary calculations are performed by the circuit, enabling onstate resistance and package inductance to be accurately estimated in the milliohm and nanohenry ranges, respectively.
This work was funded by the Office of Naval Research MVDC Risk Reduction program.

Figure 6. Set-up enabling reliable on-state resistance characterization

Figure 7. Circuit for injecting sinusoidal current in the MHz range