Clarification of Error Factors in Thermal Impedance Measurements Using SiC-MOSFET Body Diodes Compared to SWITCH-MOS

In this paper, we measured and compared the thermal impedance (Zth) of silicon carbide (SiC) power module assembled with a Schottky barrier diode wall-integrated trench MOSFET (SWITCH-MOS; hereafter SMOS) and a conventional trench-gate MOSFET (UMOS). The temperature was detected by the Schottky barrier diode (SBD) for the SMOS and the pin diode for the UMOS. Since the knee voltage in UMOS varies with the gate voltage, a deep negative gate bias was needed to avoid this effect. A gate bias of –18 V is applied to the UMOS. However, no gate bias was required for the SMOS. The measured Zth was in good agreement between the UMOS and SMOS modules. Therefore, we can conclude that the SMOS can measure transient temperature at the same location as UMOS. In addition, the SBD built into the SMOS allows for easier and more accurate measurement of SiC-MOSFET junction temperature.