Transient Thermal Dynamics of Power SiC MOSFETs

As power densities in Wide Band Gap (WBG) semiconductors increase, traditional steady-state cooling methods often fail to address the rapid thermal transients. This paper investigates a diversity of cooling architectures for discrete Silicon Carbide (SiC) MOSFETs, and a frequency-dependent thermal characterization of different cooling technologies. This paper also presents a new measurement method of heat transfer through multilayer systems, which determines the thermal diffusivity of the power device in real dynamic operation. The measurement of the stored energy in the active component using temperature sensors proves itself to be a practical, rapid, low-cost, and non-invasive method. The results show that the active Peltier stage significantly allows for more frequent current bursts before reaching the thermal limit, thereby proving the system’s capability in high-frequency transient applications to be thermally stable. The analysis of different power systems with different types of cooling, for a range of frequencies of the drive signal for SiC MOSFETs, enables power electronic engineers to evaluate the efficacy of the cooling systems related to the operating frequency and not only as a function of the dissipated power. Analysis of thermal faults in MOSFETs with SEM/EDS methods reveals the weak points in the design of these WBG devices.