Improved Thermal Transient Testing of Wide Bandgap Devices with Extremely Low Channel Resistance

Thermal transient testing (TTT) is an essential technique for characterizing electronic systems, including packaged devices, modules, and subassemblies. These tests serve two closely related purposes: first, they enable determination of peak operating temperatures under various power conditions; on the other hand, they allow extraction of partial thermal resistances within the tested structure and identification of structural details near the active devices. The latter objective has become increasingly challenging with the advent of wide bandgap devices featuring extremely low on-state resistance, such as GaN HEMTs. This paper first identifies the temperature-sensitive electrical parameters and heater structures relevant for TTT of semiconductor devices. It then narrows the focus on GaN power devices and analyzes how external series resistances, originating from HEMT packages and the associated printed circuit boards, affect thermal impedances and structure functions. To remove the influence of these external resistances, which distort the extracted thermal descriptors, an analytical correction methodology has been developed. The proposed approach is validated through measurements performed on real devices. The results demonstrate that the method successfully restores the intrinsic thermal properties of the devices, yielding more accurate and physically meaningful thermal characteristics.