Analysis of Multi-Finger GaN HEMTs Using Gate Resistance Thermometry, Raman Thermometry, and Infrared Thermal Microscopy

Gallium nitride (GaN) high electron mobility transistors (HEMTs) are key components in high-power, high-frequency applications. Unfortunately, their performance is limited by self-heating effects, particularly in multifinger configurations where thermal crosstalk occurs. In this work, 16-finger GaN HEMTs incorporating gate resistance thermometry (GRT) structures were fabricated to experimentally quantify the channel temperature distribution. GRT measurements, which provide an average temperature throughout the gate metal, were validated against localized Raman thermometry. Additionally, a 3D finite element analysis (FEA) thermal model was built based on the measured material thermal properties from multi-frequency/spot-size time-domain thermoreflectance (TDTR). Infrared thermography, though widely used, was found to underestimate channel temperatures due to spatial resolution limitations and material transparency. Through the use of three thermal characterization methods as well as a thermal model, the presence of thermal crosstalk was confirmed, with the center channel exhibiting a ~22 % greater temperature rise compared to the outer channel. These results highlight the importance of selecting the proper combination of electrical, optical, and modeling techniques for accurate thermal analysis of multifinger GaN HEMTs.