Understanding parasitic effects to improve the “3ω” measurement of GaN HEMTs thermal impedance

The thermal impedance of Gallium Nitride based High Electron Mobility Transistors (GaN HEMTs) has been characterized using the “3ω method”. The method was initially proposed by D.G. Cahill to measure the thermal conductivity of bulk materials or layers. We already demonstrated in a previous work that under certain conditions the voltage oscillation at the third harmonic is the real image of the thermal impedance of the device in the frequency domain. In this work, we propose both a theoretical approach to understand the limitation of our 3ω test bench and a comparison with measurements.