Numerical Modeling of Dynamic Thermal Coupling in GaN HEMTs Calibrated by Transient Measurements

The dynamic thermal coupling within gallium nitride (GaN) high electron mobility transistors (HEMTs) is characterized and modeled in a finite element method (FEM) solver to determine the thermal impedance of the HEMT. The study presents a method for calibrating the FEM model based on transient measurements with integrated temperature sensors placed 7.5, 91.5, and 175.5 μm away from a heat source. A sensitivity analysis is presented to show that the influence of the epitaxial layers, substrate, and die-attach layer can be differentiated. The method is used to calibrate a model that accurately replicates the measured thermal coupling. The model is assessed for different baseplate temperatures and a time-varying signal. Finally, an example is presented to show how thermal coupling changes the thermal impedance of GaN HEMTs and how the results can be used for layout optimization. The presented model and calibration method can also be used to evaluate how the device's packaging influences its thermal impedance.