Dahmani, Samir; Mengistu, Endalkachew S.; Kompa, Günter (University of Kassel, Department of High Frequency Engineering, Wilhelmshöher Allee 73, D-34121 Kassel, Germany)
Self-heating is known to affect greatly the performance of power devices. In the past, several methods were developed to estimate the average channel temperature of FETs. Some of these methods are based on approximate closed form expressions. These techniques give acceptable results under limited conditions and only for specific device layouts. In this proposed work, we present an accurate method for the extraction of the thermal profile of large-size power AlGaN/GaN HEMTs using the FEM. The thermal investigation of the complete structure of the device permits an accurate calculation of the distributed device temperature taking into account the temperature dependence of the thermal conductivities of the different layers in the HEMT structure. This analysis also helps device designers in tuning of structure’s physical and geometrical parameters. The thermal resistances under each finger and of the whole FET structure are calculated. Using this procedure, we have succeeded in estimating accurately the temperature profile of the AlGaN/GaN HEMT and implemented the resulting junction thermal resistance in a large-signal model of the HEMT. This model is implemented as a look-up table in the Advanced Design Systems Software (ADS). The simulated static I(V) characteristics of the large-signal electro-thermal model are in good agreement with the measured data.