A distributed electro-thermal model of AlGaN/GaN HEMT power-bar derived from the elementary cell model

This paper deals with the development of a 120W AlGaN/GaN power bar model starting from the modeling of the elementary cell of the device. The approach consists in coupling a distributed thermal model of the power bar to each electro-thermal model of the elementary cells which constitute the power bar. The distributed nature of the temperature is taken into account by mean of a thermal RC network generated from the 3D Finite Element (FE) simulations. These thermal simulations take into account of the non linearity of the thermal conductivity with the temperature and the thermal coupling between the cells. The studied power bar is made of fifteen elementary cells juxtaposed, i.e. 15×(6×400μm) AlGaN/GaN HEMT devices. First, a full on wafer characterizations campaign, i.e. pulsed I(V) with pulsed S parameters and load-pull measurements, has been led on the elementary cell devices in order to extract and validate the unitary cell model 6×400μm. Then, preliminary stability tests and S parameters have been performed in order to validate the ability to safely measure the power bar mounted on the dedicated test vehicle. Load-pull measurements were then performed on the power bar and compared to the simulations given by the developed power bar model. Finally, a last comparison between the simulation of the High Power Amplifier (HPA) design and its breadboard measurement in L band fully validated the power bar model and the practical methodology used.