Optimization of a Gallium Nitride HEMT design for a high frequency DC-DC converter application

This paper presents the optimization of the AlGaN/GaN HEMT design for a high frequency switching application. The optimization process was based on a physical model which provided the relations between the design parameters of the device (gate electrode width and length, the field plate thickness and width etc.) on one hand and parasitic capacitances together with the on-resistance of the HEMT on the other. Implementation of the physical model into hybrid analytical-behavioural power loss model of a high frequency buck converter provided the possibility of the variation of the design parameters by minimization of the conduction and switching losses in the converter. Since the package of the nominal de-sign was TO220 with high values of the parasitic inductances, it was necessary to make the comparison between the new (optimized) and the old (nominal) design by using DirectFET package for both designs. In that way, the efficiency improvement obtained by device design optimization was clearly shown in the simulation results. Observing the low range of the output power (which is the range of interest for the transmission of the signals with high peak-to-average power ratio), the maximum efficiency improvement of 25 % was obtained at 20 MHz of switching frequency.