Optimization of AlGaN/GaN HEMTs for high frequency operation

In this paper, the structure and processing of AlGaN/GaN high electron mobility transistors have been optimized for maximum small signal gain at high frequencies. The effect of the gate resistance, gate-to-drain capacitance and output conductance on the power gain cut-off frequency,f(max), of the devices has been experimentally studied. The reduction of the gate width allowed a 4-fold decrease in gate resistance which resulted in almost a 100% increase influx. To minimize C-gd, F-shape gates have been processed instead of the conventional T-shape submicron gates. Finally, to reduce the output conductance, the confinement of the 2-dimensional electron gas was increased by using an ultra-thin InGaN layer below the GaN channel. This InGaN back-barrier caused a 2-fold improvement in output conductance which allowed a 20% increase in f(max). By optimizing all these parameters, AlGaN/GaN transistors with a record f(max) of 230 GHz were obtained. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.