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Many field plate structures have been applied to improve the breakdown voltage in high electron mobility transistors (HEMTs). In this paper, the effects of various gate field plate structures on DC and RF performance of AlGaN/GaN HEMTs have been compared. The devices were fabricated on a 3 in sapphire substrate with 0.8 µm gate length, 3 µm source–drain distance, and 50 µm gate width. The results show that the discontinuous field plate structures can improve the cut-off frequency characteristics, but the breakdown characteristics will be weakened. And the increase of the field plate length can improve the breakdown characteristics. Thus, the breakdown characteristics and the cut-off frequency characteristic need to be balanced according to the actual applications by adjusting the length and the area of the field plate structure.

The effects of various notch structures on direct current (DC) and radio frequency (RF) performances of AlGaN/GaN high electron mobility transistors (HEMTs) are analyzed. The AlGaN/GaN HEMTs, each with a 0.8-μm gate length, 50-μm gate width, and 3-μm source–drain distance in various notch structures at the AlGaN/GaN barrier layer, are manufactured to achieve the desired DC and RF characteristics. The maximum drain current (I ds,max), pinch-off voltage (V th), maximum transconductance (g m), gate voltage swing (GVS), subthreshold current, gate leakage current, pulsed I–V characteristics, breakdown voltage, cut-off frequency (f T), and maximum oscillation frequency (f max) are investigated. The results show that the double-notch structure HEMT has a 30% improvement of gate voltage swing, a 42.2% improvement of breakdown voltage, and a 9% improvement of cut-off frequency compared with the conventional HEMT. The notch structure also has a good suppression of the current collapse.