DC, RF, and microwave noise performances of AlGaN/GaN HEMTs on sapphire substrates

High-performance AlGaN/GaN high electron-mobility transistors with 0.18-μm gate length have been fabricated on a sapphire substrate. The devices exhibited an extrinsic transconductance of 212 mS/mm, a unity current gain cutoff frequency (f _T) of 101 GHz, and a maximum oscillation frequency (f _MAX) of 140 GHz. At V _ds = 4 V and I _ds = 39.4 mA/mm, the devices exhibited a minimum noise figure (NF _min) of 0.48 dB and an associated gain (G _a) of 11.16 dB at 12 GHz. Also, at a fixed drain bias of 4 V with the drain current swept, the lowest NF _min of 0.48 dB at 12 GHz was obtained at I _ds = 40 mA/mm, and a peak G _a of 11.71 dB at 12 GHz was obtained at I _ds = 60 mA/mm. With the drain current held at 40 mA/mm and drain bias swept, the NF _min increased almost linearly with the increase of drain bias. Meanwhile, the G _a values decreased linearly with the increase of drain bias. At a fixed bias condition (V _ds = 4 V and I _ds = 40 mA/mm), the NF _min values at 12 GHz increased from 0.32 dB at -55°C to 2.78 dB at 200°C. To our knowledge, these data represent the highest f _T and f _MAX, and the best microwave noise performance of any GaN-based FETs on sapphire substrates ever reported.