AlGaN/GaN HEMTs on SiC with over 100 GHz f_T and low microwave noise

High performance AlGaN/GaN high electron mobility transistors (HEMTs) with 0.12 μm gate-length have been fabricated on an insulating SiC substrate. The devices exhibited an extrinsic transconductance of 217 mS/mm and current drive capability as high as 1.19 A/mm. The threshold voltage of the devices was -5.5 V. For AlGaN/GaN HEMTs with the same gate-length, a record high unity current gain cut-off frequency (f_T) of 101 GHz and a maximum oscillation frequency (f_MAX) of 155 GHz were measured at V_ds = 16.5 V and V_gs = 5.0 V. The microwave noise performances of the devices were characterized from 2 to 18 GHz at different drain biases and drain currents. At a drain bias of 10 V and a gate bias of -4.8 V, the devices exhibited a minimum noise figure (NF_min) of 0.53 dB and an associated gain (G_a) of 12.1 dB at 8 GHz. Also, at a fixed drain bias of 10 V with the drain current swept, the lowest NF_min of 0.72 dB at 12 GHz was obtained at I_ds = 100 mA/mm and a peak G_a of 10.59 dB at 12 GHz was obtained at I_ds = 150 mA/mm. With the drain current held at 114 mA/mm and drain bias swept, the lowest NF_min of 0.42 dB and 0.77 dB were obtained at V_ds = 8 V at 8 GHz and 12 GHz, respectively. To our knowledge, these are the best microwave noise performances of any GaN-based FETs ever reported.