Enhanced Performance of GaN HEMTs in X‐band Applications Using SixN/Si₃N₄ Bilayer Passivation Technique

In order to achieve high‐performance gallium nitride (GaN) high‐electron‐mobility‐transistors (HEMTs) capable of operating in the X‐band, a bilayer passivation technique is employed. The technique involves creating a stacked passivation layer consisting of a 20‐nm Si‐rich silicon nitride (Si x N) passivation layer and a 100‐nm N‐rich silicon nitride (Si 3 N 4 ) passivation layer. This effectively reduces radio frequency scattering in GaN HEMTs without compromising the breakdown voltage (BV). On the one hand, the Si x N passivation layer effectively suppresses the surface states of devices, resulting in low current collapse. On the other hand, the Si 3 N 4 passivation layer can effectively reduce gate leakage caused by the Si x N passivation layer, allowing the device to reliably operate at higher voltages. Consequently, a GaN HEMTs with Si x N/Si 3 N 4 bilayer passivation achieve a low current collapse of 5% and a high BV of 157 V. The device features a current gain cutoff frequency ( f T ) and maximum oscillation frequency ( f max ) of 57.9 and 96.8 GHz, respectively. Additionally, it exhibits excellent radio frequency performance in the X‐band, with an output power density ( P out ) of 13.7 W mm −1 and power added efficiency of 60.8% at a drain voltage ( V D ) bias of 50 V.