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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 (SixN) passivation layer and a 100‐nm N‐rich silicon nitride (Si3N4) passivation layer. This effectively reduces radio frequency scattering in GaN HEMTs without compromising the breakdown voltage (BV). On the one hand, the SixN passivation layer effectively suppresses the surface states of devices, resulting in low current collapse. On the other hand, the Si3N4 passivation layer can effectively reduce gate leakage caused by the SixN passivation layer, allowing the device to reliably operate at higher voltages. Consequently, a GaN HEMTs with SixN/Si3N4 bilayer passivation achieve a low current collapse of 5% and a high BV of 157 V. The device features a current gain cutoff frequency (fT) and maximum oscillation frequency (fmax) of 57.9 and 96.8 GHz, respectively. Additionally, it exhibits excellent radio frequency performance in the X‐band, with an output power density (Pout) of 13.7 W mm−1 and power added efficiency of 60.8% at a drain voltage (VD) bias of 50 V. [ABSTRACT FROM AUTHOR]

A new simple model of threshold voltage for AlGaN/GaN nanowire channel high electron mobility transistors (NC-HEMTs) is built in this work. Firstly, four NC-HEMTs with different nanowire channel width are fabricated, and the conventional HEMT is produced for comparison. With the nanowire channel width decreasing, the threshold voltage of NC-HEMTs moves positively. Then, the dependence of electron concentration on the nanowire channel width is studied by Silvaco simulation software. With the nanowire channel width decreasing, the electron concentration reduces. Finally, we recognize the threshold voltage model of conventional HEMT for NC-HEMT modeling, and the new model of threshold voltage of NC-HEMT is obtained. This model can explain the dependence of electron concentration on nanowire channel width. The depletion region width formed by side gate is about 37 nm which is obtained by the equation of the new model. [ABSTRACT FROM AUTHOR]