In this work, ultrathin barrier (∼6 nm) AlGaN/GaN high-electron-mobility transistors (HEMTs) with in situ SiN gate dielectric and slant-field plate (SFP) T-gates were fabricated and analyzed. Since the proposed scheme of gate dielectric and SFP effectively suppresses the gate leakage and alleviates the peak electric field (E-field) around gate region, the maximum breakdown voltage ( VBK) was improved to 92 V, which is 54 V higher than that of the conventional device. The fabricated ultrathin AlGaN/GaN HEMT with 60-nm SFP-T-gate exhibited the peak fT of 177 GHz and peak fmax of 393 GHz, yielding high figure-of-merits of fT · VBK = 16 THz V and fmax·VBK = 36 THz V. Moreover, load-pull measurements at 30 GHz reveal that these devices deliver output power density ( Pout) of 4.6 W/mm at Vds  =  20 V and high power-added efficiency up to 52.5% at Vds  =  10 V. Essentially, the experimental results indicate that the employment of SFP and in situ SiN gate dielectric is an attractive approach to balance the breakdown and speed for millimeter wave devices.

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In this paper, a self-supporting T-shaped gate (SST-gate) GaN device and process method using electron beam lithography are proposed. An AlGaN/GaN HEMT device with a gate length of 100 nm was fabricated by this method. The current gain cutoff frequency (fT) is 60 GHz, and the maximum oscillation frequency (fmax) is 104 GHz. The current collapse has improved by 13% at Static bias of (VGSQ, VDSQ) = (-8 V, 10 V) and gate manufacturing yield has improved by 17% compared to the traditional floating T-shaped gate (FT-gate) device.