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In this work, a high linearity AlGaN/GaN HEMT integrated dual threshold coupling (DT) technology and Schottky–Ohmic drain (SOD) were fabricated and analyzed. Since the architecture of DT synthesized planar- and recess-HEMT periodically along the gate width, SOD alleviated the peak electric field (E-field) around the gate region and the peak transconductance ( Gm-max) of 248 mS/mm with the associated transconductance plateau of ∼4.0 V at Vds = 28 V was obtained, which is evidently flatter than that of HEMT without the SOD structure. Attributed to the improved Gm linearity at high E-field, the DT-SOD HEMT exhibits the predicted linearity figure of merit of 5–13 dB when biased at class AB operation, which is ∼10 dB higher than that of DT-HEMT. Moreover, the fabricated device yields a nearly constant fT/ fmax of 47/118 GHz over a wide gate voltage, and load-pull measurements at 30 GHz reveal that these devices deliver output power density ( Pout) of 7.8 W/mm with the associated 1-dB compression point ( P1 dB) of 28.5 dBm at Vds = 28 V. The experimental results indicate that the employment of DT technology and SOD structure is an attractive approach to enhance the linearity at high E-field for millimeter wave devices.

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.