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A hybrid Schottky–ohmic drain technology for millimeter-wave (mmW) AlGaN/GaN high-electron-mobility transistors (HEMTs) is proposed. The Schottky metal extension in the ohmic region of drain reduces the actual source–drain spacing, resulting in a smaller ON-resistance and a higher maximum current. Extended Schottky metal in the drain region modulates the electric-field distribution, thereby leading to an improved breakdown voltage, suppressed current collapse, and high reliability. Compared with the ohmic drain, the current gain cutoff frequency (${f}_{T}$) was improved from 64 to 76 GHz, and the maximum oscillation frequency (${f}_{\text {max}}$) was improved from 125 to 157 GHz, resulting from the decreased parasitic drain resistance (${R}_{d}$). Moreover, large-signal measurements in continuous wave (CW) at 30 GHz demonstrated a peak power-added efficiency (PAE) of 45.5% and a saturated output power density (${P}_{\text {sat}}$) of 8.5 W/mm at ${V}_{\text {ds}}= {30}$ V. In addition, the direct current (DC) and radio frequency (RF) characteristics showed a negligible degradation after large-signal measurements at 30 GHz. [ABSTRACT FROM AUTHOR]

In this article, we report on the effective transconductance (gm) and gain linearity improvement of submicrometer gate AlN-barrier-based transistors using GaN/InGaN coupling-channel structures. The fabricated AlN/GaN/InGaN coupling-channel high electron mobility transistor (CC-HEMT) showed flat gm profile, greatly reduced gm derivatives, and constant dynamic source resistance compared with an AlN/GaN HEMT using the same fabrication process. The highest extrinsic current gain cutoff frequency (ƒT) of 55 GHz and the maximum oscillation frequency (ƒmax) of 80 GHz were obtained for 0.15- μm gate-length transistors, both of which remain constant values across wide input voltage (VGS) of 4 V. Moreover, a significant theoretical OIP3 value boost by 7.1 dB has been observed using the CC-HEMT as compared to the AlN/GaN HEMT. The superior linearity performance of the CC-HEMT can be attributed to the strong channel-to-channel coupling effect. The drain bias-dependence of gm, ƒT, and ƒmax versus VGS profiles illustrate that the linearity characteristics of the CC-HEMT greatly improve with an increase in VDS. These results demonstrate the AlN/GaN/InGaN material system as a viable platform for high frequency requiring high-linearity applications. [ABSTRACT FROM AUTHOR]

Gate-recessed AlGaN/AlN/GaN metal–oxide–semiconductor heterostructure high-mobility transistors (MOS-HEMTs) on SiC substrate are fabricated. The device with a gate length of 0.6 \mu\m and a gate periphery of 100 \mu\m exhibits a maximum dc drain current density of 1.59 A/mm at VGS = \3\ \V with an extrinsic transconductance (gm) of 374 mS/mm. An extrinsic current gain cutoff frequency (fT) of 19 GHz and a maximum oscillation frequency (f\max) of 50 GHz are deduced from S-parameter measurements. The output power density is 13 W/mm, and the associated power-added efficiency is 73% at 4-GHz frequency and 45-V drain bias. The power performance is comparable to state-of-the art AlGaN/GaN HEMTs, which demonstrates the great potential of gate-recessed MOS-HEMTs as a very promising alternative to GaN HEMTs. [ABSTRACT FROM AUTHOR]