High-Performance AlGaN/GaN HEMTs With Hybrid Schottky–Ohmic Drain for Ka-Band Applications

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.