Highly Linear AlN/GaN/AlGaN HEMTs Demonstrated Using 40-GHz Two-Tone Active Load-Pull with Record PAE at 30dBc C/IM3

This paper presents, for the first time, two-tone active load-pull measurements at 40 GHz applied to AlN/GaN HEMTs with and without a carbon-doped AlGaN back-barrier. The per-tone active load-pull architecture enables accurate synthesis of large and independent reflection coefficients at each fundamental tone, overcoming the limitations of passive load-pull at mmWave. The back-barrier device exhibits significantly improved large-signal performance, achieving 2.5 W/mm output power and 64.5% peak PAE under one-tone excitation. Under two-tone operation, the device reaches 30 dBc C/IM3 at 1.65 W/mm output power with a record PAE of 56.8% at 40 GHz, compared to 41.3% for the reference wafer. Remarkably, the back-barrier device achieves the 30 dBc linearity target without requiring output-power back-off, a consequence of its reduced transconductance curvature and strongly mitigated trapping effects. These results demonstrate that back-barrier engineering provides a highly effective route for enhancing efficiency and linearity of next generation mmWave GaN based power amplifiers.