Deeply-Scaled E/D-Mode GaN-HEMTs for Sub-mm-Wave Amplifiers and Mixed-Signal Applications

In this paper, we report state-of-the-art high-frequency performance of GaN-based HEMTs achieved through innovative device scaling technologies such as vertically-scaled AlN/GaN/AlGaN double-heterojunction (DH) HEMT epitaxial structure, low-resistance n+-GaN ohmic contacts regrown by MBE, and manufacturable 20-nm self-aligned sidewall gate process. Engineering top barrier layer structure enabled both enhancement- and depletion-mode (E/D) device operations with record cutoff frequencies while maintaining Johnson figure of merit (JFoM) breakdown performance. Furthermore, E/D-mode devices were monolithically integrated using a full epitaxial regrowth technique with a successful demonstration of DCFL ring oscillator circuits. Deeply-scaled E/D-mode GaN-HEMTs with an unprecedented combination of high-frequency and high-breakdown characteristics offer practical advantages in circuit applications such as sub-millimeter-wave power amplifiers, ultra-linear mixers, and increased output power digital-to-analog converters.