0.1- $\mu \text{m}$  InAlN/GaN High Electron-Mobility Transistors for Power Amplifiers Operating at 71–76 and 81–86 GHz: Impact of Passivation and Gate Recess
We have developed 0.1-μm gate-length InAlN/GaN high electron-mobility transistors (HEMTs) for millimeterwave (MMW) power applications, particularly at 71-76 and 81-86 GHz bands. The impacts of depth and width of the gate recess groove on electrical performance have been analyzed and compared. Competing passivation technologies, atomic layer deposition (ALD) aluminum oxide (Al2O3) and plasma-enhanced chemical vapor deposition (PECVD) SiN, have also been assessed in terms of dc, pulsed-IV, and high-frequency characteristics. It has been found that while PECVD SiN-passivated HEMTs and the monolithic microwave integrated circuits slightly underperform their ALD Al2O3-passivated counterparts, their MMW power performance can be further boosted with the gate recess due to the improved aspect ratio and scaling characteristics. When biased at a drain voltage of 10 V, a first-pass two-stage power amplifier design based on recessed PECVD SiN-passivated 0.1-μm depletion-mode devices has demonstrated an output power of 1.63 W with a 15% power-added efficiency at 86 GHz.