Ultra-scaled GaN HEMTs on Sapphire with fT/fmax = 229/528 GHz and NFmin ~ 1 dB

With advanced down-scaling technology, GaN HEMTs on the cost-effective sapphire substrate may achieve exceptional RF performance, W-band power performance, and low noise performance, making them suitable for 6G/Terahertz communication. In this study, by employing electron beam lithography, ultra-scaled InAlN/GaN HEMTs on sapphire with T-gates with a gate length of ~50 nm and source-drain distance of ~200 nm were fabricated, achieving an impressive current gain cutoff frequency (f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf>) of 229 GHz and high power cutoff frequency (f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf>) of 528 GHz. The W-band loadpull analysis indicated that the devices exhibit a linear gain of 6.7 dB, an output power of 14.4 dBm, and a power-added efficiency of 12.5%. Device scaling resulted in low parasitic resistances, leading to an outstandingly low noise figure of 1 dB across the 25-35 GHz frequency range. To the best of the author’s knowledge, our devices have the highest f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf>/f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> and lowest noise figure among GaN HEMTs on sapphire, which are comparable with those state-of-the-art counterparts on SiC substrates.