High-Performance AlN/GaN HEMTs on Sapphire Substrate With an Oxidized Gate Insulator

This letter presents transistor device results on ultrathin AlN/GaN high-electron mobility transistors grown on a sapphire substrate with high dc/RF performance, including low gate leakage and high transconductance. Devices with 80- and 180-nm T-gates are compared, which demonstrate drain-induced off -state gate leakage currents below <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">10⁻⁶\ A/mm</tex> </formula> and extrinsic transconductance <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">gₘ ~ 500\ mS/mm </tex></formula> by utilizing a <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">~</tex></formula> 2–3 nm amorphous oxide layer formed under the T-gate during processing. In addition, excellent dc results such as <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">RC < 0.50\ Ω · mm</tex></formula> and pulsed <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">IDS, max ~ 1.75\ A/mm</tex></formula> are reported. Small-signal RF performance using an 80-nm T-gate achieved <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">fₜ > 100 \ GHz</tex></formula> operation, which is among the best so far reported for AlN/GaN technology.