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

Abstract

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">$\hbox{10}^{-6}\ \hbox{A/mm}$</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">$g_{m} \sim \hbox{500}\ \hbox{mS/mm}$ </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">$\sim$</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">$R_{C} &lt; \hbox{0.50}\ \Omega \cdot \hbox{mm}$</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">$I_{DS, \max} \sim \hbox{1.75}\ \hbox{A/mm}$</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">$f_{t} &gt; \hbox{100} \ \hbox{GHz}$</tex></formula> operation, which is among the best so far reported for AlN/GaN technology.