Impact of $\hbox{Al}_{2}\hbox{O}_{3}$ Passivation Thickness in Highly Scaled GaN HEMTs

Abstract

This letter studies the influence of the passivation thickness on the device characteristics of InAlGaN/GaN high-electron-mobility transistors with a gate length between sub-30 and 70 nm. As the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> passivation thickness increases, the current collapse in 80-μs pulsed- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> measurements decreases from 30% to 13%, while dc characteristics are almost unchanged with the exception of increasing drain-induced barrier lowering. The thicker passivation increases the fringing gate capacitance, which can be about 30% of the total gate capacitance in the devices with a gate length below 35 nm. This capacitance results in a significant drop of current-gain cutoff frequency ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ), and its effect is more important in the shorter gate length devices.