Impact of Al₂O₃ Passivation Thickness in Highly Scaled GaN HEMTs

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 2 O 3 passivation thickness increases, the current collapse in 80-μs pulsed- I - V 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 ( f T ), and its effect is more important in the shorter gate length devices.