Effect of gate structures on the DC and RF performance of AlGaN/GaN HEMTs

Abstract This work analyzes the effect of various gate structures on the DC and radio frequency (RF) performance of AlGaN/GaN high-electron mobility transistors (HEMTs). AlGaN/GaN HEMT devices with a 3 μ m drain-to-source spacing, 125 μ m gate width and 0.3 μ m gate length in various gate structures were fabricated to achieve the desired frequency response with a robust, high yield, and repeatable process. The maximum drain current (I _DS , _max ), maximum DC transconductance (g _m ), pinch-off voltage (V _th ), current-gain cutoff frequency (f _T ), maximum oscillation frequency (f _max ), and RF characteristics of the devices in terms of the small-signal gain and RF output power (P _out ) at 8 GHz were investigated. The results showed that the output power is increased by 1 dB when the gate structure is changed from field plate to gamma gate. The V _th , g _m , f _T and f _max values are maximized when the thickness of the passivation layer between the gate foot and the gate head is minimized. It is shown that the I _DS,max is decreased and P _out is increased when the gate recess etching process is performed.