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

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 μm drain-to-source spacing, 125 μm gate width and 0.3 μm 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,), maximum DC transconductance (g), pinch-off voltage (V), current-gain cutoff frequency (f), maximum oscillation frequency (f), and RF characteristics of the devices in terms of the small-signal gain and RF output power (P) 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, g, f and f 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 is decreased and P is increased when the gate recess etching process is performed.