Impact of Relative Gate Position on DC and RF Characteristics of High Performance AlGaN/GaN HEMTs

We have investigated the impact of relative gate position between source and drain on the DC and RF characteristics for AlGaN/GaN high electron mobility transistors. Devices with fixed source drain separation ( ${L}_{\text {SD}}$ ) of $5~\mu \text {m}$ , width ( ${W}$ ) of ${2}\times {50}\,\,\mu \text {m}$ and gate length ( ${L}_{G}$ ) of 200 nm are fabricated and characterized. The relative position of the gate is varied with constant ${L}_{\text {SD}}$ . The value of saturation drain current ( ${I}_{\text {DS},\text {sat}}$ ) and maximum transconductance ( ${g}_{m,\text {max}}$ ) change from 740 mA/mm and 168 mS/mm for gate to source separation ( ${L}_{\text {GS}}$ ) of $3.8~\mu \text {m}$ to 1071 mA/mm and 245 mS/mm for ${L}_{\text {GS}} = {0.25}\,\,\mu \text {m}$ , respectively. The corresponding breakdown voltage ( ${V}_{\text {br}}$ ) significantly improves from 65 V (for ${L}_{\text {GS}} = {3.8}\,\,\mu \text {m}$ ) to 189 V (for ${L}_{\text {GS}} = {0.25}\,\,\mu \text {m}$ ). The unity current gain frequency ( ${f}_{T}$ ) is observed to remain constant at 55 GHz for all positions of the gate. However, output power density is found to increase from 3.8 to 5.1 W/mm for the same relative change in the gate position.