Impact of Relative Gate Position on DC and RF Characteristics of High Performance AlGaN/GaN HEMTs
Yogendra Yadav, Bhanu B. Upadhyay, Jaya Jha, Swaroop Ganguly, Dipankar Saha
Abstract
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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SD</sub> ) of 5 μm, width (W) of 2×50 μm and gate length (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> ) of 200 nm are fabricated and characterized. The relative position of the gate is varied with constant L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SD</sub> . The value of saturation drain current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS,sat</sub> ) and maximum transconductance (g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m,max</sub> ) change from 740 mA/mm and 168 mS/mm for gate to source separation (LGS) of 3.8 μm to 1071 mA/mm and 245 mS/mm for L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GS</sub> = 0.25 μm, respectively. The corresponding breakdown voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">br</sub> ) significantly improves from 65 V (for L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GS</sub> = 3.8 μm) to 189 V (for L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GS</sub> = 0.25 μm). The unity current gain frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) is observed to remain constant at 55GHz 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.