Breakdown-Voltage-Enhancement Technique for RF-Based AlGaN/GaN HEMTs With a Source-Connected Air-Bridge Field Plate

Abstract

An AlGaN/GaN high-electron-mobility transistor (HEMT) with a novel source-connected air-bridge field plate (AFP) is proposed. The device features a metal field plate (FP) that jumps from the source over the gate region and lands between the gate and drain. The fabrication process is based on a commercially available radio-frequency GaN-on-SiC technology. Device characteristics for this work were optimized via layout changes only. When compared to a similar-sized HEMT device with a conventional FP structure, the AFP not only minimizes the parasitic gate-to-source capacitance but also exhibits a higher off-state breakdown voltage and one order of magnitude lower drain leakage current. In a device with a gate-to-drain distance of 6 μm and a gate length of 0.8 μm, a three-times-higher forward blocking voltage of 375 V was obtained at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GS</sub> = -5 V. In contrast, a similar-sized HEMT with a conventional FP can only achieve a breakdown voltage no higher than 125 V using this process, regardless of device dimensions. The specific on-resistance for the device with the proposed AFP is 0.58 mΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GS</sub> = 0 V, which compares favorably with 0.79 mΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for the best device with a conventional FP.