High <i>f<sub>max</sub> </i> × <i>L<sub>G</sub> </i> Product of AlGaN/GaN HEMTs on Silicon With Thick Rectangular Gate
Li-Cheng Chang, Kai–Chieh Hsu, Yung-Ting Ho, Wei-Cheng Tzeng, Yu-Li Ho, Chao‐Hsin Wu
Abstract
In this letter, we successfully demonstrated a AlGaN/GaN high-electron mobility transistor on silicon substrate with high product of maximum oscillation frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) and gate length (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> ) by reducing the gate resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) using a thick, high aspect ratio rectangular gate (R-gate) structure with an L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> of 265 nm and thickness of 315 nm which was fabricated using a thick polymethyl methacrylate lift-off process. The maximum drain current is over 1 A/mm, and the peak transconductance is 291 mS/mm. The values of cutoff frequency and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> are 43.7 GHz and 126.5 GHz at a drain voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ) of 12 V, respectively. R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> is extracted through the small-signal model, and the value is given as 0.21 Ω-mm which is comparable to devices with the T-gate structure. This low R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> results in a high f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> and high f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> × L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> product of 33.52 GHz-μm, comparable to previously reported GaN-on-Si transistors for both R-gate and T-gate structures.