Influence of Double-Deck T-gate Structures on Cut-Off Frequency in $\text{Al}_{0.3} \ \text{Ga}_{0.7} \ \text{N/AlN/GaN}$ HEMTs

This study investigates the impact of various Tgate structures on the performance of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Al}_{0.3} \ \text{Ga}_{0.7} \ \text{N/AlN/GaN}$</tex> HEMTs fabricated on SiC substrates. Five T-gate designs were analyzed, comprising a conventional T-gate and four double-deck T-gate variations. Reducing the width of the source-side 2<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> foot resulted in a cut-off frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\left(f_{i}\right)$</tex> improvement of up to 7 GHz, while the head position was found to have minimal impact. Through capacitance calculations, the contribution of the 2nd foot width to the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{t}$</tex> enhancement was analyzed.