Record JFOM (> 11.5 THz∙V) for ultra-wide bandgap high frequency Al_0.62Ga_0.38N channel HEMT

Ultra-wide bandgap semiconductors, including AlN, AlGaN, diamond and Ga<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>, exhibit superior advantages over wide bandgap semiconductor materials. Al rich ($\gt60 \%$) AlGaN channel high electron mobility transistors (HEMTs) have the potential to realize high frequency power amplifiers with high efficiency due to the large bandgap, high breakdown field and decent saturation velocity [1]. Consequently, $\gt60 \% \mathrm{Al}$ composition AlGaN channel transistors have been explored [2–8]. The AlGaN channel ($\mathrm{Al}\gt60 \%$) transistors have demonstrated good unity gain frequency ($f_{T}$) of $\sim 40 \mathrm{GHz}$, but the breakdown performance was only 45 V which was limited by the high leakage. In authors’ previous work [9], an $\mathrm{Al}_{0.64} \mathrm{Ga}_{0.36} \mathrm{~N}$ channel HFET with $f_{T}$ of 15.7 GHz and $\mathrm{V}_{\mathrm{BR}}$ of 360 V was reported. In this work, with optimized T-shape gate design and reduced gate length $\left(\mathrm{L}_{\mathrm{G}}\right)$ as well as source and drain access resistances, higher $f_{T}$ and $f_{\text {max }}$ (35.6 GHz and 50.2 GHz, respectively) have been obtained with similar breakdown voltage performance ($\sim 300 \mathrm{~V}$). A high Johnson’s figure of merit (JFOM) of $\gt11.5 \mathrm{THz} \cdot \mathrm{V}$ was achieved. To the best of authors’ knowledge, this JFOM was the highest among the UWBG high frequency transistors.