A Novel L<sub>G</sub> = 40 nm AlN-GDC-HEMT on SiC Wafer With f<sub>T</sub>/I<sub>DS,peak</sub> of 400 GHz/3.18 mA/mm for Future RF Power Amplifiers
B. Mounika, Asisa Kumar Panigrahy, J. Ajayan, N. Khadar Basha, Vakkalakula Bharath Sreenivasulu, M. Durga Prakash, Sandip Bhattacharya, D. Nirmal
Abstract
In this work, we report the RF/DC performance of novel AlN/GaN/Graded-AlGaN/GaN double-channel HEMT (AlN-GDC-HEMT) on SiC wafer for the first time. The study compares the performance between conventional AlGaN/GaN/Graded-AlGaN/GaN double-channel HEMT (AlGaN-GDC-HEMT) and the AlN-GDC-HEMT. Two quantum wells are formed in both devices, leading to distinct double peak features in transconductance and cut-off frequency plots, highlighting efficient inter-channel connection behavior. The study investigates the relative performance of AlN-GDC-HEMT and AlGaN-GDC-HEMT, exploring the influence of gate recess length (L<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {R}}$ </tex-math></inline-formula>) and top barrier thickness. Additionally, the scaling behavior of the HEMTs is examined with varying gate lengths (L<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {G}}$ </tex-math></inline-formula>). Furthermore, the impact of gate engineering and lateral scaling on both devices’ DC/RF behavior is explored. Extensive comparative analysis shows that the AlN-GDC-HEMT outperforms the conventional AlGaN-GDC-HEMT, mainly attributed to AlN’s higher polarization (spontaneous) density and its wider bandgap. The optimized AlN-GDC-HEMT with L<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {G}} =40$ </tex-math></inline-formula> nm, L<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {GS}} =250$ </tex-math></inline-formula> nm, and L<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {GD}} =400$ </tex-math></inline-formula>nm exhibits superior performance resulting in transconductance (G<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {M}}$ </tex-math></inline-formula>) values of 203.1 and 787.5 mS/mm at two peaks, an I<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {DS\_peak}}$ </tex-math></inline-formula> of 1.97 A/mm, I<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {DS\_sat}}$ </tex-math></inline-formula> of 3.18 A/mm, and the highest fT derived from the left and right peaks was 285.1 and 416.8 GHz, respectively. The promising results from this first investigation indicate the potential and applicability of AlN-GDC-HEMTs in future RF power amplifiers.