Comprehensive evaluation of T-gated AlN/GaN/SiC MOSHEMTs with ZrO2/Al2O3 dielectrics towards performance enhancement through lateral scaling and passivation optimization for power switching and RF applications

At the nanoscale regime, achieving substantial RF performance in GaN-based MOSHEMTs requires a high aspect ratio, which is particularly crucial in AlN/GaN MOSHEMTs due to the thin AlN barrier layer. This study compares the performance of AlN/GaN MOSHEMTs using two dielectric materials, ZrO₂ and Al₂O₃. The analysis systematically examines the effects of varying barrier thickness (t_b), oxide thickness (t_ox), and gate length (L_G) to optimize device characteristics. As t_b and t_ox are reduced, both dielectrics exhibit an increase in gate capacitance (C_GG) due to reduced separation between the gate and channel, which enhances gate control and improves device performance. Furthermore, L_G scaling reveals that at 40 nm, both devices exhibit enhanced performance due to stronger electric fields and increased carrier velocity enabled by reduced channel length. From the comprehensive analysis, it is observed that ZrO₂ consistently surpasses Al₂O₃ in terms of key performance metrics across varying structural parameters. Notably, the ZrO₂ device outperforms the Al₂O₃ counterpart achieving peak values of 2.4 A/mm (I_D), 536.8 mS/mm (G_M), and f_T of 300.5 GHz with an L_G of 40 nm. This superior performance is attributable to the higher dielectric constant of ZrO₂, which enables greater physical thickness, effective gate control, better interface quality, and enhanced transport properties due to the shorter gate length. Besides, we investigated the impact of passivation materials, using SiO₂, Al₂O₃, and Si₃N₄, and found that SiO₂ provides superior performance owing to efficient reduction in surface states. Additionally, the effects of passivation thickness on device performance were examined using SiO₂, revealing that increased passivation thickness leads to improved overall electrical characteristics with peak values of 2.45 A/mm (I_D), 552.28 mS/mm (G_M), and f_T of 409.54 GHz, due to a reduction of surface traps and suppressed leakage currents. The study demonstrates the superior performance and compatibility of ZrO₂ under various scaling conditions, establishing it as a highly intriguing gate dielectric material for GaN HEMTs, particularly in sub-50 nm regimes. These findings underscore the potential of ZrO₂ for optimized RF performance in scaled AlN/GaN MOSHEMTs for future RF & power-switching applications.