Monolithically integrated E/D-mode InAlN HEMTs with ƒt/ƒmax > 200/220 GHz

Although recent years have seen impressive progress on high speed GaN HEMTs [1-3], fabrication approaches allowing for monolithic integration of E and D-mode devices with simplicity and low-cost, such as gate recess and plasma treatment, remain challenging. Carrier mobility in channels subject to gate recess or plasma treatment generally degrades, which is difficult to fully recover even after post-processing annealing etc. In this work, we report high-performance monolithically integrated D-mode and gate-recessed E-mode InAlN/AlN/GaN HEMTs with a nominal gate length of 30 nm (Fig. 1) and 2-level metal interconnects. The D-mode HEMTs show an extrinsic g_m of 920 mS/mm and f_t/f_max of 194/220 GHz. The gate-recessed E-modes show an extrinsic g_m of 1306 mS/mm and f_t/f_max of 225/250 GHz. The higher speed of the E-modes stems from the higher intrinsic g_m, which is also found to be comparable to that reported in epitaxially defined E-modes with a 4.5 nm barrier and 20-nm gate length by Shinohara et al. [1], ~ 1700 mS/mm, suggesting that the carrier mobility likely suffers from negligible degradation in our monolithically integrated E-mode HEMTs.