Fabrication of sub-50-nm-gate i-AlGaN/GaN HEMTs on sapphire

We fabricated sub-50-nm-gate i-AlGaN/GaN high electron mobility transistors (HEMTs) on sapphire and measured their DC and RF characteristics at room temperature. The fabricated HEMTs exhibited true device operation and good pinch-off characteristics down to a gate length L-g of 25 nm. For the HEMTs with a source-drain spacing L-sd of 2 mum, we obtained the Lg dependence of the cutoff frequency f(T) under a drain-source voltage V-ds of 3 V. The peak f(T) was measured to be 102 GHz at L-g = 35 nm. At L-g = 25 nm, f(T) started to decrease due to the short-channel effect. The highest fT of 110 GHz was obtained by reducing L-sd from 2 to 1.5 mum and by increasing V-ds from 3 to 4 V. (C) 2003 WILEY-VCH Vertag GmbH & Co. KGaA, Weinheim.