Novel HEMT processing technologies and their circuit applications

Abstract

The monolithic integration of enhancement- and depletion-mode high-electron mobility transistors (E- and D-HEMTs) suitable for high-speed and low power circuit applications in the lattice-matched InP material system is examined. E-HEMT devices with gate-lengths of 0.25, 0.5 and 1.0 μm fabricated using a buried-Pt gate process demonstrate threshold voltages ( V T) ranging from +200 to +258 mV and maximum extrinsic transconductances ( g mext) as high as 800 mS mm −1, while D-HEMT devices of identical gate-lengths exhibited a V T ranging from −599 to −405 mV, and a g mext as high as 578 mS mm −1. The devices showed excellent rf characteristics, exhibiting unity current-gain cutoff frequencies ( f t) as high as 106 GHz. Based on these results, 11, 23, and 59 stage ring oscillators using direct-coupled FET logic (DCFL) technology were fabricated and characterized. Room temperature propagation delays of 9.27 ps/stage with a power-delay product of 2.37 fJ/stage were achieved.