Millimeter-wave GaNHFET technology

This paper describes device process and characteristics of sub-100-nm-gate AlGaN/GaN heterostructure field-effect transistors (HFETs) for millimeter-wave applications. We developed three techniques to suppress short-channel effects and thereby enhance high-frequency device characteristics: high-Al-composition and thin AlGaN barrier layers, SiN passivation by catalytic chemical vapor deposition, and sub-100-nm Ti-based gates. The Al0.4Ga0.6N(6 nm)/GaN HFETs with a gate length of 60 nm on a 4H-SiC substrate showed a maximum drain current density of 1.6 A/mm and a maximum transconductance of 424 mS/mm. The use of the techniques led to record current-gain cutoff frequency (f(T)) and maximum oscillation frequency (f(max)) of 190 and 241 GHz, respectively. The f(T) and f(max) kept high values over the wide range of drain voltage and current. These results indicate significantly high potential of GaN HFETs for high-power applications in the millimeter-wave frequency range.