Effect of source-drain spacing on DC and RF characteristics of 45 nm-gate AlGaN/GaN MIS-HEMTs

A report is presented of the fabrication of 45 nm-gate AlGaN/GaN MIS-HEMTs with a source-drain spacing Lsd range from 0.5 to 2.0 m on sapphire substrate. Their DC and RF characteristics have been measured. The maximum transconductance gm increased with decreasing Lsd. On the other hand, the cutoff frequency fT and maximum oscillation frequency fmax had maximum values at Lsd = 1.0 μm. The maximum values of fT and fmax were 188 GHz and 173 GHz, respectively. The reduction of fT and fmax at Lsd = 0.5 μm results from the greatly increased parasitic gate capacitance.