Metal-Semiconductor-Metal Varactors Based on InAlN/GaN Heterostructure With Cutoff Frequency of 308 GHz

Abstract

Metal-semiconductor-metal (MSM) varactor diodes based on InAlN/GaN high electron mobility transistor structures were fabricated and characterized. Among the MSM varactors with gate lengths ranging from 90 to 270 nm and gate distances of 2 and 4 mu m, the highest performance was obtained from the MSM varactor with gate length of 90 nm and gate spacing of 2 mu m. The capacitance switching ratio (C-max/C-min) of 2.31 together with a high cutoff frequency (f(o)) of 308 GHz was demonstrated. The calculated figures of merit (FOMs), which were defined to be f(o) . C-max/C-min for the comparison of devices performance, were 523 and 769 GHz for devices with gate spacing of 4 and 2 mu m, respectively. The FOMs were not dependent on gate length of the devices, but highly dependent on gate spacing.