E-beam fabricated Metal-Semiconductor-Metal (MSM) varactor based on AlGaN/GaN HEMT with rectangular gate of 450nm

The fabrication and characteristics of balanced metal-semiconductor-metal (MSM) two-dimensional electron gas (2DEG) varactors based on AlGaN/GaN high electron mobility transistor (HEMT) for terahertz circuits were presented. The cathodes were designed to be strip-gates with submicron length of $\sim 450$ nm and manufactured by using electron beam lithography (EBL). The anodes lengths are ranging from $\sim 450$ nm to $\sim 2 \mu$m to study the influence of anode size on DC and high frequency characteristics. The DC and high frequency measurements were carried out, current-voltage and capacitance-voltage characteristics were investigated. As increasing the size of anode size to 2 $\mu $ m, the cutoff frequency of the MSM varactors was increasing as well. By matching the equivalent circuit at zero bias voltage with anode size of 2 $\mu$ m, the series resistance (R 0 ) of $\sim$ 32.43 $\Omega$, and the capacitance (C 0 ) of $\sim$ 5.09 fF were abstracted respectively, and the cutoff frequency of $\sim$ 964.6 GHz and the figure of merit (FOM) of 4.07 THz were obtained.