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 ~450nm and manufactured by using electron beam lithography (EBL). The anodes lengths are ranging from ~450nm to ~2μm 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 2μm, the cutoff frequency of the MSM varactors was increasing as well. By matching the equivalent circuit at zero bias voltage with anode size of 2μm, the series resistance (R
₀
) of ~32.43 Ω, and the capacitance (C
₀
) of ~5.09 fF were abstracted respectively, and the cutoff frequency of ~964.6 GHz and the figure of merit (FOM) of 4.07 THz were obtained.