Metal-Semiconductor-Metal (MSM) Varactor Based on AlGaN/GaN Heterostructure with Cutoff Frequency of 914.5GHz for Terahertz Frequency Multiplication

The design, fabrication and characteristics of planar metal-semiconductor-metal (MSM) two-dimensional electron gas (2DEG) varactors based on AlGaN/GaN high electron mobility transistor (HEMT) for terahertz multiplication are presented. The gate length of ~450nm and the gate distance of 1μm are processed by using electron beam lithography (EBL). The DC characteristic shows a very low current leakage of ~7.3 ×10 ^-11 A/mm, which is advantageous to the power consumption of terahertz multiplier. S-parameters are measured to obtain the high-frequency performance. The series resistance (R ₀ )of ~ 41.26 Ω, and the capacitance (C ₀ ) of ~4.22 fF are abstracted respectively by matching the equivalent circuit at zero bias voltage. The cutoff frequency is of ~ 914.5 GHz. The capacitance switching ration (C _max /C _min ) is ≥ 2.4, and the figure of merit (FOM) is above 2.2 THz.