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 $1\mu\ \text{m}$ are processed by using electron beam lithography (EBL). The DC characteristic shows a very low current leakage of ~7.3 $\times 10^{-11}\quad \mathbf{A}/\mathbf{mm}$ , which is advantageous to the power consumption of terahertz multiplier. S-parameters are measured to obtain the high-frequency performance. The series resistance $(\mathbf{R})\mathbf{of}\sim 41.26\ \Omega$ , and the capacitance $(\text{C}_{0})$ of ~4.22fF are abstracted respectively by matching the equivalent circuit at zero bias voltage. The cutoff frequency is of $\sim 914.5$ GHz. The capacitance switching ration $(\mathbf{C}_{\max}/\mathbf{C}_{\min})$ is $\geqslant 2.4$ , and the figure of merit (FOM) is above 2.2 THz